Human Evolution, Food, Digestion, Ketosis, Hunting and Meat, Adaptations, and Paleoanthropology
The main question this wiki page is trying to answer is what kind of diet did modern man evolve with and how can we use those insights to influence our modern nutrition?
Gastric acidity is likely a key factor shaping the diversity and composition of microbial communities found in the vertebrate gut. The study conducted a systematic review to test the hypothesis that a key role of the vertebrate stomach is to maintain the gut microbial community by filtering out novel microbial taxa before they pass into the intestines. The study proposes that species feeding either on carrion or on organisms that are close phylogenetic relatives should require the most restrictive filter (measured as high stomach acidity) as protection from foreign microbes. Conversely, species feeding on a lower trophic level or on food that is distantly related to them (e.g. herbivores) should require the least restrictive filter, as the risk of pathogen exposure is lower. Comparisons of stomach acidity across trophic groups in mammal and bird taxa show that scavengers and carnivores have significantly higher stomach acidities compared to herbivores or carnivores feeding on phylogenetically distant prey such as insects or fish. In addition, the study found when stomach acidity varies within species either naturally (with age) or in treatments such as bariatric surgery, the effects on gut bacterial pathogens and communities are in line with our hypothesis that the stomach acts as an ecological filter. Together these results highlight the importance of including measurements of gastric pH when investigating gut microbial dynamics within and across species.
Common Name Trophic Group pH Common Buzzard Obligate Scavenger 1.1 White Backed Vulture Obligate Scavenger 1.2 Common Pied Oystercatcher Generalist Carnivore 1.2 Bald Eagle Facultative Scavenger 1.3 Barn Owl Facultative Scavenger 1.3 Little Owl Facultative Scavenger 1.3 Common Crow Obligate Scavenger 1.3 Common Moorhen Omnivore 1.4 Humans Omnivore 1.5 Ferret Generalist Carnivore 1.5 Wandering Albatross Obligate Scavenger 1.5 Possum Facultative Scavenger 1.5 Black-Headed Gull Facultative Scavenger 1.5 Common Kestrel Generalist Carnivore 1.5 Swainson’s Hawk Facultative Scavenger 1.6 Beaver Herbivore/Hindgut 1.7 American Bittern Facultative Scavenger 1.7 Grey Falcon Facultative Scavenger 1.8 Peregrine Falcon Facultative Scavenger 1.8 Red Tailed Hawk Facultative Scavenger 1.8 Rabbit Herbivore/Foregut 1.9 Common Starling Specialist Carnivore/Insect 2.0 Cynomolgus Monkey Omnivore 2.1 Mallard Duck Omnivore 2.2 Magellanic Penguin Specialist Carnivore/Fish 2.3 Bottlenose Dolphins Specialist Carnivore/Fish 2.3 Gentoo Penguin Specialist Carnivore/Fish 2.5 Snowy Owl Generalist Carnivore 2.5 Domesticated Pig Omnivore 2.6 Woylie Brush Tailed Bettong Herbivore/Hindgut 2.8 King Penguins Specialist Carnivore/Fish 2.9 Great Cormorant Specialist Carnivore/Fish 3.0 Great Horned Owl Generalist Carnivore 3.1 Rhino Herbivore/Hindgut 3.3 Elephant Herbivore/Hindgut 3.3 Southern Hairy Nosed Wombat Herbivore/Hindgut 3.3 Skyes Monkey Omnivore 3.4 Crab-Eating Macaque Omnivore 3.6 Cat Generalist Carnivore 3.6 Baboon Omnivore 3.7 Chicken Specialist Carnivore/Insect 3.7 Mouse Omnivore 3.8 Ox Herbivore/Foregut 4.2 Guinea Pig Herbivore/Foregut 4.3 Hippo Herbivore/Hindgut 4.4 Rat Omnivore 4.4 Horse Herbivore/Foregut 4.4 Howler Monkey Herbivore/Hindgut 4.5 Dog Facultative Scavenger 4.5 Porcupine Herbivore/Foregut 4.5 Sheep Herbivore/Foregut 4.7 Gerbil Herbivore/Foregut 4.7 Hamster Herbivore/Foregut 4.9 Common Pipistrelle Bat Specialist Carnivore/Insect 5.1 Minke Whale Specialist Carnivore/Fish 5.3 Brocket Deer Herbivore/Foregut 5.5 Collared Peccary Herbivore/Foregut 5.8 Langur Monkey Herbivore/Foregut 5.9 Silver Leafed Monkey Herbivore/Foregut 5.9 Shetland Ponies Herbivore/Hindgut 5.9 Colobus Monkey Herbivore/Foregut 6.3 Camel Herbivore/Foregut 6.4 Echidna Specialist Carnivore/Insect 6.8 Macropodid Herbivore/Foregut 6.9 Llama Herbivore/Foregut 7.0 Guanaco Herbivore/Foregut 7.3
*Obligate - Animals that depend solely on that diet. Generalist - Is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources. Specialist - Can thrive only in a narrow range of environmental conditions or has a limited diet. Eats only insects or fish as a carnivore, for example. Facultative - Does best on a said diet, but can survive-but-not-thrive on a different one.
In total, the studies’ literature search yielded data on 68 species (25 birds and 43 mammals) from seven trophic groups (Table 1). A general linear model based on diet explained much of the variation in the stomach pH (R2 = 0.63, F1,6 = 17.63, p < 0.01). The trophic groups that were most variable in terms of their stomach pH were omnivores and carnivores that specialize in eating insects or fish.
The studies’ hypothesis was that foregut-fermenting herbivores and animals that feed on prey more phylogenetically–distant from them would have the least acidic stomachs. Tukey-Kramer comparisons indicated that scavengers (both obligate and facultative) had significantly higher stomach acidities compared to herbivores (both foregut and hindgut) and specialist carnivores feeding on phylogenetically distant prey. Specifically, foregut-fermenting herbivores had the least acidic stomachs of all trophic groups while omnivores and generalist carnivores, with more intermediate pH levels, were not distinguishable from any other group (Fig 1).
The special case of herbivory
Carrion feeding imposes one sort of constrain on the ecology of the gut, an increase in the potential for pathogens. Herbivory imposes another, the need to digest plant material refractory to enzymatic digestion (cellulose and lignin). In order to digest these compounds, herbivores rely disproportionately on microbial processes. Different regions of the gastrointestinal tract (either rumen, caecum or in the case of the hoatzin a folded crop) function primarily as fermentation chambers. Thus, a challenge with fermentative guts is favoring those microbes that are useful for digestion while reducing the risk of pathogen entry into the gut. The study suggests that because the threat of microbial pathogens is relatively low on live leaves , herbivores can afford to maintain a chamber that is modestly acidic and therefore less restrictive to microbial entry. However, it finds several interesting exceptions to this generality. Beavers, which are known to store food caches underwater where there is a high risk of exposure to a protozoan parasite Giardia lamblia, have very acidic stomachs. The high stomach acidity may have evolved to manage this prevalent environmental pathogen. The other herbivore in our dataset with a very acidic stomach is the rabbit, which provides an interesting example of a behavioral modification of the stomach environment. Rabbits are known to engage in frequent coprophagy which allows them re-inoculate themselves with microbes. The specialized soft pellets that house microbes also reduce the stomach acidity creating an environment suitable for fermentation.
Human evolution and stomach pH
It is interesting to note that humans, uniquely among the primates so far considered, appear to have stomach pH values more akin to those of carrion feeders than to those of most carnivores and omnivores. In the absence of good data on the pH of other hominoids, it is difficult to predict when such an acidic environment evolved. Baboons (Papio spp) have been argued to exhibit the most human–like of feeding and foraging strategies in terms of eclectic omnivory, but their stomachs–while considered generally acidic (pH = 3.7)– do not exhibit the extremely low pH seen in modern humans (pH = 1.5). One explanation for such acidity may be that carrion feeding was more important in humans (and more generally hominin) evolution than currently considered to be the case. Alternatively, in light of the number of fecal-oral pathogens that infect and kill humans, selection may have favored high stomach acidity, independent of diet, because of its role in pathogen prevention.
TES Editor Note: Maybe the 1.5 extremely low pH seen in modern humans is an indication we are facultative carnivores - to digest meat.
Carrion Feeder - Any animal that feeds on dead and rotting flesh.
The human stomach and the loss of mutualistic microbes
In general, stomach acidity will tend to filter microbes without adaptations to an acidic environment. Such adaptations include resistant cell walls, spore-forming capabilities or other traits that confer tolerance to high acidities and rapid changes in pH conditions. The study considered the role of the stomach as a pathogen barrier within the context of human evolution. Another potential consequence of high stomach acidity, when considered in light of other primates and mammals, is the difficulty of recolonization by beneficial microbes. A large body of literature now suggests that a variety of human medical problems relate to the loss of mutualistic gut microbes, whether because those mutualists failed to colonize during hyper-clean C-section births or were lost through use of antibiotics, or other circumstances. The pH of the human stomach may make humans uniquely prone to such problems. In turn, it might be expected that, among domesticated animals, that similar problems should be most common in those animals that, like humans, have very acidic stomachs.
The special risk to juvenile and elderly humans
If, in carnivores and carrion-feeders, the stomach’s role is to act as an ecological filter then it would also be expected to see higher microbial diversity and pathogen loads in cases where stomach pH is higher. We see evidence of this in age-related changes in the stomach. Baseline stomach lumen pH in humans is approximately 1.5 (Table 1). However, premature infants have less acidic stomachs (pH > 4) and are susceptibility to enteric infections. Similarly, the elderly show relatively low stomach acidity ( pH 6.6 in 80% of study participants) and are prone to bacterial infections in the stomach and gut. It is important to note that these differences may be related to differences in the strength of the immune system however it is argued here that the stomach needs more consideration when studying these patterns.
