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The Expensive-Tissue Hypothesis: The Brain and the Digestive System in Human and Primate Evolution
Abstract
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.
... En adultos, se estima que la masa corporal que ocupa este órgano es de un 2%; sin embargo, la energía que consume es de más del 20% en reposo (Aiello et al. 1995). En los niños el cerebro alcanza su pico de consumo alrededor de los 5 años, momento en el que se destina a su desarrollo casi el 70% de la energía consumida (Hublin et al. 2015). ...
... La carne probablemente comenzó a ser un recurso habitual en la dieta desde Homo ergaster / erectus, especie en la que convergen dos características de vital importancia: crecimiento craneoencefálico y aparición de herramientas líticas complejas. Esta es la hipótesis de Aiello y Wheeler (Aiello et al. 1995), fundamental para entender cómo pudieron haber sido saciadas las demandas de un cerebro de tal envergadura, a la vez necesario para satisfacer tales demandas. Otros autores también apuntan hacia la importancia de los recursos marinos, ricos en omega 3, para la encefalización, como prueban los mamíferos marinos, generalmente portadores de grandes cerebros (Crawford 1992, como se cita en McBrearty et al. 2001). ...
... La carestía metabólica del cerebro no puede, en ningún caso, deberse a un rasgo derivado neutro, pues su mantenimiento sacrifica parte del coste de otros órganos importantes (Aiello et al. 1995). El tamaño y organización del cerebro no resulta indiferente a la evolución; es protagonista en la obra y sus exigencias fuerzan a una adaptación integral, en aras de las ventajas que proporciona. ...
Resumen Se presenta la contribución de las disciplinas biológicas y neurológicas en la elaboración de un modelo psicobiológico de aplicación al re-gistro arqueológico, desde el enfoque cognitivo. Los datos neurobiológicos sobre nuestra especie y el estado de la investigación sobre los neandertales, permiten elaborar un modelo sobre una parte importante de la "infraestructura" de la mente. La cognición emerge como el producto de la combinación de la información ge-nética heredada (biología) y aprendida (cultura). El modelo psicobiológico comprende los niveles neurológico, psicológico y antropológico. A medida que escalamos este continuum, la frontera entre biología y cultura se difumina. Estas líneas se centran en el polo de la información heredada, especialmente en la biología y la neurología sobre las que la cultura esculpi-rá la cognición. Como conclusión, se sugiere que los neandertales habrían contado con un "potencial de maleabilidad" de su infraestructura mental menor, traducido en una cognición quizás menos fluida y un comportamiento menos flexible. Abstract It is presented the biological and neurological disciplines contribution to the elaboration of a psychobiological model for its application to the archaeological record, from the cognitive approach. Neurobiological data concerning our species and the investigation state about neanderthals, allow to elaborate a model about an important part of the mind's hardware. Cognition emerges as the combination product of inherited genetic information (biology) and the learned one (culture). The psychobiological model comprises, in addition, the neurological, psycological and anthropogical levels. As this continuum is climbed up, the border between biology and culture gets blurred. These lines focus on the inherited information pole, specially on the biology and neurology upon which culture will sculpt cognition. As a conclusión, it is suggested that neanderthals would have possessed a lower degree of hardware "maleability potential", which is translated into a less fluent cognition and a less flexible behaviour.
... Over the past decade, biological anthropologists have increasingly begun to rely on energetic models for understanding patterns and trends in hominin evolution (e.g., Leonard andRobertson, 1994, 1997a;Aiello and Wheeler, 1995;Leonard, 2002). The study of energetics is important to evolutionary research for several reasons. ...
... Analyses of human and primate body composition have suggested possible answers to the first question. Aiello (1997) and Aiello and Wheeler (1995) have argued that the increased energy demands of the human brain were accommodated by the reduction in size of the gastrointestinal tract. Since the intestines are similar to the brain in having very high energy demands (so-called expensive tissues), the reduction in size of the large intestines of humans, relative to other primates, is thought to provide the necessary energy savings required to support elevated brain metabolism. ...
... Since the intestines are similar to the brain in having very high energy demands (so-called expensive tissues), the reduction in size of the large intestines of humans, relative to other primates, is thought to provide the necessary energy savings required to support elevated brain metabolism. Aiello and Wheeler (1995) have shown that among a sample of eighteen primate species (including humans), increased brain size was associated with reduced gut size. However, recent analyses by Snodgrass, Leonard, and Roberson (1999) have failed to demonstrate significant differences in gastrointestinal size between primates and nonprimate mammals that are predicted from the "expensive tissue hypothesis." ...
Over the past decade, biological anthropologists have increasingly begun to rely on energetic models for understanding patterns and trends in hominin evolution (e.g., Leonard and Robertson, 1994, 1997a; Aiello and Wheeler, 1995; Leonard, 2002). The study of energetics is important to evolutionary research for several reasons. First, food energy represents a critical interface between organisms and their environment. The search for food energy, its consumption, and ultimately its allocation for biological processes are all critical aspects of an organism’s ecology (McNab, 2002). In addition, the energy dynamic between organisms and their environments—energy expenditure in relation to energy consumed—has important adaptive consequences for both survival and reproduction. Energy thus provides a useful currency for measuring fitness. Indeed, the two components of Darwinian fitness—survival and reproduction—are reflected in the way that total energy budgets for animals are typically divided (see fig. 18.1). “Maintenance” energy expenditure represents the costs of keeping an animal alive on a day-to-day basis.
... Therefore, brain size evolution may be limited by an organism's total energy budget . The expensive tissue hypothesis (ETH) states that animals can meet the metabolic cost of a large brain by reducing the amount of energy for other organs with high metabolic expenses (Aiello & Wheeler 1995). Aiello & Wheeler (1995) found a significant negative correlation between relative brain weight and relative intestinal weight in anthropoid primates. ...
... The expensive tissue hypothesis (ETH) states that animals can meet the metabolic cost of a large brain by reducing the amount of energy for other organs with high metabolic expenses (Aiello & Wheeler 1995). Aiello & Wheeler (1995) found a significant negative correlation between relative brain weight and relative intestinal weight in anthropoid primates. Since then, substantial evidence supporting the ETH was obtained in other mammalian groups (Jones & MacLarnon 2004), birds (Isler & van Schaik 2006), amphibians , Huang et al. 2018, and fishes (Kotrschal et al. 2013, Tsuboi et al. 2016. ...
... Mean ( demand for maintaining a large brain is met without increase in total energy budget (Aiello & Wheeler 1995). Based on this hypothesis, comparative studies had been performed on many vertebrate groups (Isler & van Schaik 2006, Navarrete et al. 2011, Tsuboi et al. 2015, Yang et al. 2018. ...
Conferring cognitive ability on animals, the brain is one of the most metabolically costly organs in vertebrates, and thus a large amount of energy associated with brain tissue maintenance should constrain brain size evolution. The expensive-tissue hypothesis (ETH) states that decrease in the sizes of other metabolically costly tissues compensates for increase in brain. In this paper, we tested ETH in a single species, Bufo gargarizans. We found no negative correlation between brain weight and intestinal length and no negative correlation between brain weight and the weight of other organs (heart, lungs, stomach, liver, kidneys, spleen, and testes). Therefore, our results do not support the ETH. We also found that intestinal length, stomach weight, liver weight and kidneys weight were positively correlated with each other, which may reflect the close functional relationships among these organs. However, a negative correlation was found between intestinal length and testes weight, indicating a trade-off between the testes and gut. Our findings suggest that energetic cost of a large brain in this species cannot be compensated by decreasing weight of other expensive organs.
... Pairwise partial correlations, controlling for SVL and phylogeny, revealed positive covariation or nonsignificant associations among all tissue masses ( Figure S5). As such, our data do not support the expensive tissue (Aiello and Wheeler, 1995) or the more general energy trade-off hypotheses (Isler and van Schaik, 2006), which predict brain size trade-offs with the digestive tract or other costly organs, respectively. However, since brain size differed from fat, hindlimb muscles and testes in allometric relationships and responses to brumation, pairwise correlations may not capture more complex allocation. ...
... In pairwise comparisons, the relative sizes of the tissues examined here, including the brain, were generally positively correlated. These results reject both the expensive tissue and energy trade-off hypotheses (Aiello and Wheeler, 1995;Isler and van Schaik, 2006), which predict trade-offs of brain size with the size of the digestive tract or other costly organs, respectively. This lack of support in anurans aligns with a previous report in mammals (Navarrete et al., 2011) despite their smaller brains and vastly different ecology and physiology, including a lower metabolic rate and largely lacking physiological thermoregulation. ...
Environmental seasonality can promote the evolution of larger brains through cogni-tive and behavioral flexibility but can also hamper it when temporary food shortage is buffered by stored energy. Multiple hypotheses linking brain evolution with resource acquisition and allocation have been proposed for warm-blooded organisms, but it remains unclear how these extend to cold-blooded taxa whose metabolism is tightly linked to ambient temperature. Here, we integrated these hypotheses across frogs and toads in the context of varying brumation (hibernation) durations and their environmental correlates. We showed that protracted brumation covaried negatively with brain size but positively with reproductive investment, likely in response to brumation-dependent changes in the socio-ecological context and associated selection on different tissues. Our results provide novel insights into resource allocation strategies and possible constraints in trait diversification, which may have important implications for the adaptability of species under sustained environmental change. eLife assessment In this important paper, the authors report a link between brumation (or "hibernation") and tissue size in frogs, summarizing convincing evidence that extended brumation is associated with smaller brain size and increased investment in reproduction-related tissues. The research is of broad interest to ecologists, evolutionary biologists, and those interested in global change biology, as the dataset involves significant field work and advanced statistical analyses for insights into how expensive tissues in these ectothermic animals respond to environmental seasonality.
... However, the teeth of australopithecines were primarily adapted for eating fruits and seeds (Peterson et al., 2018). Although they may have eaten some meat, the extreme male advantage in physical size preceded the evolutionary emergence of consistent hunting and meat eating as a major feature of our ancestors' subsistence (Aiello and Wheeler, 1995). Hunting has clearly been an important feature of human evolution and now influences male-male competition and female choice in traditional cultures (Hill, 1982), but it is not likely to be the initial evolutionary source of many human sex differences. ...
... The biological and social evolution of hunting and cooking competencies are critically important, as they likely released an energetic constraint on brain evolution and enabled substantive increases in brain volume with the emergence of the genus Homo ( Fig. 8; Aiello and Wheeler, 1995). The selection pressures that drove these increases are debated and include adaptation to different ecological niches with different climates (Potts and Faith, 2015), the demands of learning subsistence activities (Kaplan et al., 2000), and social competition (Dunbar, 1993(Dunbar, , 1998Flinn et al., 2005;. ...
