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Are we carnivores? e implication for protein
Miki Ben-Dor
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Are we carnivores? e implication for protein consumption
Protein, Paleo Diet, Ethnography, Evolution
The Paleo Diet evolutionary mismatch principle means that the closer we stay to
the diet that we evolved to consume the better chances we have to stay healthy.
In this context, the question of the evolutionary level of protein consumption
during the Paleolithic has never received adequate attention. Since there is
relatively little protein in plants, the answer is derived from the relative amount of
animal food in the human diet. If animal food consumption were relatively high
during the Paleolithic, then relative protein consumption would have also been
Quite a few authors tried to estimate the Plant: Animal ratio (DPA) in the
humans Paleolithic diet [1-7]. A wide variation of DPA’s was predicted with
averages ranging between 66% plants and 33% animal to 35% plants and 65%
animal. Alas, because in the archaeological record plants preserve poorly or not at
all, all of the estimates relied to a great extent on the diets of recent hunter-
gatherers groups with a tacit claim for the analogy between the periods. However,
I claim that the hunter-gatherer's ethnographic record should not be used to
predict Paleolithic diets, or indeed even variability in the diet, as the ecologies of
the two periods are so different as to deny any scientific validity to such
prediction. Here I outline a short review of the relevant ecological conditions in
support of my claim. A full paper is in preparation.
Recent hunter-gatherers ethnography is a misleading source
of Paleolithic diet reconstruction
In discussing the use of ethnographic sourced analogies in archaeology, Ascher
(8) summarized his contemporaries, Clack, Willey, and Childes’ opinions thus:
“…the cannon is: seek analogies in cultures which manipulates similar
environments in similar ways.” In other words, the degree of similarity between
the ecological and technological conditions of the known and unknown periods is
the key criteria in judging the validity of ethnographic sourced analogies.
A review of the recent ecological conditions reveals that especially in one crucial
aspect, availability and size of faunal and floral resources, there is a drastic and
unbridgeable gap between the Paleolithic and the recent period.
In a recent paper Smith et al. [9] calculated the mean body weight of non-volant
(not flying) terrestrial mammals during the last 2.5 million years. A drastic
decline from approximately 500 kgs to about ten kgs occurred during this period.
In the same vein, Bibi et al. [10] compared the faunal assemblages of Olduvai
Middle Bed II at 1.7-1.4 million years ago (Mya) to faunal communities in the
present day Serengeti. They concluded that “The sheer diversity of species,
including many large-bodied species, at Neogene and Pleistocene African sites
like Olduvai, is perplexing and makes extant African faunas look depauperate in
Ben-Dor: Are we carnivores? The implication for protein consumption
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comparison.” Indeed, they present a hypothesis, supported by reduced carnivore
richness in the Early Pleistocene [11], that human predation may have been the
cause of the loss of large herbivores during the Pleistocene.
A significant part of the reduction occurred in the Late Pleistocene and is a global
phenomenon. During the Late Quaternary Megafauna Extinction, about 90 genera
of animals weighing >44 kg became extinct beginning some 50 Kya [12]. The rate
of extinction by body size follows a typical pattern in which the largest size
genera became more completely extinct. In all the continents, apart from Africa
and the Indian sub-continent, all genera exceeding 1000 kg became completely
extinct, and those in the 1000-320 kg category became 50-100% extinct. In
Africa, Some 25% of what was left in the Late Quaternary’s megafauna (>45 kg)
became extinct [13].
In Africa, however, even the few large animals that remained were hardly
available for hunting by HG groups that form the basis for many analogies with
the Paleolithic, the Hadza, and the San. Elephants were hunted by Europeans with
guns in the Hadza and San’s territories for over a hundred years. Evidence for a
drastic decline in the availability of animals as a result of herders and farmers
encroachment abound [14, 15]. The result is that the Hadza no longer hunt the
three largest animals, elephants, rhinos and hippos.
