Folio-Frugivore by Nature


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  The Evolution of Early Hominin Diet


Diet is an essential part of the relationship between an organism and its environment (Ungar 2012). For living primates, diet influences several facets of their lives, including geographic range, body size, breeding strategy, and locomotion (Clement and Hillson 2013; Ungar and Sponheimer 2011). Likewise, it was undoubtedly equally as important and influential in the lives of our extinct hominin ancestors. Environmental changes, which often alter available food resources and introduce new challenges, Òhave surely driven changes in early hominin diets and with them the evolution of our genusÓ (Ungar 2012). In fact, major changes in diet are often considered Òkey milestonesÓ in hominin evolution (Ungar and Sponheimer 2011). The change from a primarily plant-based diet to one with meat has often  been cited as a key motivation behind the transition to early Homo (Bunn 2006), although others suggest the inclusion of underground storage organs was more important (OÕConnell et al. 2002; OÕConnell et al. 1999; Ungar 2012). Still others suggest that the additional  preparation of food with tools and cooking was critical (Ungar 2012; Wrangham and Conklin-Brittain 2003; Wrangham et al. 1999). Understanding how diet shifted between  AustralopithecusParanthropus, and early  Homo  can illuminate some of the major driving forces of human evolution. Modeling major changes in the evolution of hominin diet can be done through the examination of several lines of evidence, using both direct and indirect methods. However, which methods are usable varies depending on the time period being studied, as well as the archaeological and fossil evidence available. Archaeological remains, such as stone tools and animal bones, can be used to estimate the diet of more recent hominins, however the earliest hominins are non-existent archaeologically. Their limited representation in the fossil record is an additional problem. Fortunately, the parts of the skeleton most relevant to the study of diet, teeth and jaws, are also the most likely tissue to fossilize (LeeÐThorp 2002). Dental tissues are considerably more resistant than normal bone to chemical and physical degradation (Clement and Hillson 2013; LeeÐThorp 2002). The size, shape, structure, and microwear  patterns of teeth are commonly examined to infer aspects of diet (Ungar 2012). Further information can be gathered through stable isotope analyses and trace elements (Lee ‐Thorp et al. 2003; Sponheimer et al. 2013). Reconstructing paleoenvironments can also suggest what types of food were available during the time periods and regions in which our hominin ancestors lived (Alemseged and Bobe 2009). In this essay I will discuss the various lines of evidence used to study and evaluate the diet of early hominins and how it evolved over time. I will also discuss the dietary importance of plants and animal foods and how the development of cooking influenced human evolution.

