ArticleLiterature Review

Energetic Consequences of Being a Homo Erectus Female

Authors:
  • Wenner-Gren Foundation for Anthropological Research
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Abstract

Body size is one of the most important characteristics of any animal because it affects a range of behavioral, ecological, and physiological traits including energy requirements, choice of food, reproductive strategies, predation risk, range size, and locomotor style. This article focuses on the implications of being large bodied for Homo erectus females, estimated to have been over 50% heavier than average australopithecine females. The energy requirements of these hominins are modeled using data on activity patterns, body mass, and life history from living primates. Particular attention is given to the inferred energetic costs of reproduction for Homo erectus females based on chimpanzee and human reproductive scheduling. Daily energy requirements during gestation and lactation would have been significantly higher for Homo erectus females, as would total energetic cost per offspring if the australopithecines and Homo erectus had similar reproductive schedules (gestation and lactation lengths and interbirth intervals). Shortening the interbirth interval could considerably reduce the costs per offspring to Homo erectus and have the added advantage of increasing reproductive output. The mother would, however, incur additional daily costs of caring for the dependent offspring. If Homo erectus females adopted this reproductive strategy, it would necessarily imply a revolution in the way in which females obtained and utilized energy to support their increased energetic requirements. This transformation is likely to have occurred on several levels involving cooperative economic division of labor, locomotor energetics, menopause, organ size, and other physiological mechanisms for reducing the energetic load on females.

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... In our previous iteration of these ideas (Swedell and Plummer, 2012), we explicitly linked behavioral processes in hamadryas baboons with those in Plio-Pleistocene hominins, particularly H. erectus. H. erectus has been argued to be a pivotal species in human evolution in that its larger brain and body size as well as more extensive ranging patterns increased the costs of reproduction for females (Zihlman, 1978;Parker, 1990;Foley and Lee, 1991;Leonard and Robertson, 1997;Aiello and Key, 2002;Aiello and Wells, 2002;Ant on et al., 2002;Ellison, 2008). These higher costs of reproduction, exacerbated by increasingly difficult to acquire, nutrient-dense foods, may have been alleviated via a strengthening of male-female bonds, i.e., male provisioning in the context of a sexual division of labor, a "sex contract", and the evolution of monogamy, a suite of features that have been proposed to have evolved at various points during human evolution (Darwin, 1871;Isaac, 1978;Lovejoy, 1981Lovejoy, , 2009Fisher, 1983;Foley and Lee, 1989;Kaplan et al., 2000). ...
... Increased ranging across the landscape is also suggested by adaptations for endurance walking and running in H. erectus (Bramble and Lieberman, 2004). A larger body size and home range size (Ant on et al., 2002) is correlated with an increase in energy expenditure (Leonard and Robertson, 1997;Aiello and Key, 2002;Steudel-Numbers, 2006). An expansion of the daily energy budget in H. erectus likely reflects a greater reliability in calorie acquisition e from both plant and animal foods e than the australopiths, and may be linked to increased reproductive investment as well (Pontzer, 2012). ...
... If H. erectus also exhibited secondary altriciality, their infants would also have been in greater need of assistance than those of australopiths (Ant on et al., 2014;Cofran and DeSilva, 2015). H. erectus females could have mitigated these increased costs of reproduction by shortening their period of lactation and developing a support system whereby helpers assist in provisioning and feeding of weanlings and older dependent juveniles, thereby reducing the energetic burden on the mother and ultimately shortening interbirth intervals as well (Aiello and Key, 2002). Who these "helpers" were, however, has been the subject of some speculation, with suggestions including the traditional view of males provisioning pair bonded females via a sexual division of labor and a "sex contract" (Isaac, 1978;Lovejoy, 1981;Fisher, 1983), postreproductive grandmothers provisioning their daughters and grandchildren (Hawkes et al., 1997;O'Connell et al., 1999;Hawkes et al., 2000), older siblings provisioning younger ones (Peccei, 2001), and males provisioning females to reduce interbirth intervals and enhance mating opportunities (Kaplan et al., 2000;Aiello and Key, 2002). ...
Article
Reconstructions of hominin evolution have long benefited from comparisons with nonhuman primates, especially baboons and chimpanzees. The hamadryas baboon (Papio hamadryas) is arguably one of the best such models, as it exhibits both the male kin bonding and the cross-sex pair bonding thought to have been important in hominin evolution. Here we link processes of behavioral evolution in hamadryas baboons with those in a Plio-Pleistocene hominin, provisionally identified as Homo erectus (sensu lato) - a pivotal species in that its larger body and brain size and wider ranging patterns increased female costs of reproduction, increasing the importance of sociality. The combination of these higher costs of reproduction and shifts in diet and food acquisition have previously been argued to have been alleviated either via strengthening of male-female bonds (involving male provisioning and the evolution of monogamy) or via the assistance of older, post-reproductive females (leading to post-reproductive longevity in females, i.e., the grandmother hypothesis). We suggest that both arrangements could have been present in Plio-Pleistocene hominins if they lived in multilevel societies. Here we expand on our earlier scenario with two sets of recent data in support of it, (1) archaeological data from the 2 million year old Oldowan site of Kanjera South, Kenya and other sites that are suggestive of tool dependent foraging on nutrient dense resources (animal carcasses and plant underground storage organs), cooperation, and food sharing; and (2) a pattern of genetic variation in hamadryas baboons that suggests the operation of kin selection among both males and females at multiple levels of society. Taken together, these two sets of data strengthen our model and support the idea of a complex society linked by male-male, male-female, and female-female bonds at multiple levels of social organization in Plio-Pleistocene hominins.
... Overall, the Homo lineage experienced brain volume expansion of ~1000 cubic centimeters over that of Australopithecus; the average brain volume in modern humans is ~1400cc (Aiello and Wheeler, 1995;Potts, 1996). A portion of this enlargement occurred along with increases in body size (Potts, 1996;Deacon, 1997;Aiello and Key, 2002), although brain growth in the period of ~800 to 200 thousand years ago appears to have been independent of body size changes (Antón et al., 2014). ...
... The human species is thus habitually placed at the 'slow' end of the life history continuum, although some 'faster' life history traits including early infant weaning and short inter-birth intervals complicate this (Hawkes et al., 1998;Kennedy, 2005;Kuzawa and Bragg, 2012;Wells 2012aWells , 2016. Nevertheless, humans grow incredibly slowly and thus take longer than other primates to reach maturity, and they invest considerable resources in large bodies and brains (Potts, 1996;Aiello and Wheeler, 1995;Aiello and Key, 2002;Gurven and Walker, 2006;Robson and Wood, 2008 ...
... Nevertheless, if the authors' hypothesis is correct, a trade-off between the brain and gut was incorporated over time into the hominin life history strategy through genetic adaptation. It has long been recognized that investment in body size is an important component of the human strategy (Potts, 1996;Aiello and Key, 2002), however Aiello and Wheeler (1995) highlighted that tissues and organs of the body may be equally subject to allocation trade-offs, and should be considered as well. 'Why' and 'how' questions are both important for increasing our understanding of human brain evolution; a life history perspective underscores the importance of metabolic cost questions by highlighting that no tissue can be understood in isolation if the energy budget is fixed. ...
Conference Paper
The ‘expensive-tissue’ hypothesis of Aiello and Wheeler is well-known in anthropology for positing that an increasingly small gut was a key factor in the evolution of the large hominin brain. The insight that organs and tissues in the body compete for energy resources was also central to the ‘thrifty phenotype’ hypothesis of Hales and Barker, which proposed that nutritional stress in fetal life resulted in differential growth of the brain and pancreas. Both hypotheses are consistent with life history theory, which assumes that energy allocation trade-offs occur in energylimited environments. The prediction that somatic traits trade off against one another in the context of the body’s fixed energy budget has, however, yet to be rigorously tested in humans. The current thesis project aimed to fill this gap by recruiting 70 healthy young women and obtaining comprehensive, high-quality data on their brain and body composition. This included, specifically, measures of brain gray and white matter volume, fat mass, skeletal muscle mass, and volumes of the heart, liver, kidneys and spleen. Additional outcomes included resting energy expenditure and two proxies of early-life growth: birth weight, a marker of fetal weight gain, and tibia length, a marker of linear growth indexing postnatal experience. With these data, three principal hypotheses were tested: 1) there is variation in the energy expenditure of tissues and organs; 2) trade-offs are observed between brain and body organs/tissues; and 3) trade-off relationships are mediated by early-life growth. Results suggest the metabolic cost of organs and tissues is variable, and that the brain – in particular its gray matter component – trades off against lean tissues in the body (i.e. skeletal muscle, the liver and kidneys), but not fat mass. However, less support was found for the prediction that trade-offs are mediated by fetal and infant growth.
... The ability to cook allowed for a step-change in diet quality and, it is argued, accelerated the rate of evolution within Homo erectus (Aiello and Wheeler, 1995;Wrangham et al., 1999;Aiello and Key, 2002;Wrangham, 2009). Cooked starchy plants would have provided a source of pre-formed glucose, essentially pre-digested foods, offering greatly increased energy availability for the brain, red blood cells and developing fetus (Hardy et al., 2015). ...
... Cooked starchy plants would have provided a source of pre-formed glucose, essentially pre-digested foods, offering greatly increased energy availability for the brain, red blood cells and developing fetus (Hardy et al., 2015). Between two million and 500 kya, the cranial capacity of H. erectus doubled, their body size increased, particularly in females, and their teeth reduced in size; it is argued that the energy for these key morphological changes came in particular from cooked plant starches (Aiello and Key, 2002;Carmody and Wrangham, 2009;Wrangham, 2009;Hardy et al., 2015). ...
... Only humans cook, and cooking is considered to have been a turning point in human evolution. Cooking makes food more digestible and in starchy plant foods such as roots and tubers, cooking pre-digests the starch turning it into preformed glucose (Aiello and Key, 2002;Wrangham and Conklin-Brittain, 2003;Carmody and Wrangham, 2009;Wrangham, 2009). The increased energy yields are considered to be around 30% more than from similar quantities of foraged food (Carmody et al., 2016). ...
... However, large brains also entail significant evolutionary costs, due to high energetic demands (e.g. Aiello and Key 2002;Isler and van Schaik 2009;Navarrete et al. 2011). This suggests encephalising hominins faced strong selection pressures favouring brain growth. ...
... They are so-called expensive tissues, accounting for a large proportion of human energy expenditure (Aiello and Wheeler 1995). Energetic demands are highest for pregnant and lactating females (Aiello and Key 2002;Kaplan et al. 2000;Leonard et al. 2003). To 'finance' larger brains, improved dietary quality, likely resulting in increased meat consumption, and provisioning of pregnant and lactating females were needed (Leonard et al. 2003). ...
... Increases in brain size also led to changes in social structure and cooperation (Boyd and Richerson 2009). As brains' energy consumption increased, provisioning became important-likely prior to the appearance of H. sapiens (Aiello and Key 2002;Kaplan, et al. 2000;Navarrete, et al. 2011). Because hunted meat comes in relatively large 'packages', the increased importance of hunting stimulates food sharing (also see Blurton Jones 1987;Jaeggi and Gurven 2013;Kaplan and Hill 1985), which in turn may have fostered increased cooperative behaviour and a division of labour (Aiello and Key 2002). ...
Article
Full-text available
We develop a framework to differentiate the technological niches of co-existing hominin species by reviewing some theoretical biases influential in thinking about techno-behaviours of extinct hominins, such as a teleological bias in discussing technological evolution. We suggest that some stone-tool classification systems underestimate technological variability, while overestimating the complexity of the behaviours most commonly represented. To model the likely technological niches of extinct populations, we combine ecological principles ( i.e. competitive exclusion) with physical anthropology and the archaeological record. We test the framework by applying it to the co-existence of Homo naledi and Homo sapiens during the late Middle Pleistocene in southern Africa. Based on our analysis, we suggest that tool use was probably not an essential part of H. naledi ’s niche, but that technology occasionally provided caloric benefits. In contrast, tool use was a structural part of the H. sapiens way of life. We provide reasoning for our interpretation that the latter population is associated with more sophisticated reduction strategies and the development of prepared core technology. The method also has applicability to cases such as the co-existence of different toolmakers during the Earlier Stone Age (ESA) in East Africa and the co-existence of Neanderthals and H. sapiens in Eurasia.
... However, large brains also entail significant evolutionary costs, due to high energetic demands (e.g. Aiello and Key 2002;Isler and van Schaik 2009;Navarrete et al. 2011). This suggests encephalising hominins faced strong selection pressures favouring brain growth. ...
... They are so-called expensive tissues, accounting for a large proportion of human energy expenditure (Aiello and Wheeler 1995). Energetic demands are highest for pregnant and lactating females (Aiello and Key 2002;Kaplan et al. 2000;Leonard et al. 2003). To 'finance' larger brains, improved dietary quality, likely resulting in increased meat consumption, and provisioning of pregnant and lactating females were needed (Leonard et al. 2003). ...
... Increases in brain size also led to changes in social structure and cooperation (Boyd and Richerson 2009). As brains' energy consumption increased, provisioning became important-likely prior to the appearance of H. sapiens (Aiello and Key 2002;Kaplan, et al. 2000;Navarrete, et al. 2011). Because hunted meat comes in relatively large 'packages', the increased importance of hunting stimulates food sharing (also see Blurton Jones 1987;Jaeggi and Gurven 2013;Kaplan and Hill 1985), which in turn may have fostered increased cooperative behaviour and a division of labour (Aiello and Key 2002). ...