... It has been argued that predation pressure acting on early hominins may have selected for increasing group size (Coward and Gamble 2008;Hart and Sussman 2005) demanding a larger brain geared towards negotiating a greater number of more complex social relationships, necessitating adaptations such as language (Aiello and Dunbar 1993;Dunbar 1993;Arsuaga and Martínez 1998;Gamble 2002;Gowlett 2006). The expensive tissue hypothesis, which claims that decreasing gut size energetically facilitated increasing brain size, is one explanation as to how the brain could so rapidly expand (Aiello and Wheeler 1995). Cooking may have reduced the caloric cost of digestion, providing the necessary free energy to help stimulate this cognitive advancement across generations (Boback et al. 2007;Aiello and Wheeler 1995;Henrich 2015). ...
... The expensive tissue hypothesis, which claims that decreasing gut size energetically facilitated increasing brain size, is one explanation as to how the brain could so rapidly expand (Aiello and Wheeler 1995). Cooking may have reduced the caloric cost of digestion, providing the necessary free energy to help stimulate this cognitive advancement across generations (Boback et al. 2007;Aiello and Wheeler 1995;Henrich 2015). Yet, for all the attested importance of pre-ceramic cooking, the physical practices and methods of containment and heating technologies remain relatively under-researched and discussed (Wrangham 2007;Wright 2004). ...
The ability to control and direct fire is a major evolutionary step in the human story. The development of aceramic cooking technologies is less well understood as they rarely survive in the archaeological record. However, inferential evidence such as fire-cracked rocks, earthen pits and heated bones suggest a variety of cooking methods were used prior to the invention of ceramics. Yet there is a paucity of experimental evidence testing the efficacy of perishable organic containers in tasks involving their use with heat. The study presents experimental results of organic containers and their use for heating water related to cooking. Containers were made from deer hide and pig stomach and water was heated using two different techniques: placing the container directly above a fire and placing hot stones into the container. The results suggest that different organic containers and heating types could attain and maintain a sub-boiling cooking temperature; however, not all could reach boiling point. It is argued that these sub-boiling methods may be as, or perhaps more, desirable than boiling, with potential implications for the development of vessels prior to the adoption of ceramics.
... It has been established that the discovery of how to control fire and cook meat has affected the human brain and our development. For example, Aiello and Wheeler (1995) have reasoned that the nutritionally dense muscle mass of other animals was the key food that contributed to the evolution of our large brains. Aiello and Wheeler (1995) maintain that without the abundance of calories afforded by meat-eating, the human brain simply could not have evolved to its current form (see also Pobiner 2016). ...
... For example, Aiello and Wheeler (1995) have reasoned that the nutritionally dense muscle mass of other animals was the key food that contributed to the evolution of our large brains. Aiello and Wheeler (1995) maintain that without the abundance of calories afforded by meat-eating, the human brain simply could not have evolved to its current form (see also Pobiner 2016). However, that meat was crucial for the development of the human brain has been refuted (Chiles and Fitzgerald 2018). ...
This article takes as its point of departure an event in which a plant-based version of the space alien, the Extra-Terrestrial (‘E.T.’), from the science fiction film bearing its name, was barbecued and served as a meal to participants at a conference. The soy dish produced different reactions: some laughed, while others seemed appalled. These different sentiments provide the basis for a broad green cultural criminology analysis of the traditions of meat-eating, tracing its role in human history and in the barbecue. The purpose of this is to explore why humans treat different categories of animals so differently. To understand the reactions the meal produced, the article addresses two contrasting aspects of the human–non-human animal relationship—‘carnism’ and ‘pet-keeping’—and contemplates these in relation to the reactions to eating E.T. The goal is to expand on the study of the human–animal relationship, particularly speciesism—understood as ideology and practice that legitimise and produce animal abuse through the analytical concept categorical discriminatory speciesism.
... If sodium accumulates intracellularly, the neuron will swell and eventually rupture (Pasantes-Morales and Tuz, 2006). The human brain consumes about 20% of the body's energy (Aiello and Wheeler, 1995), most of which is spent powering the Na + /K + -ATPase pump to maintain electrochemical gradients (Attwell and Laughlin, 2001). The pump removes three Na + ions in exchange for two K + ions per ATP. ...
... Natural selection balances costs and benefits; for example, the elongated tail of the male widowbird is advantageous for mating but disadvantageous for flying and hiding from predators (Andersson, 1982). Likewise, the encephalized human brain is more sophisticated but also costly such that the gut size became smaller to save energy (Aiello and Wheeler, 1995). Below we discuss how signal-to-noise ratio (SNR) and bandwidth are inversely correlated with energy efficiency. ...
Neurons maintain their average firing rate and other properties within narrow bounds despite changing conditions. This homeostatic regulation is achieved using negative feedback to adjust ion channel expression levels. To understand how homeostatic regulation of excitability normally works and how it goes awry, one must consider the various ion channels involved as well as the other regulated properties impacted by adjusting those channels when regulating excitability. This raises issues of degeneracy and pleiotropy. Degeneracy refers to disparate solutions conveying equivalent function (e.g., different channel combinations yielding equivalent excitability). This many-to-one mapping contrasts the one-to-many mapping described by pleiotropy (e.g., one channel affecting multiple properties). Degeneracy facilitates homeostatic regulation by enabling a disturbance to be offset by compensatory changes in any one of several different channels or combinations thereof. Pleiotropy complicates homeostatic regulation because compensatory changes intended to regulate one property may inadvertently disrupt other properties. Co-regulating multiple properties by adjusting pleiotropic channels requires greater degeneracy than regulating one property in isolation and, by extension, can fail for additional reasons such as solutions for each property being incompatible with one another. Problems also arise if a perturbation is too strong and/or negative feedback is too weak, or because the set point is disturbed. Delineating feedback loops and their interactions provides valuable insight into how homeostatic regulation might fail. Insofar as different failure modes require distinct interventions to restore homeostasis, deeper understanding of homeostatic regulation and its pathological disruption may reveal more effective treatments for chronic neurological disorders like neuropathic pain and epilepsy.
... Increased metabolic rate and energy uptake as a result of higher, non-lethal temperatures could result in tadpoles developing and maintaining larger brains, as nervous tissue is energetically expensive and has been shown to account for 2-10% of vertebrate metabolic output, despite nervous tissue representing a much smaller percentage of total body weight (Aiello and Wheeler, 1995;Mink et al., 1981). Whether this increase in relative brain size has cognitive benefits for the host is beyond the scope of this study, but increased size of the brain and larger body-brain ratios are associated with increased cognition in numerous animal taxa (Roth and Dicke, 2005). ...
... These changes could also be attributed to host metabolism, as other studies have found that newly hatched tadpoles that developed in sterilized water exhibited altered metabolism and growth rates, although this result may vary across different species (Warne et al., 2019). Because of the energetic cost to maintain and develop nervous tissue, any changes in brain morphology are expected to be adaptive responses to the external environment (Aiello and Wheeler, 1995;Gonda et al., 2013). In particular, we expect that the changes in brain mass and shape induced by our treatments contribute to changes in behavior. ...
Understanding how the global climate impacts the physiology of wildlife animals is of importance. Amphibians are particularly sensitive to climate change, and it is hypothesized that rising temperatures impair their neurodevelopment. Temperature influences the composition of the gut microbiota, which is critical to host neurodevelopment through the microbiota-gut-brain (MGB) axis. Most research investigating the link between the gut microbiota and neurodevelopment occurs in germ-free mammalian model systems, leaving the nature of the MGB axis in non-mammalian wildlife unclear. Here, we tested the hypothesis that the temperature and the microbial environment in which tadpoles were raised shapes neurodevelopment, possibly through the MGB axis. Newly hatched Green Frog tadpoles (Lithobates clamitans) were raised in natural pond water or autoclaved pond water, serving as an experimental manipulation of the microbiota by reducing colonizing microbes, at three different water temperatures: 14°C, 22°C, and 28°C. Neurodevelopment was analyzed through measures of relative brain mass and morphology of brain structures of interest. We found that tadpole development in warmer temperatures increased relative brain mass and optic tectum width and length. Further, tadpole development in autoclaved pond water increased relative optic tectum width and length. Additionally, the interaction of treatments altered relative diencephalon length. Lastly, we found that variation in brain morphology was associated with gut microbial diversity and the relative abundance of individual bacterial taxa. Our results indicate that both environmental temperature and microbial communities influence relative brain mass and shape. Furthermore, we provide some of the first evidence for the MGB axis in amphibians.
... Brain tissue is metabolically expensive, accounting for 50% of the energy expenditure in young children and 16% in adults (Aiello and Wheeler 1995). e large heads of babies and small children require substantial resource transfers long before immatures can support themselves. ...
... Socially transmitted extraction techniques, coupled with intragroup food transfers, can provide the calories and macronutrients necessary for developing large brains, which can in turn support imitation and learning to extract high-quality, hard-to-get foods. Aiello and Wheeler (1995) argue that the metabolic costs of brains were traded o against similarly expensive gut tissue, exacerbating our need to exploit nutrient-dense foods. ese foods require not only great skill, specialized technology, and hard work to exploit, but also a social, cooperative temperament to pool high-quality resources in order to create a dependable diet. ...
What does it mean for our species—or for any species—to be successful? Human Success: Evolutionary Origins and Ethical Implications examines the concept of human success from a variety of disciplinary perspectives, with contributions from leading paleobiologists, anthropologists, geologists, philosophers of science, and ethicists. It tells the tale of how the human species grew in success-linked metrics, such as population size and geographical range, and how it came to dominate ecological systems across the globe. It explores how culture, technology, and creativity have contributed to human success. However, there is a darker side of human success, as has become apparent in a world affected by climate change and the destruction of biodiversity. This leads us to ask whether the human species can really be called successful, and what our future success will look like in terms of our bodies, minds, morals, and our place in the universe. The essays in this book probe us to reflect on what has led to our apparent evolutionary success—and, most important, what this success implies for the future of our species.
... Testes size in terrestrial mammals A positive association between RTS and litter rate would be expected if it is costly for males to invest in testes (Hayward & Gillooly, 2011;Schulte-Hostedde et al., 2005). If large testes size represents an 'expensive' investment, then investment in large testes may result in a trade-off with the maintenance of other tissues ('expensive-tissue hypothesis'; Aiello & Wheeler, 1995) or other energetically expensive costs of body maintenance, locomotion, or reproduction ('energy trade-off hypothesis'; Isler & van Schaik, 2006). Our findings could suggest that, on average, testes are 'expensive' enough for promiscuous and polygynous species to decrease size investment in species with fewer litters per year (resulting in fewer opportunities for males to mate). ...