Lines of Evidence

Adaptive Evidence
Teeth are adapted to provide preliminary processing of food and for most mammals, the morphology of their teeth is correlated with diet (Andrews et al. 1991). The abundance of teeth in the hominin fossil record has allowed researchers to investigate the evolution of hominin diet using several aspects of dental morphology including tooth size, tooth shape, and enamel structure.
Incisor Size
For primates, there is a correlation between incisor size (relative to body or first molar (M1 size) and type of diet. Frugivorous primates tend to have relatively large incisors, likely adapted for consuming large, husked fruits, while folivores tend to have relatively small incisors, as they eat smaller objects that do not require large front teeth (Andrews et al. 1991; Groves and Napier 1968; Hylander 1975; Teaford and Ungar 2000; Ungar 2012). In the hominin lineage,  Australopithecus  taxa plot on or near the regression line for incisor allometry in extant catarrhines (Figure 1), demonstrating a moderate incisor size, while
 Paranthropus robustus  plots below with a relatively small incisor. Relative incisor size appears to then increase above the line with  Homo habilis  and   Homo rudolfensis, followed by a decrease back to the line in Homo erectus and then below it again with  Homo sapiens. The differences in incisor size suggests that there were notable shifts in diet related to incisor use, however, it is important to note that sample sizes for each hominin species are extremely small (n =1-2) and the body weight estimates are rough and uncertain (Teaford et al. 2002; Ungar 2012).
Molar Size
Relative molar size has also been used as an indicator of diet, although the same limitations in sample size and weight estimates still apply. In living primates, folivores have longer molars than frugivores for most primate groups, however this is not the case in cercopithecoids (Kay 1977; Vinyard and Hanna 2005) and in many primate species, there is a significant difference in relative cheek teeth size between males and females (Harvey et al. 1978). Because the relationship between molar size and diet is inconsistent among living  primates, any conclusions drawn should be done cautiously. Several studies have shown an increase in molar size (in both absolute surface area and megadontia quotient) throughout time in the  Australopithecus and Paranthropus taxa, followed by a reduction in
 Homo (Figure 2) (McHenry and Coffing 2000; Teaford and Ungar 2000; Ungar 2012). The significance of this change is unclear, although the enlarged cheek teeth and robust jaws of the australopithecines are typically explained as an adaptation to processing large amounts of low-quality, hard foods, such as nuts and hard-shelled fruits (Ungar and Sponheimer 2011), while the reduction in  Homo could be the result of a relaxation in selection pressures due to the introduction of tools and cooking (Ungar and Sponheimer 2011).
Tooth Morphology and Structure
The shape of primate teeth, in particular molar teeth, also reflects the fracture  properties of the food each species eats. For example, primates that eat tough leaves often have more occlusal relief than those who typically eat hard objects and these relationships are conserved with wear (Kay 1984; M’kirera and Ungar 2003; Meldrum and Kay 1997; Ungar and M’kirera 2003). Occlusal morphology differences between hominins suggest that
 Paranthropus consumed more hard-brittle food, while early  Homo would have been better at shearing tough items and  Australopithecus falls somewhere in the middle (Bailey and Wood 2007; Teaford et al. 2002; Ungar 2007; Wood and Strait 2004). Tooth enamel thickness is also argued to be an adaptation related to diet and food fracture properties. Thicker enamel  protects better against breakage, but thinner enamel wears quicker and provides a jagged surface, beneficial for processing tough foods (Dumont 1995; Kay 1981; Ungar et al. 2006; Ungar and M’kirera 2003). Studies focusing on tooth size, shape, and structure offer important evidence about fracture properties and masticatory stresses in early hominin diets, however their results can  be misleading (Ungar and Sponheimer 2011). They indicate the dietary adaptation and  phylogenetic history of each species and what they are capable of eating, but that does not always match what specific individuals actually eat (LeeThorp et al. 2003; Ungar and Sponheimer 2011). Even extant primate taxa regularly eat food that does not match the current morphology of their teeth (LeeThorp et al. 2003). For more precise evidence of what each fossil specimen ate, we need to use other methods.
Non-Adaptive Evidence
Dental Microwear
Dental microwear, the study of microscopic wear on the surface of teeth, is one of the  best methods for reconstructing early hominin diets (Scott et al. 2005; Walker et al. 1978). Scratches and pits appear on the surface of a tooth as a direct result of use and each mark is representative of an actual chewing event (Ungar 2011; Ungar and Sponheimer 2011). Different types of food leave behind different wear patterns. Hard, brittle foods (nuts, bones) typically leave pit marks on the occlusal surface of teeth, while tough foods that require shearing (leaves, meat) leave long, parallel striations (Figure 3) (Ungar 2010; Ungar and Sponheimer 2011). Surface complexity corresponds to the hardness of food eaten (Figure 4) (high complexity = heavy pitting) and the directionality (anisotropy) of the wear corresponds to food toughness (high anisotropy = highly aligned scratches) (Ungar and Sponheimer 2011). Studies of early hominin microwear (Scott et al. 2005; Ungar et al. 2008; Ungar et al. 2012; Ungar et al. 2010) reveal somewhat surprising microwear patterns that do not always match what is expected based on morphology.  Australopithecus individuals and  Paranthropus boisei do not have the microwear pattern of high complexity and heavy pitting consistent with a hard-object feeder, unlike originally expected; they also have low to moderate anisotropy, indicating they did not shear tough leaves (Ungar and Sponheimer 2011).  Paranthropus robustus, in contrast, had very high complexity and very low anisotropy, as well as the highest amount of variation of all early hominins (Scott et al. 2005). This distribution is similar to hard-object fallback feeders, which eat harder foods when their  preferred softer foods are absent (Scott et al. 2005). Early  Homo microwear patterns show evidence of a generalized diet (Ungar et al. 2012).  Homo erectus, in particular, has much more variation in the levels of microwear complexity than  Homo habilis, suggesting a very  broad diet (Ungar and Sponheimer 2011). Microwear analyses provide important and direct details of hominin diets, but they still have limitations. Microwear can really only indicate the consistency of food eaten and studies must omit foods that do not leave impressions on the surfaces of teeth, such as insects and flesh (Lee‐Thorp et al. 2003). The Òlast supper effectÓ should also be taken into account; microwear features are constantly worn over and only reflect diet in the last few days or weeks of life (Grine 1986).
Stable Carbon Isotopes
Stable carbon isotope analyses can be used to determine the relative proportion of C3 (trees, bushes, shrubs, forbs) and C4 (grasses, sedges) plants in an extinct hominin individualÕs diet (Ungar and Sponheimer 2011). The stable isotopes of plants eaten by an individual (or for faunivores, the plants eaten by its prey) are incorporated into the teeth and  bones of that individual and the isotopic composition of these tissues becomes reflective of its diet (Cerling et al. 1999; Koch et al. 1998; Lee-Thorp et al. 1989; Ungar and Sponheimer 2011). In the case of human evolution, stable isotope analyses can be used to determine if any of the early hominin species had diets similar to those of extant apes and evaluate the  percentage of C3 and C4 plants in their diets based on! 13 C values (Figure 5). Results indicate that the early hominins that have been analyzed using stable isotopes can be roughly separated into three groups: those with relatively low! 13 C values ( Ardipithecus ramidus and Australopithecus anamensis) similar to the C3 dominated diets of savanna chimpanzees (Schoeninger et al. 1999; Sponheimer et al. 2013; Sponheimer et al. 2006a), those with intermediate! 13 C values ( Australopithecus africanus, Australopithecus afarensis, Paranthropus robustus, and early  Homo) (Lee-Thorp et al. 2000; Sponheimer et al. 2006b; van der Merwe et al. 2008; van der Merwe et al. 2003) indicating a mixed C3/C4 diet, and those with high! 13C values and strongly a C4 diet (Paranthropus boisei (va)n der Merwe et al. 2008). While stable carbon isotope analyses reveal useful and interesting information, there is some difficulty in explaining the results, as there can be several possible explanations for what is observed. In particular, we cannot discriminate between folivorous, frugivorous, or carnivorous diets as all three are based on C3 plants, nor can we tell which type of C3 or C4 foods were eaten (Clement and Hillson 2013; Sponheimer et al. 2013).