Conference Paper
A small-brained species of hominin, Homo naledi was discovered in the Cradle of Humankind World Heritage Site. It was recently determined to date to the Middle Pleistocene, in contrast with previous suggestions for a much older age. Its date demonstrates that H. naledi co-existed with larger-brained hominins in South Africa’s central interior. Moreover, it is contemporary with the beginning of the Middle Stone Age in the region (characterized by prepared core or mode 3 assemblages). In light of this, its discoverers have explicitly cast it as a potential producer of Middle Stone Age technologies (Berger et al. 2017). We develop a hypothesis on the ecological and technological niche Homo naledi likely occupied. We briefly review relevant elements H. naledi’s anatomy and their implications for its ecology. We provide an overview of the characteristics of the South African archaeological record contemporary with H. naledi. We reason from the principle of competitive exclusion and suggest a technological repertoire consisting of simple cores and flakes functioning in a niche focusing on extracted foods is most likely for Homo naledi. We contend that prepared core assemblages were associated with larger-brained populations, fossil remains of which are also known from South Africa’s central interior. Berger, L.R., Hawks, J., Dirks, P.H.G.M., Elliott, M., Roberts, E.M. (2017). Homo naledi and Pleistocene hominin evolution in subequatorial Africa. eLife, 6, e24234.
... We assumed that physiological responses to little or no paternal investment may be guided by evolved mechanisms and can be predicted by evolutionary theories. Comparative studies indicate that human offspring are costly to produce, mature slowly, and reach nutritional independence late [32]. These features imply demanding parental care requirements, which can rarely be supplied by the mother alone [32][33][34]. ...
... Comparative studies indicate that human offspring are costly to produce, mature slowly, and reach nutritional independence late [32]. These features imply demanding parental care requirements, which can rarely be supplied by the mother alone [32][33][34]. The cooperative breeding hypothesis states that allomaternal assistance must have been essential for child survival during our evolutionary past [33,35]. ...
Article
Full-text available
According to life-history theory, paternal investment affects the well-being of offspring. We hypothesized that environmental stress caused by a lack of paternal investment may diminish maternal resource allocation during pregnancy, especially for women who already have dependent children. Our study was conducted on a representative group of more than 80,500 singleton, live-born, full-term infants born in Krakow, Poland in the period 1995–2009. Birth data were obtained from the birth registry. We found that missing data about fathers (a proxy measure of low paternal investment) was associated with higher probability of multiparous mothers giving birth to low-birth-weight infants (1.48; 95% CI 1.05–2.08), but this was not the case with primiparous mothers (1.19; 95% CI 0.89–1.59). The statistically significant synergistic effect between parity and paternal investment was found (Synergy Factor = 2.12; 95% CI 1.47–3.05, p<0.001). These findings suggest that in situations of low paternal investment, multiparous mothers face trade-offs between investing in existing versus unborn children, therefore investment in the latter is lower. Such a strategy may benefit maternal fitness due to investment in older children, who have higher reproductive value.
... Regarding the subsequent taxa, the discovery of new specimens of early Homo and Homo erectus has expanded our knowledge on the potential body size dimorphism of these groups (Aiello and Key, 2002;Spoor et al., 2007;Rightmire et al., 2008;Ant on, 2012;Ant on and Josh Snodgrass, 2012). Some studies support the interpretation that the taxon Homo habilis/Homo rudolfensis appears to show bimodality in its body mass, which could imply strong size dimorphism (Plavcan, 2012). ...
... Furthermore, the results obtained for Krapina match those obtained by Trinkaus (1980), who observed levels of dimorphism in Krapina postcranial remains indistinguishable from those of modern humans. While the available evidence seems to be consistent with a reduction in sexual dimorphism in early Homo and H. erectus compared with the high levels of dimorphism observed in Australopithecus (McHenry, 1992(McHenry, , 1994Aiello and Key, 2002;Spoor et al., 2007;Rightmire et al., 2008;Ant on, 2012; Ant on and Snodgrass, 2012), the intrapopulation variability in Middle Pleistocene groups is less understood. The conclusions obtained from this research do not seem to support the view that Middle Pleistocene populations had higher levels of sexual dimorphism than modern humans in their canine dental tissues. ...
... Brain development has been changed by increases in a mother's investment during pregnancy and lactation in her young, particularly by extending pregnancy duration (Dufour and Sauther, 2002). This has considerably increased the energy needed by Homo mothers (Aiello and Key, 2002). Human immaturity, however is important and occurs over an extended dependency stage (Bogin 1997). ...
... This weight is mostly due to adipose tissue that provides an energy reserve that protects the brain and its high energy needs against temporary energy intake disruption (Kuzawa, 1998). Human mothers also provide more energy early on in their lactation (Aiello and Key, 2002). This difference can be seen in figure 4 which shows the different neonatal energy consumption by chimpanzees and huntergatherer humans. ...
Article
Full-text available
Human childhood and adolescence is the period in which adult cognitive competences (including those that create the unique cooperativeness of humans) are acquired. It is also a period when neural development puts a juvenile’s survival at risk due to the high vulnerability of their brain to energy shortage. The brain of a 4 year-old human uses ≈50% of its total energy expenditure (TEE) (cf. adult ≈12%). This brain expensiveness is due to (1) the brain making up ≈6% of a 4 year-old body compared to 2% in an adult, and (2) increased energy metabolism that is ≈100% greater in the gray matter of a child than in an adult (a result of the extra costs of synaptic neuromaturation). The high absolute number of neurons in the human brain requires as part of learning a prolonged neurodevelopment. This refines inter- and intraarea neural networks so they become structured with economical “small world” connectivity attributes (such as hub organization and high cross-brain differentiation/integration). Once acquired, this connectivity enables highly complex adult cognitive capacities. Humans evolved as hunter-gatherers. Contemporary hunter-gatherers (and it is also likely Middle Paleolithic ones) pool high energy foods in an egalitarian manner that reliably supported mothers and juveniles with high energy intake. This type of sharing unique to humans protects against energy shortage happening to the immature brain. This cooperation that protects neuromaturation arises from adults having the capacity to communicate and evaluate social reputation, cognitive skills that exist as a result of extended neuromaturation. Human biology is therefore characterized by a presently overlooked bioenergetic-cognition loop (called here the “HEBE ring”) by which extended neuromaturation creates the cooperative abilities in adults that support juveniles through the potentially vulnerable period of the neurodevelopment needed to become such adults.
... Although partly offset by a reduction in gut size (Aiello & Wheeler 1995), our large brains are still energetically expensive to grow and to maintain (Aiello & Wells 2002). Aiello and Key (2002) estimate the daily resting metabolic rates of 1,448kcal for a 56kg human female and 1,694kcal for a human male. With additional energetic expenditure, a daily energetic requirement of 1,930 kcal is estimated for women. ...
... With additional energetic expenditure, a daily energetic requirement of 1,930 kcal is estimated for women. Crucially, gestation increases energetic costs by 25% and lactation increases total costs by 39% over the baseline (Aiello & Key 2002). Even after weaning, offspring remain energetically dependent until their late teenage years (Kaplan et al 2000, Kaplan 1994, Gurven and Walker 2006. ...
Conference Paper
Much that is remarkable about human behaviour relates in some way to our advanced social cognition. Understanding why this advanced social cognition evolved benefits from an understanding of the kind of social organisation that is promoted by hunting-and-gathering, the dominant mode of subsistence throughout most of human evolutionary history. In this thesis, I explore the social organisation of hunter-gatherers in general and of the Palanan Agta in particular. In chapter four, I present data that demonstrate that, like many small-scale hunter-gatherer societies, the Agta live in small groups of fluid composition in which a large number of unrelated individuals co-reside. I present the results of a model that simulates the process of camp assortment and which suggests that sex equality in residential decision making may serve to constrain group relatedness. In chapter five, I challenge traditional biological conceptions of relatedness, arguing that under conditions of stable pair-bonding, individuals can derive inclusive fitness benefits through aiding affinal kin. In chapter six, I explore multilevel social organisation among the Agta and argue that it serves to provide individuals with access to the range of social relationships required to overcome both short-term variability in foraging returns and long-term energetic deficits resulting from the demands of having an energetically expensive life-history strategy.
... Cooperative breeding, which affects parental care (shorter birth intervals, juvenile dependence), is presumed to appear in the Lower Pleistocene with early H. erectus (O'Connell et al., 1999;Hrdy, 2009;van Schaik and Burkart, 2010). Indeed, Aiello and Key (2002), suggest that H. erectus females were able to cope with increased energetic costs per offspring (daily energy requirements during gestation and lactation) by shortening interbirth intervals and cooperating with others in feeding dependent children. Moreover, Wrangham and Conklin-Brittain (2003) have also suggested that cooking, which makes raw food soft enough for young individuals to chew, may have facilitated shorter interbirth intervals. ...
... However, as mentioned in the previous paragraph, extreme caution should be taken with this proxy. For example, it has been estimated that the daily energy expenditure (DEE) of a H. erectus female was 2,086 kilocalories per day, 2,269 during gestation and 2,487 during lactation (Aiello and Key, 2002), and that she had to chew raw meat for 5.7-6.2 h/day to satisfy her energetic needs (Wrangham and Conklin-Brittain, 2003). ...
Article
Full-text available
Despite the omnivorous diet of most human populations, meat foraging gradually increased during the Paleolithic, in parallel with the development of hunting capacities. There is evidence of regular meat consumption by extinct hominins from 2 Ma onward, with the first occurrence prior to 3 Ma in Eastern Africa. The number of sites with cut-marked animal remains and stone tools increased after 2 Ma. In addition, toolkits became increasingly complex, and various, facilitating carcass defleshing and marrow recovery, the removal of quarters of meat to avoid carnivore competition, and allowing the emergence of cooperative (i.e., social) hunting of large herbivores. How can we assess the energy costs and benefits of meat and fat acquisition and consumption for hunter-gatherers in the past, and is it possible to accurately evaluate them? Answering this question would provide a better understanding of extinct hominin land use, food resource management, foraging strategies, and cognitive abilities related to meat and fat acquisition, processing, and consumption. According to the Optimal Foraging Theory (OFT), resources may be chosen primarily on the basis of their efficiency rank in term of calories. But, could other factors, and not only calorific return, prevail in the choice of prey, such as the acquisition of non-food products, like pelts, bone tools or ornaments, or symbolic or traditional uses? Our main goal here is to question the direct application of behavioral ecology data to archeology. For this purpose, we focus on the issue of animal meat and fat consumption in human evolution. We propose a short review of available data from energetics and ethnographic records, and provide examples of several various-sized extant animals, such as elephants, reindeer, or lagomorphs, which were some of the most common preys of Paleolithic hominins.
... In humans, however, decreased mortality is unexpectedly coupled with a decrease in the inter-birth interval. Human cooperative breeding has been proposed to be the driver of this pattern, with the sharing of offspring care responsibilities possibly facilitating more rapid reproduction by mothers (Aiello and Key, 2002;Robson and Wood, 2008). ...
... Cooperative breeding in the form of provisioning of juveniles by both kin and non-kin (Kaplan et al., 2000) may have initially allowed for this reduction of inter-birth intervals and the lengthening of the prereproductive period before enabling increased postmenopausal longevity (Bogin, 2009). Regardless, cooperative breeding in the form of provisioning dependent juveniles appears to be a key feature in human life history evolution (Aiello and Key, 2002). ...
Article
Humans are thought to exhibit an unusual suite of life history traits relative to other primates, with a longer lifespan, later age at first reproduction, and shorter interbirth interval. These assumptions are key components of popular hypotheses about human life history evolution, but they have yet to be investigated phylogenetically. We applied two phylogenetic comparative methods to investigate whether these human life history traits differ from expectations based on other primates: one fits and selects between Brownian and Ornstein-Uhlenbeck models of trait evolution; the other tests for phylogenetic outliers by predicting phenotypic characteristics based on trait covariation and phylogeny for a species of interest. We found that humans have exceptionally short interbirth intervals, long lifespans, and high birth masses. We failed to find evidence that humans have a delayed age at first reproduction relative to body mass or other covariates. Overall, our results support several previous assertions about the uniqueness of human life history characteristics and the importance of cooperative breeding and socioecology in human life history evolution. However, we suggest that several hypotheses about human life history need to be revised in light of our finding that humans do not have a delayed age at first reproduction.
... The rate of increase then accelerated from around 800 kya, and this has been linked to the adoption of cooking (Aiello and Wheeler 1995). Increased body size, particularly the relative size of females and the presence of fat deposits in infants, would have required increased dietary intake to meet additional daily energy expenditure, although a larger body size may have improved the ability of early Homo to procure food (Leonard and Robertson 1997;Aiello and Key 2002;Steudel-Numbers 2006). Encephalization has also been proposed as a secondary change, occurring after dietary and other morphological changes (Antón and Snodgrass 2012). ...
... The evolution of human characteristics, including omnivory, incremental encephalization, and the ability to colonize varied environments, is proposed to have been the result of positive feedback based on ecological adaptability (Wells 2012a,b). Increased mobility and habitat range have been linked to an increase in carnivory (O'Connell et al. 1999;Aiello and Key 2002), with consumption of meat suggested to act as a buffer against environmental change and to support expansion into unfamiliar environments (Potts 2012). However, we propose that high-starch plant foods would have been a plentiful, reliable, and important part of the diet. ...
... and anatomical features throughout our evolutionary past (Aiello and Key 2002;Aiello and Wheeler 1995;Bird and O'Connell 2006;Pontzer et al. 2017). Moreover, many researchers have suggested that locomotor economy was a key target of selection in human postcranial evolution (Carrier et al. 1984;Kuhn et al. 2016;Steudel-Numbers and Tilkens 2004) and that the energetic savings of an increased efficiency of locomotion could play a significant role in the evolution of the life history traits in the genus Homo (Aiello and Key 2002). ...