Sperm production represents a costly reproductive investment by males. High reproductive competition within the female reproductive tract may select for higher sperm counts or quality resulting in selection for larger testes size. In species where females mate multiply or have more offspring per litter (litter size), or more litters per year (litter rate), male reproductive competition may select for larger relative testes size (i.e., scaled by body mass). Given that different mating systems vary in the alternative forms of reproductive investment available to males, sperm production levels may vary with social system. Here, we examined the relationship between testes size and mating systems, litter size, and litter rate while considering male lifespan and investment in paternal care in 224 terrestrial mammalian species in 15 orders. Relative testes size was larger in species where females mated with multiple males. Furthermore, in species with multiple mating females, species with higher litter rates had larger testes compared to species with fewer litters per year. In contrast, in monogamous species, species that had multiple litters per year had smaller relative testes sizes compared to species with fewer litters per year. Neither longevity nor paternal care influenced testes size. Our results elucidate the effect of female reproductive strategies on relative testes size is nuanced and varies between mating systems. Our findings suggest that the interplay between male reproductive investment and female reproductive investment may be different within similar social mating systems.
... Finally, one can imagine a situation where the decreased cost of the digestive function, related to the acquisition of cooking techniques destroying toxins, leaves some rooms for costly mutations linked to the development of brain. This is what is suggested by the tenants of the expensive tissue hypothesis (Aiello & Wheeler, 1995). ...
During the last few years, various authors have called for the elaboration of a theoretical framework that would better take into account the role of organisms in evolutionary dynamics. In this paper, I argue that an organism-centered evolutionary theory, which implies the rehabilitation of an organizational thinking in evolutionary biology and should be associated with what I will call a heuristic of collaboration, may be completed by an organizational perspective of biological inheritance. I sketch this organizational perspective – which allows going beyond gene-centrism –, show how it grounds a systemic concept of heritable variation suited to the new evolutionary framework, and highlight some of its explanatory value and theoretical implications for evolutionary thinking.
... The questions of human energetics in the Paleolithic are not easy to address, and require consideration of different factors: biological and cognitive capacities of hominins, prey choice, paleoenvironmental constraints, etc. Indeed, it has been suggested that the increased encephalization throughout human evolution was, in part, fueled by the increasing importance of animal resources in the diet (Aiello and Wheeler, 1995). In addition to archeological and biogeochemical data, actualistic data and ecological models used for example in human behavioral ecology (HBE) can help (Smith, 1992). ...
This chapter focuses on the modalities of large fauna exploitation by human groups and their carnivorous competitors throughout the Paleolithic. It highlights the great diversity of hominin-animal interactions throughout human evolution, particularly in Africa and Eurasia. Carnivorous diet gradually increased within human populations, in parallel with the development of hunting capacities. There is evidence of regular animal meat and fat consumption by extinct hominins from 2 Ma onward, with the first occurrence prior to 3 Ma in Eastern Africa. The consumption of meat and fat may have had significant consequences on human evolution in terms of biology, culture and also in terms of energetic cost and benefit. Thus, the aim of this chapter is to present the main aspects, stages and degrees of complexity of hominin-animal relationships during the Paleolithic of the old world. Animals have undoubtedly always represented a major food, technological and symbolism resource for hunter-gatherer groups.
... A significant body of research links humans' increased meat consumption to human brain evolution, as it is thought that meat provided some of the calories and nutrients required by the energetic demands of an expanding human brain (Pfefferle, 2011). Furthermore, Aiello and Wheeler suggested that a dietary transition to meat enabled the size of the intestines to shrink, thus releasing the intestines' energetic demand to facilitate brain expansion (Aiello, 1995), although more recent research disputes this idea (Navarrete, 2011). ...
Humans are considered to have a unique reliance on meat compared to other primates, as much of humans unique evolutionary trajectory, such as human brain expansion, is linked to the increased consumption of meat for calories and nutrients. However, other primates such as chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) are also known to consume meat. While humans meat consumption is considered to be unique in humans' increased incorporation of tools to process the prey carcass and consumption of a broader range of prey, these distinctions are less obvious when contextualized within the broader behavioral repertoire of Pan species carnivory. This research seeks to identify if the taste perception of meat is different between humans and other ape clades through gene selection analyses. Specifically, this work examines the umami taste receptor genes, TAS1R1 and TAS1R3, which enable the savory flavor perceived when eating meat. Using PAML, we test for positive selection in these genes across several ape clades. We infer positive selection in TAS1R1 for the homininae clade and positive selection in TAS1R3 for the Homo/Pan clade. No selection was detected in only the human lineage, which complicates claims that human carnivory is unique compared to other primates while simultaneously suggesting the role of meat may be unappreciated in chimpanzees and bonobos as well as the role of insectivory in gorillas.
... The Acheulean is traditionally recognized through the presence of a characteristic tool type known as Large Cutting Tools (LCTs). Early assemblages with LCTs are thought to represent the onset and proliferation of several behavioral innovations, including the expansion of foraging ranges and raw material procurement, increased depth of planning, expanded consumption of animal tissues, and perhaps also increased hominin brain size (F eblot-Augustins, 1993;Ruff and Walker, 1993;Aiello and Wheeler, 1995;Potts, 1998;Braun and Harris, 2003;Sampson, 2006;de la Torre et al., 2014). Despite the precocious nature of LCT technologies when viewed against preceding African ESA industries, in the few Acheulean contexts potentially associated with hominin remains, LCTs have not been associated with the activities of anatomically modern hominins (Clark et al., 2003;Klein et al., 2007;Potts et al., 2018). ...
... However, the CBH cannot explain trade-offs between developmental costs and benefits of larger brains [64]. Larger brains need either an increase in total metabolism or a reduction in allocation of energy to other organs [65,66]. In contrast to the CBH, the expensive-brain framework hypothesis (EBF) states that a relatively smaller brain results when animals experience energy shortages in fluctuating environments [67]. ...
Adaptive evolution is the process by which organisms change their morphological, physiological and biochemical characteristics to adapt to different environments during long-term natural selection. Especially, researching variation in organ size can provide important insights into morphological adaptation in amphibians. In this study, we comparatively studied differences in organ sizes (heart, lungs, liver, gallbladder, kidneys, spleen, digestive tract, testes and brain) among five geographical populations of the Asian common toad Duttaphrynus melanostictus. Our results revealed significant variations in the size of these nine specific organs among the populations. Notably, we observed a significant positive correlation between the relative size of the testes and latitude and/or altitude. However, no correlation was found between the relative size of the heart and the length of the digestive tract with altitude across populations, respectively, contradicting Hesse’s rule and the digestion theory. These findings suggest that our study does not provide substantial theoretical support for the adaptive evolution of organ size in this particular toad species, but rather contributes to the understanding of the evolution and adaptations of species’ different environmental conditions. Further research is warranted to delve deeper into the factors influencing organ size in amphibian populations.
... Similarly, the loss of estrus is probably a phenomenon of the domestication syndrome but could have a more extended history. Females who were receptive for longer periods would be expected to conceive more frequently than others and would be more likely to have been provisioned with protein and fat needed for successful and frequent pregnancies [49][50][51][52][53][54]. This does not contradict the "grandmother hypothesis" [55], which endeavors to explain the large fraction of post-fertile years women live [56,57]. ...
The domestication of humans is not an issue of domesticity but of the effects of the domestication syndrome on a hominin species and its genome. These effects are well expressed in the ‘anatomically modern humans’, in their physiology, behavior, genetic defects, neuropathology, and distinctive neoteny. The physiological differences between modern (gracile) humans and their ancestors, robust Homo sapiens types, are all accounted for by the domestication syndrome. From deductions we can draw about early human behavior, it appears that modifications are attributable to the same cause. The domestication hypothesis ascribes the initiation of the changes to selective breeding introduced by the consistent selection of neotenous features. That would trigger genetic pleiotropy, causing the changes that are observed.
... Life history theory suggests that energy savings in other organs or tissues could allow for energetic diversion to the brain, without the need to increase overall metabolic expenditure (Isler & van Schaik, 2006;McNab & Eisenberg, 1989). Trade-offs at an evolutionary timescale have been proposed between brain size and digestive tract development (Aiello & Wheeler, 1995), adiposity (Navarrete et al., 2011) and skeletal musculature (Leonard et al., 2003). ...
Objectives:
Evolutionary life history theory has a unique potential to shed light on human adaptive capabilities. Ultra-endurance challenges are a valuable experimental model allowing the direct testing of phenotypic plasticity via physiological trade-offs in resource allocation. This enhances our understanding of how the body prioritizes different functions when energetically stressed. However, despite the central role played by the brain in both hominin evolution and metabolic budgeting, cognitive plasticity during energetic deficit remains unstudied.
Materials:
We considered human cognitive plasticity under conditions of energetic deficit by evaluating variability in performance in three key cognitive domains. To achieve this, cognitive performance in a sample of 48 athletes (m = 29, f = 19) was assessed before and after competing in multiday ultramarathons.
Results:
We demonstrate that under conditions of energetic deficit, performance in tasks of spatial working memory (which assessed ability to store location information, promoting landscape navigation and facilitating resource location and calorie acquisition) increased. In contrast, psychomotor speed (reaction time) remained unchanged and episodic memory performance (ability to recall information about specific events) decreased.
Discussion:
We propose that prioritization of spatial working memory performance during conditions of negative energy balance represents an adaptive response due to its role in facilitating calorie acquisition. We discuss these results with reference to a human evolutionary trajectory centred around encephalisation. Encephalisation affords great plasticity, facilitating rapid responses tailored to specific environmental conditions, and allowing humans to increase their capabilities as a phenotypically plastic species.
... Over this time period, megafauna experienced climatic changes 19,20 , severe drought 14 , and changes in vegetation across landscapes 10,13,15,16 . Simultaneously, hominins may have overhunted megafauna 8,[21][22][23][24][25][26][27][28][29][30][31] , spread disease to them 24 , and/or encroached on their habitats and food sources 4,17,32 , though these effects may have been mitigated in Africa (where hominins first evolved) by the long-term coevolution of megafauna with hominins 4,33,34 . The timing of megafaunal diversity losses, as well as their association with the emerging hominin clade and environmental change, has been heavily studied 1,8,13,14,16,24,31,[35][36][37][38][39][40] . ...