Moreover, the disappearance of large animals, and especially elephants, caused a
critical increase in the availability of plant food sources. Elephants are known to
be a formidable predator of baobab trees [16]. Baobab is the single largest
contributor of calories to the Hadza as well as a home for their most popular
species of honey bees. The same phenomenon occurs in the San (!Kung) territory
where the mongongo tree, their main staple food source, was subject to partial
destruction and growth retardation when elephants were present in its vicinity
In summary, the differences in the relative availability of plants and animals and
especially big animals, between the Paleolithic and the recent period are so
critical that they prevent any prediction from the recent HG DPA and Paleolithic
DPA, including any conclusion regarding the degree of DPA variability during
the Paleolithic.
So, if not Ethnography and not Archaeology, are there other fields of knowledge
we can explore? As it turns out, physiology can be a trove of information for
evolutionary DPA, as adaptations to one DPA or another are stored in our body in
the forms of genetics, morphology, metabolism, and sensitivity to pathogens.
Reconstruction of the Paleolithic diet based on human
A more detailed reconstruction which was performed as a part of my Ph.D. thesis
and is in preparation for publication. What follows is a short review of some of
Submission to Journal of Evolution and Health
the physiological adaptations or lack thereof that provide evidence for the nature
of our past diet. The first three adaptations are unique in that the authors
themselves point out (maybe to their surprise) that according to their findings
humans were carnivores.
Weaning like a carnivore
Life history (length of gestation, weaning, mating, and death) is strongly defined
in a species. Psouni et al. [18] compared the difference in the age of weaning
between carnivores and other animals. Humans were found to be in the
carnivores’ group while chimpanzees and other primates with the non-carnivores.
The explanation that they provide is that the external food of carnivores is much
more similar to the milk of the mothers, so a shorter adjustment time suffice. They
conclude: "Our findings highlight the emergence of carnivory as a process
fundamentally determining human evolution."
Many smaller fat cells like all carnivores
Pond and Mattacks (19) compared the structure of fat cells in various types of
animals. Carnivores were found to have a higher number of smaller fat cells and
omnivores a smaller number of larger fat cells. Humans were found to be at the
top of the carnivorous pattern. Pond and Mattacks conclude: “These figures
suggest that the energy metabolism of humans is adapted to a diet in which lipids
and proteins rather than carbohydrates, make a major contribution to the energy
Stomach acidity of a unique carnivore
Beasley et al. [20] found that carnivores’ stomachs are more acidic than
omnivores stomachs. Moreover, scavengers, which have to deal with the highest
load of pathogens, have the highest level of stomach acidity. Humans had the
highest level of acidity among all the 54 reviewed animals. Producing acidity, and
retaining the stomach walls to contain that acidity, is energetically expensive, so
would only evolve if the level of pathogens in the human diet was high. The
authors surmise that humans were more of a scavenger than we thought.
However, there is a more likely conclusion if we take into account that humans
were a particular kind of carnivore. Unlike other carnivores, they took the meat
and fat of the big animals they hunted to a central place. Big animals, like
elephants and bison, and even smaller animals like zebra, provide enough calories
to last a 25 member HG group for days and weeks. During this time the pathogen
load would have increased to a higher level than even a regular scavenger is
bound to encounter under normal circumstances and hence the need for high
Ben-Dor: Are we carnivores? The implication for protein consumption
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Reduced energy extraction capacity from plants
Most plant eaters extract a large part of their energy from the fermentation of fiber
by gut bacteria. For example, a gorilla extracts some 60% of its energy from fiber
[21]. The fruits that chimps are consuming are also very fibrous, and fiber can be
calculated, based on [22], to contribute approximately 50% of their energy.
Therefore, any adaptation that prevents humans from efficient exploitation of
fiber to energy points to a shift in the dietary emphasis away from plants towards
specialization in animal’s sourced food [See 23 considering criteria for
specialization]. A reduced mastication system already 1.7 million years ago (Mya)
in H. erectus indicates that his gut size was reduced [24]. Our gut is 40% smaller,
our colon, where fiber is processed to energy, is 77% smaller than that of a
chimpanzee. The size and our small intestine, where glucose fat and protein are
absorbed is 62% longer. Since the Chimpanzee was able to absorb a large amount
of sugar with a shorter small intestine, it is safe to assume that the 66% extension
represents an adaptation to consuming more fat and protein.