... and anatomical features throughout our evolutionary past (Aiello and Key 2002;Aiello and Wheeler 1995;Bird and O'Connell 2006;Pontzer et al. 2017). Moreover, many researchers have suggested that locomotor economy was a key target of selection in human postcranial evolution (Carrier et al. 1984;Kuhn et al. 2016;Steudel-Numbers and Tilkens 2004) and that the energetic savings of an increased efficiency of locomotion could play a significant role in the evolution of the life history traits in the genus Homo (Aiello and Key 2002). ...
... Of particular importance to the occupation of the north may be the emphasis in the human model of early weaning: this strategy places infants at risk, as they are unskilled at finding appropriate foods (of sufficient high quality to fuel brain growth, but also suitable for small, deciduous teeth), are essentially defenceless, and can be competing with other adults (Aiello and Key, 2002;Kennedy, 2003). It therefore has notable dietary strategy implications, but it also has significant implications for infant care. ...
... Since early weaning is associated with shorter inter-birth intervals, other forms of childcare are required for the 'weanlings', in order to avoid excessive DEE (daily energy expenditure) loads on the large-bodied and large-brained Homo females (i.e. normal DEE þ gestation/lactation þ nursing of 'weanlings'; Aiello and Key, 2002). This alloparenting can come from grandmothers (e.g. ...
Article
Full-text available
In light of changing views regarding the identity and evolutionary positions of Europe's Lower Palaeolithic hominins, a re-consideration of the hominin occupation of north-west Europe from c. 1 million years ago (mya) to c. 400 thousand years ago (kya) is timely. A change in the scale and character of the overall European Palaeolithic record around c. 800–600 kya has been well documented and argued over since the mid-1990s. Hominin expansion into the European north-west, potentially from southern Europe, Africa or south-western Asia, has been linked to the introduction of a new lithic technology in the form of the biface. We evaluate three potential drivers for this northern range expansion: changing palaeo-climatic conditions, the emergence of an essentially modern human life history, and greater hominin behavioural plasticity. Our evaluation suggests no major changes in these three factors during the c. 800–600 kya period other than enhanced behavioural plasticity suggested by the appearance of the biface. We offer here a model of hominin occupation for north-west Europe termed the ‘punctuated long chronology’ and suggest that the major changes in the European Lower Palaeolithic record that occur at a species-wide level may post-date, rather than precede, the Anglian Glaciation (marine isotope stage (MIS) 12).
... Skeletal weight is a significant portion of the body mass and comprises, on average, approximately 14% of the body mass in modern humans (Shephard, 1991;Clarys et al. 1999;Zilhman & Bolter, 2015). Therefore, changes in skeletal weight during our evolutionary history would have affected numerous adaptive and ecologically relevant characteristics, such as biomechanical efficiency (Ruff et al. 1991), energetic requirements (Froehle & Churchill, 2009), skeletal growth and development (Ruff, 2003), pregnancy and childbirth (Aiello & Key, 2002), brain growth (Ponce de Leon et al. 2008), encephalization (Ruff et al. 1997) and population growth (Sorensen & Leonard, 2001), among others. ...
Article
Body mass estimation in fossil human species is a crucial topic in paleoanthropology as it yields information about ecologically relevant characteristics. Nevertheless, variables crucial to body mass estimation such as bone volume and skeletal weight have never before been calculated in a fossil human species. The exceptional state of preservation of several fossil human long bones from the Sima de los Huesos (SH) Middle Pleistocene site, in the Sierra de Atapuerca, makes it possible to calculate for the first time the absolute bone volume in five complete long bones (two femora and three humeri) of a fossil human species, an approach not possible in fragmentary or poorly preserved fossils. We have relied on computed tomography scans and 3D reconstructions to calculate bone volume. A sample of 62 complete bones of robust recent humans was also used for comparative purposes. The male SH femora (weight-bearing bones) and humeri (non-weight-bearing bones) have, relative to their size, greater bone volume (volume of bone tissue over total bone volume) than the equivalent bones in our recent human sample. As mass is volume 9 density, and bone tissue density (as a material) is similar across mammals, we calculate bone mass, and our results show that the SH hominins had on average heavier long bones than extant humans of the same size. From the femoral weight at hand, we have estimated the total skeletal weight in two SH individuals, which is about 36% heavier than in the recent humans of the equivalent body size. Using different methods and skeletal variables, including skeletal weight, to estimate body mass in these two SH humans, we highlight the considerable differences in body mass estimates we obtained, and that the largest body mass estimate is the one based on the skeletal weight. Our results suggest that we cannot assume the same relative proportion of bone volume and bone and skeletal weight characterized the entire genus Homo. Given that skeletal weight has a significant influence on body mass, current body mass estimates of fossil Homo specimens could be systematically underestimated. Thus, the significantly larger bone volume and heavier bones, probably throughout the entire skeleton, of SH humans could have had consequences for many biological parameters in this Pleistocene population and considerable importance for studies focusing on adaptive and ecologically relevant characteristics. Although more recent human samples should be analyzed, in our view, the high skeletal robusticity of the SH sample, including larger bone volume and skeletal weight, is part of their adaptive body type selected for throughout the Pleistocene to support different mechanical and activity regimes and formed under tight genetic control, including control over bone formative and regulatory processes.
... Such a diet is unlikely to meet this energy requirement. Plant foods such as roots and tubers provide more digestible starches and fewer nsps, increasing the energy available from that food and reducing the need for a large gut to process large quantities of highly fibrous plant food (Aiello & Key 2002). Savannas and wetlands were prime sources for these underground storage organs and it is these roots and tubers, combined with an increased meat diet, which are most likely to have given early Homo the energy resource to make significant morphological changes (Hardy et al. 2015). ...
... One likely point is somewhere between the origin of the genus Homo, and the evolution of our species, Homo sapiens. Modelling work by Aiello and Key (2002) on the energetic requirements of Homo erectus suggest that, because brain and body size increase with the evolution of this species, females would have been unable to provision their infants by their own efforts alone; as a result, they would have needed to look to other adults, either female relatives and/or a male, for help. If so, then monogamy may have evolved at this point (Opie and Power 2008). ...
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There has been a long history of attempts to explain the evolution of monogamy in mammals in general (Kleiman 1977), and primates in particular (Alexander 1979), partly because of the implications that it may have for the evolution of monogamy in humans. Monogamy is a complex term though, with some species invariably found in pairs (such as owl monkeys), whereas other species can be monogamous, but flexibly take up other mating systems (such as callitrichid monkeys). Humans fit with the latter flexible group, as well as having the additional distinction between their mating system and their marriage system. However, it is fairly well established that monogamy is common in birds (90% of species) (Lack 1968) due to the short time period between mating and egg laying that allows a male to increase his reproductive success through sharing high levels of offspring care (incubating, hatching and rearing), rather than leaving the female he has just mated with to look for other females with whom to mate. The particular reproductive strategy of mammals, with a long gestation period followed by lactation, reduces the opportunities for a male to provide direct care for his offspring, therefore most males move on after mating to seek other fertile females. As a result, monogamy is rare among mammals (5% of species) (Lukas and Clutton-Brock 2013). It is surprising, then, that monogamy is unusually prevalent in one particular mammal order, namely the primates (where 30% of species are monogamous) (Opie, et al. 2013a), with monogamy occurring in all the major primate families (Opie, et al. 2012).
... With the emergence of the genus Homo at 2.0 mya (H. ergaster/erectus) [4], there was a marked increase in body size, mainly in females, who almost double in size compared with Australopithecine [5]. The oldest fossil evidence for Homo sapiens is from Southern and Eastern Africa, dating to about 160-250 kya [6,7]. ...
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Abstract Background Humans and other primates have evolved particular morphological and biological traits (e.g., larger brains, slower growth, longer-lived offspring) that distinguish them from most other mammals. The evolution of many distinctive human characteristics, such as our large brain sizes, reduced gut sizes, and high activity budgets, suggest major energetic and dietary shifts. Main body Over the course of the last three million years, hominin brain sizes tripled. It is often taken for granted that the benefit of a larger brain is an increase in “intelligence” that makes us stand out among other mammals, including our nearest relatives, the primates. In the case of humans, brain expansion was associated with changes in diet, foraging, and energy metabolism. The first marked expansion occurred with the appearance of the genus Homo. Improved diet quality, allomaternal subsidies, cognitive buffering [by earlier weaning and longer juvenile periods], reduced costs for locomotion and by cooperative behavior, and reduced allocation to production, all operated simultaneously, thus enabling the extraordinary brain enlargement in our lineage. Conclusion It appears that major expansion of brain size in the human lineage is the product of synergistically interacting dietary/nutritional and social forces. Although dietary change was not being the sole force responsible for the evolution of large brain size, the exploitation of high-quality foods likely fueled the energetic costs of larger brains and necessitated more complex behaviors that would have selected for greater brain size.
... In the Pleistocene, this intersection has also been examined in terms of wider trends in hominin evolution (e.g. Aiello & Key 2002;Snodgrass & Leonard 2009). However, specific references to women's lives and behaviours, and especially gender, are limited (Peterson 2010, 254; for a discussion on gender in early agricultural societies based on nonarchaeological data, see Hansen et al. 2015). ...
Article
In the last 20 years, demography has re-emerged as a key research area within archaeology. This research has refined archaeological demographic methods and examined the relationships between demographic, cultural and environmental change. Here, I discuss how the results of the growing corpus of archaeological demographic studies can contribute to gender archaeology, aiding the incorporation of women into narratives of the past. By considering the important role of women in the demographic regimes of small-scale societies, I explain how archaeological demography can provide insights into the behaviour and lives of women, without relying on the often problematic identification of gendered artefacts, activities and/or places. Archaeological demography as a tool for gender archaeology also permits a move away from the female empiricism of simply adding women into archaeological narratives, to provide an alternative framework for the analysis of gender roles and practices. I demonstrate the feasibility and benefits of this approach using an example from the Upper Palaeolithic of southwestern France.
... One of the most important proxies for social behavior in a fossil species is its sexual dimorphism, which has the potential to provide a unique window into the social structure of an extinct population [1][2][3][4][5] . Considerable research has been invested in determining what information can be inferred from different patterns of sexual dimorphism [6][7][8][9][10][11][12][13][14][15] , as well as ensuring that statistical inferences of dimorphism in fragmentary fossil samples are accurate [16][17][18][19][20] . ...
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Sexual dimorphism can be one of the most important indicators of social behavior in fossil species, but the effects of time averaging, geographic variation, and differential preservation can complicate attempts to determine this measure from preserved skeletal anatomy. Here we present an alternative, using footprints from near Ileret, Kenya, to assess the sexual dimorphism of presumptive African Homo erectus at 1.5 Ma. Footprint sites have several unique advantages not typically available to fossils: a single surface can sample a population over a very brief time (in this case likely not more than a single day), and the data are geographically constrained. Further, in many cases, the samples can be much larger than those from skeletal fossil assemblages. Our results indicate that East African Homo erectus was more dimorphic than modern Homo sapiens, although less so than highly dimorphic apes, suggesting that the Ileret footprints offer a unique window into an important transitional period in hominin social behavior.
... Compared to other great apes we manage quite a feat by producing and simultaneously raising, on average, six to eight highly dependent offspring (Table 1.1, (Campbell and Wood, 1988)). This extreme dependency of infants stems from our energetically expensive brains (Aiello & Wheeler 1995) as gestation and lactation both significantly increase the energetic demands on the mother (by 25% and 39%, respectively (Aiello & Key 2002)). Furthermore, given our prolonged juvenile period and arguably minimal productive ability, offspring remain dependent on parents for many years as they, like many animals with slow life histories, invest in growth, development and skills (Kaplan et al. 2003). ...
Thesis
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Time is finite and no organism can avoid the allocation dilemma that this necessarily entails. A quintessential trade-off is that between parental investment and reproduction, otherwise known as the quality-quantity trade-off. However, humans may be exceptional among apes given our high quantity production of high quality offspring. This success has been argued only to be possible by breeding communally. In this thesis I explore questions surrounding trade-offs, communal breeding and their fitness consequences in a small-scale foraging society, the Agta. The first analysis examines the composition of Agta childcare using an innovative form of data collection to maximise sample sizes, previously a major limitation in hunter-gatherer research. The Agta, like many small-scale societies are prolific communal breeders. However, contra previous conclusions, juveniles and non-kin appeared to provide more allocare than grandmothers. Interactions with non-kin were associated with significant decreases in maternal workload, while interactions with siblings and grandmothers were not. The next analysis explores why both kin and non-kin behave cooperatively, finding support for kin selection among close kin and reciprocity for distant kin and non-kin allocare. Communal breeding appears to be an important mechanism to ensure enough childcare was received in the absence of other strategies to counter shortfalls in household energy budgets. The next analysis asks, what are the fitness consequences of maternal social networks and allocare? Mothers’ network centrality positively correlated with non-kin allocare as well as reproductive success, revealing the adaptive value of communal breeding. These results highlight the optimising nature of hunter-gatherer cooperation and life history strategies.
... Pyrotechnological skill represents a major shift in hominin behavior, allowing for an expansion of food resources, protection from nocturnal predators, and an extension of socializing hours in a day. The morphology of Pleistocene hominins, including Homo erectus (with its larger body size, relatively smaller teeth and probably less complex gut (Walker and Leakey, 1993;Aiello and Wheeler, 1995;Aiello and Key, 2002;Aiello and Wells, 2002;Evans et al., 2016), suggests to some researchers that hominins had controlled use of fire for cooking (Wrangham et al., 1999;Wrangham and Conklin-Brittain, 2003;Carmody and Wrangham, 2009;Wrangham, 2009Wrangham, , 2017Wrangham and Carmody, 2010;Carmody et al., 2011). Others have suggested that fire was a prerequisite for the consistent habitation of environments outside equatorial and tropical regions (Gowlett, 2006;Gowlett and Wrangham, 2013). ...