Trace Elements (Sr/Ca)
It is possible, however, to distinguish between folivorous, carnivorous, or underground storage organ based diets through the use of trace elements (LeeThorp et al. 2003). The ratio of strontium (Sr) to calcium (Ca) in an individualÕs teeth or bones is reflective of the foods eaten and their trophic level. Herbivores have lower Sr/Ca ratios than the plants they eat, and carnivores have lower Sr/Ca ratios relative to their prey (Elias et al. 1982; Ungar and Sponheimer 2013). Additionally, leaf-eating herbivores would have lower Sr/Ca ratios compared to animals that eat stems or underground storage organs (Sillen et al. 1995). It is important to note however, that a carnivore would only have a reduced Sr/Ca ratio compared to the particular prey it eats, and as a result, it may overlap with herbivores (Lee-Thorp et al. 2003). There is also a high level of variability within species, further complicating any analyses (Burton et al. 1999; Sillen 1992). When Sr/Ca ratios are examined in South African early hominins,  Australopithecus africanus had the highest ratios, early  Homo the lowest, and Paranthropus robustus was intermediary (Figure 6) (Balter et al. 2012). When compared to other fauna, early Homo fit within the Sr/Ca range for carnivores,  Paranthropus robustus for browsers, and  Australopithecus africanus
 was indistinguishable from both grazers and browser (Balter et al. 2012). It is possible that early Homo and Paranthropus robustus both had relatively typical  browser/carnivore diets, while  Australopithecus africanus had a more complex diet.
Contextual Evidence
Paleoenvironmental Reconstruction
As diet is a direct link between an individual and its environment, dynamic changes in environment likely influenced dietary and adaptive changes throughout human evolution (Alemseged and Bobe 2009; Ungar et al. 2006). Reconstructing the paleoenvironmental context of each hominin taxa can provide an additional angle from which to assess potential hominin diets. The type of environment an individual lives in can limit and influence their food choices (e.g a savanna animal is more likely to rely on grasses than tree fruits) (Ungar and Sponheimer 2013). Additionally, if any of the early hominins depended on a specific food for survival and those food sources disappeared with an environmental shift, it could have led to their extinction or been the driving force behind an adaptive morphological transition (Ungar et al. 2006). Environments can be reconstructed using many different methods. Often the most common taxa of a fossil assemblage are used to infer the most likely environment and confirmed using sedimentological and other related evidence (Alemseged and Bobe 2009). Fossilized plant remains, pollen, phytoliths, and soil isotopes are additional methods that are useful in interpreting paleoenvironments (Bamford 1999; Bonnefille et al. 2004; Cerling 1992; WoldeGabriel et al. 1994). Unfortunately, even if we are able to reconstruct the environments early hominins likely inhabited, this does not tell us much about what they actually ate. Rather, it shows what would have been available and provides context for other lines of evidence. Additionally, we need to know the distribution of edible foods in these landscapes in order to understand their eating habits (Peters 2007; Ungar and Sponheimer 2013). It can show, however, whether specific hominin taxa were specialized for particular environments or more generalized and lived in diverse habitats, as well any similarities or inconsistencies in hominin diet across environment type (Alemseged and Bobe 2009). 
Archaeological and Zooarchaeological Remains
Archaeological evidence can be an important source of information for the diets of hominin taxa, however there are limitations on what survives in the archaeological record. For most early hominins we do not have any archaeological artifacts from the time period that they were alive. Of the early hominin archaeological material we do have, stone tools and butchery marks on animal bones reveal the most about diet. The earliest examples of stone tools appear around 2.6 million years ago (Semaw et al. 1997; Semaw et al. 2003) and the earliest cut marks on bone are from around 2.5 million years ago (De Heinzelin et al. 1999) (although there is controversial evidence of cut-marked bones from 3.4 million years ago (McPherron et al. 2010)). It is likely that hominins from earlier time periods also made and used tools, but out of perishable materials (Panger et al. 2002). The existence of early stone tools alone does not prove they were used in food acquisition, however the presence of  butchery marks on animal bones provides support for this idea (Ungar et al. 2006). Furthermore, stone tools were probably very versatile implements. Microwear on some Oldowan stone tool artifacts suggests they were used to prepare vegetation, possibly for food or to construct tools from plant materials (Keeley and Toth 1981). The function of stone tool kits also probably varied between hominin taxa and groups, as they do for extant chimpanzee groups and modern human foragers (Ungar et al. 2006). At any rate, it is clear that the development of stone tools greatly expanded hominin dietary options. The presence of cut-marked animals bones suggests that the development of stone tools enabled a shift in the hominin diet from a primarily frugivorous diet that may have included small animals, to one that included medium to large sized animals (Blumenschine and Pobiner 2007). The combination of both cut marks and carnivore teeth marks on zooarchaeological remains demonstrates which other animals hominins interacted and competed with for food sources (Blumenschine and Pobiner 2007). Butchery marks from stone tools are clearly morphologically distinct from carnivourous teeth marks, as well as rodent gnawing and other taphonomic marks (Blumenschine and Pobiner 2007). The development of stone tools greatly expanded the dietary options of early hominins, and butchery marks on zooarchaeological remains provides concrete evidence that,  beginning about 2.5 million years ago, these hominins were incorporating food from larger animals into their diet. What is less clear, however, is exactly which hominin taxa were making these stones tools and using them in food acquisition. Several hominin species were alive around 2.5 million years ago and multiple species are often found at the same site. This makes it nearly impossible to determine which species was the creator of the stone tool artifacts or cut marks on bones (Lee‐Thorp et al. 2003; Ungar et al. 2006).
Plant vs. Animal Food in Hominin Diets