Endurance running
Bramble and Lieberman [25] list 22 specific adaptations to endurance running and
claim they represent an adaptation to ‘persistence hunting.’ There is some
disagreement as to the final purpose of the adaptation [26], but as it represents an
adaptation to better mobility, it indicates adaptations to operating in a larger home
range. Carnivores with a large proportion of flesh in their diets have particularly
large home-ranges [27].
Adaptation to a spear throwing
A similar indication of evolution towards carnivory is described by Roach et al.
[28]. Our shoulder is perfectly adapted to throwing, which must be used mainly in
hunting and protection from predators. The chimpanzee’s shoulder is adapted to
climbing trees, so we have another example of an adaptation, like the smaller gut,
that reduces our capability to obtain plants, fruits in this case.
High-fat reserves
Humans have much higher fat reserves than chimps [29]. Carrying a high amount
of fat cost energy and reduce the speed of chasing or fleeting. Most carnivores
and fleeting herbivores do not pack much fat. Recent HG were found to have
enough fat reserves to fast for three weeks for men and six weeks for women [30].
This ability may represent a unique adaptation to carnivory of large animals,
where bridging the variance of success is vital due to the larger animals’ relatively
lower abundance.
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Incomplete adaptation to metabolize starch
Humans have a varying number of AMY1 gene copies which synthesize salivary
amylase, representing different degrees of adaptation to consuming starch [31].
This variance in itself can be a testimony that the adaptation is relatively recent
and was not fixed yet.
Recent genetic adaptation to tuber consumption
Tubers are mentioned as a good candidate for Paleolithic plant-based diet [32].
Populations that presently depend on tubers are enriched in genes that are
associated with starch metabolism, folic acid synthesis, and glycosides
neutralization, but other populations are not [33]. These adaptations presumably
compensate for these tubers’ poor folic acid and relatively high content of
glycosides. The very limited geographic distribution of these genes may mean that
their presence in humans is quite recent so that tubers did not form an important
part of the human Paleolithic diet.
The earliest evidence for caries - 15,000 years ago
A high prevalence of cavities (carries), a sign of intensive consumption of
carbohydrates, first appears some 15.0 Kya in a site in Morocco, together with
evidence for exploitation of starchy foods [34]. On the other hand, the oldest H.
sapiens jaws present a perfect set of teeth 300 Ka [35], which is typical
throughout the Paleolithic. This may mean that high carbohydrates (plants)
consumption is a recent phenomenon.
Reconstruction based on human Physiology conclusion
Looking into the information that is stored in our body and behavior it is clear that
we were primarily carnivores during most of our evolution and remain adapted to
carnivory despite over 10,000 years of agricultural subsistence. It transpires, then,
that we are adapted to consume high quantities of protein but how high? The
answer lies in reconstructing our attitudes toward fat [36, 37].
How much protein? The answer is in the fat
Protein processing for energy in humans is limited to 35-50% of calories although
no definitive limit is universally accepted [38, 39] . It means that if humans were
at the protein limit, the remaining 50-65% of the calories should have come either
from fat or carbohydrates, namely plants.
The archaeological record shows that many of humans’ particular hunting and
food exploitation behaviors can be interpreted as stemming from the need to
obtain fat. The preference of hunting larger animals and prime adults [36, 40, 41],
the preference to bring fatty parts to a central place and the extraction of bone fat
Ben-Dor: Are we carnivores? The implication for protein consumption
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[42], at great energetic costs, all point to a strategy of fat maximization. These
energetically expensive set of behaviors supports the conclusion that plants could
not provide a significant contribution to complement the protein at the limit of its
This reconstruction also answers the question that is asked in the title of this
paper. If humans invested so much energy in obtaining fat, it means that they
were at the limit of their protein consumption.
This limit translates to approximately 3.8 gram per kg of body weight for energy
[43] plus 0.6-0.8 gram per kg bodyweight for protein replacement so in total 4.4
4.6 grams per kg bodyweight although, as noted, there is no universally accepted
In conclusion, a high consumption of protein a high consumption of fat and low
consumption of plant-sourced food seems to be the human evolutionary status
during the Paleolithic.