Article
Hominin fire use in the early Pleistocene has been debated since the early 1970s when consolidated reddened sediment patches were identified at FxJj20 East and Main, Koobi Fora, Kenya. Since then, researchers have argued for evidence of early Pleistocene fire use at a handful of archaeological sites with evidence of combustion. Some argue that morphological evidence of early Homo erectus fossils indicates a dietary shift to higher quality food sources, which could be achieved by cooking. Others contend that fire use does not become a regular behavior until later, in the middle Pleistocene, when archaeological sites begin to show regular evidence for fire use. An early date for hominin control of fire would help to explain the grade changes seen with the appearance of H. erectus, while a later date would mean that fire would have had little influence on the early development of the lineage. Early hominins would have encountered fire regularly on the landscape, increasing the possibility of hominins interacting with and habituating to natural landscape fire. Only a detailed understanding of the patterns of controlled and natural fires can lead to understanding of early hominin fire use. We present new work on the evidence of fire at the FxJj20 Site complex in Koobi Fora, dated to 1.5 Ma. We highlight evidence of burning found on site through Fourier Transform Infrared spectrometry, and describe ongoing work to investigate the association of hominin behavior and fire evidence. We present data supporting the hypothesis that the site is undisturbed and discuss spatial relationships showing burned material associated with non-burned material. We present data on a type of stone fragment, the Thermal Curve Fragment (TCF), which is indicative of knapped material being exposed to high heat. Finally, we suggest future directions on the topic of fire in the early Pleistocene.
... While human and chimpanzee mothers have a fairly similar body weight, adult humans today have upward of three times the brain volume of a chimp . This is an exceptional feat of energy provision in reproduction by human foremothers, because brain tissue is very energetically expensive (Aiello & Key, 2002;Aiello & Wheeler, 1995;Foley & Lee, 1991;Power & Aiello, 1997). ...
Chapter
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Are there constraints on the social conditions that could have given rise to language and symbolic cognition? Language has emerged in no other species than humans, suggesting a profound obstacle to its evolution. If language is seen as an aspect of cognition, limitations can be expected in terms of computational capacity. But if it is seen it as fundamentally for communication, then the problems will be found in terms of social relationships. Below a certain threshold of cooperation and trust, no language or symbolic communication could evolve (Knight & Lewis, 2017a); this has been termed a “platform of trust” (Wacewicz, 2017).... In this chapter, I argue that quite specific social conditions were prerequisite for the evolution of language- and symbol-ready hominins. One of the requirements differentiating our ancestors from other African apes was a switch to mainly female philopatry – females living with their relatives, rather than dispersing at sexual maturity – coevolving with an increasing tendency to egalitarianism....How did increasing egalitarianism affect males and potentially “feminize” male behavior for cooperative offspring care? How were male and female relations affected in the evolution of genus Homo and Homo sapiens?
... Maya (Kramer 2005a:227): observation period 7:00am-6:00pm, n 5 9 breastfeeding children (all <3 years of age); instantaneous scan sampling. Trinidad (Flinn 1992:66): observation period unspecified, instantaneous scan samples; children aged 0-4, number unspecified; values report direct care of children; grandmothers not reported separately, but included as "other." is even more expensive for mothers-almost 600 kcal per day (Aiello and Key 2002;Butte et al. 2004;Dufour and Sauther 2002;Thomson et al. 1970; note that sources vary slightly around these caloric estimates). If a pregnant woman did not receive help, she would have to increase her food production by 14%, and a lactating woman by 28%. ...
Article
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How There Got to Be So Many of Us: The Evolutionary Story of Population Growth and a Life History of Cooperation KAREN L. KRAMER, Journal of Anthropological Research 2019 One of the defining features of human evolution is our demographic success. As of August 2019, the world’s population exceeds 7.7 billion. The human capacity for population growth has profound effects on people’s lives today, but it is also one of the remarkable stories of our evolutionary past. Although most research and public attention has centered on the past 200 years, when growth has increased exponentially, global population growth prior to that was not trifling. Before the industrial era, humans populated all of the world’s environments with more than a billion people. Importantly, it was deep in the past when the biological and social underpinnings were established that allow humans to excel as reproducers and survivors. The evolutionary trends in fertility and survival that gave rise to human demographic success were fundamentally shaped by our ability to cooperate. This essay focuses on how the human dietary niche and life history presented novel opportunities for cooperation that tied younger and older generations together in ways that gave us our demographic edge. Key words: human demography, population growth, cooperation
... True even of our distant ancestors; seeAiello, Key (2002). ...
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Aim: This paper is on purpose provocative, in order to trigger off discussion on the future of human society. Humankind finds itself in a dire situation. Solutions have been put forth, but none has made a significant impact on carbon release or resources depletion. I add my proposal, the literary device of the dictator, as a possible scenario for dealing with the current crisis.. Design / Research methods: This paper is part of a larger project which uses micro-and macro-sociology and cliodynamics, archaeology, evolutionary biology, and dissipative systems theory to describe both our global system, and its implications for our species. I briefly critique three other approaches regarding their likelihood of success. Conclusions / findings: The self-organized dissipative system drives population, population density, and the exploitation and depletion of natural resources. The system is the interface between humans and the environment. It is unlikely any approach which is not 1. dramatic, 2. inclusive, and 3. determinedly focused on disarming the global system will prevent the complete depletion of the natural world, and the continued mass extinction. Originality / value of the article: The paper challenges commonly held assumptions regarding the system and human participation in it. The paper should be of interest to anyone concerned about humankind, given the breadth of our crisis; that is, the number of systems involved, from the climate, to the ocean, to the very nature of the global complex system itself. 1 "Rational" here has the common meaning: founded on cognition, reason and facts, and not emotion; dispassionate. Laurenc L. DE VITA 68 Implications of the research: The paper has strong implications for policy. It describes how perpetuating ideas like "sustainable growth" can only ensure the collapse of the global system, and perhaps the collapse of the natural systems as well. The consequence of applying the research would be desperate, frighteningly objective, but will allow, perhaps, Homo to continue. Limitations of the research: Future research could focus on re-interpreting data gathered by previous paradigms. Cliodynamics provides insight into the future by considering complex relationships. The limitations to the implications of the research lie in the fact that it is difficult to distinguish between "humankind" and the system.
... To give a life history example of the effects of food cooperation, if mothers did not receive food from others, they would have to increase their calorie production by 14% to 28% to fund gestation and lactation, respectively (this assumes that pregnancy across gestation costs an average of an extra 282 kcal/day, lactation costs an average of 567 extra kcal/day and a typical nonpregnant woman consumes 2000 kcal/ day; other sources vary slightly around these calorie estimates [109][110][111][112]). However, pregnant and lactating mothers often decrease, not increase, their time spent foraging for food, in agricultural work or other domestic activities [82,[113][114][115][116]. ...
Article
The human diet has undergone substantial modifications since the emergence of modern humans and varies considerably in today's traditional societies. Despite these changes and cross-cultural differences, the human diet can be characterized by several common elements. These include diverse, high quality foods, technological complexity to acquire and process food, and the establishment of home bases for storage, processing and consumption. Together these aspects of the human diet challenge any one individual to independently meet all of his or her daily caloric needs. Humans solve this challenge through food sharing, labor exchange and the division of labor. The cooperative nature of the human diet is associated with downstream effects on our life history and physiology. This paper overviews the constellation of traits that likely led to a cooperative economy of food, and draws on ethnographic examples to illustrate its effects on human life history and physiology. Two detailed examples using body composition, time allocation and food acquisition data show how cooperation among Savanna Pumé hunter-gatherers affects activity levels, sexual dimorphism in body fat, maturational pace and age at first birth.
... Together these properties not only directly affect consumer nutrient intake, but may also result in a more favorable balance among the nutrients of food, which in turn can play a critical role in food selection (Felton et al., 2009). Therefore, foods in the late stages of fermentation could have represented a critical nutritional resource to hominids, particularly as energetically expensive life-history traits such as long juvenile periods, short interbirth intervals, and large brains emerged across evolutionary time (Aiello & Key, 2002;Antón et al., 2014;Leonard & Robertson, 1992. The consumption of other high-quality diet items such as meat and cooked food has also been hypothesized to have provided essential nutritional resources for the development and maintenance of these traits in hominids (Aiello & Wells, 2002;DeCasien et al., 2017;Wrangham, 2009;Wrangham & Conklin-Brittain, 2003). ...
Article
Objectives Although fermented food use is ubiquitous in humans, the ecological and evolutionary factors contributing to its emergence are unclear. Here we investigated the ecological contexts surrounding the consumption of fruits in the late stages of fermentation by wild primates to provide insight into its adaptive function. We hypothesized that climate, socioecological traits, and habitat patch size would influence the occurrence of this behavior due to effects on the environmental prevalence of late‐stage fermented foods, the ability of primates to detect them, and potential nutritional benefits. Materials and methods We compiled data from field studies lasting at least 9 months to describe the contexts in which primates were observed consuming fruits in the late stages of fermentation. Using generalized linear mixed‐effects models, we assessed the effects of 18 predictor variables on the occurrence of fermented food use in primates. Results Late‐stage fermented foods were consumed by a wide taxonomic breadth of primates. However, they generally made up 0.01%–3% of the annual diet and were limited to a subset of fruit species, many of which are reported to have mechanical and chemical defenses against herbivores when not fermented. Additionally, late‐stage fermented food consumption was best predicted by climate and habitat patch size. It was more likely to occur in larger habitat patches with lower annual mean rainfall and higher annual mean maximum temperatures. Discussion We posit that primates capitalize on the natural fermentation of some fruits as part of a nutritional strategy to maximize periods of fruit exploitation and/or access a wider range of plant species. We speculate that these factors contributed to the evolutionary emergence of the human propensity for fermented foods.
... In all, the fossil record indicates that H. erectus evolved slowed general maturation, more helpless infants, larger adult brains, and increasing sophisticated tools-all of which adds to an adaptive network of higher-quality offspring, long and intense learning, and reliance on complex behavior. Taken together with evidence of larger body size in females, Aiello and Key (2002) pointed out the enormous energy demands for reproduction in an H. erectus female, demands that necessitate change in energetic strategies. Whenever it did evolve, a childhood period would at first diminish the reproductive cost of this "high-quality strategy," and eventually allow the strategy to become even more extreme. ...
Chapter
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http://deepblue.lib.umich.edu/bitstream/2027.42/134403/1/Bogin & Smith_2000_Evolution of the Human Life Cycle rd.pdf
... Our ancestors relied on foraging and hunting. The Pleistocene environments in southern and eastern Africa were open and xeric with dispersed resources (Aiello & Key, 2002;Benyshek & Watson, 2006). Through lactation, a mother could buffer her breastfed infant from periodic shortfalls in food supply because milk production can utilize maternal adipose tissue. ...
Chapter
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In this chapter, we use an evolutionary lens to deepen understanding of maternal and family needs in the early postpartum period so that health care can be more aligned with confronted realities. The discussion is centered around the concept of the 4th trimester, which is the period between birth and the first 3 months postpartum. This framework encourages a holistic understanding of perinatal health by drawing attention to evolved maternal-infant needs. By addressing these ultimate-level contributors to health issues, we can facilitate more effective clinical support, comprehensive research, and a fuller “village” to enable new families to thrive. Core to this approach is the concept of trade-offs between parents and offspring, exemplified by lactation as a prime example of the complexities of dyadic needs and gap between the current culture of health and optimal support.
... absolute mesenteric and omental fat depots, abdominal girth, and adipocyte area) was unexpected, particularly within the context of the predictive adaptive responses or thrifty phenotype theories, which would predict a greater propensity for energy storage (and hence fat accumulation). Although this may reflect an overall healthier metabolic state, adiposity in females provides the metabolic means of producing energetically costly offspring 24 . Therefore, the long-term implications of altered body composition on reproductive function remain an important question for future studies. ...
Article
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Stressors during the fetal and postnatal period affect the growth and developmental trajectories of offspring, causing lasting effects on physiologic regulatory systems. Here, we tested whether reduced uterine artery blood flow in late pregnancy would alter body composition in the offspring, and whether feeding offspring a western diet (WD) would aggravate these programming effects. Pregnant rats underwent bilateral uterine artery ligation (BUAL) or sham surgery on gestational day (GD)18 (term = GD22). At weaning, offspring from each group received either a normal diet (ND) or a WD. BUAL surgery increased fetal loss and caused offspring growth restriction, albeit body weights were no longer different at weaning, suggesting postnatal catch-up growth. BUAL did not affect body weight gain, fat accumulation, or plasma lipid profile in adult male offspring. In contrast, while ND-fed females from BUAL group were smaller and leaner than their sham-littermates, WD consumption resulted in excess weight gain, fat accumulation, and visceral adiposity. Moreover, WD increased plasma triglycerides and cholesterol in the BUAL-treated female offspring without any effect on sham littermates. These results demonstrate that reduced uterine artery blood flow during late pregnancy in rodents can impact body composition in the offspring in a sex-dependent manner, and these effects may be exacerbated by postnatal chronic WD consumption.
... The most likely candidates are Homo ergaster or Homo erectus due to the estimate that females of these species were 50% heavier than australopithecine and earlier Homo females. Their larger body size would have necessitated greater energy consumption, which may have been supplied via cooperation in division of labor and the provisioning of food (Aiello and Key, 2002). ...
Chapter
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The postnatal life cycle of the social mammals, including the nonhuman primates, has three basic stages of development: infant, juvenile, and adult. Human beings are unusual and add a childhood stage after infancy and an adolescence stage after the juvenile stage. The human pattern of life history in both brain and body growth entails a large investment of energy and time by older members of the social group toward infants and children. This is achieved via a new type of breeding strategy called biocultural reproduction. The evolution of human life history results in enhanced reproductive success for the individuals and our species.