The increasing incorporation of animal meat and tissue into the hominin diet was one of the most dramatic and influential dietary changes that occurred during human evolution (Bunn 2006). It is thought that the spread of savanna grasslands and the decrease of forest resources pushed hominins to include more and more meat in their diets in order to maintain the same level of dietary quality (Milton 1999; Milton 2003; Ungar et al. 2006). The development of stone tools also improved and expanded their hunting abilities and strategies. A feedback loop was created, with the increase in protein and energy from the meat allowing for the growth of larger brains, which in turn led to greater intelligence and more complex cognition; resulting in more complex social systems, division of labor, and better hunting strategies (Isaac 1971; Isler and van Schaik 2009; Ungar et al. 2006; Washburn 1963). Several hypotheses have been proposed to explain the role meat eating has played in human evolution, with particular emphasis on a relationship with brain size (Aiello and Wheeler 1995; Isler and van Schaik 2009; Milton 1999; Milton 2003). The habitual eating of large amounts of meat provided an important nutritional increase. The ÒExpensive Tissue HypothesisÓ (Aiello and Wheeler 1995) and ÒExpensive Brain HypothesisÓ (Isler and van Schaik 2009) both point to an increase in available metabolic energy as crucial to the growth of a larger brain. Although it is clear that meat eating was critical to the evolution of the human lineage, other researchers suggest that underground storage organs played an important role in the diet of early human evolution (Dominy et al. 2008; Laden and Wrangham 2005; OÕConnell et al. 2002; OÕConnell et al. 1999). It is suggested that hominins are specially adapted to eating underground storage organs (such as tubers, roots, corms, and bulbs), particularly as fallback foods, and the development of these adaptations was key in the initial differentiation between early hominins and other primate species (Hatley and Kappelman 1980; Laden and Wrangham 2005; Wolpoff 1973). Additionally, OÕConnell et al. (1999) suggest that climate and food resource changes around 2 million years ago led to adjustments in foraging  practices, reducing the foods that children could gather themselves and increasing the importance of grandmothers helping to gather food for the children. Underground storage organs are suggested as the mostly likely exploited resource at this time due to their availability and nutrients (OÕConnell et al. 2002; OÕConnell et al. 1999; Ungar et al. 2006).
Impact of Cooking on Hominin Diets
The development of cooking was another dramatic and crucial event in hominin evolution (Wrangham and Conklin-Brittain 2003; Wrangham et al. 1999). It is argued that cooking selected for a more human-like social system, due to the delay in the consumption of food and necessity to be stored and protected from theft (Wrangham and Conklin-Brittain 2003; Wrangham et al. 1999). Additionally, cooking makes food easier to digest and increases energy intake, expanding the range of possible plant and animal foods that were edible to early hominins (Wrangham and Carmody 2010; Wrangham et al. 1999). It also alleviated effects of toxic and digestion-inhibiting elements found in many plants, meaning more of these plants could be consumed if cooked than raw (Attwell et al. 2015; Stahl et al. 1984; Wrangham and Carmody 2010). The Òpre-digestingÓ done by cooking reduces the energy needed for digestion once eaten, opening up more energy for allocation elsewhere (Attwell et al. 2015; Carmody and Wrangham 2009). It is likely that cooking, in addition to the inclusion of meat in the diet, had a morphological effect on hominin evolution,  particularly brain size and cranial and dental morphology. Both the ÒExpensive Tissue HypothesisÓ (Aiello and Wheeler 1995) and ÒExpensive Brain HypothesisÓ (Isler and van Schaik 2009) can be applied to the higher quality diet cooking provides. The reduced masticatory strain caused by cooking also probably relaxed the selective pressures on tooth size, leading to a reduction in the cheek teeth of  Homo erectus and an eventual reduction in facial size of later hominin species (Lieberman et al. 2004). The earliest date for the adoption of cooking is estimated to be at the origin of Homo erectus, although this is based on biological evidence (reduced teeth, increase in female body size, increased brain size), not archaeological evidence (Wrangham et al. 1999). A recent  phylogenetic study based on feeding time and molar size, also found results supporting an origin around the evolution of  Homo erectus (~1.9 million years ago) (Organ et al. 2011). The earliest evidence for the controlled use of fire, however, is from around 1 million years ago (Berna et al. 2012; Goren-Inbar et al. 2004).
It is clear that hominin diet changed drastically from the beginning of the hominin lineage to the start of the genus  Homo. The earliest hominins had plant-based diets similar to other primates of the time, although the specific make up each hominin taxaÕs diet varied widely. The inclusion of more animal foods, as well as the development of cooking, acted as a catalyst for major morphological changes, such as an increase in brain size and decrease in dental and facial size. Reconstructing the diet of early hominins and how it evolved throughout hominin evolution can be done using many difference sources of evidence. Each line of evidence reveals different aspects of the hominin diet and the results are not always interpreted to show the same conclusions. Adaptive evidence, such as tooth size and morphology, can suggest the foods that each hominin taxa has adapted to be able to eat, and therefore more accurately reflects the diet of past generations rather that the one currently  being studied. Non-adaptive lines of evidence, such as dental microwear, stable isotopes, and trace elements, provide the best direct indication of individual hominin diets. Contextual evidence, such as paleoenvironmental reconstructions and archaeological and zooarchaeological remains, provides context for the interpretation of other dietary evidence, as well as material evidence for significant dietary shifts, like meat eating and cooking. Although each method answers different questions and the results are not always in congruence, all lines of evidence should be used in combination in order to reconstruct the most complete picture of early hominin diet.
Figure 1 ÒIncisor allometry. The dashed lines indicate 95% confidence limits of the least squares regression.Ó Reproduced from Ungar (2012). Figure 2 “Cheeck-tooth occlusal areas and megadontia quotients of early hominins. Occlusal areas (the sum of the products of mesiodistal and buccolingual diameters of P4, M1, and M2) are presented above (A),
 and megadontia quotients (occlusal areas divided by 12.15 x body mass0.86) are illustrated below (B). The values in these graphs are from McHenry and Coffing (2000), and taxonomic attributions are as presented by those authors.Ó Reproduced from Ungar (2012). Figure 3 “Microwear textures of early hominins. A model for microwear formation, wherein hard and brittle foods are crushed between opposing teeth, causing pitting with complex, isotropic surface textures; in contrast, soft and tough foods are sheared between opposing teeth that slide past one another, causing parallel scratches and simpler, anisotropic surfaces.Ó Reproduced from Ungar and Sponheimer (2011). Figure 4 “Microwear texture complexity values for individual fossil hominins by species.” Reproduced from Ungar and Sponheimer (2011)
 Figure 5 “Carbon isotope compositions (13C/12C) of early hominins. Top: Carbon flows from C3 and C4 plants (blue and pink arrows, respectively) into the tooth enamel of the consumer (in this case P. robustus, SK 1), and its resulting carbon isotope composition reveals the proportions of these plant types consumed. Bottom: Quantile plot with carbon isotope ratio data for all early hominins analyzed to date [data from (34Ð38, 49)]. Darker shading indicates a greater degree of C3 plant consumption. Each data point reflects a homininÕs diet for a period ranging from months to years depending on the sampling procedure used (red rectangles represent hypothetical sampling areas). Carbon isotope ratios (13C/12C) are expressed as d values in parts per thousand relative to the PeeDee Belemnite standard.Ó Reproduced from Ungar and Sponheimer (2011).
 Figure 6 “Sr/Ca ratios of hominin and bovid enamel. For both ratios, error bars are 2-sigma standard deviations of the mean, and the shaded areas contain data from a previous study (Sponheimer and Lee-Thorp 1999).” Reproduced from Balter et al. (2012).
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vegan by nature - biology