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Ben-Dor: Are we carnivores? The implication for protein consumption
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We review the evolutionary origins of the human diet and the effects of ecology economy on the dietary proportion of plants and animals. Humans eat more meat than other apes, a consequence of hunting and gathering, which arose ∼2.5 Mya with the genus Homo. Paleolithic diets likely included a balance of plant and animal foods and would have been remarkably variable across time and space. A plant/animal food balance of 40–60% prevails among contemporary warm-climate hunter-gatherers, but these proportions vary widely. Societies in cold climates, and those that depend more on fishing or pastoralism, tend to eat more meat. Warm-climate foragers, and groups that engage in some farming, tend to eat more plants. We present a case study of the wild food diet of the Hadza, a community of hunter-gatherers in northern Tanzania, whose diet is high in fiber, adequate in protein, and remarkably variable over monthly timescales. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see for revised estimates.
Full-text available
Since the late Pleistocene, large-bodied mammals have been extirpated from much of Earth. Although all habitable continents once harbored giant mammals, the few remaining species are largely confined to Africa. This decline is coincident with the global expansion of hominins over the late Quaternary. Here, we quantify mammalian extinction selectivity, continental body size distributions, and taxonomic diversity over five time periods spanning the past 125,000 years and stretching approximately 200 years into the future. We demonstrate that size-selective extinction was already under way in the oldest interval and occurred on all continents, within all trophic modes, and across all time intervals. Moreover, the degree of selectivity was unprecedented in 65 million years of mammalian evolution. The distinctive selectivity signature implicates hominin activity as a primary driver of taxonomic losses and ecosystem homogenization. Because megafauna have a disproportionate influence on ecosystem structure and function, past and present body size downgrading is reshaping Earth's biosphere.
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Fossil evidence points to an African origin of Homo sapiens from a group called either H. heidelbergensis or H. rhodesiensis. However, the exact place and time of emergence of H. sapiens remain obscure because the fossil record is scarce and the chronological age of many key specimens remains uncertain. In particular, it is unclear whether the present day 'modern' morphology rapidly emerged approximately 200 thousand years ago (ka) among earlier representatives of H. sapiens1 or evolved gradually over the last 400 thousand years2. Here we report newly discovered human fossils from Jebel Irhoud, Morocco, and interpret the affinities of the hominins from this site with other archaic and recent human groups. We identified a mosaic of features including facial, mandibular and dental morphology that aligns the Jebel Irhoud material with early or recent anatomically modern humans and more primitive neurocranial and endocranial morphology. In combination with an age of 315 ± 34 thousand years (as determined by thermoluminescence dating)3, this evidence makes Jebel Irhoud the oldest and richest African Middle Stone Age hominin site that documents early stages of the H. sapiens clade in which key features of modern morphology were established. Furthermore, it shows that the evolutionary processes behind the emergence of H. sapiens involved the whole African continent.
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Alpha-amylase exists across taxonomic kingdoms with a deep evolutionary history of gene duplica- tions that resulted in several a-amylase paralogs. Copy number variation (CNV) in the salivary a-amylase gene (AMY1) exists in many taxa, but among primates, humans appear to have higher average AMY1 copies than nonhuman primates. Additionally, AMY1 CNV in humans has been associated with starch content of diets, and one known function of a-amylase is its involvement in starch digestion. Thus high AMY1 CNV is considered to result from selection favoring more effi- cient starch digestion in the Homo lineage. Here, we present several lines of evidence that challenge the hypothesis that increased AMY1 CNV is an adaptation to starch consumption. We observe that a- amylase plays a very limited role in starch digestion, with additional steps required for starch digestion and glucose metabolism. Specifically, we note that a-amylase hydrolysis only produces a minute amount of free glucose with further enzymatic digestion and glucose absorp- tion being rate-limiting steps for glucose availability. Indeed a-amylase is nonessential for starch digestion since sucrase-isomaltase and maltase-glucoamylase can hydrolyze whole starch granules while releasing glucose. While higher AMY1 CN and CNV among human populations may result from natural selection, existing evidence does not support starch digestion as the major selective force. We report that in humans a-amylase is expressed in several other tissues where it may have potential roles of evolutionary significance.