The study demonstrates that stomach acidity increases with the risk of food-borne pathogen exposure and propose that the stomach plays a significant role as an ecological filter and thus a strong selection factor in gut microbial community structure and primate evolution in particular. In light of modern lifestyle changes in diet, hygiene and medical interventions that alter stomach pH, we suggest that stomach acidity in humans is a double-edged sword. On one hand, the high acidity of the human stomach prevents pathogen exposure but it also decreases the likelihood of recolonization by beneficial microbes if and when they go missing. However, in those cases where acidity is reduced, the gut is more likely to be colonized by pathogens. Though it is widely discussed in both the medical and ecological literature, data on pH are actually very scarce. Thus, to fully understand the patterns highlighted here more detailed studies on the gut microbiota across stomach acidities and diet are required.
It’s interesting how the only other omnivore other than humans on the list with a pH below 2, is the Common Moorhen. Others with a pH below 2, were all facultative scavengers, obligate scavengers and generalist carnivores (as stated in the study: It is interesting to note that humans, uniquely among the primates so far considered, appear to have stomach pH values more akin to those of carrion feeders than to those of most carnivores and omnivores). Additionally, in the case of the elderly, it is indeed suspected that is it ill health which resulted in higher pH, not in fact increased age. The study also shows the harmful effects of antibiotics and hyper-clean C-section births, among others.
The gastric acid and fluid secretion rates, gastric volume, and pH values for humans, beagle dogs, pigs, and Rhesus monkeys are given in Table 4. In dogs, the gastric acid secretion rate at the basal state is low. Therefore, the stomach pH of the dog can be as high as its duodenal contents in the unstimulated state.I9 Following stimulation (i.e., food, histamine), gastric acid secretion rates in dogs exceed those of the human and pig (Table 4). In humans, the stomach pH after food is initially higher due to the strong buffering action of food. However, the pH returns to a low value after about one hour (Table 4).
In 1995, anthropologists Leslie C. Aiello and Peter Wheeler published a paper on a theory they termed The Expensive Tissue Hypothesis (ETH). Expensive refers to human brain tissue, which is uniquely metabolically demanding compared to other primate brains (Aiello & Wheeler, 1995). However, human total metabolic rate is close to what would be predicted for a primate human size, so according to the ETH, humans compensated for the increased metabolic costs of the brain by evolving less metabolically expensive splanchnic organs, which include the gut and liver. Humans were able to fuel their large brains using only a relatively small gut because increased dietary quality reduced the need for gut mass. The hypothesis was that the main driver of this increased dietary quality was the increased use of animal products.
Graph of relative brain mass versus relative gut mass in primates, determined on the basis of the higher-primate equations given in figure 3 and expressed as the residuals between the logged observed and expected sizes.
Common Name Relative Gut Mass (Based on graph, may be hard to understand) Relative Brain Mass (Based on graph, may be hard to understand) Venezuelan Red Howler 0.3 -0.2 Tufted Capuchin -0.05 0.2 Silvered Leafed Monkey 0.2 -0.2 Maroon Leaf Monkey -0.15 0.05 Siamang 0.15 0 Lar Gibbon -0.05 0.15 Humans -0.18 0.47
Aiello and Wheeler
This hypothesis rests on assuming that reduced gut size coincided with the major jump in encephalization experienced by hominids millions of years ago. In their calculations, Aiello and Wheeler used the modern human gut to demonstrate its uniquely small size. Unfortunately, using the modern human gut as a hallmark has some problems, as there is some evidence that it has been reduced in size due to dietary innovations that may have taken place long after encephalization and since these innovations it has possibly continued to evolve. The trend in human innovation has been towards a diet of increased quality and this innovation continues even today. In response to these dietary changes, the human population shows variation in dietary adaptations. The reorganization and variation of the human colon provides important clues about this process.
Exactly how unusual is the modern human gut? Based on a reduced major axis equation computed for higher primates, the human gut should be about 781 grams larger (Aiello & Wheeler, 1995).
Organ Average Observed Weight in Grams Average Expected Weight in Grams Brain 1250 Grams 500 Grams Gut 1250 Grams 2000 Grams Liver 1400 Grams 1500 Grams Kidney 600 Grams 650 Grams Heart 300 Grams 250 Grams
It is hard to know when this change started, as guts do not fossilize nor do they leave their impressions as brains do in endocasts. However, it is possible to infer some information from post-cranial anatomy. Living apes with big guts have protuberant abdomens to accommodate them.
Skeletally, they have a rounded abdomen continuous with the lower portion of the rib cage, giving it a funnel shape, as well as a wide pelvis with flared upper margins. In the fossil record we can see that Australopithecus afarensis had skeleton anatomy that would indicate a large gut if this pattern holds.
In contrast, the human pelvis size is reduced and the abdomen has a defined waist region. Hominids start exhibiting this in the fossil record starting with Homo erectus, about 1.5 million years ago. However, there is some evidence that this anatomical change may not have to do with gut size. For one, it is not entirely a consistent pattern among hominids. Reconstructions of a post-cranial Neanderthal skeleton based on the 70,000 year old La Ferrassie 1 and 60,000 year old Kebara 2 specimens shows a wider trunk showing up again (Sawyer & Maley, 2005).
It is possible that the trunk and pelvis size represented adaptations to cold, a type of hunting, or some other lifestyle variable (Bramble & Lieberman, 2004). Until more data is collected and analyzed tying post-cranial anatomy to gut mass, it is hard to tell if the inference is valid.
In response to the ETH paper in 1995, Katherine Milton questioned whether the data presented was really representative of our species. She stated that our guts may have played a larger role before the relatively recent invention of agriculture when fiber consumption was much greater and our guts might have been larger then because of “gut plasticity.” She mentioned that what really sets us apart from our primate relatives is the reorganization of the gut morphologically rather than the size.
In humans compared to primates, the gut is reorganized. The size of the colon is much reduced and the size of the small intestine is increased. The human colon takes up 17-23% of the digestive tract. In chimpanzees, orangutans, and gorillas it occupies 52-54%. Instead of a large colon, humans have a small intestine that represents 56-67% of the gut (Milton, 1989).
Relative Gut Volume Proportions for Some Hominoid Species from Milton
Common Name Stomach Small Intestine Cecum Colon Gorilla 25 14 7 53 Orangutan 17 28 3 54 Chimpanzee 20 23 5 52 Siamang 24 25 1 49 Pillated Gibbon 24 29 2 45 Human 17 67 n.a. 17
These are important to note because of their role in digesting food. The small intestine is where primate enzymes digest and absorb nutrients immediately available in food. In contrast, the colon can be thought of as a bioreactor, where bacteria digest otherwise useless dietary constituents into important nutrients and other chemical byproducts. These include short-chain fatty acids (SCFA), organic fatty acids with 1-6 carbon atoms created by the fermentation of polysaccharides, oligosaccharides, protein, peptides, and glycoprotein precursors in the colon. The major source of these in primates is through the fermentation of fiber and some types of starch. The major difference in this matter between humans and the other great apes is that apes such as the gorilla are able to use their larger colons to obtain as much as 60% of their caloric intake from SCFA alone (Popovich et al., 1997). Upper estimates for human caloric use of SCFA range from seven to nine percent (2-9%). (McNeil, 1984).
Foods are 90% water. Stems and fruit contained more total dietary fiber than leaves and > vines. Afer accounting for hindgut fiber fermentation:
Nutrient Kcal per 100 Grams (total of 194 kcal) Protein 47 kcal (24% energy) Carbohydrate 30 kcal (16% energy) Fat 5 kcal (3% energy) Short Chain Saturated Fats 111 kcal (57% energy)
In conclusion: Gorilla diet is at least 60% of energy from fat, 57% from saturated fats.
Despite a genetic difference of as little as 2% between humans and gorillas (Sibley and Ahlquist 1984), the human colon may contribute as little as 2–9% to total energy (Livesey and Elia 1995, McBurney 1994, McNeil 1984) compared with possibly 30–60% for the gorilla. Assuming that the diets of the great apes are closer to the diet on which our common ancestor evolved before the clade split 4.5–7.5 million years ago (Pilbeam 1984), the high fiber folifrugivorous diet may have important implications for both human health and the health of captive great apes.
Herschel et al. (1981) concluded that although the total energetic contribution of SCFAs absorbed in the dog colon (approximately 7%) may be relatively small, their absorption is significant to normal colonic absorptive processes. It is probable that the dog and cat would gain similar amounts of digestible energy from NSPs, since in vitro fermentation of fibrous substrates resulted in similar amounts of SCFA production when either dog or cat fecal inoculum was used (Sunvold et al., 1995a).
People may have their colon removed as a way to treat colon cancer or Crohn’s disease, or in some cases, to prevent colon cancer. People can live without a colon, but may need to wear a bag outside their body to collect stool. However, a surgical procedure can be performed to create a pouch in the small intestine that takes the place of the colon, and in this case, wearing a bag is not necessary, according to the Mayo Clinic.
Humans were able to fuel their large brains using only a relatively small gut because increased dietary quality reduced the need for gut mass. The hypothesis was that the main driver of this increased dietary quality was the increased use of animal products. The great apes such as the gorilla are able to use their larger colons to obtain as much as 60% of their caloric intake from SCFA alone. Upper estimates for human caloric use of SCFA range from seven to nine percent (2-9%). The information about the processing of SCFA in Gorillas and Humans comes from Popovich et al, who are advocates of a Plant-Based diet. Considering the large amounts of energy the great apes get from SCFAs, they would most likely not be able to survive without them. Remember, dogs and cats have an energetic contribution of SCFAs at around 7%, possibly even more than humans. Humans can also live without a colon, completely eliminating energetic contribution of SCFAs.