By Mark Blackburn What is a Human Diet?  Is it: What the USDA says it is?  What the Cattleman’s Association says it is?   What they still eat in rural China, where they never have heart attacks or cancer? Is a human diet similar to what some other animals eat? And, if so, which animals?   When I was a boy I read most of Edgar Rice Burrough’s Tarzan books.  These  books were about life in the strange dark continent of Africa.  They detailed the  (then) sum of man’s knowledge of life in the jungle, and life among the wild  beasts of the jungle.   The point was often made that part of the reason Tarzan became so much  stronger than a normal or ‘civilized’ man was because he ate so much meat.   He ate the same as the great anthropoid apes from whom [some say] we are  descended…fresh meat (uncooked meat) from the kill.   I didn’t really like eating meat, but, because I wanted to be strong like Tarzan, I  gave in to my Father’s demands that I eat more meat.   Burroughs was enormously successful in promoting two radical ideas around  the turn of the century–One was that humans should eat more meat.  This  coincided with the British Beefeater movement, which was a concerted effort to  get the British to eat meat.   The other was to reinforce the then recently introduced Darwinian “Theory of  Evolution,” in which it was postulated that the ancestors of man were apes.   The Caveman illusion: Most of us think about early man in terms of a Neanderthal stooping in front of a fire on which he just roasted a brontosaurus burger, or perhaps a drumstick from  a pterodactyl.  I know all the books I read as a boy had just such an illustration.   So, I ask you three questions: Did your ancestors eat mostly meat?   Did man eat more meat 10,000 years ago than today?   Were our ancestors carnivores?   Does it matter what apes eat?  Does it matter what early man ate?   Let me ask another question.  Most land animals are divided into one of the  following dietary habits: Carnivore, Herbivore, or Omnivore.  Into which of these do you see Humans as  fitting?   Carnivore (Dogs, Cats, lions, tigers, wolves, etc.) Herbivore (cattle, rabbits, elephants, horses, most dinosaurs, sheep) Omnivore (Pigs, Bears) Other Applied Naturalism We are modern men and women.  We live in houses, we drive cars.  We buy  stocks, food, drugs, sex, rock ‘n’ roll, and books, over the Internet.  Most of us get  most of our food from grocery stores or at restaurants.   But as advanced and dignified as we all are, we all arrived in this life naked and  helpless.  With a very cursory look to the other mammals, we should be able to deduce that we (as Human infants) should subsist for our first few years almost entirely on Human breast milk.   How many know that they did?  I did not.  If you did, you have a much lower incidence of allergy, asthma, and have a stronger immune system.  Your IQ is also higher than those who like me who were given some substitute for what is obviously “Human Baby Food.” It’s interesting to note that no other mammal drinks the milk of another mammal. Only Western man in his arrogant ignorance has vastly degraded his own health and well being through such an illogical, costly, contrivance.   It might interest you to know that while Mother’s milk has life-giving enzymes, no  formula and no cow’s milk (as it’s served in the USA) has any at all.  In fact, due  to our pasteurizing of commercial cow’s milk, it is rendered toxic to calves!   Pasteurizing kills all the essential enzymes.  Therefore, if you took a calf nursing  milk from its mother, and asteurized it’s milk before feeding it to the calf, the calf  will die within several months, for lack of enzymes and usable nutrients.   Nature would instruct us that drinking the milk of another animal is foolish.  If we’re a duck, we should quack like a duck.  If we’re a human baby, we should eat nature’s obvious food for human babies, not a hideously distorted and depleted  substitute from another species, which has components such as lactase to  which all humans are allergic.   Natural man lived without our houses and cars.  He had no personal computer.  He entered the world naked as we have, but he was more comfortable that way than Americans seem to be.   He had few clothes until he ventured into colder areas.  He interacted directly with his environment in a wonderful way.   Do you know what it is like to interact directly with your environment for more  than a few hours?  I’m reminded of the charming story of the Igor Boutenko  Family of Ashland, Oregon.   This family of four went on a little hike together in 1997.  They hiked from Mexico  to Canada in six months along Pacific Crest Trail.  During this time their food  consisted 80% of edible plants found on the trail.   Although they saw many animals, they did not find it necessary to hunt, kill, or eat any of them.   Obviously ancient men and women lived in a natural setting.  There were no gas stations, McDonalds, or Drug Stores–not even a Border’s Bookstore.  There was  just the environment and humans.   That environment was populated with many other animals and plants.  How did early man know what to eat?  There were no Chocolate Chip Bushes, no Big Mac Trees.   To determine a proper diet from a natural and anthropological perspective, let’s examine 3 key areas: 1. Human History Man’s natural diet in his natural setting is probably his correct diet.  By studying  what man ate in his natural environment, we can come to some conclusion about  the original & optimum diet for man.   It is necessary to study the diet of man prior to 10,000 BC to get correct  information, as since this time electricity, refrigeration, biotech agriculture, machinery and modern appliances have greatly degraded the diet of man.   And, the distortions brought about by grain agriculture beginning about 10,000 years ago should be dismissed as the beginning of distorted, mechanized human feeding.   2. Human Taxonomy and Biological Adaptation Man is classified as a primate.  As such our body’s structure and system bears much in common with other primates.  We are 98% anatomically identical to   chimpanzee.   Our digestive system from our dentition to our colons is structurally and  functionally very similar to the rest of our primate cousins.  Throughout the animal kingdom similar digestive systems digest similar types of food.   Therefore it should be assumed that our natural diet could quite easily be very similar to, or identical to other primates.  Biological adaptation includes the study of the character, temperament, and behavior of living things by species or families.   3. Human Health Man’s health is largely affected by his diet.  So is his longevity.  If we want to study proper diet, we should embrace the latest information on diet and it’s effect on health & longevity.   An Excursion to our Natural Roots Let’s suppose I take you to a remote but tropical part of the planet.  There are no other humans within 100 miles.  I wind you up and let you go except for one thing.  I’ve removed from your memory banks all memory of eating.   You have no recollection of what you used to eat.  You are in your “natural” environment.  What will you eat?  Are you a carnivore?  Will you accelerate rapidly and viscously pounce upon your prey, sinking your teeth into its neck?   Will the victim’s blood spurting into your mouth increase your blood lust?  Or, will you be attracted instead to beautiful and fragrant flowers and to the soft sweet juicy fruits, which abound in your natural habitat?   Anthropologists say we were once exclusively fruit eaters The most recent and widely held view of the historical diet of humans is that early man was exclusively a fruit eater.   Dr. Alan Walker, an anthropologist of John Hopkins University has turned the science of Anthropology on its ear with his abrupt dismissal of the “cave-man-as-carnivore” theory.   Using electron microscopes to study fossilized teeth and fossilized human remains, Dr. Walker’s research team has proven that our ancestors until quite recently were total fruitarians.   The essence of the Walker research is that even though humans have adopted  omnivorous eating practices in very recent history, our anatomy and physiology have not changed—we remain biologically a species of fruit eaters.   The adaptation to fruits (and some vegetables) has occurred over 60 million years.  A few hundred years or even a few thousand years of perverted eating will not change our dietary requirements.   Although confirmed and accepted by the scientific world, this disclosure of early man’s diet is still not widely known or understood by the general public.  The New York Times carried a feature article on the Walker research on May 15, 1979.   We have answered the question of the history of the human diet.  This history has profound bearing on current human dietary needs.   Let’s return for a moment to our “excursion to our Natural Roots.”  Will you find a few juicy scorpions and maybe a lizard to eat?  How about a freshly hatching ostrich chick and a small dog?   If you have revulsion at the thought, it is because you are not a carnivore or omnivore.  Besides having none of the anatomical traits of a carnivore, there is nothing in the character of a man that seeks to hunt and kill other animals the way a carnivore or omnivore would.  Since you are a fruit eater you would be guided by your sense of sight and smell  and taste very readily to a sweet tasting piece of fruit.   Incidentally, next time an ever-so-helpful meat eater tries to tell you there’s no variety in a vegetarian diet, you might mention that there are, in fact over 160,000 edible plants in the world.  If you tried a new one every single day from your birth,  you’d be 438 years old before you tried them all.   When you eat one simple apple, you are ingesting over 191 known friendly phyto-chemical compounds.  Many of these are much more valuable than the outdated vitamins we learned of as children.  Eating one apple launches over 1300 chemical reactions in your frugivore gut to properly break down and dispatch the molecular components of the apple.   If you ingest a piece of meat or dairy your gut does not have the strong acid required to digest it.   An allergic reaction takes place.  Excess mucous is summoned to coat the toxins and pass them as quickly as possible.  But, because meat or dairy have no dietary fiber, they pass extremely slowly, putrefying along the way, filling your digestive tract and body with toxins and varnishing your colon with layers of impacted mucous.   Human Taxonomy and Biological Adaptation But, wait!  What about the great Anthropoid Apes–the ones who taught Tarzan how to hunt for wild game?   Sorry, friends, this only occurred in the fictional world of Tarzan.  Real apes, just like gorillas, monkeys, chimpanzees, orangutans, humans, etc. are frugivores (meaning “fruit eaters”).   All are members of the Primate order, and all are anatomically similar.  With minor exception all primates are frugivores.  When Burroughs wrote Tarzan of the Apes, he was either complicit with the Beefeater movement, or just plain ignorant.   Clearly, however, Burroughs understood the extreme importance of identifying the ancestral human diet.  By propagating the myth that early man ate meat, Burroughs gave license to millions of people to eat something they were not otherwise disposed to do.  He even convinced many of you who thought early man ate more meat than we now do.   Contrary to what we might think, during the period of recorded human history beginning with the Egyptian empire on and through the 1800s, eating of animals was rare and indulged in generally only by the rich and then on special occasion.   Please note that the amazing, highly dexterous and articulated hands shared by most primates allow us to peel bananas and pick and eat fruits very easily.  No other order besides primates can pick a soft ripe peach from a tree and eat it. You are marvelously adapted to be a fruit eater.   Let’s face it–most animals can run away from humans.  They are faster than we are.  If we were meant to be carnivores, would we not be faster than our prey? But there is another answer: we can eat food, which doesn’t run away—food like bananas, berries, or celery.   It should be noted that Primates who stick to a primate diet of fruit do not get diabetes, cancer, or heart disease, or any of the other leading causes of death in omnivorous America.   Incidentally, all primates have blood types like humans.  None of them eat differently in a natural setting based upon their blood type (debunking “Eat Right for your Type”).   I recall telling my good friend Doug at Hewlett-Packard that I was a “frugivore.”   He had inquired about my eating habits.  Then, one day when he and a group of my colleagues were discussing sending out for a pizza, he said, “Oh, Mark won’t have any of that—he’s a frugivore.”   I’m sure none of them had ever heard the term ‘frugivore.’  Well, Doug was right on both counts.   I wouldn’t have pizza, and I was a frugivore.  What struck me, though, was the fact that they were all frugivores, too.  They just didn’t know they were.   What is the cost of not knowing you’re a frugivore?  It’s Staggering.  It’s living in  the most unhealthy country in the world–a country where over 50% of its citizens have at least one chronic illness.   It’s living in a country where over 50% of its men will die of heart disease, and another 30% will die of cancer.  It’s a country where 6 of the 10 leading causes of death are quite preventable–but aren’t prevented, simply because almost nobody knows they are actually frugivores.   Our own Department of Health, Education, and Welfare in its landmark 1977 study entitled “Dietary Goals for the United States” wrote: “It has become clear that only by preventing disease rather than treating it later, can we hope to achieve any major improvement in the nation’s health.   Our diets have changed radically within the last 50 years with great and very harmful effects on our health.  Too much fat, sugar, or salt can be and are linked directly to heart disease, cancer, obesity and stroke, among other killer diseases.  In all, six of the ten leading causes of death in the US have been linked to diet…”  the study states.   Yet, in many countries, which still eat a frugivore diet, our six leading causes of death in the USA are unheard of.   If 6 of the 10 leading causes of death are dietary diseases, isn’t it OBVIOUS that there exists a profound problem with our DIETS!  Is this rocket-science?   Every major independent health study conducted in every country of the world  confirms what we know in our frugivore gut: being a complete vegetarian  (avoiding all animal foods including dairy) is the healthiest possible diet.  Followers of vegan diet reduce the likelihood of dying of America’s number 1 killer by 95%!   In the early 1990s Dr. T. Colin Campbell was winding down the largest dietary study ever undertaken: the Cornell-Oxford-China Study.  This study was independently funded by Cornell and Oxford Universities, and not by any government or farm bureau supported by a conglomeration of factory farms.   It was unbiased.  It is the ‘Grand-Prix’ of all dietary studies.  This study has profound implications for all unhealthy Americans: There is no threshold of health improvement as one removes animal products from the diet: “Our study suggests that the closer one approaches a total plant-food diet, the greater the health benefit.” Consumption of cooked animal-based proteins are more closely correlated to cancer than is consumption of dietary fat.   A diet rich in a variety of plant foods–stems, roots, shoots, fruits & flowers.(the historical human diet) is clearly optimal for health.   Another prodigious diet-researcher I would like to cite is Dr. Joel Fuhrman.  His “Fasting and Eating for Health” is an outstanding reference on proper human diet.   Dr. Fuhrman stresses that being slightly hungry much of the time is a good thing.  He confirms that in all laboratory observations all test species live longer as they eat less food.  Indeed in many cases cutting the food intake in half will nearly double the lifespan.   For this reason, Dr. Fuhrman presents the concept of eating the “Highest Nutrient per calorie Ratio.”   What foods is he speaking of?  Not potato chips.  They would have among the lowest Nutrient/calorie ratios.  Besides fresh fruits and vegetables, Dr. Fuhrman stresses eating lots of leafy green vegetables.   Another implication of research of others as well as Dr. Fuhrman is that of each man or woman having an allotted amount of food to eat.  When you have eaten your allotment, you die.   If you eat your allotment more quickly, your life span is shorter.  If you eat your allotment more slowly, your life span is longer.   Many of us have recently concluded a raw foods prep class in Carmel.  I have made the transition to 100% raw or living foods, with excellent results.   From the perspective of replicating the natural human diet in a natural setting,  eating raw or living foods is about as good as you can get.   We have answered the following 3 crucial questions: What did early man eat?  Fruit & Vegetables.   What do other primates eat?  Fruit & Vegetables.   What does the latest diet research teach us to eat?  Fruit & Vegetables.   Now, one last time I will ask you, “Why do you eat what you eat?”