Full-text available
Salivary amylase is a glucose-polymer cleavage enzyme that is produced by the salivary glands. It comprises a small portion of the total amylase excreted, which is mostly made by the pancreas. Amylases digest starch into smaller molecules, ultimately yielding maltose, which in turn is cleaved into two glucose molecules by maltase. Starch comprises a significant portion of the typical human diet for most nationalities. Given that salivary amylase is such a small portion of total amylase, it is unclear why it exists and whether it conveys an evolutionary advantage when ingesting starch. This review will consider the impact of salivary amylase on oral perception, nutrient signaling, anticipatory metabolic reflexes, blood sugar, and its clinical implications for preventing metabolic syndrome and obesity.
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Salivary amylase activity is partially determined by genetic factors and is possibly related with postprandial plasma glucose levels. The aim of this study is to evaluate the association of salivary amylase activity with plasma glucose and insulin levels after consumption of a gelatinized starchy model food (80% amylopectin; 70% gelatinization), as well as to assess the influence of the salivary amylase gene (AMY1) copy-number variation in amylase activity and concentration. Our results show a strong and significant relation between copy-number variation of AMY1 gene measured through qPCR with salivary amylase concentration, with an enhanced correlation with amylase activity when corrected by salivary flow (r = 0.83, P-value = 0.003). Subjects with high salivary amylase activity tend to have a higher early increase in plasma insulin concentration and a lower glycemic response after starch ingestion compared to subjects with low salivary amylase activity, although these observations did not achieve statistical significance (r = 0.41; P-value = 0.23). In conclusion, we found a strong association between copy-number of AMY1 gene with salivary amylase activity and concentration. However, we did not find evidences for a major role of salivary amylase activity on glycemic response after starch consumption.
Background: Salivary α-amylase gene (AMY1) copy number (CN) correlates with the amount of salivary α-amylase, but beyond this, the physiologic significance is uncertain. Objective: We hypothesized that individuals with higher AMY1 CN would digest starchy foods faster and show higher postprandial responses and lower breath hydrogen excretion compared with those with low CN. Design: Four linked studies were conducted. In Study 1, we genotyped 201 healthy subjects with the use of real-time quantitative polymerase chain reaction and determined glucose tolerance, insulin sensitivity, salivary α-amylase activity, body mass index (BMI), and macronutrient intake. In Study 2, a pool of 114 subjects tested 6 starchy foods, 3 sugary foods, 1 mixed meal, and 2 reference glucose solutions, containing either 50 or 25 g of available carbohydrate. In Study 3, we compared glycemic and insulin responses to starchy foods with responses to glucose in 40 individuals at extremes of high and low CN. In Study 4, we compared breath hydrogen and methane responses over 8 h in 30 individuals at extremes of CN. Results: AMY1 CN correlated positively with salivary α-amylase activity (r = 0.62, P < 0.0001, n = 201) but not with BMI, glucose tolerance, or insulin sensitivity. However, CN was strongly correlated with normalized glycemic responses to all starchy foods (explaining 26-61% of interindividual variation), but not to sucrose or fruit. Individuals in the highest compared with the lowest decile of CN produced modestly higher glycemia (+15%, P = 0.018), but not insulinemia, after consuming 2 starchy foods. Low-CN individuals displayed >6-fold higher breath methane levels in the fasting state and after starch ingestion than high-CN individuals (P = 0.001), whereas hydrogen excretion was similar. Conclusions: Starchy foods are digested faster and produce higher postprandial glycemia in individuals with high AMY1 CN. In contrast, having low CN is associated with colonic methane production. This trial was registered at as ACTRN12617000670370.