... It has been suggested that this adaptation facilitated the increased population density characteristic of sedentary communities by enhancing defence against infections [26]. Humans also have shorter periods of lactation and shorter interbirth intervals than other apes [27]. This may have been facilitated by the development of a complementary feeding period, during which the offspring simultaneously receives nutrition from milk and from other foods provided by the mother. ...
Article
Promoting breastfeeding is an important public health intervention, with benefits for infants and mothers. Even modest increases in prevalence and duration may yield considerable economic savings. However, despite many initiatives, compliance with recommendations is poor in most settings-particularly for exclusive breastfeeding. Mothers commonly consult health professionals for infant feeding and behavioural problems.
... It is therefore likely that ancestral hominins engaged in at least as much kin care as other primate species do today. Ancestral hominins are argued to have shifted to a strategy of cooperative breeding [102][103][104] with increased birth rates leading to greater numbers of dependent young [105] with immature immune systems. Based on the links between infant rearing systems and care for sick kin in other taxa, a shift to a more intensive breeding system may have produced a corresponding increase in care for sick kin (who were necessary for cooperative infant care). ...
Article
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The COVID-19 pandemic has revealed an urgent need for a comprehensive, multidisciplinary understanding of how healthcare systems respond successfully to infectious pathogens –and how they fail. This paper contributes a novel perspective that focuses on the selective pressures that shape healthcare systems over evolutionary time. We use a comparative approach to trace the evolution of care-giving and disease control behaviours across species and then map their integration into the contemporary human healthcare system. Self-care and pro-health environmental modification are ubiquitous across animals, while derived behaviours like care for kin, for strangers, and group-level organisational responses have evolved via different selection pressures. We then apply this framework to our behavioural responses to COVID-19 and demonstrate that three types of conflicts are occurring: 1) conflicting selection pressures on individuals, 2) evolutionary mismatches between the context in which our healthcare behaviours evolved and our globalised world of today and 3) evolutionary displacements in which older forms of care are currently dispensed through more derived forms. We discuss the significance of understanding how healthcare systems evolve and change for thinking about the role of healthcare systems in society during and after the time of COVID-19—and for us as a species as we continue to face selection from infectious diseases.
... According to this model, multi-level societies in extinct hominins would have increased benefits for both sexes in terms of reproduction, feeding and protection of the offspring. Indeed, bonds between females would have been highly beneficial, as they would have allowed some cooperative foraging and breeding, which can decrease the individual costs [96,97]. Regarding males, the variable spatial distribution of female H. erectus at least seasonally may have placed selective pressures on them to become the resident or the alpha male of small groups [94] and to keep track of a limited number of females to facilitate mating access. ...
Article
Maintaining the balance between costs and benefits is challenging for species living in complex and dynamic socio-ecological environments, such as primates, but also crucial for shaping life history, reproductive and feeding strategies. Indeed, individuals must decide to invest time and energy to obtain food, services and partners, with little direct feedback on the success of their investments. Whereas decision-making relies heavily upon cognition in humans, the extent to which it also involves cognition in other species, based on their environmental constraints, has remained a challenging question. Building mental representations relating behaviours and their long-term outcome could be critical for other primates, but there are actually very little data relating cognition to real socio-ecological challenges in extant and extinct primates. Here, we review available data illustrating how specific cognitive processes enable(d) modern primates and extinct hominins to manage multiple resources (e.g. food, partners) and to organize their behaviour in space and time, both at the individual and at the group level. We particularly focus on how they overcome fluctuating and competing demands, and select courses of action corresponding to the best possible packages of potential costs and benefits in reproductive and foraging contexts. This article is part of the theme issue ‘Existence and prevalence of economic behaviours among non-human primates’.
... Diet is intimately linked to the production of healthy offspring, as described by Aiello and Key (2002) for Homo erectus. Glucose provides the main energy source for the growing fetus, and low glucose availability can compromise fetal survival (Herrera, 2000;Baumann et al., 2002). ...
Article
Evidence for plants rarely survives on Paleolithic sites, while animal bones and biomolecular analyses suggest animal produce was important to hominin populations, leading to the perspective that Neanderthals had a very-high-protein diet. But although individual and short-term survival is possible on a relatively low-carbohydrate diet, populations are unlikely to have thrived and reproduced without plants and the carbohydrates they provide. Today, nutritional guidelines recommend that around half the diet should be carbohydrate, while low intake is considered to compromise physical performance and successful reproduction. This is likely to have been the same for Paleolithic populations, highlighting an anomaly in that the basic physiological recommendations do not match the extensive archaeological evidence. Neanderthals had large, energy-expensive brains and led physically active lifestyles, suggesting that for optimal health they would have required high amounts of carbohydrates. To address this anomaly, we begin by outlining the essential role of carbohydrates in the human reproduction cycle and the brain and the effects on physical performance. We then evaluate the evidence for resource availability and the archaeological evidence for Neanderthal diet and investigate three ways that the anomaly between the archaeological evidence and the hypothetical dietary requirements might be explained. First, Neanderthals may have had an as yet unidentified genetic adaptation to an alternative physiological method to spare blood glucose and glycogen reserves for essential purposes. Second, they may have existed on a less-than-optimum diet and survived rather than thrived. Third, the methods used in dietary reconstruction could mask a complex combination of dietary plant and animal proportions. We end by proposing that analyses of Paleolithic diet and subsistence strategies need to be grounded in the minimum recommendations throughout the life course and that this provides a context for interpretation of the archaeological evidence from the behavioral and environmental perspectives.
... Together these properties not only directly affect consumer nutrient intake, but may also result in a more favorable balance among the nutrients of food, which in turn can play a critical role in food selection (Felton et al., 2009). Therefore, foods in the late stages of fermentation could have represented a critical nutritional resource to hominids, particularly as energetically expensive life-history traits such as long juvenile periods, short interbirth intervals, and large brains emerged across evolutionary time (Aiello & Key, 2002;Antón et al., 2014;Leonard & Robertson, 1992. The consumption of other high-quality diet items such as meat and cooked food has also been hypothesized to have provided essential nutritional resources for the development and maintenance of these traits in hominids (Aiello & Wells, 2002;DeCasien et al., 2017;Wrangham, 2009;Wrangham & Conklin-Brittain, 2003). ...
Article
Objectives: Although fermented food use is ubiquitous in humans, the ecological and evolutionary factors contributing to its emergence are unclear. Here we investigated the ecological contexts surrounding fermented food use by wild primates to provide insight into its adaptive function. We hypothesized that climate, socio-ecological traits, and habitat size would influence the occurrence of this behavior due to effects on the environmental prevalence of fermented foods, the ability of primates to detect them, and potential nutritional benefits. Materials and Methods: We compiled data from field studies lasting at least nine months to describe the contexts in which primates were observed consuming fruits in the late stages of fermentation. Using generalized linear mixed-effects models, we assessed the effects of 18 predictor variables on the occurrence of fermented food use in primates. Results: Fermented foods were consumed by a wide taxonomic breadth of primates. However, they generally made up less than 3% of the annual diet and were limited to a subset of fruit species, many of which are reported to have mechanical and chemical defenses against herbivores when not fermented. Additionally, fermented food consumption was best predicted by climate and habitat size. It was more likely to occur in larger habitats with lower annual mean rainfall, higher annual mean maximum temperatures, and lower annual mean minimum temperatures. Discussion: We posit that primates capitalize on the natural fermentation of some fruits as part of a nutritional strategy to maximize periods of fruit exploitation and/or access a wider range of plant species. We speculate that these factors contributed to the evolutionary emergence of the human propensity for fermented foods.
... It has been suggested that this adaptation facilitated the increased population density characteristic of sedentary communities by enhancing defence against infections [26]. Humans also have shorter periods of lactation and shorter interbirth intervals than other apes [27]. This may have been facilitated by the development of a complementary feeding period, during which the offspring simultaneously receives nutrition from milk and from other foods provided by the mother. ...
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Background: Promoting breastfeeding is an important public health intervention, with benefits for infants and mothers. Even modest increases in prevalence and duration may yield considerable economic savings. However, despite many initiatives, compliance with recommendations is poor in most settings - particularly for exclusive breastfeeding. Mothers commonly consult health professionals for infant feeding and behavioural problems. Main body: We argue that broader consideration of lactation, incorporating evolutionary, comparative and anthropological aspects, could provide new insights into breastfeeding practices and problems, enhance research and ultimately help to develop novel approaches to improve initiation and maintenance. Our current focus on breastfeeding as a strategy to improve health outcomes must engage with the evolution of lactation as a flexible trait under selective pressure to maximise reproductive fitness. Poor understanding of the dynamic nature of breastfeeding may partly explain why some women are unwilling or unable to follow recommendations. Conclusions: We identify three key implications for health professionals, researchers and policymakers. Firstly, breastfeeding is an adaptive process during which, as in other mammals, variability allows adaptation to ecological circumstances and reflects mothers' phenotypic variability. Since these factors vary within and between humans, the likelihood that a 'one size fits all' approach will be appropriate for all mother-infant dyads is counterintuitive; flexibility is expected. From an anthropological perspective, lactation is a period of tension between mother and offspring due to genetic 'conflicts of interest'. This may underlie common breastfeeding 'problems' including perceived milk insufficiency and problematic infant crying. Understanding this - and adopting a more flexible, individualised approach - may allow a more creative approach to solving these problems. Incorporating evolutionary concepts may enhance research investigating mother-infant signalling during breastfeeding; where possible, studies should be experimental to allow identification of causal effects and mechanisms. Finally, the importance of learned behaviour, social and cultural aspects of primate (especially human) lactation may partly explain why, in cultures where breastfeeding has lost cultural primacy, promotion starting in pregnancy may be ineffective. In such settings, educating children and young adults may be important to raise awareness and provide learning opportunities that may be essential in our species, as in other primates.
... By two million years ago, there is an apparent increase in the body mass of Homo (Pontzer, 2012;Antón et al., 2014), which in turn is related to its wider geographic distribution compared to other hominins (Antón, 2003) and an increase in energy expenditure (Aiello and Key, 2002;Aiello and Wells, 2002). Additionally, there was a shift in the archaeological record from assemblages of low-density artifact scatters in narrower depositional contexts to denser concentrations of archaeological material in a broader array of habitat settings (Plummer and Finestone, 2018). ...
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Climate variability and hominin evolution are inextricably linked. Yet, hypotheses examining the impact of large-scale climate shifts on hominin landscape ecology are often constrained by proxy data coming from off-site lake and ocean cores and temporal offsets between paleoenvironmental and archaeological records. Additionally, landscape response data (most commonly, records of vegetation change), are often used as a climate proxy. This is problematic as it assumes that vegetation change signifies global or regional climate shifts without accounting for the known non-linear behavior of ecological systems and the often-significant spatial heterogeneity in habitat structure and response. The exploitation of diverse, rapidly changing habitats by Homo by at least two million years ago highlights that the ability to adapt to landscapes in flux had emerged by the time of our genus’ African origin. To understand ecosystem response to climate variability, and hominin adaptations to environmental complexity and ecological diversity, we need cross-disciplinary datasets in direct association with stratified archaeological and fossil assemblages at a variety of temporal and spatial scales. In this article, we propose a microhabitat variability framework for understanding Homo ’s adaptability to fluctuating climates, environments, and resource bases. We argue that the exploitation of microhabitats, or unique ecologically and geographically defined areas within larger habitats and ecoregions, was a key skill that allowed Homo to adapt to multiple climates zones and ecoregions within and beyond Africa throughout the Pleistocene.
... Together these properties not only directly affect consumer nutrient intake, but may also result in a more favorable balance among the nutrients of food, which in turn can play a critical role in food selection (Felton et al., 2009). Therefore, foods in the late stages of fermentation could have represented a critical nutritional resource to hominids, particularly as energetically expensive life-history traits such as long juvenile periods, short interbirth intervals, and large brains emerged across evolutionary time (Aiello & Key, 2002;Antón et al., 2014;Leonard & Robertson, 1992. The consumption of other high-quality diet items such as meat and cooked food has also been hypothesized to have provided essential nutritional resources for the development and maintenance of these traits in hominids (Aiello & Wells, 2002;DeCasien et al., 2017;Wrangham, 2009;Wrangham & Conklin-Brittain, 2003). ...
Article
Objectives Although fermented food use is ubiquitous in humans, the ecological and evolutionary factors contributing to its emergence are unclear. Here we investigated the ecological contexts surrounding the consumption of fruits in the late stages of fermentation by wild primates to provide insight into its adaptive function. We hypothesized that climate, socioecological traits, and habitat patch size would influence the occurrence of this behavior due to effects on the environmental prevalence of late‐stage fermented foods, the ability of primates to detect them, and potential nutritional benefits. Materials and methods We compiled data from field studies lasting at least 9 months to describe the contexts in which primates were observed consuming fruits in the late stages of fermentation. Using generalized linear mixed‐effects models, we assessed the effects of 18 predictor variables on the occurrence of fermented food use in primates. Results Late‐stage fermented foods were consumed by a wide taxonomic breadth of primates. However, they generally made up 0.01%–3% of the annual diet and were limited to a subset of fruit species, many of which are reported to have mechanical and chemical defenses against herbivores when not fermented. Additionally, late‐stage fermented food consumption was best predicted by climate and habitat patch size. It was more likely to occur in larger habitat patches with lower annual mean rainfall and higher annual mean maximum temperatures. Discussion We posit that primates capitalize on the natural fermentation of some fruits as part of a nutritional strategy to maximize periods of fruit exploitation and/or access a wider range of plant species. We speculate that these factors contributed to the evolutionary emergence of the human propensity for fermented foods.