Early Human Diet Category
Are Humans Natural Carnivores? By: Harry Mather Nice comparison of the human anatomy and carnivorous animals.   “Carnivores kill their prey and usually eat it whilst still warm.  Human hunters carry their prey home and cook it with tasty herbs before they will eat it.   Our front teeth are well adapted for biting fruit and cutting up vegetables.   Plant foods show themselves to be well adapted for providing the wide range of minerals and vitamins that our bodies require.”
Relating Chimpanzee Diets To Early Human Diets Nancy Lou Conklin-Brittain, Richard W. Wrangham, Catherine C. Smith   Harvard Researchers working in Uganda discovered that chimps ate less than 1 percent of meat in their diet. “Although a need for protein or fat is often assumed to explain   increasing amounts of hunting throughout hominid evolution, primates do not have metabolic demands for high levels of protein or fat. Chimpanzees  were much more Frugivorous. They maintained a fairlylow protein intake, due to their focus on Fruit.”
The Comparative Anatomy of Eating By: Milton R. Mills, M.D. Great Article, one of the Best studies ever done comparing human anatomy with that of carnivores, herbivores and omnivores.   Dr. Mills concludes that humans are anatomical frugivores.   “While most humans are clearly “behavioral” omnivores, the question still remains as to whether humans are anatomically  suited for a diet that includes animal as well as plant foods.”
Natural Human Diet According To Biological & Evolutionary Evidence By: Jonathan Reed Excellent Comprehensive Article. “Human teeth are not designed for tearing flesh as in the Lion, Wolf or Dog, but rather compare closely with other fruit-eating animals.  Human teeth correspond almost identically to the Chimpanzees and other Frugivores.   In conclusion, our natural diet should consist primarily of Fruits, Nuts, and Green Vegetables.”