The human brain stands out among mammals by being unusually large. The expensive-tissue hypothesis explains its evolution by proposing a trade-off between the size of the brain and that of the digestive tract, which is smaller than expected for a primate of our body size. Although this hypothesis is widely accepted, empirical support so far has been equivocal. Here we test it in a sample of 100 mammalian species, including 23 primates, by analysing brain size and organ mass data. We found that, controlling for fat-free body mass, brain size is not negatively correlated with the mass of the digestive tract or any other expensive organ, thus refuting the expensive-tissue hypothesis. Nonetheless, consistent with the existence of energy trade-offs with brain size, we find that the size of brains and adipose depots are negatively correlated in mammals, indicating that encephalization and fat storage are compensatory strategies to buffer against starvation. However, these two strategies can be combined if fat storage does not unduly hamper locomotor efficiency. We propose that human encephalization was made possible by a combination of stabilization of energy inputs and a redirection of energy from locomotion, growth and reproduction.
The brain is one of the most energetically expensive organs in the vertebrate body. Consequently, the energetic requirements of encephalization are suggested to impose considerable constraints on brain size evolution. Three main hypotheses concerning how energetic constraints might affect brain evolution predict covariation between brain investment and (1) investment into other costly tissues, (2) overall metabolic rate, and (3) reproductive investment. To date, these hypotheses have mainly been tested in homeothermic animals and the existing data are inconclusive. However, there are good reasons to believe that energetic limitations might play a role in large-scale patterns of brain size evolution also in ectothermic vertebrates. Here, we test these hypotheses in a group of ectothermic vertebrates, the Lake Tanganyika cichlid fishes. After controlling for the effect of shared ancestry and confounding ecological variables, we find a negative association between brain size and gut size. Furthermore, we find that the evolution of a larger brain is accompanied by increased reproductive investment into egg size and parental care. Our results indicate that the energetic costs of encephalization may be an important general factor involved in the evolution of brain size also in ectothermic vertebrates.
In the ongoing discussion about brain evolution in vertebrates, the main interest has shifted from theories focusing on energy balance to theories proposing social or ecological benefits of enhanced intellect. With the availability of a wealth of new data on basal metabolic rate (BMR) and brain size and with the aid of reliable techniques of comparative analysis, we are able to show that in fact energetics is an issue in the maintenance of a relatively large brain, and that brain size is positively correlated with the BMR in mammals, controlling for body size effects. We conclude that attempts to explain brain size variation in different taxa must consider the ability to sustain the energy costs alongside cognitive benefits.
Kidney: As you’re probably aware, humans have two kidneys, but need only one to survive. People may be born with just one kidney, or have one removed after injury or for a donation. In general, people with one kidney have few or no health problems, and have a normal life expectancy, according to the National Kidney Foundation. Technically, people can live with no kidneys, but require dialysis.
Spleen: The spleen filters blood and helps the body fight infections, but it’s not essential for survival. The spleen can be removed if, for instance, it’s damaged. However, people without a spleen are more prone to infections. Reproductive organs: Women can have their uterus removed in a hysterectomy as a treatment for cancer, uterine fibroids, chronic pelvic pain, or other reasons. About 1 in 3 women in the United States had had the procedure by age 60, according to the National Institutes of Health. Men may have their testicles removed as a treatment for testicular cancer.
Stomach: The whole stomach is sometimes removed as a treatment for stomach cancer, a procedure called a total gastrectomy. In this procedure, the small intestine is connected to the esophagus. People who’ve had a total gastrectomy receive nutrition through a vein for a few weeks while they recover. After that, they are able to eat most foods, but may need to eat smaller meals, and take dietary supplements if they have problems absorbing vitamins, according to the National Health Service of England.
Colon: People may have their colon removed as a way to treat colon cancer or Crohn’s disease, or in some cases, to prevent colon cancer. People can live without a colon, but may need to wear a bag outside their body to collect stool. However, a surgical procedure can be performed to create a pouch in the small intestine that takes the place of the colon, and in this case, wearing a bag is not necessary, according to the Mayo Clinic.
Appendix: The appendix is a small, tube-shaped organ that juts out from the first part of the large intestine. It’s unclear what its function is, but it can be removed if it becomes inflamed or ruptures.
Basically, our kidneys have a remarkable tolerance to salt.
Although humans have a longer period of infant dependency than other hominoids, human infants, in natural fertility societies, are weaned far earlier than any of the great apes: chimps and orangutans wean, on average, at about 5 and 7.7 years, respectively, while humans wean, on average, at about 2.5 years. Assuming that living great apes demonstrate the ancestral weaning pattern, modern humans display a derived pattern that requires explanation, particularly since earlier weaning may result in significant hazards for a child. Clearly, if selection had favored the survival of the child, humans would wean later like other hominoids; selection, then, favored some trait other than the child’s survival. It is argued here that our unique pattern of prolonged, early brain growth—the neurological basis for human intellectual ability—cannot be sustained much beyond one year by a human mother’s milk alone, and thus early weaning, when accompanied by supplementation with more nutritious adult foods, is vital to the ontogeny of our larger brain, despite the associated dangers. Therefore, the child’s intellectual development, rather than its survival, is the primary focus of selection. Consumption of more nutritious foods—derived from animal protein—increased by ca. 2.6 myr ago when a group of early hominins displayed two important behavioral shifts relative to ancestral forms: the recognition that a carcass represented a new and valuable food source—potentially larger than the usual hunted prey—and the use of stone tools to improve access to that food source. The shift in the hominin “prey image” to the carcass and the use of tools for butchery increased the amount of protein and calories available, irrespective of the local landscape. However, this shift brought hominins into competition with carnivores, increasing mortality among young adults and necessitating a number of social responses, such as alloparenting. The increased acquisition of meat ca. 2.6 Ma had significant effects on the later course of human evolution and may have initiated the origin of the genus Homo.
The large human brain, long life span and high fertility are key elements of human evolutionary success and are often thought to have evolved in interplay with tool use, carnivory and hunting. However, the specific impact of carnivory on human evolution, life history and development remains controversial. In the study it is shown in quantitative terms that dietary profile is a key factor influencing time to weaning across a wide taxonomic range of mammals, including humans. In a model encompassing a total of 67 species and genera from 12 mammalian orders, adult brain mass and two dichotomous variables reflecting species differences regarding limb biomechanics and dietary profile, accounted for 75.5%, 10.3% and 3.4% of variance in time to weaning, respectively, together capturing 89.2% of total variance. Crucially, carnivory predicted the time point of early weaning in humans with remarkable precision, yielding a prediction error of less than 5% with a sample of forty-six human natural fertility societies as reference. Hence, carnivory appears to provide both a necessary and sufficient explanation as to why humans wean so much earlier than the great apes. While early weaning is regarded as essentially differentiating the genus Homo from the great apes, its timing seems to be determined by the same limited set of factors in humans as in mammals in general, despite some 90 million years of evolution. The analysis emphasizes the high degree of similarity of relative time scales in mammalian development and life history across 67 genera from 12 mammalian orders and shows that the impact of carnivory on time to weaning in humans is quantifiable, and critical. Since early weaning yields shorter interbirth intervals and higher rates of reproduction, with profound effects on population dynamics, the findings highlight the emergence of carnivory as a process fundamentally determining human evolution.
All the meat-eaters, including ferrets, killer whales, and humans, reached that point of brain development earlier than herbivores or omnivores, the researchers found. They classified humans as carnivores based on the percentage of meat in the typical human diet and despite the moderate meat consumption of Homo sapiens, humans fit the prediction of time to weaning based on fully specialized carnivores.
The origins of the genus Homo are murky, but by H. erectus, bigger brains and bodies had evolved that, along with larger foraging ranges, would have increased the daily energetic requirements of hominins. Yet H. erectus differs from earlier hominins in having relatively smaller teeth, reduced chewing muscles, weaker maximum bite force capabilities, and a relatively smaller gut. This paradoxical combination of increased energy demands along with decreased masticatory and digestive capacities is hypothesized to have been made possible by adding meat to the diet, by mechanically processing food using stone tools, or by cooking. Cooking, however, was apparently uncommon until 500,000 years ago, and the effects of carnivory and Palaeolithic processing techniques on mastication are unknown. Here we report experiments that tested how Lower Palaeolithic processing technologies affect chewing force production and efficacy in humans consuming meat and underground storage organs (USOs). We find that if meat comprised one-third of the diet, the number of chewing cycles per year would have declined by nearly 2 million (a 13% reduction) and total masticatory force required would have declined by 15%. Furthermore, by simply slicing meat and pounding USOs, hominins would have improved their ability to chew meat into smaller particles by 41%, reduced the number of chews per year by another 5%, and decreased masticatory force requirements by an additional 12%. Although cooking has important benefits, it appears that selection for smaller masticatory features in Homo would have been initially made possible by the combination of using stone tools and eating meat.
On a high grassy plateau in Algeria, just 100 kilometers from the Mediterranean Sea, early human ancestors butchered extinct horses, antelopes, and other animals with primitive stone tools 2 million to 2.4 million years ago. The dates, reported today, push back the age of the oldest tools in North Africa by as much as a half a million years and provide new insight into how these protohumans spread across the continent. After 25 years of excavations at the Ain Hanech complex—a dry ravine in Algeria—an international team reports the discovery of about 250 primitive tools and 296 bones of animals from a site called Ain Boucherit. About two dozen animal bones have cut marks that show they were skinned, defleshed, or pounded for marrow. Made of limestone and flint, the sharp-edged flakes and round cores—some the size of tennis balls—resemble those found in east Africa. Both represent the earliest known toolkit, the so-called Oldowan technology, named for the site where they were found 80 years ago at Olduvai in Tanzania. The cut-marked bones represent “the oldest substantive evidence for butchery” anywhere, says paleoanthropologist Thomas Plummer of the City University of New York’s Queens College, who was not involved with the study. Although other sites of this age in east Africa have stone tools, the evidence for actual butchery of animals is not as strong, he says.