Mammalian megafauna have been critical to the functioning of Earth’s biosphere for millions of years. However, since the Plio-Pleistocene, their biodiversity has declined concurrently with dramatic environmental change and hominin evolution. While these biodiversity declines are well-documented, their implications for the ecological function of megafaunal communities remain uncertain. Here, we adapt ecometric methods to evaluate whether the functional link between communities of herbivorous, eastern African megafauna and their environments (i.e., functional trait-environment relationships) was disrupted as biodiversity losses occurred over the past 7.4 Ma. Herbivore taxonomic and functional diversity began to decline during the Pliocene as open grassland habitats emerged, persisted, and expanded. In the mid-Pleistocene, grassland expansion intensified, and climates became more variable and arid. It was then that phylogenetic diversity declined, and the trait-environment relationships of herbivore communities shifted significantly. Our results divulge the varying implications of different losses in megafaunal biodiversity. Only the losses that occurred since the mid-Pleistocene were coincident with a disturbance to community ecological function. Prior diversity losses, conversely, occurred as the megafaunal species and trait pool narrowed towards those adapted to grassland environments.
... Our original findings that brain size has reduced surprisingly recently (~5,000-3,000 years ago) is consistent with previous research and led to our hypothesis that population growth and knowledge specialization associated with cooperative intelligence led to a decrease in the volume of the brain, which is energetically expensive to develop and operate (Aiello and Wheeler, 1995;Navarrete et al., 2011;Heldstab et al., 2022). We drew parallels with patterns of brain evolution in ants, an entirely eusocial clade in which workers of different species have also undergone selection for both increased and reduced brain size in relation to higher levels of social complexity (Traniello et al., 2022). ...
Human brain reduction from the Late Pleistocene/Holocene to the modern day is a longstanding anthropological observation documented with numerous lines of independent evidence. In a recent study (DeSilva et al., 2021; Front. Ecol. Evol .), we analyzed a large compilation of fossil and recent human crania and determined that this reduction was surprisingly recent, occurring rapidly within the past 5,000 to 3,000 years of human history. We attributed such a change as a consequence of population growth and cooperative intelligence and drew parallels with similar evolutionary trends in eusocial insects, such as ants. In a reply to our study, Villmoare and Grabowski (2022; Front. Ecol. Evol. ) reassessed our findings using portions of our dataset and were unable to detect any reduction in brain volume during this time frame. In this paper, responding to Villmoare and Grabowski’s critique, we reaffirm recent human brain size reduction in the Holocene, and encourage our colleagues to continue to investigate both the timing and causes of brain size reduction in humans in the past 10,000 years.
... Early stone technologies, notably, Mode 1 tools (Oldowan industry) allowed Homo habilis to manipulate their surroundings in new ways and thereby extract unprecedented amounts of energy from their environments. This is why as stone technologies were consolidated in the hominid cultural repertoire, we see a considerable expansion of the human brain (Aiello and Wheeler 1995;Antón et al. 2014;Rightmire 2004;Wrangham et al. 1999). In other words, the exponential increase in energy capture that tools enabled, provided a nonhuman species with the new and rich energy regime that was needed to evolve into a new species with larger brains-Homo habilis. ...
This chapter explores universal evolution as it is applied to cultural evolution, focusing on major transitions in religious culture from the early Paleolithic to the rise of world (axial) religions. The perspective I take is an evolutionary-systems approach, which integrates insights from biological and cultural evolutionary theory, systems theory, information theory, the cognitive science of religion, religious studies, and cultural anthropology. The chapter argues for the necessity of a holistic evolutionary theory that integrates physical, biological, and cultural evolution.
... An important aspect to consider when addressing the evolutionary link between brain morphology and cognitive ability is that neural tissue is energetically costly and constrained by the individual's total energy budget. Growing larger brains, for instance, is often a manifestation of an energy trade-off by selective investment in the brain at the expense of other expensive (energydemanding) tissues like the gut (17,43). For this reason, we first tested whether an overall increase in brain volume accompanied the increased telencephalon size. ...
Executive functions are a set of cognitive control processes required for optimizing goal-directed behavior. Despite more than two centuries of research on executive functions, mostly in humans and nonhuman primates, there is still a knowledge gap in what constitutes the mechanistic basis of evolutionary variation in executive function abilities. Here, we show experimentally that size changes in a forebrain structure (i.e. telencephalon) underlie individual variation in executive function capacities in a fish. For this, we used male guppies (Poecilia reticulata) issued from artificial selection lines with substantial differences in telencephalon size relative to the rest of the brain. We tested fish from the up- and down-selected lines not only in three tasks for the main core executive functions: cognitive flexibility, inhibitory control, and working memory, but also in a basic conditioning test that does not require executive functions. Individuals with relatively larger telencephalons outperformed individuals with smaller telencephalons in all three executive function assays but not in the conditioning assay. Based on our findings, we propose that the telencephalon is the executive brain in teleost fish. Together, it suggests that selective enlargement of key brain structures with distinct functions, like the fish telencephalon, is a potent evolutionary pathway toward evolutionary enhancement of advanced cognitive abilities in vertebrates.
... Besides the advantages of having a larger brain with more neurons providing more processing power, increase in brain size comes at a cost. Brain tissue is one of the most energetically demanding tissues in the mammalian body 108 . For example, in Homo sapiens, the adult brain requires 20% of the daily energy intake, even though it makes up only about 2% of the body mass 109 , and cerebral blood flow estimations based on the size of cranial foramina for some related mammalian species indicate that their brains are similarly expensive 54 . ...
Fossil endocasts record features of brains from the past: size, shape, vasculature, and gyrification. These data, alongside experimental and comparative evidence, are needed to resolve questions about brain energetics, cognitive specializations, and developmental plasticity. Through the application of interdisciplinary techniques to the fossil record, paleoneurology has been leading major innovations. Neuroimaging is shedding light on fossil brain organization and behaviors. Inferences about the development and physiology of the brains of extinct species can be experimentally investigated through brain organoids and transgenic models based on ancient DNA. Phylogenetic comparative methods integrate data across species and associate genotypes to phenotypes, and brains to behaviors. Meanwhile, fossil and archeological discoveries continuously contribute new knowledge. Through cooperation, the scientific community can accelerate knowledge acquisition. Sharing digitized museum collections improves the availability of rare fossils and artifacts. Comparative neuroanatomical data are available through online databases, along with tools for their measurement and analysis. In the context of these advances, the paleoneurological record provides ample opportunity for future research. Biomedical and ecological sciences can benefit from paleoneurology’s approach to understanding the mind as well as its novel research pipelines that establish connections between neuroanatomy, genes and behavior.
... By softening food texture, increasing calorie density, and lowering toxins at this time, the employment of cooking methods and the discovery of fire aided in the evolution of human GI physiology [77]. The "expensive tissue theory" [78][79][80] states that a decrease in the size of an energetically costly GI tract results in an increase in the size of an energetically expensive brain, which in humans may have been facilitated by improvements in diet [80]. ...
Food, a vital component of our daily life, is fundamental to our health and well-being, and the knowledge and practices relating to food have been passed down from countless generations of ancestors. Systems may be used to describe this extremely extensive and varied body of agricultural and gastronomic knowledge that has been gathered via evolutionary processes. The gut microbiota also underwent changes as the food system did, and these alterations had a variety of effects on human health. In recent decades, the gut microbiome has gained attention due to its health benefits as well as its pathological effects on human health. Many studies have shown that a person’s gut microbiota partially determines the nutritional value of food and that diet, in turn, shapes both the microbiota and the microbiome. The current narrative review aims to explain how changes in the food system over time affect the makeup and evolution of the gut microbiota, advancing obesity, cardiovascular disease (CVD), and cancer. After a brief discussion of the food system’s variety and the gut microbiota’s functions, we concentrate on the relationship between the evolution of food system transformation and gut microbiota system transition linked to the increase of non-communicable diseases (NCDs). Finally, we also describe sustainable food system transformation strategies to ensure healthy microbiota composition recovery and maintain the host gut barrier and immune functions to reverse advancing NCDs.
... Injury risks would have been combined with other direct costs involved in the manufacture of stone-cutting tools, such as the time spent gathering materials, learning time, and energy expended in achieving both; this emphasizes the significance of this extension of hominin behavioral strategies at this time to an activity that no other living nonhuman primate exhibits today. Although the inception of knapping itself may not necessarily have required cognitive or behavioral capabilities beyond those possessed by the last common ancestor that humans share with the genus Pan Wynn and McGrew 1989), the longer-term biological implications of this behavioral shift in strategies (Aiello and Wheeler 1995;Key and Lycett 2023), as well of the technological beginnings of a more "plastic" world in which virtually all human artifacts are "cut," cannot be overstated. ...
For at least three million years, knapping stone has been practiced by hominin societies large and small, past and present. Thus, understanding knapping, knappers, and knapping cultures is fundamental to anthropological research around the world. Although there is a general sense that stone knapping is inherently dangerous and can lead to injury, little is formally, specifically, or systematically known about the frequency, location, or severity of knapping injuries. Toward this end, we conducted a 31-question survey of modern knappers to better understand knapping risks. Responses from 173 survey participants suggest that knapping injuries are a real and persistent hazard, even though a majority of modern knappers use personal protective equipment. A variety of injuries (lacerations, punctures, aches, etc.) can occur on nearly any part of the body. The severity of injury sustained by some of our participants is shocking, and nearly one-quarter of respondents reported having sought or received professional medical attention for a flintknapping-related injury. Overall, the results of this survey suggest that there would have likely been serious, even fatal, costs to knappers in past societies. Such costs may have encouraged the deployment of any social learning capacities possessed by hominins or delayed the learning or exposure of young infants or children to knapping.
... Some theoretical insights may however be provided by cognitive trade-off hypotheses which predict that physical constraints and general limitations to brain resources may have played an important role in shaping brain systems and a species' specific behavioral and cognitive repertoire (75)(76)(77)(78)(79)(80). The brain is considered an expensive tissue (81)(82)(83) and spatial and metabolic constraints of cognitive networks force a compromise between controlling "costs" and allowing the emergence of expensive but adaptive topological patterns and functions (77,84). Such constraints have led to evolutionary adaptations in fundamental properties of axonal organization to maintain long-range brain synchronization and communication in larger brains (85). ...
A long-standing topic of interest in human neurosciences is the understanding of the neurobiology underlying human cognition. Less commonly considered is to what extent such systems may be shared with other species. We examined individual variation in brain connectivity in the context of cognitive abilities in chimpanzees (n = 45) and humans in search of a conserved link between cognition and brain connectivity across the two species. Cognitive scores were assessed on a variety of behavioral tasks using chimpanzee- and human-specific cognitive test batteries, measuring aspects of cognition related to relational reasoning, processing speed, and problem solving in both species. We show that chimpanzees scoring higher on such cognitive skills display relatively strong connectivity among brain networks also associated with comparable cognitive abilities in the human group. We also identified divergence in brain networks that serve specialized functions across humans and chimpanzees, such as stronger language connectivity in humans and relatively more prominent connectivity between regions related to spatial working memory in chimpanzees. Our findings suggest that core neural systems of cognition may have evolved before the divergence of chimpanzees and humans, along with potential differential investments in other brain networks relating to specific functional specializations between the two species.