Human Teeth

Wolf Teeth

Lion Teeth

Chimp Hunting & Flesh-Eating By: Laurie Forti Great analysis of the Chimp diet,  chimps actually eat very little meat in the wild and not everyone in the family partakes of the meat.  More like a trophy for defeating a local group of monkeys competing for the same fruit, than hunting for nutrition. “When we examine the way flesh is captured, killed, distributed, and eaten, Chimp flesh-eating is merely a social pathology, just as it is in the human. If meat was necessary it would be consumed by all on a regular basis; it simply is not.”

Chimp Teeth

Food For Thought: Dietary Change Was A Driving Force In Human Evolution By: William R. Leonard, Professor of Anthropology at Northwestern Univ. Laurie Forti: Reviews The Book: Laurie Forti disagrees with the author who is misrepresenting the facts when it comes to early human diet. “I am always amused by such pseudo scientific claims regarding the great wonders conferred to our species by flesh-eating, when the proponents of such claims can not explain just why the human did not evolve the sharp, pointy tools seen among all natural  flesh-eaters, and especially why we did not evolve instincts to capture, kill, and eat flesh raw.”
Tasty Tidbits & Dastardly Dietary Dogma By: Laurie Forti   Once again Laurie Forti with great wit and intelligence challenges “scientists” who claim that humans are Omnivores.  Very logical, well-written. “One of the most ridiculous and persistent false claims made by armchair nutritionists, meatarian propagandists, and even academics, is that the human species is an “omnivore” that is, it should eat both plant and animal matter.  Just looking at our bodies will conclusively prove that we do not have the claws or talons necessary to catch and hold animal prey, and we do not have the sharp, shearing teeth necessary to tear, not chew, animal flesh.”
Humans are Omnivores By: John McArdle, Ph.D Laurie Forti: Examines The Flimsy Evidence Excellent review of scientific paper distorting the facts regarding nutrition and the human anatomy. “Humans are totally incapable of killing, tearing asunder, and consuming raw their prey with their natural, biological equipment, as all natural omnivores do.  I have challenged people who adamantly claim that they are “omnivores” for over 35 years to prove they are natural “omnivores” by simply killing and eating raw a small animal with their natural equipment, and none has ever done so to actually  test their irrational belief.  Not one.”  
Comparative Anatomy & Taxonomy By: John Coleman Short Article substantiating that Humans are anatomical Frugivores. Humans prefer culture and technology over nature, and since our natural role is as a raw food herbivore, and because our bodies are only suited to that role, any significant perversion of it must, and does, lead to ill health.  Our anatomy is clearly unsuited to deal with animal matter in the diet, however our digestive chemistry can deal with animal tissues and obtain some nutrition.   But this does not indicate biological suitability or desirability.”
The Heretic’s Feast – A History of Vegetarianism By: Colin Spencer Excerpt From The Book: A brief history of the human diet.   “Some anthropologists suggest that our brain development did not begin until red meat entered our diet.  If there was a correlation between the consumption of red meat and the enlargement of brain cells, big cats would have the largest brains and be the dominant species in the world today.  Research shows us that a herbivore diet is by far the healthiest and it may well be that a raw Vegetable and Fruit diet, chosen from produce in season, is the optimum healthy diet, as it is so similar to the diet of our evolution.”
Meat In The Human Diet By: John A. McDougall, M.D. Great Article, written by a medical doctor who understands the connection between diet & disease.   “The early ancestors of modern humans, from at least 4 million years ago, followed diets almost exclusively of plant-foods.  The ancestors of modern humans were believed to live primarily on plant foods, eating wild Fruits, leaves, roots, and other high quality plant parts with a few animal foods in their daily diet.  These pre-humans ate like our nearest primate relatives, the apes of today.  Our dentition evolved for processing starches, Fruits, and Vegetables, not tearing and masticating Flesh.”

Yes, from our beginning and for millions of years hominids ate a plant based diet.

In addition to the physical characteristics evidencing humans as herbivores, consider that hominids existed for millions of years before tools, and before fire.

Listen to your own primal nature.  Envision hunting without any tools.  Ripping into flesh without sharp claws.  Sinking your teeth into raw animal tissue without piercing chompers.  How natural does that feel?

Now envision, or actually go outside and try picking berries, gathering leaves, pulling tubers, harvesting mushrooms.  How natural does that feel?  Even if you’ve only eaten modern processed food, the answer is still within you.  It’s in your nature.

Have Humans Adapted to Eating Meat and Does it Even Matter?

From Huffington Post article, Shattering the Meat Myth:

Physicians Committee for Responsible Medicine President Dr. Neal Barnard says in his book, The Power of Your Plate, in which he explains that “early humans had diets very much like other great apes, which is to say a largely plant-based diet, drawing on foods we can pick with our hands. Research suggests that meat-eating probably began by scavenging—eating the leftovers that carnivores had left behind. However, our bodies have never adapted to it. To this day, meat-eaters have a higher incidence of heart disease, cancer, diabetes, and other problems.”