Chapter
Schimpansen leben in einem polygynandrienen Paarungssystem, in dem sich Weibchen mit mehreren Männchen und Männchen mit mehreren Weibchen paaren. Vermutlich haben sich Menschen nach dem pan-homo Split vor ca. 7 Millionen Jahren von einem polygynandrienen zu einem polygynen (Harem) und dann zu einem überwiegend monogamen Paarungssystem entwickelt. Die Sexualität des Jetzt-Menschen zeigt zugleich Merkmale des älteren polygynen und des neueren monogamen Paarungssystems. In diesem Kapitel werden zahlreiche Beispiele von Anpassungen an das ältere und an das jüngere Paarungssystem des Menschen erläutert. Im Ergebnis bedeutet es, dass wir Menschen ein sexuelles Mischwesen sind. Daraus können sich Probleme in unserer Sexualität und Partnerschaft ergeben. Die Kenntnis dieser sehr verschiedenen sexuellen Strategien des Jetzt-Menschen hilft, die eigene Sexualität und insbesondere die des Gegengeschlechts besser zu verstehen und eine gute Sexualtherapie zu machen.
Thesis
L’organisation biologique, du niveau moléculaire jusqu’au niveau des performances de l’organisme. La locomotion est une fonction neurophysiologique hautement intégrée illustrant un tel processus multi-échelle. Le déclin des performances de locomotion avec l’âge, comme la vitesse maximale, a été observé pour de nombreuses espèces, aussi bien en captivité qu’en milieu naturel. Cependant, ces descriptions restent souvent succinctes, sans précision sur la progression de ces performances au cours du vieillissement. Dans ces travaux, nous utilisons une équation bi-phasique pour décrire la relation entre performance de locomotion et âge sur l’ensemble de la durée de la vie pour Caenorhabditis elegans, Mus domesticus, Canis familiaris, Equus caballus et Homo sapiens. Les performances maximales de locomotion se révèlent être des bio-marqueurs robustes pour suivre la progression des performances sur l’ensemble de la durée de vie des animaux, permettant ainsi d’estimer le pic physiologique et le début du déclin des performances. De plus, dans tous les cas, nous remarquons que la forme de progression des performances maximales selon l’âge est similaire et conservée d’une espèce à l’autre ; seule varie la pente dans le temps, dépendant de l’espèce et la performance mesurée. L’observation des performances selon le genre ne montre pas de différence dans la forme de l’enveloppe. Néanmoins, elle révèle des écarts variables dans les performances maximales entre femelles et mâles selon les espèces. Enfin, les conditions thermiques affectent les performances maximales de locomotion, mais la forme de l’enveloppe reste aussi préservée. Nous avons ensuite étudié le développement et l’expansion de cette dynamique au cours du siècle dernier pour les performances athlétiques maximales d’Homo sapiens. Cette étude révèle que la forme s’est progressivement précisée au cours du temps en s’étendant à tous les âges et suivant homothétiquement la progression des records du monde. Néanmoins, la progression semble ralentir au cours des dernières décennies, laissant présager l’atteinte possible des limites biologiques d’Homo sapiens. Ces travaux offrent de nouvelles perspectives sur l’utilité des approches comparatives et l’utilisation d’un bio-marqueur comme les performances de locomotion pour suivre les dynamiques sur l’ensemble de la durée de vie à différentes échelles. Elles apportent aussi un regard novateur sur la progression des performances avec l’âge, en intégrant à la fois les processus de développement et de vieillissement, permettant ainsi de préciser les pics physiologiques et la forme des progressions des performances sur toute la durée de la vie.
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The fact that world-over people seem inexplicably motivated to allocate time and effort to apparently useless cultural practices, like the arts, has led several evolutionary scholars to suggest that these might be costly Zahavian signals correlated with genetic fitness, such as the infamous peacock’s tail. In this paper, I review the fundamental arguments of the hypothesis that art evolved and serves as a costly Zahavian signal. First, I look into the hypothesis that humans exert mate choice for indirect benefits and argue that the data supports mate choice for direct benefits instead. Second, I argue that art practice may well be a costly signal, however not necessarily related to good genes. Third, I suggest that Thorstein Veblen’s original concept of conspicuous signals as social tools to obtain and convey prestige provides a better account than the Zahavian model for the evolution and function of art in society. As a Veblenian signal, art could still have many of the effects suggested for visual art as a Zahavian signal, except not for the indirect benefits of optimal offspring, but for the direct benefits of acquiring and conveying social status.
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Cambridge Core - Biological Anthropology and Primatology - The Evolutionary Biology of the Human Pelvis - by Cara M. Wall-Scheffler
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Humans are the only species to have evolved cooperative care-giving as a strategy for disease control. A synthesis of evidence from the fossil record, paleogenomics, human ecology, and disease transmission models, suggests that care-giving for the diseased evolved as part of the unique suite of cognitive and socio-cultural specializations that are attributed to the genus Homo. Here we demonstrate that the evolution of hominin social structure enabled the evolution of care-giving for the diseased. Using agent-based modeling, we simulate the evolution of care-giving in hominin networks derived from a basal primate social system and the three leading hypotheses of ancestral human social organization, each of which would have had to deal with the elevated disease spread associated with care-giving. We show that (1) care-giving is an evolutionarily stable strategy in kin-based cooperatively breeding groups, (2) care-giving can become established in small, low density groups, similar to communities that existed before the increases in community size and density that are associated with the advent of agriculture in the Neolithic, and (3) once established, care-giving became a successful method of disease control across social systems, even as community sizes and densities increased. We conclude that care-giving enabled hominins to suppress disease spread as social complexity, and thus socially-transmitted disease risk, increased.
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In humans, high levels of investment are required to raise offspring, because of the prolonged developmental period and short interbirth intervals. The costs borne by individual mothers may be mitigated by obtaining social support from others. This strategy could be particularly valuable for first-time mothers, who lack first-hand experience and whose offspring have higher mortality risk than later-born siblings. As raising children is potentially stressful, mothers may gain from others sharing their experience, providing knowledge/information and emotional support. Being genetically related to both mother and grandchild, maternal grandmothers may be especially well placed to provide such support, while also gaining fitness benefits. We tested the over-arching hypothesis that first-time mothers and their young children supported by the maternal grandmother would have lower levels of stress and better health outcomes, compared to mother–infant dyads lacking such grandmaternal support. A cohort of 90 mother–infant dyads (52 with grandmaternal support, 38 without) was recruited in Merida, Mexico. We assessed anthropometry and body composition in both mother and child, along with maternally perceived stress and child temperament, and documented maternal social relationships. No differences were found in perceived stress/temperament or anthropometry of either mothers or children, according to the presence/absence of grandmaternal support. However, a composite score of whether grandmothers provided advice on infant feeding was positively associated with child nutritional status. Mothers without grandmaternal support reported seeking more informational and emotional support from other female relatives for childcare, potentially compensating for limited/absent grandmaternal support. Our findings may help develop interventions to improve maternal and child health by targeting the dynamics of maternal social networks.
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Choosing a mate is perhaps the most important decision a sexually reproducing organism makes in its lifetime. And yet, psychologists lack a precise description of human mate choice, despite sustained attention from several theoretical perspectives. Here, I argue this limited progress owes to the complexity of mate choice and describe a new modeling approach, called “couple simulation,” designed to compare models of mate choice by challenging them to reproduce real couples within simulated mating markets. I present proof-of-concept simulations that demonstrate couple simulation can identify a population’s true model of mate choice. Furthermore, I apply couple simulation to two samples of real couples and find that the method (a) successfully reconstructs real-world couples, (b) discriminates between models of mate choice, and (c) predicts a wide range of dimensions of relationship quality. Collectively, these results provide evidence that couple simulation offers a framework useful for evaluating theories of human mate choice.
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Beginning in the early 1990s, the theme of mobility became central to many studies of Paleolithic lithic technology. Models relating group movements to the design, production, and treatment of stone artifacts have been widely employed both to explain features of Paleolithic assemblages, and as a source of information about the ecology of Pleistocene foragers. However, many of the questions that “mobility thinking” was originally adopted to answer are no longer at the center of inquiry in Paleolithic research. To remain relevant to new research agendas, new approaches to mobility and lithic technology should be developed. In keeping with the theme of this special issue, this paper discusses three areas where relatively simple changes in theory and practice could help to integrate “mobility thinking” into emerging research questions of broad, cross-disciplinary relevance: these include territories and ranging patterns, social networks, and intra-group variation in mobility.
Chapter
The Evolutionary Biology of the Human Pelvis - by Cara M. Wall-Scheffler January 2020
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Reproductive senescence in human females takes place long before other body functions senesce. This fact presents an evolutionary dilemma since continued reproduction should generally be favored by natural selection. Two commonly proposed hypotheses to account for human menopause are (a) a recent increase in the human lifespan and (b) a switch to investment in close kin rather than direct reproduction. No support is found for the proposition that human lifespans have only recently increased. Data from Ache hunter-gatherers are used to test the kin selection hypothesis. Ache data do not support the proposition that females can gain greater fitness benefits in old age by helping kin rather than continuing to reproduce. Nevertheless, one crucial parameter in the model, when adjusted to the highest value within the measured 95% confidence interval, would lead to the evolution of reproductive senescence at about 53 years of age. Further investigation is necessary to determine whether the kin selection hypothesis of menopause can account for its current maintenance in most populations.
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SYNOPSIS. On behavioral, hormonal, and physiological grounds, mammalian reproduction can be compartmentalized into the following continuous sequence of events: mating (courtship, estrous), gestation, parturition, lactation, post-lactational parental care, and maternal recovery. We point out that comparing the relative allocation of energy for these events across mammals is difficult because of life history variability (e.g., litter size, birth weight), allometry, phylogeny, and individual variation. We review the empirical and theoretical literature on each of these events with respect to: different methodologies in measuring energy use;broad patterns of energy consumption across diverse mammalian taxa; and, identification of particular reproductive characteristics (e.g., birthing, parental care) which may be costly but have yet to receive energetic measurements. Although most studies have consideredgestation and lactation the critical reproductive events for energy expenditure, variation in these events is substantial and almost certainly is a function of relative allocation of time togestation vs. lactation as well as the presumed energetic costs of mating, birthing and parental care. In addition, repeated observations show that behavioral compensation is an extremely important strategy for minimizing energy requirements during reproduction. From this review, we argue that more complete analyses will come from (1) incorporating energetic measurements in studies of mammalian behavior and (2) including mechanisms of behavioral compensation into physiological studies.
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One hypothesis for the evolution of hominid bipedalism is that bipedalism was more efficient than quadrupedalism for long-distance terrestrial locomotion, and was favored when resources became scarcer and more widely separated during the drying of African forests in the Miocene. Here we extend this scenario for the evolution of bipedalism based on principles of behavioral ecology of extant primates. Daily travel distance is not only an increasing function of resource scarcity, but also of group size (because of intragroup scramble competition). When faced with Miocene drying, hominoids were forced to evolve either energetically more efficient locomotory abilities or smaller group sizes. The cost of the latter strategy is that smaller groups are less successful than larger groups in intergroup contest competition (smaller groups are supplanted from limiting resources). Among the earliest hominids, bipedalism may have been favored over small group size as an alternative energetic response to decreased resource availability. The alternative was to maintain quadrupedal locomotion but evolve fission–fusion grouping to reduce daily travel distance for individuals and hence, their energetic costs of travel. We suggest that this strategy represents the evolutionary pathway taken by chimpanzees. This divergence of strategies may have been a result of inherent differences in feeding ecology, but could also have been enhanced by the pre-empting of niche space by the two closely related and presumably competing hominoid ancestors of humans and chimpanzees. If so, it could have been a potential factor in the speciation process that led to modern humans and chimpanzees.
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The relationships among initial energy stores (body mass index), energy turnover (physical activity levels), and seasonal energy balance (weight changes) were examined in subsistence agropastoralists in rural Nepal. The population experiences no actual food shortage, but has a seasonal increase in physical activity levels, which are moderately heavy in early winter and very heavy in the monsoon season [men, 1.88 and 2.22 × basal metabolic rate (BMR); women, 1.77 and 2.01 × BMR in the respective seasons]. Repeated anthropometry in 1982 (29 men and 34 women), 1983 (29 men and 29 women), 1991 (22 men and 48 women), and 1993 (48 men and 72 women) showed a consistent interannual pattern of significant but modest seasonal weight change (<4% of initial values) and remarkable interindividual variation (men, −5.6 to 5.6 kg; women, −5.6 to 4.8 kg). Thinner individuals showed no significant change in body weight or workloads, and sustained high levels of total energy expenditure throughout the year. Heavier individuals lost weight (men −2.7 kg, women −0.9 kg) and increased total energy expenditure by 23% over the same period. Elements of lifestyle, especially during the season of less constraining workloads, allow for the continuation of hard work or taking a respite for nutritional recovery. The nature of household labor organization, featuring a highly flexible distribution of tasks, also contributes to the relatively short-term, reversible changes in energy balance in this population. © 1996 Wiley-Liss, Inc.
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Human life histories, as compared to those of other primates and mammals, have at least four distinctive characteristics: an exceptionally long lifespan, an extended period of juvenile dependence, support of reproduction by older post-reproductive individuals, and male support of reproduction through the provisioning of females and their offspring. Another distinctive feature of our species is a large brain, with its associated psychological attributes: increased capacities for learning, cognition, and insight. In this paper, we propose a theory that unites and organizes these observations and generates many theoretical and empirical predictions. We present some tests of those predictions and outline new predictions that can be tested in future research by comparative biologists, archeologists, paleontologists, biological anthropologists, demographers, geneticists, and cultural anthropologists.