A. bahrelghazali δ13C values range from −0.8 to −4.4‰. They are similar to, but reach slightly lower values than, those of the Alcelaphini, Reduncini, Equidae, Suidae, and Proboscidea from the KT sites (Fig. 2, Table S1). The detailed laser scan data for two of the hominids are given in Table S2. The results indicate a predominance of C4 dietary resources (∼55–80% by linear interpolation). Carbon isotope data alone cannot distinguish whether carbon of C4 origin was from plant or animal sources, but in this case, the high proportions suggest that the primary C4 dietary resources were plant staples. Consumption of animals (e.g., termites, rodents, grazing herbivores) reliant on the abundant C4 vegetation cannot be excluded and they may have formed components of the diet, as inferred for the South African australopithecines (5, 7, 28). Very high proportions of animal food, however, are not plausible for hominins given that even recent humans such as the Kalahari San rely most heavily on plant foods (∼80%) and less on game (29). Moreover, hominins lack the appropriate dental morphology. Therefore, we focus on C4 plants in the discussion below.
Whether the A. bahrelghazali individuals relied on C4 grasses or sedges, or both, these resources are seldom consumed (if at all) by most primates.
Current consensus holds that the 3-million-year-old hominidAustralopithecus africanus subsisted on fruits and leaves, much as the modern chimpanzee does. Stable carbon isotope analysis ofA. africanus from Makapansgat Limeworks, South Africa, demonstrates that this early hominid ate not only fruits and leaves but also large quantities of carbon-13–enriched foods such as grasses and sedges or animals that ate these plants, or both. The results suggest that early hominids regularly exploited relatively open environments such as woodlands or grasslands for food. They may also suggest that hominids consumed high-quality animal foods before the development of stone tools and the origin of the genus Homo.
Little is known about the diets of hominids that predate the genus Homo, because they did not leave archaeological traces such as “kitchen middens” and stone tools. Consequently, researchers have made dietary inferences based on craniodental morphology (1–4), gross dental wear (1, 2, 5), and dental microwear (6, 7). Some researchers have stressed the importance of animal foods in the diets of these hominids (1, 8, 9); others have suggested that they were primarily adapted for the consumption of plant foods such as grass seeds and roots (3, 4). The current consensus, however, is that these early hominids ate fleshy fruits and leaves (6, 7, 10, 11). This agrees with evidence that they occupied relatively heavily wooded habitats, not open savannas (12–16). In contrast, there is evidence suggesting that the later hominids (∼2.5 million years ago) Homo and Paranthropusinhabited more open environments (13, 16) and were omnivorous (17–20). Here we provide direct isotopic evidence of the diet of an early hominid, the 3-million-year-old Australopithecus africanus from Makapansgat Limeworks in Northern Province, South Africa (13, 16, 21).
Previous studies have shown that the ratio of 13C to12C in tooth enamel can be used to provide dietary information about extinct fauna (19, 22). The foundation of this approach is our knowledge of photosynthesis in plants. Trees, bushes, shrubs, and forbs (C3 plants) discriminate more markedly against the heavy 13C isotope during fixation of CO2 than do tropical grasses and sedges (C4 plants). As a result, C3 plants have δ13C values of –22 per mil (‰) to –30‰, with an average of about –26.5‰ (23), whereas C4plants have δ13C values of –10 to –14‰, with an average of about –12.5‰ (24, 25). Animals incorporate their food’s carbon into their tooth enamel with some additional fractionation (26). Hence, the relative proportions of C3 and C4 vegetation in an animal’s diet can be determined by analyzing its tooth enamel with stable isotope mass spectrometry. Animals that eat C3vegetation (including fruits, leaves, and the roots of trees, bushes, and forbs) have δ13C values between about –10 and –16‰; animals that eat C4 tropical grasses (including blades, seeds, and roots) have δ13C values between 2 and –2‰; and mixed feeders that eat both fall somewhere in between these two extremes. Carnivores have tooth enamel δ13C values similar to those of their prey (26).
Analysis of variance shows that the δ13C values forA. africanus are significantly different from the values for grazers, browsers, and mixed feeders from Makapansgat (P < 0.01) (Table 1). The only taxon from which they are not significantly different is the carnivore Hyaena makapani. Three of the four hominid specimens (MLD 12, MLD 28, and MLD 30) fall outside the range of C3 (fruit, herb, or leaf) feeders at Makapansgat. MLD 30 is so enriched in 13C (–5.6‰) that it falls closer to the mean of the grazers than of the browsers. The δ13C values for these specimens are inconsistent with a diet of fruits and leaves (C3 plants). One specimen (MLD 41), however, does fall within the range of C3 eaters. These data show that (i) A. africanus had a highly variable diet (its range of δ13C values is greater than 18 of the 19 other taxa analyzed), and (ii) the majority of the Makapansgat hominids habitually obtained dietary carbon from C4 plants such as grasses and sedges or from animals that ate C4foods, or both.
An equally plausible explanation is thatA. africanus had a preference for high-quality animal foods, which included C4 plant-eating insects such asTrinervitermes trinervoides or the young of grazing mammals like R. darti, or both. There is limited evidence to help us decide whether one or both of these alternatives is correct. Researchers comparing the dental microwear of A. africanusand modern primates did not conclude that these hominids ate grasses (6, 7), but these studies included no grass-eating modern primates. A comparison of the dental microwear ofA. africanus and modern Papio populations from open environments, whose diet is 25 to 50% grasses (9), would be ideal, but no such study has been undertaken. Recent research demonstrates, however, that the percentage of pitting versus scratching on the molars of modern T. gelada (∼10%) (35) is different from the percentage previously reported for A. africanus (∼30%) (7). Theropithecus gelada consumes grass blades, seeds, and roots nearly exclusively (9, 30), making it a less than ideal analog for a hominid eating 25 to 50% grass foods. Nonetheless, the large difference in microwear features between Theropithecus andA. africanus suggests that we must seriously consider the possibility that these hominids were 13C-enriched because they consumed animal foods.
It is believed that the encephalization of early Homo was made possible by the consumption of energy- and nutrient-rich animal foods to “pay” for its metabolically expensive brain (39, 40). Our results raise the possibility, however, that dietary quality improved (through the consumption of animal foods) before the development of Homo (41) and stone tools (42) about 2.5 million years ago. Moreover, trace element (Sr/Ca) (43) and stable carbon isotope analyses (44) do not seem to indicate that earlyHomo from Swartkrans consumed more animal foods than didA. africanus. Therefore, the primary dietary difference between A. africanus and Homo may not have been the quality of their food but their manner of procuring it. One key difference may have been that stone tools allowed Homo to disarticulate bones and exploit bone marrow from large carcasses (obtained through hunting or scavenging) that A. africanuscould not (17, 18, 45).
What makes humans unique? This question has fascinated scientists and philosophers for centuries and it is still a matter of intense debate. Nowadays, human brain expansion during evolution has been acknowledged to explain our empowered cognitive capabilities. The drivers for such accelerated expansion remain, however, largely unknown. In this sense, studies have suggested that the cooking of food could be a pre-requisite for the expansion of brain size in early hominins. However, this appealing hypothesis is only supported by a mathematical model suggesting that the increasing number of neurons in the brain would constrain body size among primates due to a limited amount of calories obtained from diets. Here, we show, by using a similar mathematical model, that a tradeoff between body mass and the number of brain neurons imposed by dietary constraints during hominin evolution is unlikely. Instead, the predictable number of neurons in the hominin brain varies much more in function of foraging efficiency than body mass. We also review archeological data to show that the expansion of the brain volume in the hominin lineage is described by a linear function independent of evidence of fire control, and therefore, thermal processing of food does not account for this phenomenon. Finally, we report experiments in mice showing that thermal processing of meat does not increase its caloric availability in mice. Altogether, our data indicate that cooking is neither sufficient nor necessary to explain hominin brain expansion.
Hunting for meat was a critical step in all animal and human evolution. A key brain-trophic element in meat is vitamin B3 / nicotinamide. The supply of meat and nicotinamide steadily increased from the Cambrian origin of animal predators ratcheting ever larger brains. This culminated in the 3-million-year evolution of Homo sapiens and our overall demographic success. We view human evolution, recent history, and agricultural and demographic transitions in the light of meat and nicotinamide intake. A biochemical and immunological switch is highlighted that affects fertility in the ‘de novo’ tryptophan-to-kynurenine-nicotinamide ‘immune tolerance’ pathway. Longevity relates to nicotinamide adenine dinucleotide consumer pathways. High meat intake correlates with moderate fertility, high intelligence, good health, and longevity with consequent population stability, whereas low meat/high cereal intake (short of starvation) correlates with high fertility, disease, and population booms and busts. Too high a meat intake and fertility falls below replacement levels. Reducing variances in meat consumption might help stabilise population growth and improve human capital.