There is no more authoritative source on anthropological issues than paleontologist Dr. Richard Leakey, who explains what anyone who has taken an introductory physiology course might have discerned intuitively—that humans are herbivores. Leakey notes that “[y]ou can’t tear flesh by hand, you can’t tear hide by hand…. We wouldn’t have been able to deal with food source that required those large canines” (although we have teeth that are called “canines,” they bear little resemblance to the canines of carnivores).

In fact, our hands are perfect for grabbing and picking fruits and vegetables. Similarly, like the intestines of other herbivores, ours are very long (carnivores have short intestines so they can quickly get rid of all that rotting flesh they eat). We don’t have sharp claws to seize and hold down prey. And most of us (hopefully) lack the instinct that would drive us to chase and then kill animals and devour their raw carcasses. Dr. Milton Mills builds on these points and offers dozens more in his essay, “A Comparative Anatomy of Eating.”

The point is this: Thousands of years ago when we were hunter-gatherers, we may have needed a bit of meat in our diets in times of scarcity, but we don’t need it now. Says Dr. William C. Roberts, editor of the American Journal of Cardiology, “Although we think we are, and we act as if we are, human beings are not natural carnivores. When we kill animals to eat them, they end up killing us, because their flesh, which contains cholesterol and saturated fat, was never intended for human beings, who are natural herbivores.”

If humans were “designed” to eat meat, why is it that most of our leading causes of death are directly linked to the ingestion of animal proteins (yes, even when it’s organic, boiled and skinless)? Why are vegans generally healthier and live longer lives? Doesn’t sound like our bodies have adapted too well to these products yet, if they’re still killing us. I’ve never heard of a lion with high cholesterol, after all.

Here’s a chart of our anatomy, compared to other animals:

Noting the similarities, I think it’s safe to conclude that we have indeed developed to be herbivores (specifically, frugivores).

But does any of our evolutionary background even matter in terms of modern-day veganism? I would say no. Since it is apparent that humans can thrive on a plant-based diet, it seems entirely irrelevant what we may have adapted to eating in the past.

So the question isn’t ‘is meat healthy’? (it isn’t) or ‘did our ancestors eat meat’? (they didn’t) or ‘do our bodies align with meat-eaters’? (they don’t). The question is ‘if we can live long, healthy lives without animal products (we can), why do we continue to exploit and abuse sentient, feeling beings?’ The answer is in the hands of carnists because I can’t see any way to justify it. Maybe they think “humane” meat is better, but if the whole process of breeding, enslaving, and killing animals is unnecessary (and actually, very unhealthy) how can we defend it at all?

24th Mar 2015 | 215 notes

Why “we evolved to eat meat” is not true

Many people believe that early hominids evolved large brains as a result of eating meat. However, this theory ignores several major aspects of human/primate evolution, neurobiology, and genetics.

Primates are an extremely social order. Studies have shown that “evolution of primate brains is thought to be associated with the demands of living in a complex social environment”. Because a large social group is harder to understand and negotiate, early hominids may have had to evolve larger brains to better cooperate with other group members. Multiple pieces of evidence support this.

“The fossil remains of several australopithecine and paranthropine species show that diet varied between 4.5 and 1.2 Ma, but that overall these hominids had large molars lacking well-developed shearing crests, thick enamel and powerful jaws. These dental traits indicate crushing of hard food items during mastication and a diet that included seeds, rich in protein and fat, but do not preclude a diet including underground storage organs (USOs), such as roots and tubers, covered with abrasive soil and rich in carbohydrates”. This suggests that early hominids had access to highly nutritious, plant-based foods about 4.5 million years ago (MYA). Genomic studies have shown that humans and chimpanzees diverged roughly 6.3 MYA.

“Early Homo may have relied more on tough fallback resources, perhaps including meat”, about 2.5 MYA. Humanoid tooth marks were found on bones that dated to 2.5 MYA, suggesting some meat-consumption. However, as individual humans are less than intimidating, it is likely that early Homo must have formed groups in order to scare predators away from their kills (aggressive scavenging). This also happened roughly 2.5 MYA.

So we’ve established that there was a break of just under 4 million years between our divergence from chimps and the beginning of meat-eating. This is a relatively long time for us to have developed larger brains, which makes sense, considering that “brain-expressed and brain-specific genes may all be slowly evolving for reasons of shared constraints. It seems possible that the stronger selective pressure on brain expressed genes is the consequence of the higher complexity of the biochemical network in the brain”.

When combined with the discoveries that “mammals tend to meet the energy costs of evolutionary changes in brain size by some combination of increased energy intake or reduced allocation to other functions such as growth, reproduction, digestion or locomotion“, and that “primates exhibit a strong signature for a quantitative group size effect on brain size, but all the other taxa do not. In primates, the relationship between brain and group sizes is much stronger than the relationship between brain size and any other factor”, it can be inferred that our social groups were, at least in part, responsible for development of our larger brains.

“Another trade-off prediction comes from Leonard et al., who suggest that a decrease in muscle mass and an increase in adiposity provided a potential source of energy to fuel the evolution of the human brain in two main ways. First, an energetically expensive tissue, skeletal muscle, was reduced. Second, a tissue known for its ability to store energy, fat, was increased.” This would have allowed early Homo to redirect more nutrients to the brain.

The first signs of active human hunting were found about 500,000 years ago, in “stone points from the archaeological site of Kathu Pan 1 (KP1), South Africa, which functioned as spear tips”. By this time, Homo had had a couple million years of evolution in which to develop large brains, as well as complex social structures needed for hunting. When the evolution of carnivores was examined, it was found that their brain size was extremely variable, and that “explanations other than sociality must be sought for the multiple brain-size increases and decreases observed during the evolutionary history of this clade (Carnivora)”. This suggests that humans and carnivores evolved brain size by separate mechanisms.

The disparity between humans and other primates may be attributed to  “distinctive aspects of primate cognition that evolved mainly in response to the especially challenging demands of a complex social life of constant competition and cooperation with others in the social group [the social intelligence hypothesis…humans are not just social but “ultra-social”. That is, whereas primates in general have evolved sophisticated social-cognitive skills for competing and cooperating with conspecifics, humans have also evolved skills that enable them to actually create different cultural groups, each operating with a distinctive set of artifacts, symbols, and social practices and institutions”

In conclusion, it cannot be assumed that humans evolved large brains as a result of eating meat, but rather that meat consumption and hunting were relatively recent byproducts of complex brains by way of social evolution. The effect of social groups on brain size can still be seen today, as a correlation has been found between the number of online friends a person has, and anatomical size of specific brain regions.