Since the middle of the 19th Century, when the first elephant remains were excavated near Madrid (Spain), continuous discoveries of proboscideans have taken place on the riverbanks of the middle and lower courses of the Manzanares and Jarama rivers. The pioneering research carried out by Aguilera y Gamboa in Torralba and Ambrona (Soria, Spain) in the early 20th Century was followed decades later by Howell and others. These various studies have ensured that the Iberian Peninsula is central to the debate over the human exploitation of proboscideans during the Lower and Middle Palaeolithic in Europe. An updated revision of the relationship between hominins and proboscideans in the interior of the Iberian Peninsula, specifically in the area located along the valleys of the Manzanares and Jarama rivers, has been carried out by the authors and is presented in this paper. European sites which show evidence of proboscidean exploitation are substantially greater in number during the Lower Palaeolithic than during the Middle Palaeolithic. In the Manzanares and Jarama valleys, a substantial number of sites with Acheulean lithic industry associated with elephant remains have been recorded, although plenty of evidence dating to the Middle Palaeolithic has also been found. This implies that Mousterian groups made use of these animal resources in a similar way to the Acheulean groups, and that there were no substantial changes to their subsistence strategies in relation to these mammals. Therefore, the exploitation of mega-mammals for food was a recurrent phenomenon during the Acheulean and Middle Palaeolithic in the interior of the Iberian Peninsula.
Eight years of excavation work by the Olduvai Geochronology and Archaeology Project (OGAP) has produced a rich vertebrate fauna from several sites within Bed II, Olduvai Gorge, Tanzania. Study of these as well as recently re-organized collections from Mary Leakey's 1972 HWK EE excavations here provides a synthetic view of the faunal community of Olduvai during Middle Bed II at ∼1.7-1.4 Ma, an interval that captures the local transition from Oldowan to Acheulean technology. We expand the faunal list for this interval, name a new bovid species, clarify the evolution of several mammalian lineages, and record new local first and last appearances. Compositions of the fish and large mammal assemblages support previous indications for the dominance of open and seasonal grassland habitats at the margins of an alkaline lake. Fish diversity is low and dominated by cichlids, which indicates strongly saline conditions. The taphonomy of the fish assemblages supports reconstructions of fluctuating lake levels with mass die-offs in evaporating pools. The mammals are dominated by grazing bovids and equids. Habitats remained consistently dry and open throughout the entire Bed II sequence, with no major turnover or paleoecological changes taking place. Rather, wooded and wet habitats had already given way to drier and more open habitats by the top of Bed I, at 1.85-1.80 Ma. This ecological change is close to the age of the Oldowan-Acheulean transition in Kenya and Ethiopia, but precedes the local transition in Middle Bed II. The Middle Bed II large mammal community is much richer in species and includes a much larger number of large-bodied species (>300 kg) than the modern Serengeti. This reflects the severity of Pleistocene extinctions on African large mammals, with the loss of large species fitting a pattern typical of defaunation or 'downsizing' by human disturbance. However, trophic network (food web) analyses show that the Middle Bed II community was robust, and comparisons with the Serengeti community indicate that the fundamental structure of food webs remained intact despite Pleistocene extinctions. The presence of a generalized meat-eating hominin in the Middle Bed II community would have increased competition among carnivores and vulnerability among herbivores, but the high generality and interconnectedness of the Middle Bed II food web suggests this community was buffered against extinctions caused by trophic interactions.
Natural selection, as both a process and a scientific concept, is eloquently simple. Unfortunately, this simplicity sometimes belies Darwin’s broader view of evolution as a multifaceted process that proceeds from both ecological pressures and phylogenetic history. Darwin further understood that it is not just physical traits that are transmitted generationally, but also behavioural patterns, both of which are subject to the shaping influences of environment and phylogeny. Chimpanzees, bonobos and humans are the most carnivorous extant primates, an observation that serves as the basis of our extended argument that vertebrate predation is a synapomorphy of these sister taxa. From there, we use archaeological data to trace the inferred polarity of hominin carcass foraging and meat-eating from their first archaeological indications ∼2.6 million years ago (Mya). A review of the early Pleistocene African record demonstrates that taphonomic evidence of a hominin predatory/meat-eating behavioral module clarifies ∼2.0 Mya, a critical time period characterised by traces of advanced carcass foraging, which, in turn, suggest that an earlier phase(s) of vertebrate capture by hominins was/were simpler. In rounding out this meta-analytical consideration of hominin carnivory, we draw on comparative primatology, ecology and archaeology in order to build a holistic model of this fundamental behavioural adaptation.