... Though human brain is unusually large-three times larger than chimpanzee (Bruhn, 1936), relative whole-body energy consumption rates are about equal. According to the "expensive-tissue trade-off" theory, this phenomenon is a result of dietary shift (Aiello, 1995), as we can cope with a smaller digestive tract. ...
According to the expensive brain hypothesis, periodic energy level determines the brain mass. However, various environmental and biological factors directly or indirectly relevant to energy intake have not been well studied. Here, we systematically examined how body mass, hibernation, diurnally, substrate use, diet individually and synergistically determine brain mass in a large dataset of more than 1000 species. We found that body mass and hibernation are the major determinants of brain mass in most species. These findings will shed light on future studies of how evolutionary constraints acting on brain size.
Brain tissue is metabolically expensive. Consequently, the evolution of humans’ large brains must have occurred via concomitant shifts in energy expenditure and intake. Proposed mechanisms include dietary shifts such as cooking. Importantly, though, any new food source must have been exploitable by hominids with brains a third the size of modern humans’. Here, we propose the initial metabolic trigger of hominid brain expansion was the consumption of externally fermented foods. We define “external fermentation” as occurring outside the body, as opposed to the internal fermentation in the gut. External fermentation could increase the bioavailability of macro- and micronutrients while reducing digestive energy expenditure and is supported by the relative reduction of the human colon. We discuss the explanatory power of our hypothesis and survey external fermentation practices across human cultures to demonstrate its viability across a range of environments and food sources. We close with suggestions for empirical tests.
Becoming Neolithic examines the revolutionary transformation of human life that was taking place around 12,000 years ago in parts of southwest Asia. Hunter-gatherer communities were building the first permanent settlements, creating public monuments and symbolic imagery, and beginning to cultivate crops and manage animals.
These communities changed the tempo of cultural, social, technological and economic innovation. Trevor Watkins sets the story of becoming Neolithic in the context of contemporary cultural evolutionary theory. There have been 70 years of international inter-disciplinary research in the field and in the laboratory. Stage by stage, he unfolds an up-to-date understanding of the archaeology, the environmental and climatic evidence and the research on the slow domestication of plants and animals. Turning to the latest theoretical work on cultural evolution and cultural niche construction, he shows why the transformation accomplished in the Neolithic began to accelerate the scale and tempo of human history. Everything that followed the Neolithic, up to our own times, has happened in a different way from the tens of thousands of years of human evolution that preceded it.
This well-documented account offers a useful synthesis for students of prehistoric archaeology and anyone with an interest in our prehistoric roots. This new narrative of the first rapid transformation in human evolution is also informative to those interested in cultural evolutionary theory.
TABLE OF CONTENTS
Introduction |7 pages
chapter 1|14 pages
A Concentration of Opportunity
chapter 2|23 pages
Changing Subsistence Strategies
Foraging to Farming
chapter 3|17 pages
Changing Subsistence Strategies
Hunting and Herding
chapter 4|18 pages
Early Epipalaeolithic – The Transformation Begins
chapter 5|21 pages
Complex Hunter-Harvesters in the Levant and beyond
chapter 6|26 pages
Early Pre-Pottery Neolithic – Transforming Their World
chapter 7|18 pages
Late Pre-Pottery Neolithic – Climax
chapter 8|15 pages
Further Transformation
Dispersal and Expansion
chapter 9|15 pages
The Evolutionary Framework for the Story
chapter 10|19 pages
The Epipalaeolithic–Neolithic Transformation
The Pivot of Cultural Evolution
chapter 11|12 pages
The Problem of Neolithic Religion
chapter 12|13 pages
The Triple A
Aggregation, Acceleration, Anthropocene
Chimpanzees regularly hunt and consume prey smaller than themselves. It seems therefore likely that early hominins also consumed small vertebrate meat before they started using and producing stone tools. Research has focused on cut marks and large ungulates, but there is a small body of work that has investigated the range of bone modifications produced on small prey by chimpanzee mastication that, by analogy, can be used to identify carnivory in pre‐stone tool hominins. Here, we review these works along with behavioral observations and other neo‐taphonomic research. Despite some equifinality with bone modifications produced by baboons and the fact that prey species used in experiments seldom are similar to the natural prey of chimpanzees, we suggest that traces of chimpanzee mastication are sufficiently distinct from those of other predators that they can be used to investigate mastication of vertebrate prey by early hominins.
El presente artículo tiene el objetivo de argumentar que hoy en día se necesita de un nuevo concepto del término “animal” dados los avances teóricos en filosofía y ciencia sobre el reino animal. La hipótesis principal de la presente investigación consiste en que la concepción y concepto de “animal” no debe ser solo la de un organismo heterótrofo y con capacidad de moverse a voluntad entre otros atributos obvios, sino que se necesita de un concepto y definición compleja que sea coherente con el término “autopoiesis” y con lo que se investigado en las ciencias de la complejidad. La metodología usada en esta investigación fue la revisión bibliográfica en cuanto al tema del concepto de animal desde el punto de vista actual filosófico y científico. Las investigaciones realizadas desde el siglo pasado, han demostrado que existe algo llamado caos y complejidad que es inherente a la realidad que perciben nuestros ojos y nuestro pensamiento convencional y que han revolucionado las demás ciencias sea la biología, la física, las ciencias sociales, entre otras. La cognición animal, un ejemplo de complejidad en el reino animal, está presente en miles de especies y es algo gradual que va desde el aprendizaje por asociación a las capacidades extraordinarias del ser humano, pero aún falta saber mucho del origen y que es lo que determina esas capacidades asombrosas en el reino animal.
The understanding of the nature and the software of the mind has generated immense debate in religion, philosophy, sciences and psychology. Drucker notes that the basic assumption about the reality is the foundation for science, axiom and algorithm adopted for the theory, concept and method. The assumption differentiates what is important from what is noise. In the medieval Europe, the Catholic Church provided a unified theory of the world as a reflection of God's grand design and purpose. They held the power to define and thus had the power to control people's lives. Their power was challenged during the Renaissance with the emergence of humanism. The Cartesian duality of separating the mind from body allowed the separation of church and state and science to flourish. In East Asia, Confucius articulated a different set of assumptions. Humans are defined as ingan 人間 ('human between') and assume relationship and compassion as the basic foundation. This is the basis of the cultural difference and theory of the mind. The Darwinian Evolutionary Theory replaced the 348 Psychology and Developing Societies 35(2) religious definition, Cartesian duality, and empathy with the biological traits, instincts and natural selection. Psychology adopted the biological model to explain human behaviour. Research in paleoanthropology, genetics, and neurobiology outline the limitations of the biological model in explaining the human mind and behaviour. Bandura has documented the importance of human agency, consciousness, and self-efficacy in explaining human behaviour and provided empirical results with greater predictive and explanatory power than the traditional psychological theories. Indigenous and cultural psychology represents the continuation of the assumptions, theory and concepts outlined by Wilhelm Wundt and Albert Bandura. Kim outlines the transactional model of science, where human agency (measured by self-efficacy) can explain a person's performance and outcome. Empirically, the Harvard Study of Adult Development, the 85-year longitudinal study, found the unexpected results that challenge the previous held assumptions. Waldinger and Schulz have found that maintaining good relationship is the most important predictor of happiness, health and longevity and not high income, success, IQ and personality. Kim and Kim found that for Millennials and Gen Z, happiness is predicted by relational and social efficacy, positive outlook, and receiving social support from family, friends and online communities, replicating previous results found across three generations and for the past 25 years in Korea. These results point to the importance of examining the basic assumptions of the theories in psychology and the scientific foundation of indigenous and cultural psychology.
The concept of adaptation , or the adjustment of an organism to its environment, is a fundamental property of all living forms. In humans, a genetic adaptation, which provides a relative benefit to an individual, is likely to be selected and retained to provide an evolutionary advantage. Other forms of phenotypic adaptation reflect the plasticity in individuals, through either developmental adaptation or short‐term adaptation resulting from homeostatic regulatory mechanisms in the body. Environmental stress arises from all kinds of human experiences, where either physical or social environmental stressors will cause a deviation from homeostasis and elicit responses that can be adaptive. Traditional models of environmental stressors leading to stress and leading, in turn, to adaptive responses may not be realistic under modern conditions of social disparities, warfare, and mass intercontinental migrations. Increased world population, global climate change, international conflict and warfare, and widespread losses in biodiversity will present dramatically new stressors requiring novel adaptive patterns for our species.
Synthetic meat made from animal cells will transform how we eat. It will reduce suffering by eliminating the need to raise and slaughter animals. But it will also have big public health benefits if it becomes widely consumed. In this paper, we discuss how "clean meat" can reduce the risks associated with intensive animal farming, including antibiotic resistance, environmental pollution, and zoonotic viral diseases like influenza and coronavirus. Since the most common objection to clean meat is that some people find it "disgusting" or "unnatural," we explore the psychology of disgust to find possible counter-measures. We argue that the public health benefits of clean meat give us strong moral reasons to promote its development and consumption in a way that the public is likely to support. We end by depicting the change from farmed animals to clean meat as a collective action problem and suggest that social norms rather than coercive laws should be employed to solve the problem.
Introduction:
The primary objective of researchers in the biology of aging is to gain a comprehensive understanding of the aging process while developing practical solutions that can enhance the quality of life for older individuals. This involves a continuous effort to bridge the gap between fundamental biological research and its real-world applications.
Purpose:
In this narrative review, we attempt to link research findings concerning the hormetic relationship between neurons and germ cells, and translate these findings into clinically relevant concepts.
Methods:
We conducted a literature search using PubMed, Embase, PLOS, Digital Commons Network, Google Scholar and Cochrane Library from 2000 to 2023, analyzing studies dealing with the relationship between hormetic, cognitive, and reproductive aspects of human aging.
Results:
The process of hormesis serves as a bridge between the biology of neuron-germ cell interactions on one hand, and the clinical relevance of these interactions on the other. Details concerning these processes are discussed here, emphasizing new research which strengthens the overall concept.
Conclusions:
This review presents a scientifically and clinically relevant argument, claiming that maintaining a cognitively active lifestyle may decrease age-related degeneration, and improve overall health in aging. This is a totally novel approach which reflects current developments in several relevant aspects of our biology, technology, and society.