Meat, NAD, and Human Evolution
Archaeological and palaeo-ontological evidence indicate that hominins increased meat consumption and developed the necessary fabricated stone tools while their brains and their bodies evolved for a novel foraging niche and hunting range, at least 3 million years ago. This ‘cradle of mankind’ was centred around the Rift Valley in East Africa where the variable climate and savannah conditions, with reductions in forests and arboreal living for apes, may have required clever and novel foraging in an area where overall prey availability but also predator dangers were high44–50 (Figure 2). Tools helped hunting and butchery and reduced time and effort spent chewing as did cooking later.51 Another crucial step may have been the evolution of a cooperative social unit with divisions of labour, big enough to ensure against the risks involved in hunting large game and the right size to succeed as an ambush hunter – with the requisite prosocial and altruistic skills to also share the spoil across sexes and ages.52 The ambitious transition from prey to predator hunting the then extensive radiation of megaherbivores so big that they are normally considered immune to carnivores, needed advanced individual and social cognition as humans do not have the usual physical attributes of a top predator.53–59 Adult human requirements to run such big brains are impressive enough, but during development, they are extraordinarily high with 80% to 90% of basal metabolic rate necessary in neonates – this is probably not possible after weaning without the use of animal-derived foods.51,60,61
Editor’s note: I believe we are designed to be nearly completely carnivorous as are dogs and cats… therefore, doesn’t it make sense that this would happen in humans when we eat processed foods as well? LOL.
Uh oh… the FDA might be waking up to this regarding dogs. But of course this is couldn’t possibly apply to humans, right?!
Endurance running may be a derived capability of the genus Homo and may have been instrumental in the evolution of the human body form. Two hypotheses have been presented to explain why early Homo would have needed to run long distances: scavenging and persistence hunting. Persistence hunting takes place during the hottest time of the day and involves chasing an animal until it is run to exhaustion. A critical factor is the fact that humans can keep their bodies cool by sweating while running. Another critical factor is the ability to track down an animal. Endurance running may have had adaptive value not only in scavenging but also in persistence hunting. Before the domestication of dogs, persistence hunting may have been one of the most efficient forms of hunting and may therefore have been crucial in the evolution of humans. >Xo and Gwi hunters at Lone Tree maintain that they concentrate on different species at different times of the year. They say that steenbok, duiker, and gemsbok can be run down in the rainy season because the wet sand forces open their hoofs and stiffens the joints. This is consistent with what Schapera (1930) reported. Kudu, eland, and red hartebeest can be run down in the dry season because they tire more easily in loose sand. Kudu bulls tire faster than cows because of their heavy horns. Kudu cows are run down only if they are pregnant or wounded. Animals weakened by injury, illness, or hunger and thirst are also run down. When there is a full moon, animals are active all night, and by daybreak they are tired and easier to run to exhaustion. The best time for the persistence hunt is at the end of the dry season (October/November), when animals are poorly nourished. When running down a herd of kudu, trackers say that they look to either side of the trail to see if one of the animals has broken away from the rest of the herd and then follow that animal. The weakest animal usually breaks away from the herd to hide in the bush when it starts to tire, while the others continue to flee. Since a predator will probably follow the scent of the herd, the stronger animals have a better chance of outrunning it, while the weaker animal has a chance to escape unnoticed.
Although humans are relatively slow runners, compared to other mammals we are exceptionally good at running long distances. The evolutionary significance of this ability becomes apparent when it is remembered that our closest living relatives, the great apes, exhibit relatively poor running performance; being specialized for climbing. We have suggested that our bipedal hominin ancestors evolved to be exceptional distance runners as a result of selection to run prey animals to exhaustion in the heat of the day (Carrier, 1984), commonly known as persistence hunting.
Humans are the only species that can throw objects both incredibly fast and with great accuracy. This unique throwing ability may have been critical to the survival and success of our hominin ancestors, helping them to hunt and protect themselves. Our research asks: How are humans able to throw so well? When did this behavior evolve? Was throwing important in our evolutionary past?
We found that humans are able to throw projectiles at incredible speeds by storing and releasing energy in the tendons and ligaments crossing the shoulder. This energy is used to catapult the arm forward, creating the fastest motion the human body can produce, and resulting in very rapid throws. We show that this ability to store energy in the shoulder is made possible by three critical changes in our upper bodies that occurred during human evolution: 1. the expansion of the waist, 2. a lower positioning of the shoulders on the torso, and 3. the twisting of the humerus (bone in the upper arm). All of these key evolutionary changes first appear together nearly 2 million years ago in the species Homo erectus.
We propose that this ability to produce powerful throws was crucial to the intensification of hunting that we see in the archaeological record at this time. Success at hunting allowed our ancestors to become part-time carnivores, eating more calorie-rich meat and fat and dramatically improving the quality of their diet. This dietary change led to seismic shifts in our ancestors’ biology, allowing them to grow larger bodies, larger brains, and to have more children.
Armed with nothing but sharpened wooden spears, the ability to throw fast and accurately would have made our ancestors formidable hunters and provided critical distance between themselves and dangerous prey.
- Humans are remarkable throwers, and the only species that can throw objects fast and accurately.
- Chimpanzees, our closest relatives, throw very poorly, despite being incredibly strong and athletic.
- We have shown that humans produce high-speed throws by storing elastic energy in the tendons, ligaments, and muscles crossing the shoulder.
- When this energy is released, it powers the rapid acceleration of the arm and the projectile, including the fastest motion the human body produces.
- Three changes to the anatomy of the torso, shoulder, and arm that occurred during human evolution make this elastic energy storage possible.
- These morphological changes are first seen together 2 million years ago in Homo erectus.
- Concurrent with these changes, archaeological evidence of more intensified hunting behavior suggests that throwing may have played a vital role in early hunting.
- Hunting had profound effects on our biology. For example, by improving diet quality our ancestors were able to grow larger brains leading to cognitive changes such as the origins of language.
- Today, most throwing athletes throw much more frequently than our hominin ancestors did and, accordingly, frequently suffer from overuse injuries.
Roach, N.T., Venkadesan, M., Rainbow, M.J., Lieberman, D.E. 2013. Elastic energy storage in the shoulder and the evolution of high-speed throwing in Homo. Nature. 498. 483-486.
Editor’s note: I keep getting the poor health of the Inuit brought up when I am trolling - See this
Fragments of a 1.5-million-year-old skull from a child recently found in Tanzania suggest early hominids weren’t just occasional carnivores but regular meat eaters, researchers say. The finding helps build the case that meat-eating helped the human lineage evolve large brains, scientists added.
“I know this will sound awful to vegetarians, but meat made us human,” said researcher Manuel Domínguez-Rodrigo, an archaeologist at Complutense University in Madrid. These findings suggest that “human brain development could not have existed without a diet based on regular consumption of meat,” Domínguez-Rodrigo said. “Regular consumption of meat at that time implied that humans were hunters by then. Scavenging only rarely provides access to meat and is only feasible in African savannas on a seasonal basis.”
Phylogenetic and divergence date analyses indicate that the occurrence of Taenia tapeworms in humans pre-dates the development of agriculture, animal husbandry and domestication of cattle (Bos spp.) or swine (Sus scrofa). Taeniid tapeworms in Africa twice independently colonized hominids and the genus Homo prior to the origin of modern humans. Dietary and behavioural shifts, from herbivory to scavenging and carnivory, as early Homo entered the carnivore guild in the Pliocene/Pleistocene, were drivers for host switching by tapeworms to hominids from carnivores including hyaenids and felids. Parasitological data provide a unique means of elucidating the historical ecology, foraging behaviour and food habits of hominids during the diversification of Homo spp.
Method and Results: In this review we have analyzed the 13 known quantitative dietary studies of HG and demonstrate thatanimal food actually provided the dominant (65%) energy source, while gathered plant foods comprised the remainder (35%).This data is consistent with a more recent, comprehensive review of the entire ethnographic data (n¼ 229 HG societies) thatshowed the mean subsistence dependence upon gathered plant foods was 32%, whereas it was 68% for animal foods. Otherevidence, including isotopic analyses of Paleolithic hominid collagen tissue, reductions in hominid gut size, low activity levels ofcertain enzymes, and optimal foraging data all point toward a long history of meat-based diets in our species. Because increasingmeat consumption in Western diets is frequently associated with increased risk for CVD mortality, it is seemingly paradoxical thatHG societies, who consume the majority of their energy from animal food, have been shown to be relatively free of the signs andsymptoms of CVD.
Conclusion: The high reliance upon animal-based foods would not have necessarily elicited unfavorable blood lipid proﬁlesbecause of the hypolipidemic effects of high dietary protein (19 – 35% energy) and the relatively low level of dietarycarbohydrate (22 – 40% energy). Although fat intake (28 – 58% energy) would have been similar to or higher than thatfound in Western diets, it is likely that important qualitative differences in fat intake, including relatively high levels of MUFA andPUFA and a lower o-6=o-3 fatty acid ratio, would have served to inhibit the development of CVD. Other dietary characteristicsincluding high intakes of antioxidants, ﬁber, vitamins and phytochemicals along with a low salt intake may have operatedsynergistically with lifestyle characteristics (more exercise, less stress and no smoking) to further deter the development of CVD
This synthesis article summarizes the multidisciplinary evidence and interpretations of the first substantial human burial of Magdalenian age to be discovered on the Iberian Peninsula. A robust, relatively tall, apparently healthy, probably female adult was buried at the rear of the living area in El Mirón Cave in the Cantabrian Cordillera of Spain about 18,700 calendar years ago. She had lived in the cold, open environment of Oldest Dryas, with a subsistence based on hunting mainly ibex and red deer, fishing salmon and some gathering of plants, including some starchy seeds and mushrooms. The technology of her group included the manufacture and use of stone tools and weapon elements made on both excellent-quality non-local flint and local non-flints, as well as antler projectile tips and bone needles. Her burial may have been marked by rock engravings suggestive of a female personage, by red ochre staining of a large block adjacent to her skeleton, and by engravings on the adjacent cave wall, and the burial layer itself was intensely stained with red ochre rich in specular hematite specially obtained from an apparently non-local source. The ochre may constitute the only demonstrable “grave offering”. The grave was partially disturbed by a carnivore of wolf size after the corpse had decomposed. Then, it is hypothesized that the skeleton was covered over again and (re-) stained by humans after they (or the carnivore) had removed the cranium and most of the large long bones.