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Large potential effects of male care on the number of offspring females successfully raise are not sufficient to select for caring males because of the pervasive importance of mating competition. Males face a version of the social dilemma, in which increased production increases the pay-off for theft. Models of the allocation of male effort partitioned between caring for babies and competing for paternity show that the optimal allocation to care is very low under a wide range of conditions. Like sex allocation where the alternatives are male versus female function or sons versus daughters, the pay-offs to one alternative are always strongly frequency dependent. Because that alternative (male function, sons, male mating effort) pays so well when rare, it cannot remain rare under most conditions. Here we consider the consequences of partitioning mating effort into mate guarding and all other forms of mating conflict. If a male gets all his partner's conceptions while guarding, gaining them at a constant rate, there are two possible regions of stability. The evolutionarily stable strategy (ESS) depends on a parameter scaling the decisiveness of (non-guarding) mating conflict. When marginal returns from conflict decrease with scale, almost all effort goes into guarding. When marginal returns increase, the ESS devotes all effort to mating. Even when the potential effect of care is large, male equilibrium strategies allocate little effort to it. We also report the results of computer simulations showing that care increases if gains from guarding saturate quickly, so that a male is assured of the paternity of most of his partner's offspring with little guarding, and consequently the pool of unguarded conceptions open to competion shrinks sharply. But even when the male's dilemma is very much reduced, it still substantially limits the allocation to care. The results of both computer simulations and mathematical analysis converge with other lines of evidence that mating has much stronger effects than parenting in shaping male strategies.
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An abundant, balanced dietary intake of long-chain polyunsaturated fatty acids is an absolute requirement for sustaining the very rapid expansion of the hominid cerebral cortex during the last one to two million years. The brain contains 600 g lipid/kg, with a long-chain polyunsaturated fatty acid profile containing approximately equal proportions of arachidonic acid and docosahexaenoic acid. Long-chain polyunsaturated fatty acid deficiency at any stage of fetal and/or infant development can result in irreversible failure to accomplish specific components of brain growth. For the past fifteen million years, the East African Rift Valley has been a unique geological environment which contains many enormous freshwater lakes. Paleoanthropological evidence clearly indicates that hominids evolved in East Africa, and that early Homo inhabited the Rift Valley lake shores. Although earlier hominid species migrated to Eurasia, modern Homo sapiens is believed to have originated in Africa between 100 and 200 thousand years ago, and subsequently migrated throughout the world. A shift in the hominid resource base towards more high-quality foods occurred approximately two million years ago; this was accompanied by an increase in relative brain size and a shift towards modern patterns of fetal and infant development. There is evidence for both meat and fish scavenging, although sophisticated tool industries and organized hunting had not yet developed. The earliest occurrences of modern H. sapiens and sophisticated tool technology are associated with aquatic resource bases. Tropical freshwater fish and shellfish have long-chain polyunsaturated lipid ratios more similar to that of the human brain than any other food source known. Consistent consumption of lacustrine foods could have provided a means of initiating and sustaining cerebral cortex growth without an attendant increase in body mass. A modest intake of fish and shellfish (6-12% total dietary energy intake) can provide more arachidonic acid and especially more docosahexaenoic acid than most diets contain today. Hence, 'brain-specific' nutrition had and still has significant potential to affect hominid brain evolution.
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Presents a study on the foraging activities of Hadza children in Tanzania, Africa. Success of children's foraging; Determinants of children's foraging; Monitoring of the activities of children; Near-camp foraging return rates; Variables underlying the patterns of foraging. journal article
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Development of the dentition is critically integrated into the life cycle in living mammals. Recent work on dental development has given rise to three separate lines of evidence on the evolution of human growth and aging; these three, based on several independent studies, are reviewed and integrated here. First, comparative study of living primate species demonstrates that measures of development (e.g., age of emergence of the first permanent molar) are highly correlated with the morphological attributes brain and body weight (as highly as r = 0.98, N = 21 species). These data predict that small-bodied, small-brained Australopithecus erupted M 1 at 3–3.5 years and possessed a life span comparable to that of a chimpanzee. Second, chronological age at death for three australopithecines who died at or near emergence of M 1 is now estimated as ∼3.25 years based on incremental lines in teeth; this differs substantially from expectations based on human growth schedules (5.5–6 years). Third, developmental sequences (assessed by the coefficient of variation of human dental age) observed in gracile Australopithecus and great apes diverge from those of humans to a comparable degree; sequences become more like modern humans after the appearance of the genus Homo . These three lines of evidence agree that the unique rate and pattern of human life history did not exist at the australopithecine stage of human evolution. It is proposed that the life history of early Homo matched no living model precisely and that growth and aging evolved substantially in the Hominidae during the last 2 million years. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/37656/1/1330860206_ftp.pdf
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Hominid evolution is marked by very significant increase in relative brain size. Because relative brain size has been linked to energetic requirements it is possible to look at the pattern of encephalization as a factor in the evolution of human foraging and dietary strategies. Major expansion of the brain is associated with Homo rather than the Hominidae as a whole, and the energetic costs are likely to have forced a prolongation of growth rates and secondary altriciality. It is calculated here that modern human infants have energetic requirements approximately 9% greater than similar size apes due to their large brains. Consideration of energetic costs of brain allow the prediction of growth rates in hominid taxa and an examination of the implications for life-history strategy and foraging behaviour.
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Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps in the evolution of African hominids and other vertebrates are coincident with shifts to more arid, open conditions near 2.8 Ma, 1.7 Ma, and 1.0 Ma, suggesting that some Pliocene (Plio)-Pleistocene speciation events may have been climatically mediated.
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Total energy expenditure (TEE) was estimated for 19 nonpregnant, nonlactating (NPNL) and 24 pregnant (P) or lactating (L) women from 3601 h of minute-by-minute observation and 168 measurements of the energy cost of activities. NPNL women significantly increased subsistence activity and TEE from 9.9 MJ [1.89 x basal metabolic rate (BMR)] in the winter to 10.5 MJ (2.01 x BMR) in the monsoon season. There were differences between NPNL,P, and L women in the winter, but not in the spring or monsoon season when all individuals sustained very heavy physical activity. High TEE values resulted from spending very long hours in tasks that, although appearing physically demanding to the casual observer, were characterized by light or moderate energy cost. The study highlights the importance of seasonal constraints on women's work, which prevent P and L women from significantly curtailing physical activity during the monsoon season, and which effectively limit the scope of behavioral mechanisms for saving energy and reducing TEE.
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As studied in SW Sierra Leone annual diet and activity budgets Colobus polykomos change seasonally: unripe tree seeds are the preferred food type, with increased time spent feeding during the peak of seed production. Time spent resting is highest during wet seasons, when seeds are not available and only leaves are eaten. The high energetic value of seeds compared to fruit flesh, young and mature leaves, is demonstrated. A diet of 100% seeds supplies sufficient calories for all estimates of energy intake and expenditure, whereas a diet of 100% leaves is unable to meet daily energy expenditure and only the highest estimates of feeding rate approach average daily metabolic needs. The advantages of detoxification, and the limitations of energy production for small-bodied fore-gut fermenters are outlined. Evidence that C. polykomos is hypometabolic is considered. The adaptations they show to periodic shortages of high energy foods are behavioural rather than physiological. -from Author
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Despite the lack of an elaborate brain cooling system, early hominids could probably tolerate slight fluctuations in body temperature, comparable to those experienced by living primates in thermally stressing environments. Estimates are presented of the reductions in drinking water requirements resulting from the use of such heat storage, both of hominids foraging continually throughout the day on the open savannah, and those suspending this behaviour during the most thermally stressing period. The findings show that periods of inactivity can offer substantial thermoregulatory benefits, but only if the animal is able to retreat into the shade. Both strategies appear to be most advantageous in the absence of functional body hair. Together heat storage and shade-seeking can reduce the estimated total daytime drinking water intakes of naked bipeds to less than one half of those maintaining a constant body temperature and remaining continually active in the open. These studies of activity, patterns likely to have been more typical of those normally utilised when foraging on the open savannah, suggest that the selection pressures favouring the evolution of a functionally naked skin by these bipedal primates may have been even greater than previous calculations based solely on continually active hominids indicated.
Article
The brain is a very expensive organ in metabolic terms. Each unit of brain tissue requires over 22 times the amount of metabolic energy as an equivalent unit of muscle tissue. There is no correlation across mammals, however, between the relative size of the brain and the relative basal metabolic rate. The Expensive Tissue Hypothesis explains this apparent paradox by looking at the metabolic cost of the brain in the context of the costs of other metabolically expensive organs in the body. The results show that the increase in brain size in humans is balanced by an equivalent reduction in the size of the gastro-intestinal tract. In other words, the increased energetic demands of a relatively large brain are balanced by the reduced energy demands of a relatively small gastro-intestinal tract. This relationship also seems to be true in non-human primates. The size of the gastro-intestinal tract is dependent on both body size and the quality of the diet. It is argued that humans (and other primates) could not have developed a relatively large brain without also adopting a high quality diet that would have permitted a reduction in the relative size of the gastro-intestinal tract. Dietary change is therefore viewed as a 'prime releaser' in brain evolution. It is argued that a high quality diet is necessary for the evolution of a relatively large brain. However, the change to such a high quality diet, which involved an increased proportion of animal based products, need not have been one of the 'prime movers' in brain evolution. In this context, and based on the archaeological and palaeoanthropological record, the factors most probably surrounding the evolution of the human brain are discussed.
Article
Brain tissue is metabolically expensive, but there is no significant correlation between relative basal metabolic rate and relative brain size in humans and other encephalized mammals. The expensive-tissue suggests that the metabolic requirements of relatively large brains are offset by a corresponding reduction of the gut. The splanchnic organs (liver and gastro-intestinal tract) are as metabolically expensive organs in the human body that is markedly small in relation to body size. Gut size is highly correlated with diet, and relatively small guts are compatible only with high-quality, easy-to-digest food. The often -cited relationship between diet and relative brain size is more properly viewed as a relationship between relative brain size and relative gut size, the latter being determined by dietary quality. No matter what is selecting for relatively large brains in humans and other primates, they cannot be achieved without a shift to a high-quality diet unless there is a rise in the metabolic rate. Therefore the incorporation of increasingly greater amounts of animal products into the diet was essential in the evolution of the large human brain.
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Menopause is a nonfacultative and irreversible cessation of fertility that occurs in all female conspecifics well before the senescence of other somatic systems and the end of the average adult life span (Fig. 1).1-3 So defined, menopause occurs only in humans and one species of toothed whales.1-4 According to evolutionary theories of senescence, there should be no selection for postreproductive individuals.5 Thus, evolutionary biologists and anthropologists have long been interested in why human females have menopause. Many have suggested that menopause is a hominine adaptation, the result of selection for a postreproductive life span that permitted increased maternal investment in existing offspring.3,6-9 Others are persuaded that premature reproductive senescence is an epiphenomenon, either the result of a physiological trade-off favoring efficient reproduction early in the fertile part of life or simply the by-product of increases in life span or life expectancies.10-17 Menopause poses two separate questions: why it originated and what is maintaining it?
Article
The study reported here tested Altmann's prediction [Baboon Mothers and Infants. Cambridge, Harvard University Press, 1980] that lactating female baboons endure a weight loss. Data from 64 adult female olive baboons (Papio anubis) residing in six troops in Kenya revealed that reproductive condition was related to weight. Lactating females weighed less and pregnant females weighed more than cycling females. There was a negative correlation between the weight of cycling females and the number of months postweighing to their next conception. These results indicate that lactation in wild baboons imposes energy costs that result in lost weight. It is suggested that female baboons may have to surpass a minimum weight threshold prior to resumption of postlactational cycling and that nutritional status is more influential than rank in affecting female reproductive success.
Article
A bioenergetics model is developed to examine changes in metabolic requirements over the course of human evolution. Data on (1) body size and resting metabolism, (2) brain size and metabolism, (3) activity budgets, and (4) foraging patterns for humans and other anthropoids are used to evaluate ecological correlates of variation in diet and energy expenditure. Analyses of variation in these extant species provide a framework for estimating (1) resting metabolic requirements, (2) brain metabolic needs, and (3) total energy requirements in fossil hominids. Anthropoid primates spend about 8% of resting metabolism to maintain their brains, a significantly larger proportion than in other mammals (3–4%), but still significantly less than 20–25% in humans. Total energy expenditure among anthropoids is positively correlated with day range and dietary quality. Human foragers fit this pattern, having high levels of energy expenditure, large foraging ranges, and a high quality diet. Within the fossil record, it appears that both total energy expenditure (TEE) and energy required by the brain increased substantially with the emergence of Homo erectus. For H. erectus, the percentage of resting metabolism used by the brain falls beyond the nonhuman primate range and approaches the modern human range. Additionally, TEE is 35–55% greater than in the australopithecines. The high total metabolic needs and the large proportion of energy required by the brain imply that important dietary changes occurred with H. erectus. These metabolic and dietary changes are linked to (1) the emergence of hunting and gathering, (2) the evolution of the human pattern of prolonged development, and (3) the coexistence and competition with the robust australopithecines.
Article
Human dietary patterns and metabolic requirements are compared to those of nonhuman primate species in order to gain insights into the evolution of our nutritional needs. In general, primate diet quality (i.e., caloric and nutrient density) is inversely related to body size and total resting metabolic requirements (RMR). Humans, however, consume a diet of much higher quality than is expected for our size and metabolic needs. This energy-rich diet appears to reflect an adaptation to the high metabolic cost of our large brain. Among primates, the relative proportion of resting metabolic energy used for brain metabolism is positively correlated with relative diet quality. Humans represent the positive extreme, having both a very high quality diet and a large brain that accounts for 20–25% of resting metabolism. Evidence from the hominid fossil record implies that major changes in diet and relative brain metabolism occurred with the emergence of the genus Homo. © 1994 Wiley-Liss, Inc.