The brain is among the most energetically costly organs in vertebrates, and thus trade-offs have been hypothesized to exert constraints on brain size evolution. The energy trade-off hypothesis (ETH) predicts that reducing the energy consumption of reproduction or other costly tissues should compensate for the cost of a large brain. Egg production in birds requires a large proportion of the total energy budget, and a clutch mass in some bird species can outweigh the body mass of the female. To date, this hypothesis has mainly been tested in mammals and ectothermic animals such as anurans and fishes. We collated data on adult brain size, body mass and egg-production traits such as clutch size, egg mass and annual broods from published studies, and conducted a phylogenetic comparative test of the interplay between egg-production investment and brain size evolution across bird species. After controlling for phylogenetic relationships and body size, we find a negative correlation between brain size and clutch size across 1395 species, which favored ETH. However, when egg mass was integrated in models, positive associations were detected between brain size and mass of eggs (via egg mass, clutch mass and annual total egg mass). Our results suggest that brain size trades off against egg-production only via certain aspects (e.g., clutch size). By contrast, a positive relationship between brain size and total egg reproduction (e.g., clutch mass and annual total egg mass) implied increased total energy budget outweighing energy allocation across bird species. Our study shows that there is no general energy trade-off between brain size and egg-reproduction investment, and suggests that brain size evolution follows mixed strategies across bird species.
Amniotes differ substantially in absolute and relative brain size after controlling for allometry, and numerous hypotheses have been proposed to explain brain size evolution. Brain size is thought to correlate with processing capacity and the brain's ability to support complex manipulation such as nest-building skills. The increased complexity of nest structure is supposed to be a measure of an ability to manipulate nesting material into the required shape. The degree of nest-structure complexity is also supposed to be associated with body mass, partly because small species lose heat faster and delicate and insulated nests are more crucial for temperature control of eggs during incubation by small birds. Here, we conducted comparative analyses to test these hypotheses by investigating whether the complexity of species-typical nest structure can be explained by brain size and body mass (a covariate also to control for allometric effects on brain size) across 1353 bird species from 147 families. Consistent with these hypotheses, our results revealed that avian brain size increases as the complexity of the nest structure increases after controlling for a significant effect of body size, and also that a negative relationship exists between nest complexity and body mass.
The Cambridge Handbook of Consciousness is the first of its kind in the field, and its appearance marks a unique time in the history of intellectual inquiry on the topic. After decades during which consciousness was considered beyond the scope of legitimate scientific investigation, consciousness re-emerged as a popular focus of research towards the end of the last century, and it has remained so for nearly 20 years. There are now so many different lines of investigation on consciousness that the time has come when the field may finally benefit from a book that pulls them together and, by juxtaposing them, provides a comprehensive survey of this exciting field. An authoritative desk reference, which will also be suitable as an advanced textbook.
The Cambridge Handbook of Consciousness is the first of its kind in the field, and its appearance marks a unique time in the history of intellectual inquiry on the topic. After decades during which consciousness was considered beyond the scope of legitimate scientific investigation, consciousness re-emerged as a popular focus of research towards the end of the last century, and it has remained so for nearly 20 years. There are now so many different lines of investigation on consciousness that the time has come when the field may finally benefit from a book that pulls them together and, by juxtaposing them, provides a comprehensive survey of this exciting field. An authoritative desk reference, which will also be suitable as an advanced textbook.
Introduction: As of now, no study has combined research from different sciences to determine the most suitable diet for humans. This issue is urgent due to the predicted population growth, the effect of this on the environment, and the deterioration of human health and associated costs.
Methods: A literature review determined whether an optimal diet for humans exists and what such a diet is, followed by six meta-analyses. The standard criteria for conducting meta-analyses of observational studies were followed. A review of literature reporting Hazard Ratios with a 95% confidence interval for red meat intake, dairy intake, plant-based diet, fiber intake, and serum IGF-1 levels were extracted to calculate effect sizes.
Results: Results calculated using NCSS software show that high meat consumption increases mortality probability by 18% on average and increases diabetes risk by 50%. Plant-based and high-fiber diets decrease mortality by 15% and 20% respectively (p < .001). Plant-based diets decreased diabetes risk by 27%, and dairy consumption (measured by increased IGF-1 levels) increased cancer probability by 48% (p < 0.01). A vegetarian or Mediterranean diet was not found to decrease the probability of heart disease. A vegetarian diet can be healthy or not, depending on the foods consumed. A Mediterranean diet with high quantities of meat and dairy products will not produce the health effects desired. The main limitations of the study were that observational studies were heterogeneous and limited by potential confounders.
Discussion: The literature and meta-analyses point to an optimal diet for humans that has followed our species from the beginnings of humankind. The optimal diet is a whole food, high fiber, low-fat, 90+% plant-based diet. This diet allowed humans to become the most developed species on Earth. To ensure people’s nutritional needs are met healthily and sustainably, governmental dietary interventions are necessary.
Evolutionary success of Homo sapiens is best understood by referring to natural selection on the twofold structure of inheritance, that is, gene and culture and also their interaction over time. Socioeconomic and technological variations have transformed lifestyles over the years. In tandem, deviations in food and physical activity forms have been crucial to the emergence of higher fatness among the world’s populations. The burden of obesity and its consequent diseases is becoming a public health concern. This article attempts to review the anthropological aspect of body fatness and size through its evolutionary perspective and bio-cultural changes in time and space.
Primates are noted for their mental abilities but the selective basis for such traits has remained obscure. It is hypothesized that the element of predictability associated with the spatial and temporal distribution patterns of plant foods in tropical forests has served to stimulate mental development in primates taking much of their food from the first trophic level. Primates able to remember the locations and phenological patterns of a wide variety of plant foods could move directly to such foods when and where available without wasting time and energy in random search. This would enhance overall foraging success by lowering procurement costs associated with a varied and patchily distributed plant diet. Membership in a cohesive social unit, that utilized the same supplying area over many consecutive generations, would also enhance foraging success by serving to transmit important information about diet to close kin. Data on the foraging behavior of howler and spider monkeys are presented to test certain implications of this hypothesis. Similar selective pressures, but applied to foods from the second trophic level, may have been of critical importance in the mental development of hominids. [primates, evolution, intelligence, plant foods, Aleles, Alouatta]
At some as-yet-unknown point during hominid evolution, a dietary shift occurred which involved incorporating a larger proportion of food derived from animal resources. Features of predatory and non-predatory mammalian species are compared in order to identify features or characteristics that would be expected to change as a consequence of this dietary shift. The record of hominid evolution is then reviewed to determine when these expected changes occurred, insofar as they are visible in the fossil record. Characteristics of Homo erectus are most congruent with those predicted for a species that has become significantly more predatory than its antecedents.
Fossils from Olduvai Gorge, Tanzania, show cutmarks which establish that hominids were using stone tools on animal tissues during the Lower Pleistocene in Africa. We identified cutmarks by elimination of other likely causes of the marks on the bone surfaces, for example, gnawing or chewing by carnivores or rodents, and damage made by tools of excavators or preparators. This was achieved by comparing the marks on the fossils with those produced by known causes on modern bones, using scanning electron microscopy (SEM). Because the fossils occur as part of accumulations of animal remains in relatively undisturbed geological contexts, we conclude that there is a functional association between the stone artefacts and bones at these sites, rather than an accidental, postmortem association1,2.
Due to the fragmentary condition of most specimens, there have been few studies on the anatomy of the early hominid bony birth canal. However, recovery of an innominate and sacrum from one individual (A.L. 288-1, Australopithecus afarensis) allows reconstruction of the complete pelvis. Although A.L. 288-1 is considered to have been a female, several morphologies of its true pelvis resemble those of human males, such as sacral angulation, ischiopubic ramus and, principally, funnelling of the pelvic cavity. The implication is that some of the pelvic dimorphisms characteristic of modern Homo sapiens developed subsequent to the emergence of bipedalism. The shape of A.L. 288-l's true pelvis is compared with that of female H. sapiens and Pan troglodytes. A.L. 288-l's pelvis is platypelloid, unlike Homo and Pan. The obstetric consequence of the difference in pelvic shape would have been a unique mechanism of birth in A.L. 288-1, with the fetus being born along the transverse axis of the outlet. Rotation of the fetal cranium within the pelvic canal, a characteristic of human birth, would not have occurred in A.L. 288-1. The platypelloid (false and true) pelvis of A.L. 288-1 is related to the requirements of locomotion and visceral accommodation and support. Although the obstetric analysis indicates that birth might have been slow and difficult in A.L. 288-1, we do not consider there to have been selection for the australopithecine fetus to have been born in a more altricial state than that in pongids. However, exactly when secondary altriciality, which is a characteristic of modern humans, emerged is a current subject of debate.
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.
A new partial skeleton of an adult hominid from lower Bed I (about 1.8 Myr ago), Olduvai Gorge, is described. This specimen's craniodental anatomy indicates attribution to Homo habilis, but its postcranial anatomy, including small body size and relatively long arms, is strikingly similar to that of some early Australopithecus individuals.
The mathematical relations between basal energy metabolism, brain size, and life span in mammals have been investigated. The evolutionary level of brain development, or encephalization (c), is a function both of brain weight (E) and of body weight (P) according to (formula; see text) Brain weight was found to be a linear function of the product of encephalization and basal metabolic rate. The oxygen consumption of the brain (Mbrain) is proportional to both encephalization and body weight according to (formula; see text) The ratio of metabolic rate in the cerebral cortex to that in the brain as a whole depends solely upon the degree of encephalization and is independent of the size of the animal. The maximum potential life span of a mammal was found to be proportional to the product of its degree of encephalization and the reciprocal of its metabolic rate per unit weight. Life span may be regarded as the algebraic sum of two components: (1) a deduced somatic component (Lb) inversely related to the basal metabolic rate per unit weight, and (2) an encephalization component (Le) related directly to the evolutionary increase of relative brain size.
Evidence from Bed I, Olduvai, supports the hypothesis that scavenging, not hunting, was the major meat-procurement strategy of hominids between 2 and 1.7 million years ago. Data used to evaluate the hunting and scavenging hypotheses are derived from studying cut marks on Bed I bovids, comparing adaptations necessary for scavenging with those of early hominids, and a pa-leoecological reconstruction of Bed I carcass biotnass, carnivore guild, and hominidforaging area.