Dietary habits are inferred from dental microwear and isotope analyses of the Magdalenian human individual from the site of El Mirón, dated to 15,460 ± 40 BP. The pattern of dental microwear was established on the buccal surface of the lower fourth premolar and on the bottom of facet 9 on the occlusal surface of the lower third molar. The results obtained through analysis of different surfaces are consistent and indicate a mixed diet for this Lower Magdalenian individual, including meat, aquatic resources and vegetables. These results are in agreement with those obtained through isotope analysis. This implies a generalized exploitation of the environment as has been previously established in other Late Upper Palaeolithic specimens.
Research on ancient foragers has tended to focus on their acquisition of large land mammals, but our ancestors in fact exploited a wider range of taxa. Depending on the local environment, this range included tortoises, birds, and hares from terrestrial habitats and mollusks, birds, and fish from aquatic habitats. These small terrestrial animals and aquatic species begin to appear occasionally in the archaeological record during the Middle Pleistocene (<780,000 y ago), occur irregularly until the Late Pleistocene (<130,000 y ago), and are abundant only within the past few tens of thousands of years (1–6). However, the exploitation of these resources in the Plio-Pleistocene has been difficult to detect because relevant samples are rare and have not always been studied in sufficient detail. Recent information on excavations at the 1.95 million-year-old Oldowan site of FwJJ20 in the East Turkana Basin of northern Kenya, published in PNAS, helps fill the void, and research shows that at least some early hominins, enjoyed a varied diet, including aquatic species that were typical of the well-watered surroundings of the site (7). This work highlights the opportunistic nature of early hominin foraging and the importance of sampling as many paleo-habitats as possible as well as the need for thorough analyses of all excavated animal remains.
The manufacture of stone tools and their use to access animal tissues by Pliocene hominins marks the origin of a key adaptation in human evolutionary history. Here we report an in situ archaeological assemblage from the Koobi Fora Formation in northern Kenya that provides a unique combination of faunal remains, some with direct evidence of butchery, and Oldowan artifacts, which are well dated to 1.95 Ma. This site provides the oldest in situ evidence that hominins, predating Homo erectus, enjoyed access to carcasses of terrestrial and aquatic animals that they butchered in a well-watered habitat. It also provides the earliest definitive evidence of the incorporation into the hominin diet of various aquatic animals including turtles, crocodiles, and fish, which are rich sources of specific nutrients needed in human brain growth. The evidence here shows that these critical brain-growth compounds were part of the diets of hominins before the appearance of Homo ergaster/erectus and could have played an important role in the evolution of larger brains in the early history of our lineage.
Genetic and anatomical evidence suggests that Homo sapiens arose in Africa between 200 and 100 thousand years (kyr) ago1,2, and recent evidence indicates symbolic behaviour may have appeared ∼135–75 kyr ago3,4. From 195–130 kyr ago, the world was in a fluctuating but predominantly glacial stage (marine isotope stage MIS6)5; much of Africa was cooler and drier, and dated archaeological sites are rare6,7. Here we show that by ∼164 kyr ago (±12 kyr) at Pinnacle Point (on the south coast of South Africa) humans expanded their diet to include marine resources, perhaps as a response to these harsh environmental conditions. The earliest previous evidence for human use of marine resources and coastal habitats was dated to ∼125 kyr ago8,9. Coincident with this diet and habitat expansion is an early use and modification of pigment, probably for symbolic behaviour, as well as the production of bladelet stone tool technology, previously dated to post-70 kyr ago10,11,12. Shellfish may have been crucial to the survival of these early humans as they expanded their home ranges to include coastlines and followed the shifting position of the coast when sea level fluctuated over the length of MIS6.
Since the Bronze Age, pastoralism has been a dominant subsistence mode on the Western steppe, but the origins of this tradition on the Eastern steppe are poorly understood. Here we investigate a putative early pastoralist population in northern Mongolia and find that dairy production was established on the Eastern steppe by 1300 BCE. Milk proteins preserved in dental calculus indicate an early focus on Western domesticated ruminants rather than local species, but genetic ancestry analysis indicates minimal admixture with Western steppe herders, suggesting that dairy pastoralism was introduced through adoption by local hunter-gatherers rather than population replacement.
Abstract The origin of anatomically modern Homo sapiens and the fate of Neanderthals have been fundamental questions in human evolutionary studies for over a century. A key barrier to the resolution of these questions has been the lack of substantial and accurately dated African hominid fossils from between 100,000 and 300,000 years ago. Here we describe fossilized hominid crania from Herto, Middle Awash, Ethiopia, that fill this gap and provide crucial evidence on the location, timing and contextual circumstances of the emergence of Homo sapiens. Radioisotopically dated to between 160,000 and 154,000 years ago, these new fossils predate classic Neanderthals and lack their derived features. The Herto hominids are morphologically and chronologically intermediate between archaic African fossils and later anatomically modern Late Pleistocene humans. They therefore represent the probable immediate ancestors of anatomically modern humans. Their anatomy and antiquity constitute strong evidence of modern-human emergence in Africa.
Hunter-gatherer populations are remarkable for their excellent metabolic and cardiovascular health and thus are often used as models in public health, in an effort to understand the root, evolutionary causes of non-communicable diseases. Here, we review recent work on health, activity, energetics and diet among hunter-gatherers and other small-scale societies (e.g. subsistence farmers, horticulturalists and pastoralists), as well as recent fossil and archaeological discoveries, to provide a more comprehensive perspective on lifestyle and health in these populations. We supplement these analyses with new data from the Hadza, a hunter-gatherer population in northern Tanzania. Longevity among small-scale populations approaches that of industrialized populations, and metabolic and cardiovascular disease are rare. Obesity prevalence is very low (<5%), and mean body fat percentage is modest (women: 24–28%, men: 9–18%). Activity levels are high, exceeding 100 min d1 of moderate and vigorous physical activity, but daily energy expenditures are similar to industrialized populations. Diets in hunter-gatherer and other small-scale societies tend to be less energy dense and richer in fibre and micronutrients than modern diets but are not invariably low carbohydrate as sometimes argued. A more integrative understanding of hunter-gatherer health and lifestyle, including elements beyond diet and activity, will improve public health efforts in industrialized populations.
Hominin evolution took a remarkable pathway, as the foraging strategy extended to large mammalian prey already hunted by a guild of specialist carnivores. How was this possible for a moderately sized ape lacking the formidable anatomical adaptations of these competing ‘professional hunters’? The long-standing answer that this was achieved through the elaboration of a new ‘cognitive niche’ reliant on intelligence and technology is compelling, yet insufficient. Here we present evidence from a diversity of sources supporting the hypothesis that a fuller answer lies in the evolution of a new socio-cognitive niche, the principal components of which include forms of cooperation, egalitarianism, mindreading (also known as ‘theory of mind’), language and cultural transmission, that go far beyond the most comparable phenomena in other primates. This cognitive and behavioural complex allows a human hunter–gatherer band to function as a unique and highly competitive predatory organism. Each of these core components of the socio-cognitive niche is distinctive to humans, but primate research has increasingly identified related capacities that permit inferences about significant ancestral cognitive foundations to the five pillars of the human social cognitive niche listed earlier. The principal focus of the present study was to review and integrate this range of recent comparative discoveries.
WHAT IT’S ALL ABOUT
Of course you are’ a human being! Everybody is. But did you know that you are also an animal–a carnivorous animal? All humans are. Did anybody ever tell you that your ancestors were exclusively carnivores for at least two and possibly twenty million years? Were you aware that ancestral man first departed slightly from a strictly carnivorous diet a mere ten thousand years ago? Well, he was and he did, and discussion of these salient points relevant to man’s diet will be the first task of this book. Over the next 9,950 years Man continued to make minor changes in his victuals as new plant substances were discovered and cultivated. These changes contributed nothing nutritionally but a more abundant supply of calories. They did promote cultural progress from feeding to eating. However, few if any of the novelties introduced to his palate during thc following centuries of dietary experimentation were sufficiently indigestible, or eaten in so great a quantity, as to incite rebellion by his digestive tract. As a consequence, man continued to nibble at them and experiment cautiously with still newer foods. He actually even grew to like some of them, especially when he was hungry and there was no meat in the larder. The low carbohydrate diet is an old diet. It was the choice of man for two million Stone Age years. He first departed from his meat-fat diet only a few thousand years ago. This was partly because of an increasing population. More important were climatic changes which decimated the large game animals, his chief source of food. Strictly from hunger, man began to eat some plant substances which were, of course, carbohydrate.
Since it is easier to begin any task with its simplest component, a comparison of man’s digestive tract with that of the meat eater and that of the grazing animal, respectively, we will begin with the former, a carnivorous animal: the dog. The digestive tracts of all carnivores are remarkably similar in structure and function. If one could be plucked from its nest in the abdomen and stretched out full length, one could see that it was rather short, being only about six times the animal’s body length. >It is composed of an uninterrupted tube, enlarged in certain areas, to which are appended certain solid organs, the glands of digestion. The dimensions of this tube will of course vary with the size of the animal. Since we plan to make comparison eventually with man, a carnivorous animal of relative size will be described. Such an animal would be a large dog-a Great Dane or a Saint Bernard-which frequently attains a weight of 150 pounds, and has other measurements comparable to a human.