Article
Resting metabolic rate (RMR) and total daily energy expenditure (TDEE) were measured on a sample of 47 adults (35 males, 12 females) from two indigenous Siberian populations, the Evenki and Keto. The Douglas bag method of indirect calorimetry was used to measure the energy cost of lying, sitting, standing, and three exercise levels of the Canadian aerobic test of fitness (step test). The flex-heart rate method of heart rate monitoring (flex-HR; Spurr et al. [1988], Am. J. Clin. Nutr. 48:552–559) was utilized to predict TDEE from the measured energy costs. Measured RMR was 6.66 kJ/min (1.59 kcal/min) for males and 5.19 kJ/min (1.24 kcal/min) for the females. Subjects living in the bush in brigade work parties had significantly higher RMRs than those residing in the villages. Comparison of RMR to selected populations suggests that the elevated metabolism of the subjects living in the brigades is due to short-term environmental acclimatization to the ambient conditions of the taiga rather than long-term adaptation to living in a northern climate. TDEE was estimated at 11.8 ± 3.0 MJ (2,815 kcal) for men and 8.6 ± 1.9 MJ (2,056 kcal) for women, and there were no brigade-town differences in DEE. Based on their physical activity level (PAL = TDEE: basal metabolic rate [TDEE:BMR]), which was 1.77 for males and 1.59 for females, the Evenki and Keto have “moderately” active lifestyles during the summer according to FAO/WHO/UNU guidelines (FAO/WHO/UNU [1985] WHO Technical Support Series No. 724). © 1994 Wiley-Liss, Inc.
Article
We examined within- and between-group differences in aspects of feeding and nutrient intake among adult females of a single population of baboons (Papio cynocephalus) in Amboseli National Park, Kenya. Differences in time spent feeding, daily energy and protein intake and feeding efficiency (nutrient intake per minute spent feeding) reflected differences in resource base, reproductive condition and parity. Baboons that partially fed from a lodge garbage dump spent less than half the time feeding than those that were feeding totally in the wild. During this greatly reduced feeding time, the garbage-feeding group had a similar daily energy intake and only a slightly lower daily protein intake relative to wild-feeding baboons. Consequently, the feeding efficiency of the semi-provisioned baboons was appreciably higher than that of the non-provisioned baboons. For the totally wild-feeding baboons, samples were large enough to permit analyses of feeding time and nutrient intake during different reproductive states and parity. Females spent more time feeding and had higher daily energy and protein intake when they were pregnant or lactating than when they were sexually cycling. Nulliparous females spent more time feeding than their multiparous counterparts. The daily energy intake of nulliparous females was higher than that of their multiparous counterparts, but their daily protein intakes did not differ significantly. Pregnant or lactating and nulliparous females had higher feeding efficiency than their sexually cycling and multiparous counterparts. The two nulliparous females in the garbage-feeding group spent more time feeding but did not take in more energy or protein per day than their multiparous counterparts.
Article
Socio-bioenergetics is presented as a practical method of estimating energy budgets of primates in a social context. Energy budgets are estimated on the basis of behavioral observations and a series of empirical formulae, which consider body weight, activity, and reproductive status. Data on a captive colony of Sykes' monkeys and baboons are incorporated as illustrations of the possible effects of group composition, body size, reproductive status, and activity patterns on energy requirements.
Article
The very broad pelvis of small early hominids (AL 288-1, STS 14, etc.) has previously been interpreted in obstetrical and biomechanical terms. However, neither of these considerations can explain the subsequent decrease in maximum pelvic breadth relative to stature in larger more recent hominids. It is shown here that this increase in relative linearity of the body with an increase in body size is consistent with basic thermoregulatory principles. Specifically, to maintain a constant surface area/body mass ratio, absolute body breadth should remain constant despite differences in body height. Variation among modern humans supports the prediction: populations living in the tropics vary greatly in stature, but show little variation in body breadth. In contrast, populations living in colder climates have absolutely wider bodies, and thus lower surface area/body mass, regardless of stature. All African early hominids—small australopithecines as well as the very tallHomo erectus KNM-WT 15000—have absolute body breadths within the modern human tropical-subtropical range; variations in relative body linearity are due almost entirely to variations in stature. A later hominid from a cold temperate climate (the Kebara 2 Neandertal) has an absolutely wide body, similar to living higher latitude populations. Thermoregulatory constraints on absolute body breadth, together with obstetric and biomechanical factors, may have contributed to the evolution of the rotational birth process and secondary altriciality with increased body and brain size inHomo erectus. Thermoregulatory considerations also suggest that AfricanH. erectus would most likely have been limited to relatively open/dry environments, while australopithecines could have inhabited either open/dry or closed/wet environments.
Article
Reproductive senescence, a life-history trait virtually unique to human females, is thought to be the result of a fitness trade-off between increased maternal investment in existing progeny and continued reproduction. With the altriciality-life span hypothesis I propose (1) that menopause arose because continuing encephalization caused hominid infants to be born in an increasing state of secondary altriciality, requiring a mother to invest more prolonged and more intensive care in her own offspring; (2) that, originally, hominid females underwent menopause at an earlier age; and (3) that reproductive senescence was instrumental in increasing maximum potential lifespan and average life expectancies, which set up a feedback that resulted in its own upward secular trend. A model generated by the altriciality-life span hypothesis supports the propositions that premature reproductive cessation can offer fitness benefits before age 50 years if it results in increases in maternal care leading to substantial improvement in offspring survival and fertility.
Article
The thermoregulatory advantages conferred by bipedalism to a large-brained primate on the African savannah could have been significant factors contributing to the adoption of this unusual mode of terrestrial locomotion. Although the major benefit is a dramatic reduction in direct solar radiation exposure, additional advantages also result from the higher distribution of the body surfaces. Windspeeds are higher and air temperatures lower away from the ground, both factors increasing the rate at which a biped dissipates heat by convection. The greater airflow and low relative humidity above any surface vegetation present will also increase the rate at which sweat can be evaporated from the skin.
Article
The first step in a behavioural ecological study of stone-tool-using hominids involves the description of the character of lithic discard and the context within which the discard occurred. We examine and put into paleogeographic context the known archaeological traces in the Turkana Basin at three successive time intervals: 2·3 million years ago (Ma), 1·9-1·8 Ma, and 1·-7-1·5 Ma. At 2·3 Ma, hominid use of stone appears restricted to small areas on the landscape where many resources such as water, shade, and stone are juxtaposed. In contrast, archaeological traces at 1·6 Ma are found in a variety of settings, which may in part be explained by the paleogeographic changes taking place at that time. This change coincides with the emergence of Homo erectus. The hominid fossil and archaeological records are shown to complement each other in the generation of ecological hypotheses of H. erectus behaviour.
Article
Despite their bipedal posture, the available fossil evidence indicates that the body proportions of australopithecines were more ape-like than those of modern humans. By at least 1·6 million years ago (m.y.a.) Homo erectus had evolved the taller linear physique typical of many human populations inhabiting hot, open environments. Such body forms are usually interpreted as thermoregulatory adaptations, increasing the area of skin available for both the evaporative and non-evaporative dissipation of body heat. Although surface area to body mass ratio is a major influence on energy exchange, other factors such as the height distribution of the body surfaces and their exposure to direct solar radiation are also important in these climates.Estimates are presented of the combined effect of these factors on the net thermal loads, and associated drinking water requirements, experienced by large naked bipedal hominids of identical body mass with physiques approximating those of Australopithecus and H. erectus. These indicate that the taller more linear Homo body form can reduce daytime (06.00-18.00 h) sweat losses by 21-29% in open equatorial environments. The corresponding reduction in total daytime drinking water requirement is between 15-18%. The findings support the contention that thermoregulatory selection pressures were probably a major influence on hominid evolution.
Article
The habitats in which extinct hominids existed has been a key issue in addressing the origin and extinction of early hominids, as well as in understanding various morphological and behavioral adaptations. Many researchers postulated that early hominids lived in an open savanna (Dart, 1925; Robinson, 1963; Howell, 1978). However, Vrba (1985, 1988) has noted that a major global climatic and environmental shift from mesic, closed to xeric, open habitats occurred in the late African Pliocene (approximately 2·5 m.y.a.), thus implying that the earliest hominids existed in these mesic, wooded environs. This climatic shift is also suggested to have contributed to a pulse in speciation events with turnovers of many bovid and possibly hominid species. Previous environmental reconstructions of hominid localities have concentrated on taxonomic identities and taxonomic uniformitarianism to provide habitat reconstructions (e.g., Vrba, 1975; Shipman & Harris, 1988). In addition, relative abundances of species are often used to reconstruct a particular environment, when in fact taphonomic factors could be affecting the proportions of taxa. This study uses the morphological adaptations of mammalian assemblages found with early hominids to reconstruct the habitat based on each species’ ecological adaptations, thus minimizing problems introduced by taxonomy and taphonomy. Research presented here compares east and south African Plio-Pleistocene mammalian fossil assemblages with 31 extant mammalian communities from eight different habitat types. All communities are analyzed through ecological diversity methods, that is, each species trophic and locomotor adaptations are used to reconstruct an ecological community and derive its vegetative habitat. Reconstructed habitats show thatAustralopithecusspecies existed in fairly wooded, well-watered regions.Paranthropusspecies lived in similar environs and also in more open regions, but always in habitats that include wetlands.Homois the first hominid to exist in areas of fairly open, arid grassland. This change from closed to open habitats occurs gradually from about 4 m.y.a. until about 2 m.y.a. when there is a major increase in arid and grazing adapted mammals. Therefore, the appearance of open savannas do not appear to have influenced the origination or adaptations of the earliest hominids, but could have contributed to their demise. As Stanley (1992) hypothesized,Homospecies appear the first to be adapted to open, arid environments.
Article
Estimates are presented of the net thermal loads, and associated drinking water requirements, experienced by naked bipedal hominids weighing between 10–100 kg. The increase in body size observed in the hominid fossil record would have conferred significant advantages to these primates when foraging on dispersed resources in open equatorial environments, where drinking opportunities were limited. Larger hominids dehydrate more slowly and are able to cover a greater distance each day before encountering thermoregulatory constraints. This substantially increases the home range area, and consequently the quantity of dietary resources, to which they would have had access. The potential relevance of these thermoregulatory factors to the high degree of sexual size dimorphism in early hominids is discussed.
Article
Benedict has shown that this law is already over ninety years old, Robiquet and Tillaye having formulated it quite clearly in 1839. The history of the surface law is given in the paper of (Harris and Benedict (1919)). We may here only briefly mention the different ways in which it has been found. The early writers derived the law from theoretical considerations on a rather small experimental basis, as did Bergmann, who in 1847 had already written a book on the subject. Respiration trials were carried out by Regnault and Reiset, and Rameaux based the surface law on measurements of the amount of air respired per minute by two thousand human beings of different sizes. (Rubner (1883)) demonstrated the law in accurate respiration trials on dogs and Richet rediscovered it empirically on rabbits. The latter writes (p. 223): “C’est aprèe coup seulement que je me suis avisé que la donnée surface était plus intéressante que la donnée poids.”
Article
When it was originally released in 1980, Jeanne Altmann's book transformed the study of maternal primate relationships by focusing on motherhood and infancy within a complex ecological and sociological context. Available again with a new foreword by the author, Baboon Mothers and Infants is a classic book that has been, in its own right, a mother to a generation of influential research and will no doubt provide further inspiration.
Article
The discovery of several associated body parts of early hominids whose taxonomic identity is known inspires this study of body size and proportions in early hominids. The approach consists of finding the relationship between various measures of skeletal size and body mass in modern ape and human specimens of known body weight. This effort leads to 78 equations which predict body weight from 95 fossil specimens ranging in geological age between 4 and 1.4 mya. Predicted weights range from 10 kg to over 160 kg, but the partial associated skeletons provide the essential clues as to which predictions are most reliable. Measures of hindlimb joint size are the best and probably those equations based on the human samples are better than those based on all Hominoidea. Using hindlimb joint size of specimens of relatively certain taxonomy and assuming these measures were more like those of modern humans than of apes, the male and female averages are as follows: Australopithecus afarensis, 45 and 29 kg; A. africanus, 41 and 30 kg; A. robustus, 40 and 32 kg; A. boisei, 49 and 34 kg; H. habilis, 52 and 32 kg. These values appear to be consistent with the range of size variation seen in the entire postcranial samples that can be assigned to species. If hominoid (i.e., ape and human combined) proportions are assumed, the males would be 10 to 23 kg larger and the females 4 to 10 kg larger.
Article
The nursing behaviour of rural Nepali women, from two castes inhabiting the same village, is quantified on the basis of 2202 hr of continuous and direct day-time observation over 1 year. Feed duration, interval, total time and daily frequency are examined in relation to women's work, particularly the type of subsistence activity and seasonality. 'Opportunity' feeds are governed both by infant demands and maternal activity. Caste differences in birth intervals are also discussed. PIP From 1982-1983, researchers observed working women from 2 castes (16 Tamang and 8 Kami) in Salme, Nepal for 11-13 hours/day to determine if breast feeding and working behaviors explain fertility differences between them. Work loads greatly increased for the agropastoralist Tamang women during the monsoon (p.0007), but not so for the low caste Kami women who worked mainly at home. Intervals between feeds and agricultural activities averaged 98 minutes while they averaged 47 minutes for husbandry activities (p.05). Neither affected feed duration. If Tamang women worked in a labor group rather than alone, they tended to provide shorter breast feeds only during the monsoon (p.05). Infant age greatly affected duration of breast feeds (p.0005), interval between feeds (p.004), and total frequency and nursing time (p.0001) among the Tamang. Sea