Dietary adaptations of early hominids are generally understood to have played a crucial role in hominid evolution. The dietary habits of Australopithecus robustus are of special interest because the robust masticatory apparatus and characteristic dental features point to a distinctive dietary niche. Suggestions have ranged anywhere between carnivory and specialist herbivory, but current consensus has focused mainly on small hard items within the context of a vegetarian diet, and more particularly, frugivory. Few studies have challenged this perspective, although the results of a recent Sr/Ca study of A. robustus at Swartkrans were found to be inconsistent with herbivory. Here we address the question of A. robustus diet using 13C/12C ratio analysis of structural carbonate in tooth enamel, which has been shown to retain biogenic isotopic composition over long periods, contra earlier arguments based on bone apatite. Results for A. robustus, compared with other fauna from Swartkrans, show a mixed diet including both C3 and C4 foods. Since the C4 contribution must derive from consumption of grass or grazing animals, the data do not support either a specialist frugivorous or graminivorous niche for A. robustus; rather, they suggest a more generalized or omnivorous diet.
European Upper Paleolithic hominids appear to exhibit less cold-adapted body proportions, despite dating from the climatically more rigorous phase of the Wurm. Recent analysis of the postcranial sample of European late glacial and early postglacial hominids sheds some light on this unexpected finding. -from Author
Many plants contain secondary compounds that are potentially antagonistic to hominids, and their presence must be considered as a factor influencing dietary selection by hominids who did not possess a means of externally detoxifying foodstuffs (eg cooking). Behavioral strategies which might have been employed as a means of reducing intake of secondary compounds include ingestion of a mix of plants in order to minimize intake of a particular allelochemical, avoidance of species or plant parts with a high proportion of secondary compounds, and/or a focus on foods with high nutrient quality, thereby providing a return despite the metabolic costs of dealing with the allelochemical. A ranking of potential foodstuffs which considers the role of secondary compounds, indigestible constituents, and soluble carbohydrate and protein content has been proposed. When combined with an assessment of the ecological characteristics of particular plant species in specific geographical settings, such a ranking should be helpful in generating models of hominid dietary selection prior to the application of fire to food preparation. Comments by K.Homewood and 9 others and a reply by the author are included.-from Author
The history of phylogenetic reconstruction in palaeoanthropology shows considerable variation in the number of taxa recognized. Recent and current interpretations allow a range from a minimum of five to a maximum of 17 taxa to be identified in the fossil record. Given this range it is appropriate to ask whether there are means by which the expected number of species can be calculated and compared with observations of the fossil record. Models of hominid diversity (numbers of species) are constructed using fossil mammalian longevity data, mammalian speciation rates and living primate and carnivore spatial patterns. These models are discussed in the context of the longevity of the hominid lineage, its geographical distribution, and its adaptive basis. The results suggest that there may be strong interactions between ecological processes and evolutionary patterns in hominid evolution, and that early and later phases may be characterized by contrasting patterns of evolution.
Perspectives have shifted recently from the traditional view that early hominids were hunters to one which now sees them as opportunistic scavengers. However, both views share the common underlying nutritional assumption that meat inevitably provides a “high quality” food that will be incorporated into human diet more or less to the extent that animals are avaible and accessible. This paper argues that meat may actually have been a relatively marginal source of sustenance for early hominids, because physiological limits to total protein intake (plant and animal), scarcity of fat in most African ungulates, comparatively high levels of protein in many plant foods, and the inability of early hominids to extract lipids from the cancellous tissue of bones, acted together to maintain their total meat intakes at modest levels, particularly during seasonal or inter-annual periods of resource stress.
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The partial skeleton of Australopithecus from the Hadar Formation, Ethiopia, is reconstructed and compared with other primates. It is demonstrated that the skull of A.L. 288-1 is not as chimplike as it was proposed for Australopithecus afarensis and that the cranial fragments do not differ from Australopithecus africanus. Structural features like the funnelshaped thorax and the pelvis, with its broad iliaca for insertion of musculus latissimus dorsi and the long lever arm of the pubic muscular attachments, invoke a high level of suspensorial behavior. In our opinion, A. africanus is a generalized hominid primate that differs from the specialized African apes, the living pongids beeing too derived to represent a model of a primitive hominoid or hominid ancestor.
A restudy of the Danish brain weight data published by Pakkenberg and Voigt ('64), using partial correlation techniques, confirms and extends their earlier conclusions regarding a much stronger allometric relationship between height and brain weight than between body weight and brain weight. The relationship is particularly strong in males, and not in females, which is hypothesized to be related to higher fat components in the latter. Comparative data for smaller samples of Pan, Gorilla, Pongo, Macaca, Papio, and Saimiri using body weights, suggest that such relationship also hold more strongly in males than females, although more reliable data are greatly needed. In addition to providing within-species ranges of variability for variously derived neural statistics (e.g., encephalization quotients, “extra neurons,” etc.), for “normal” primates, it is suggested that while allometric trends do exist within species, and particularly males, evolutionary pressures leading to larger brain size were probably very diverse, and that any one homogenistic theory is unlikely.
Oxygen consumption was measured during sleep in seven species of mustelids. Their body weight ranged from 50 g to 15 kg. When basal metabolic rate (BMR) was plotted against weight on logarithmic coordinates (Fig. 1), a break in the linearity appeared at a weight level of about one kg. In species with a body weight below one kg, the regression line of BMR against weight is best represented by the equation M = 95.8W0.55 (0.03; standard error of estimate) where M is basal metabolic rate in kcal/day and W is body weight in kg. The equation M = 84.6 W0.78 (0.15) describes the relationship of animals weighing one kg or more, indicating that the BMR is proportional to almost the same fractional power of body weight, 0.75, as that of other mammals. The high BMR observed in weasels and stoats, suggests that a metabolic adjustment has occurred in the smaller species of the mustelid family.
Opinions vary but one interpretation of the vastly expanded hominid postcranial sample from 4 to 1·3 M.Y. hominids leads to the following working hypotheses: (1) The average female of the earliest known species of Hominidae, Australopithecus afarensis, weighed about 29 kg and the male, 45 kg. (2) Average female body weight remains between 29 and 34 kg in all species of hominids before the appearance of Homo erectus at 1·7 M.Y. (3) Average male body weight ranged between 40 and 52 kg in these pre-erectus species. (4) The origin of H. erectus marked a dramatic increase in body size especially in the female. (5) The brain size increase from A. afarensis to A. africanus to the "robust" australopithecines does not appear to be an artifact of body size increase but reflects progressive encephalization. (6) The expansion of absolute brain size with the appearance of Homo is beyond what would be expected from body size increase alone. These working hypotheses have implications for how members of early hominid species behaved to enhance their chances of survival and reproduction within the constraints and requirements of their environments. For example, the relatively high level of body size sexual dimorphism in the earliest species implies a polygynous mating system and a ranging pattern in which females foraged in smaller territories than the males. Although one might expect from analogy with Pan to have social groups consisting of closely related males and less closely related females, the high level of sexual dimorphism is not expected. Perhaps the substantial body size increase and reduction in sexual dimorphism apparent in Homo by 1·7 M.Y. is related to a significant expansion in ranging area. The energetic requirement of the expanded brain may imply altered feeding strategies in both the "robust" australopithecine and Homo lineages.
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.
Strontium-calcium ratios (Sr/Ca) are normally reduced at higher trophic levels in foodwebs, due to discrimination against strontium in favour of calcium by animals. This phenomenon has not generally been applied to the study of fossil foodwebs and the diets of early hominids because of diagenetic changes which obscure or obliterate biological Sr/Ca. The examination of compartments of fossil apatite having differing solubility, however, is a promising method for independently measuring biological and diagenetic Sr/Ca. In this study, Sr/Ca in Member I fossils from the site of Swartkrans were examined using a solubility profile procedure. Sr/Ca relationships observed among Swartkrans fauna match those seen in modern African foodwebs, suggesting that biological Sr/Ca accounts for the observed variation.When specimens of the fossil hominid Australopithecus robustus were examined, Sr/Ca values were inconsistent with that of a root, rhizome or seed-eating herbivore, suggesting that the diet of this species was more diverse than previously believed, and almost certainly included the consumption of animal foods.
Contexts that elicit bipedalism in extant apes may provide evidence of the selective pressures that led to hominid bipedalism. Bipedalism was observed most commonly among chimpanzees when they fed on the small fruits of diminutive, open-forest trees. Chimpanzees fed bipedally from such trees either by reaching up to pick fruit while standing on the ground, or from within the tree, in which case bipedalism was frequently stabilized by grasping an overhead branch. The food-gathering function of chimpanzee bipedalism suggests that hominid bipedalism may have evolved in conjunction with arm-hanging as a specialized feeding adaptation that allowed for efficient harvesting of fruits among open-forest or woodland trees. Such evidence is particularly valuable when it is in accord with fossil anatomy. Australopithecus afarensis has features of the hand, shoulder and torso that have been related to arm-hanging in chimpanzees. The australopithecine hip and hind limb clearly indicate bipedalism, but also indicate a less than optimal adaptation to bipedal locomotion compared to modern humans. Locomotor inefficiency supports the hypothesis that bipedalism evolved more as a terrestrial feeding posture than as a walking adaptation. A bipedal postural feeding adaptation may have been a preadaptation for the fully realized locomotor bipedalism apparent in Homo erectus.
This contribution has two main aims. The first is to assess the applicability of allometric techniques for purposes of predication and comparison, and the second is to test the possibility that the relationship between weight and stature was more significantly different in AL 288-1 (Australopithecus afarensis) and other Plio-Pleistocene hominids than it is in modern humans.It is argued that in the great majority of cases, the reduced major axis (RMA) is the preferred allometric technique. The reason for this is that the slope of the RMA is totally independent of the correlation coefficient. Both the least squares slope (LSR) and the major axis (MA) (which are both highly affected by the correlation coefficient) converge on it as the correlation coefficient approaches unity. It is also argued that the RMA provides the best estimate of the functional relation between the two variables in the analysis when the error variance is unknown, as is most frequently the case in allometric analyses. Furthermore, it is demonstrated that the MA produces a particularly spurious best-fit line when the correlation coefficient deviates from unity and the variance of the dependent variable (e.g., body weight) is particularly large in relation to the variance of the independent variable (e.g., stature). This has important implications not only for general allometric analysis but also particularly for the prediction of body weight from skeletal measurements.When RMA is used as the basis of inference and comparison, AL 288-1 (based on the best current estimates for stature and weight) has an inferred weight for its stature that would be highly unusual for modern humans, but similar to that observed for living African apes. OH 62 is similar to AL 288-1 in this respect.
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.