Let us start with the mouth. First we would encounter the jaws, set with incisor, canine, and molar teeth. The dog possesses incisor teeth in both upper and lower jaws. Thc jaw movements are up and down which, together with the ridged character of the molar teeth, indicate a tearing or crushing function rather than that of grinding or mastication. The salivary glands do not have an important digestive function in the dog, serving merely to lubricate the chunks of meat this animal normally “wolfs,” or swallows whole. >Food, when swallowed, enters the esophagus, a tube-like structure which extends from the mouth through the chest to the stomach. When distended with food, peristaltic waves are set up in the esophagus which gradually “milk” the food into the stomach. The Great Dane’s stomach is rather small, having a capacity of only two quarts or less. It is the only bulbous enlargement encountered along the alimentary way. When distended it has somewhat the shope of a small football, and its size indicates the amount of food the animal can ingest at one time without discomfort. The chief functions of the carnivorous stomach are:
1) to serve as a reservoir; and
2) to dissolve the aliment (ingested food), which grently facilitates its complete and rapid digestion as it passes down the intestine. The reservoir function allows the animal to eat a fairly large volume of food at one time. Since the food of these animals is normally meat and fat-highly concentrated foods of small bulk-sufficient amounts may be ingested at intervals of once daily to serve their nutritional needs. Dissolving the meat and fat in the stomach is possible because this organ has the ability to manufacture and secrete into its lumen a strong mineral acid called hydrochloric acid. This same material, under the name of muriatic acid, is used widely in industry 8S a solvent of many substances, including metals, minerals, and organic material. Foodstuffs are held back in the stomach until solution has occurred. The solubility of different materials varies widely and as a consequence, some foods leave the stomach quickly, while others are retained for a longer period.Some insoluble substances, such as cellulose, large pieces of bone and cartilage, or raw vegetable material, if it should be ingested, are eventually emptied into the small intestine and pass through the remainder of the tract unchanged. If they are too large to pass through the exit from the stomach they are vomited. The carnivorous stomach, which has been filled with its normnl ration of meat and fat, wilt be able to dissolve the entire meal and evacuate it into lhe small intestine within three hours. The stomach then enters a period of rest until the next meal is eaten.The dissolved food, called “chyme” is fed into the upper end of the small intestine in a series of small suprts under the control of the pylorus, a muscular valve separating the stomach from the intestine. Very little actual digestion of food occurs in the carnivorous stomach. There is some slight brenking down of highly emulsified fats, such as cream, and insignificant digestion of some protein by the pepsin of the gastric juice. In the carnivore the stomach is not a vital organ; the animal get” along quite well even though much, or even all, of its functions has been lost through disease or surgical removal. Food leaving the stomach enters the small intestine and begins a most eventful journey through the remainder of the digestive tract.
The diameter of the small instestine is similar to that of the esophagus–about the size of a garden hose. Its length is difficult to determine with accuracy, since this dimension depends largely upon the state of its contraction or relaxation. If the small bowel (or intestine) is completely relaxed, as after death, it may he stretched out for thirty feet. Contrariwise, if a rubber tube is fed through the small intestine of a living animal, the leading tip of the tube will have traversed its entire length by the time scarcely ten feet of the tube have entered the mouth. The true functional length of our dog’s small bowel is thought by most anatomists to be about twenty feet. However, this is a most important twenty feet, for it is during transit through this portion of the tract that virtually all digestion and absorption of food must occur. The small intestine is a vital organ, for no carnivore can live without it.
Several inches from the stomach a duct or tube enters the small intestine from the side. About an inch from its point of entry into the bowel, this tube branches; the shorter branch lends to the pancreas, and the longer leads to the liver. There are the digestive glands which furnish the digestive juices to the alimentary tract. They are of vital importance to the carnivore. The gallbladder is a sac-like structure attached to and communicating with the tube leading from the liver to the intestine (bile duct). The gallbladder is well-developed and functions strongly in all carnivores. The presence of the first few spurts of chyme in the duodenum, or first division of the small intestine, alerts chemical sensors or hormones. These stimulate the production of digestive enzymes by the pancreas, which are in turn emptied into the intestine through the pancreatic duct. There they mingle with the chyme and immediately begin to break it down into its component parts. These chemical processes are continued, the chyme moves down the digestive tract, so that by the time it has reached the distal end of the small bowel, virtually all the material that can be digested has been absorbed from the digestive tube, leaving only a small indigestible residue to be emptied as a liquid suspension into the colon or large intestine for disposal as waste. The process of digesting the food by pancreatic juice is most important because meat, fat, or carbohydrate cannot be absorbed by the small intestine as such. First they must be broken down into their basic components, the only forms in which they can be assimilated.
Proteins are broken down into a variety of amino acids, fats to fatty acids and glycerol, and digestible carbohydrates to glucose. The action of the pancreatic juice and a few weak and inconstant intestinal enzymes, constitute the entire digestive potential of the carnivorous animal. These enzymes are all produced by the animal itself. This point is of great importance, as will be seen when tho carnivorous and herbivorous digestive mechanisms are compared. Meanwhile, back in the duodenum, other activities have taken place. Certain other hormones are produced which increase the muscular activities of the intestine, and produce mixing and churning movements which facilitate digestion by the enzymes. Since digestion by enzymes takes place on the surfnce of the material, the process is greatly facilitated if the size of the food particles are reduced by chewing, grinding, powdering, or-most ideally of all-by actually dissolving it. Thus, the stomach’s function of dissolving food before it enters the intestine, makes chewing or other processing of the normal carnivorous diet of ment and fat virtually unnecessary. The digestion of fat requires some special handling by the alimentary system. It has heen shown that digestion occurs efficiently only when the aliment has been dissolved before being exposed to the assault of the enzymes. Fat, however, will not dissolve in water. Bile, which is manufactured by the liver, contains certain substances called bile salts, which act very much like modern industry detergent to render fats soluble in the watery chyme, and thus render them susceptible to the action of fat-digesting enzymes. Fat in the carnivorous diet is present in large amounts on occasions and, since the need for bile is limited to times when there is considerable fat in the diet, the bile is not allowed to drain off, to be wasted during the interdigestive periods (between meals) of the carnivorous animals. Instead it is diverted to the gallbladder, where it can be stored until the presence of fat in the intestine again signals the need for its presence, whereupon a hormone, produced by the presence of fat in the intestine, causes the gallbladder to contract strongly and deliver great amounts of concentrated bile to the intestine. Digestion and absorption of the normal carnivorous diet-protein and fat with but little carbohydrate-is remarkably efficient. If “balance studies” are accomplished, which will merely measure the amount of a certain nutriment administered in the diet, and then determine how much of that same material appears in the animal’s excreta, it is found that the healthy animal never loses more than 4% of the ingested fat and only a trace of dietary protein. The distal end of the dog’s small intestine terminates by emptying into the large intestine, or colon. This connection between the two is of an “end to side” sort; that is, they join each other at a right angle. In the dog there is here a blind pouch, or cul-de-sac, which is two or three inches in length and is called the cecum. While the cecum is functionless in carnivores, it would be well to keep one’s eye on this area of the colon, for differences in it, and also the stomach, constitute two of the major points of variation between carnivorous and herbivorous design. The length of the colon, like that of the small intestine, is subject to considerable variation, according to different authorities. In a large dog it is generally considered to be about four feet. The colon terminates in the globular rectum, which is the area where fecal material is stored until enough has accumulated to make expelling it worthwhile. The opening of the rectum to the outside is called the anus. The volume of the rectum is about that of a baseball. Since digestion of food is complete by the time the small intestinal contents are emptied into the colon, the latter organ has no digestive function. The indigestible residue of the carnivorous diet is small; therefore the colon of these animals is short, of small capacity, and with a physiological activity confined to the transport of indigestible waste to the outside and reabsorption of water and a few minerals from it.
The contents of the small intestine are emptied into the colon as a water suspension. As this material is slowly moved along the colon the water is absorbed; its consistency becomes more firm and its volume smaller. By the time it reaches the rectum this waste material has become a small firm mass, possibly about the size of an egg or tennis ball. When expelled, this material constitutes the bowel movement. When on a nonnal diet of meat and fat, the dog’s stool is firm and practically odorless. Evacuation of the rectum occurs once in each twenty-four to forty-eight hours. In the carnivore the colon is by no means a vital organ; carnivorous animals get along well (albeit with less conveence) after the entire large bowel has been removed. The healthy carnivorous digestive tract furnishes residence for relatively few bacteria and no microprotozoa. These are microscopic-sized organisms; the former are plant material, while the latter are animalcules. The strong ocid of the stomach guarantees that most microorganisms swallowed with the food or otherwise will be killed, or at least be attenuated and not allowed to multiply in that area. Those escaping the stomach are rarely able to withstand the digestive activity of the small intestine. However, toward the lower end of the small intestine, where digestive activity has almost disappeared, a few surviving bacteria are to be found. But in the large intestine, myriad organisms thrive and serve some function in forming certain vitamins: pyridoxine, biotin, folic aeid, Vitamin K, and possibly others. The bacteria of the carnivorous colon are of the putrefactive type; they nourish in on alkaline medium. The digestive tract we have been considering is practically sterile (devoid of organisms) except in the large intesline. The coefficient of digestion is the percentage of ingested food thut is digested, absorbed, and utilized by the animal. It is a measure of nutritive efficiency and, in the carnivore eating its normal diet of meat and fat, the coefficient approaches 100%.
This, then, is the carnivorous digestive tract. It is simple, short, and of small capacity. A small variety of concentrated food is ingested at infrequent intervals. Food is digested only by enzymes which are manufactured by the animal itself. The meat-eating animals have no dependence upon microorganisms to assist in digesting the food. The food is almost completely digested and absorbed, leaving but little excretory bulk. Digestion is rapid, complete, and intermittent. The entire alimentnry canal functions for a few hours, then enters upon an interdigestive period of rest. Significant digestive activity is confined to the small intestine. The carnivore is able to maintain life even after losing both stomach and colon, but cannot survive a loss of the small intestine.
And A Man
To describe the structure and function of a human digestive tract would be mercly repetitious, for it is practically identical with that of the dog already delineated. The sole difference between the two is the presence in man of a rudimentary structure springing from a functionless cecum; this is called the appendix. This organ hos long been considered lo be a degenerated structure and is often cited as evidence that man was originally herbivorous and then became carnivorous. Supposedly, as this dietary change occurred, he gradually lost the use of his cecum, since he was no longer digesting vegetable material, and it gradually shriveled into the vestige we know today. Others, however, suggest that man might not be losing his appendix at all, but is attempting to gain a functioning cecum. This would suggest that he was an original carnivore and that centuries of increasing plant food consumption caused this adaptive change in his digestive tract, in an effort to afford greater digestive capability for his civilized diet. Since this is a purely philosophical matter which will not be solved in less thnn another ten thousand years, it is pointless to pursue it further.
The worldwide association of H. erectus with elephants is well documented and so is the preference of humans for fat as a source of energy. We show that rather than a matter of preference, H. erectus in the Levant was dependent on both elephants and fat for his survival. The disappearance of elephants from the Levant some 400 kyr ago coincides with the appearance of a new and innovative local cultural complex – the Levantine Acheulo-Yabrudian and, as is evident from teeth recently found in the Acheulo-Yabrudian 400-200 kyr site of Qesem Cave, the replacement of H. erectus by a new hominin. We employ a bio-energetic model to present a hypothesis that the disappearance of the elephants, which created a need to hunt an increased number of smaller and faster animals while maintaining an adequate fat content in the diet, was the evolutionary drive behind the emergence of the lighter, more agile, and cognitively capable hominins. Qesem Cave thus provides a rare opportunity to study the mechanisms that underlie the emergence of our post-erectus ancestors, the fat hunters.
The physiological ceiling on plant food intake. The intake of plant foods can conceivably be limited due to a physiological ceiling on fiber or toxins intake, limited availability, or technological and time limitations with respect to required preconsumption preparations, or a combination of these three factors. A significant contribution to the understanding of the physiological consequences of consuming a raw, largely plant-based diet was made by Wrangham et al. [17,18]. A physiological limitation seems to be indicated by the poor health status of present-day dieters who base their nutrition on raw foods, manifested in subfecundity and amenorrhea [17,18]. Presumably this limitation would have been markedly more acute if pre-agriculture highly fibrous plant foods were to be consumed. Limited availability is manifested by the travails of the obligated high-quality diet consumer of the savanna, the baboon. Baboons are somewhat similar to humans with respect to their ratio of colon to small intestine rendering the quality requirements of their diet comparable to an extent to that of humans. Baboons have been documented at times as devoting ‘‘almost all of their daylight hours to painstakingly seeking out small, nutritious food items….[the] adult male baboon (Papio cynocephalus) may pick up as many as 3000 individual food items in a single day’’ (:103). Nuts, or other high-quality foods of decent size appear only seasonally above ground in the savanna and such is the case in the Levant, too. But not only are they seasonal, they also require laborious collection and most of them contain phytic acid that inhibits the absorption of contained minerals. These foods also contain anti-nutrients and toxins such as trypsin, amylase and protease inhibitors as well as tannins, oxalate, and alkaloids the elimination of which can only be achieved (sometimes only partially) by pre-consumption processing like drying, soaking, sprouting, pounding, roasting, baking, boiling and fermentation. While these technologies are extensively used, mostly conjointly, in present day pre-consumption preparation of many plant foods, some were probably not practiced by H. erectus, especially those requiring accumulation and storage of produce for weeks (see, for example, :173 with respect to Mongongo nuts, or :31 regarding Baobab seeds). Comparing food class foraging returns among recent foragers, Stiner (:160) has found the net energy yield of 3,520–6,508 kj/hour for seeds and nuts compared to 63,398 kj/hour for large game. Roots and tubers returns are not better, ranging from 1,882 kj/hour to 6,120 kj/hour. These numbers point to the substantial time investment required in gathering and preparing plant foods for consumption.
It turns out to be a case of bad plumbing. The bacteria that are nice enough to make this nutrient for us live in our large intestine, but we are only capable of absorbing it in our small intestine. Because the small intestine comes before the large intestine in the flow of gastrointestinal traffic, we end up sending the B12 that our gut bacteria produce right to the toilet, rather than absorbing it. What a waste!
Exactly how this glitch in our gastrointestinal functioning came about is largely a mystery. Most primates are herbivorous and indeed all of our fellow apes subsist on a fully or mostly plant-based diet. It is therefore likely that we descend from a long line of vegetarians. During the millions of years our ancestors thrived on plants, they surely were able to capture the vitamin B12 that was being made by bacteria in their guts, or else they wouldn’t have survived. Once our forebears began scavenging meat and bone marrow, they found themselves with a steady supply of dietary vitamin B12, which then grew in abundance when we began to hunt. It must have been during this meat-eating stage in our evolution that we began to absorb B12 in the small intestine instead of the large one. We are now stuck with this odd arrangement, making humans, at least in this very narrow sense, obligate carnivores.
Abstract The inability of humans to synthesize L-ascor-bic acid is known to be due to a lack of L-gulono-γ-lactone oxidase, an enzyme that is required for the biosynthesis of this vitamin. Isolation of a cDNA for rat L-gulono-γ-lactone oxidase allowed us to study the basic defect underlying this deficiency at the gene level and led to isolation of a human genomic clone related to L-gulono-γ-lactone oxidase as well as three overlapping clones covering the entire coding region of the rat L-gulono-γ-lactone oxidase cDNA. Sequence analysis study indicated that the human L-gulono-γ-lactone oxidase gene has accumulated a large number of mutations since it stopped being active and that it now exists as a pseudogene in the human genome.
Introduction Vitamin C is unique among the vitamins discovered inasmuch as its essentiality as a nutrient is restricted to only a limited number of exceptional species among phylogenetically higher animals. In other words, nearly all higher animals can synthesize vitamin C, or L-ascorbic acid, in their body. In the l950s, it was demonstrated that L-ascorbic acid is synthesized from D-glucose as shown in Figure 1 (1). The first portion of the metabolic pathway (from D-glucose to L-gulonic acid) is part of the glucuronic acid cycle, one of the metabolic pathways starting from D-glucose; and the pathway of L-ascorbic acid synthesis branches from L-gulonic acid. The part after the branch point consists of two steps of enzymatic reactions, viz, lactonization and oxidation. The latter oxidation step is catalyzed by L-gulono-’y-lactone oxidase (GLO). This enzyme is missing in the above-mentioned exceptional species, eg, humans, other primates, and guinea pigs (2); as a consequence, these animals cannot synthesize L-ascorbic acid and thus need a dietary intake of vitamin C to prevent scurvy. This enzyme deficiency arose during evolution, and this trait has been carried through generations. In a sense, this is the most prevalent genetic disorder, because all individuals of scurvy-prone species carry this trait.
Therefore, we conclude that assumptions about the heuristics of single-variable models of bone surface modifications are invalidated and that the simultaneous use of all mark types provides further support for interpretations of primary access to carcasses by hominins at FLK Zinj, probably via hunting
Evolutionary medicine is an emerging field that has allowed researchers to better understand health and disease. By using modern evolutionary theory, researchers can examine the diseases of today and determine their evolutionary history in hopes of developing new preventative strategies or treatments (1,2). What has yet to be determined is if members of the field of nutrition and dietetics appreciate this interdisciplinary approach. Currently, the theory of evolution and evolutionary medicine education is not a requirement of accredited dietetic programs through the Accreditation Council for Education in Nutrition and Dietetics (3). Meanwhile, there has been a considerable amount of clinical research examining the effects of an evolutionary-based diet on health and disease (4,5.6). Last year a systematic review and meta-analyses found that within a clinical setting an evolutionary perspective on diet was able to produce greater improvements in metabolic syndrome components compared to guideline-based control diets (7). Therefore, it appears that this interdisciplinary approach has value and can contribute the field of nutrition and dietetics.
Conclusion: In line with evidence for the importance of dietary animal fat in prehistoric and traditional societies, the studied traditional societies perceived animal fat as a vital component of their diet and a profound source of health rather than an impediment to health as it is presented in many dietary recommendations today.
Theories of Human Evolutionary Trends in Meat Eating and Studies of Primate Intestinal Tracts Counterpoint? Theories of hominid evolution have postulated that switching to meat eating permitted an increase in brain size and hence the emergence of modern man. However, comparative studies of primate intestinal tracts do not support this hypothesis and it is likely that, while meat assumed a more important role in hominid diet, it was not responsible for any major evolutionary shift.
In this paper we discuss the hypothesis, proposed by some authors, that man is a habitual meat-eater. Gut measurements of primate species do not support the contention that human digestive tract is specialized for meat-eating, especially when taking into account allometric factors and their variations between folivores, frugivores and meat-eaters. The dietary status of the human species is that of an unspecialized frugivore, having a flexible diet that includes seeds and meat (omnivorous diet). Throughout the various time periods, our human ancestors could have mostly consumed either vegetable, or large amounts of animal matter (with fat and/or carbohydrate as a supplement), depending on the availability and nutrient content of food resources. Some formerly adaptive traits (e. g. the “thrifty genotype”) could have resulted from selective pressure during transitory variations of feeding behavior linked to environmental constraints existing in the past.
Created by Travis Statham @travis_statham January 15 2019