Two general kinds of theory (one ecological and one social) have been advanced to explain the fact that primates have larger brains and greater congnitive abilities than other animals. Data on neocortex volume, group size and a number of behavioural ecology variables are used to test between the various theories. Group size is found to be a function of relative neocortical volume, but the ecological variables are not. This is interpreted as evidence in favour of the social intellect theory and against the ecological theories. It is suggested that the number of neocortical neurons limits the organism's information-processing capacity and that this then limits the number of relationships that an individual can monitor simultaneously. When a group's size exceeds this limit, it becomes unstable and begins to fragment. This then places an upper limit on the size of groups which any given species can maintain as cohesive social units through time. The data suggest that the information overload occurs in terms of the structure of relationships within tightly bonded grooming cliques rather than in terms of the total number of dyads within the group as a whole that an individual has to monitor. It thus appears that, among primates, large groups are created by welding together sets of smaller grooming cliques. One implication of these results is that, since the actual group size will be determined by the ecological characteristics of the habitat in any given case, species will only be able to invade habitats that require larger groups than their current limit if they evolve larger neocortices.
This paper investigates patterns of cranial capacity evolution in Homo erectus, early Homo sapiens, and in regional subsamples of H. erectus. Specifically, models explaining evolution of cranial capacity in these taxa are evaluated with statistical techniques developed for the analysis of time series data. Regression estimates of rates of evolution in cranial capacity are also obtained. A non-parametric test for trend suggests that cranial capacity in both H. erectus and early H. sapiens may increase significantly through time. Cranial capacity in an Asian subsample of H. erectus (comprised of Chinese and Indonesian specimens) increases significantly through time. Other subsamples of H. erectus (African, Chinese, and Indonesian) do not appear to increase significantly through time. Regression results generally corroborate results of the test for trend. Spatial and temporal variation may characterize evolution of cranial capacity in H. erectus. Different patterns of cranial capacity evolution may distinguish H. erectus from early H. sapiens.
The interrelationship of brain and body sizes has been the subject of investigations for over a hundred years. These studies have demonstrated that variation in brain weights is much smaller than that in body weights; consequently, scaling studies are ones of negative allometry. Furthermore, the variability in brain weight is greater when comparisons are between species rather than among individuals of the same species, and the degree of variability in brain size differs among orders. The largest shifts in brain sizes relative to changes in body weights are found when comparing different ontogenetic stages. Debate continues as to the importance of metabolism in determining the interrelationship of brain-body weights for interpreting differences in relative brain size. Although past advances in the study of brain-body size associations have come by increasing the size of the data bases and by improved statistical analyses, the recent utilization of transgenic animals may provide new insights into the mechanism of this association.
Prosimians have smaller brains relative to their body sizes than do monkeys. Brain and body weights, however, are associated not only on the basis of the brain integrating sensorimotor functions, but also on the basis of the body's requirement to support the energetic needs of the brain. Prosimians differ from monkeys in that they have lower rates of oxygen turnover. When body size is adjusted for its rate of oxygen turnover, monkeys and prosimians have equivalent relative brain sizes. A consideration of the brain's energy requirements helps to clarify brain-body relationships.
Earlier studies have shown that the negatively allometric brain-body weight association in mature mammals changes to an isometric association when body weights are adjusted for their rates of oxygen consumption. Birds are endogenous homeotherms, and so their brain weights were analyzed according to their body weights and metabolism (estimated energy supply). As expected, the brain and body weights of the 83 species of neognathid birds have a negatively allometric association. The same species, however, have a brain weight-to-estimated energy supply which cannot be separated from isometry. While passerines have bigger brains for their body weights than altricial nonpasserines, the relative brain sizes of the two avian groups cannot be separated once the metabolic rate is used to adjust the body weights. Ratites or paleognathid birds may have a different brain-to-metabolism association. Consideration of bioenergetics helps clarify brain and body weight associations.
In mammals the weight of the heart, kidney, lungs, and other organs can be related to total body weight through power laws (allometry). Weights of primate organs are analyzed by this technique. Allometric coefficients and size-independent organ-weight or body-form ratios may be used to compare primates, including humans, and other mammals.
Comparisons of the relation between brain and body weights among extant mammals show that brain sizes have not increased as
much as body sizes. Interspecific increases in brain and body size appear to occur at the same rate, however, when the amount
of available energy is taken into account. After this adjustment, brains of primates are slightly larger than expected from
the overall mammalian data, but primates also use a larger proportion of their total energy reserves for their brains. Analyses
of relative brain size must take into account the requirements that the metabolically active brain has for the body.
More than 2,000 data on volumetric measurements of 42 structures in a variety of up to 76 species (28 insectivores, 21 prosimians, 27 simians) are given. All volumes measured in serial sections were converted to fresh volumes of a brain having a standard size within a given species. The date are available to all scientists for comparison and analysis. To allow critical evaluation, details on fixation and preparation, on determination of fresh brain weights and volumes of brain parts and on intraspecific variability are given.
While brain weight scales to body weight, the differences among brain weights are less than those among body weights. It has been assumed that this negative scaling is causally related to an isometric scaling of brain weight with surface area. For this assumption to be true, surface receptor/effector densities must be constant. Morphometric data indicate that this is not the case. Interspecific scaling of mammalian brain sizes, however, is isometric with the organisms' abilities to support the energy costs of the brain.
Studies of the relationship between brain size and body size in
terrestrial verteberates have a long history1-4.
Demonstrations of regular relationships between brain and body size
across species within selected vertebrate groups serve two purposes: (1)
in comparison of species of different body size, empirically recognized
`scaling effects' can be taken into account; (2) empirical relationships
may suggest useful working hypotheses regarding functional constraints
(although they cannot directly reveal casual connections). It is widely
accepted5,6 that brain size is scaled to keep pace with
changes in body surface area (rather than volume), and this provides the
basis for many interpretations of relative brain size. Re-examination of
brain-body size relationships for large samples of species from three
major vertebrate groups (mammals, birds, reptiles) now shows that there
is no empirical foundation for the concept of scaling to body surface
area. Instead, it seems that brain size may be linked to maternal
metabolic turnover. This has implications not only for assessment of
relative brain size in particular species, but also for pursuing links
between brain size and `life strategies'.
Three categories of dietary adaptation are recognized—faunivory, frugivory, and folivory—according to the distinctive structural and biochemical features of animal matter, fruit, and leaves respectively, and the predominance of only one in the diets of most species.
Mammals subsisting mainly on animal matter have a simple stomach and colon and a long small intestine, whereas folivorous species have a complex stomach and/or an enlarged caecum and colon; mammals eating mostly fruit have an intermediate morphology, according to the nature of the fruit and their tendency to supplement this diet with either animal matter or leaves. The frugivorous group are mostly primates: 50 of the 78 mammalian species, and 117 of the 180 individuals included in this analysis are primates.
Coefficients of gut differentiation, the ratio of stomach and large intestine to small intestine (by area, weight, and volume), are low in faunivores and high in folivores; the continuous spread of coefficients reflects the different degrees of adaptation to these two dietary extremes.
Interspecific comparisons are developed by allowing for allometric factors. In faunivores, in which fermentation is minimal, the volume of stomach and large intestine is related to actual body size, whereas these chambers are more voluminous in larger frugivores and mid-gut fermenting folivores; fore-gut fermenters show a marked decrease in capacity with increasing body size. Surface areas for absorption are related to metabolic body size, directly so in frugivores; area for absorption is relatively less in larger faunivores and more in larger folivores, especially those with large stomachs.
Indices of gut specialization are derived from these regressions by nonlinear transformation, with references to the main functional features of capacity for fermentation and surface area for absorption.
These are directly comparable with the dietary index, derived from quantitative feeding data displayed on a three-dimensional graph, with all species within a crescentic path from 100% faunivory through 557ndash;80% frugivory to 100% folivory, perhaps illustrating, at least for primates, the evolutionary path from primitive insectivorous forms through three major ecological grades.
Predatory patterns in wild chimpanzees are important evidence in the continuing debate about the role of hunting in the behavior of early hominids. Data are presented on the predator–prey ecology of red colobus monkeys (Colobus badius tephrosceles) and chimpanzees (Pan troglodytes schweinfurthii) in Gombe National Park, Tanzania, from 1982 through 1991. During this period chimpanzees were observed to kill 429 mammalian prey items, 350 of which were red colobus. Hunts were undertaken by chimpanzees in 71.5% of encounters with red colobus, and in 52.2% of all hunts at least one colobus was caught. Hunting occurred in all months, but its frequency peaked in the late dry season months of August and September, and was lowest in the rainy months of April and May. There was greater seasonality of hunting from 1982 to 1991 than previously reported for Gombe. Hunting success varied between 40% in the rainy season and 65% in the dry season. Sixty multiple kills of colobus were reported in which from two to seven colobus were killed. Approximately 75% of all colobus caught were immatures; juveniles were the most preyed upon age class.
Adult and adolescent male chimpanzees made 89.3% of all kills; the 10.7% of kills made by adult females was an increase over the 4% figure for female kills reported in the preceding decade. Hunting showed a strong “binge” tendency, with the explanation for binges likely related to social rather than ecological factors. These results are discussed in light of earlier hunting data for Gombe chimpanzees, and compared with data from other chimpanzee field studies.
The factors affecting the rate of respiration in isolated tissues are discussed with reference to the measurement of a "standard rate" of metabolic processes in vitro. Media for the suspension of tissues are devised; their composition is essentially based on the available analytical data for blood plasma. QO2 of liver, brain cortex, kidney cortex, spleen, and lung was measured for 9 mammalian species of different body size (mouse, rat, guinea-pig, rabbit, cat, dog, sheep, cattle, horse). Three different media were used ("phosphate saline without Ca", "saline low in phosphate, bicarbonate and Co2" and "saline serum substitute" containing physiological concentrations of inorganic ions in addition to organic substrates). Kidney cortex, spleen, and liver gave about the same QO2 values in all three media. QO2 for brain cortex was for all species higher in the medium containing no Ca, the average level being 37-87% higher. QO2 for liver was also higher in the absence of Ca, especially in the larger species. QO2 values of the tissues of larger animals were in general somewhat lower than the homologous values of the smaller species but no strict parallelsim between QO2 values and basal heat production of the intact animal was found. The QO2 values for the most tissues changed much less with the body weight than the date heat production. The absolute level of QO2 in the new media (which apart from glucose contain pyruvate, fumarate and L-glutamate) was higher than the values reported in the literature for saline media. They are of the same order as the highest values recorded for serum. The characteristics differences in the basal rate of heat production in animals of different size are to be attributed mainly to variation in the QO2] QQ2 of the musculature. It is suggested the the Q)in2 of tissues other than muscle is in the first place governed by the specific energy energy requirements of the tissues, and not by the heat requirements of the whole body.