This paper explores selected aspects of the question: what is the ancestral (natural) human diet range? This should not be confused with a different question that may be of interest: what diet(s) are optimal for me, here and now, under the relevant constraints (e.g., food availability, practicality, cost)? The suggestion that these questions are different from each other immediately introduces a 3^rd question: why are these questions different?

 

In the discussion that follows, we will see that these are different questions because we live in a world that is dramatically different from the one our ancestors evolved in, e.g., food options available today are radically different from those available to humans in the distant evolutionary past. Along the way, we will see the roles that raw, vegan, vegetarian diets may play in the answers to these questions, although the primary topic of this paper is the first question.

 

Overview. The definition of the range of natural diets is provided by human evolution. A short answer to the 1^st question is that humans are adapted to omnivorous diets based on unprocessed or minimally processed foods, and containing varying levels and types of both plant foods and animal products. For most of our evolution, humans were hunter-gatherers, with a significant shift in diet starting around 10K years BP (Before Present) as a result of the agricultural revolution (aka the Neolithic).

 

The hunter-gatherer diet varied by local environment and was based on, as available:

• wild plant foods, including nuts, seeds, tubers/roots, fruits, greens,  
• wild animal foods, including lean meats & organs, fish & shellfish, insects, eggs, honey.

The possible role of grains (i.e., wild grass seeds) in hunter-gatherer diets is a controversial topic. Post-agricultural revolution diets added grains and dairy, and replaced many wild foods with domesticated foods. Given these food lists, one observes that modern vegan, vegetarian diets (raw or cooked) that center on unprocessed foods can be considered to be restricted versions of the natural diet base, i.e., some food types are excluded. The role of unprocessed or minimally processed foods is important because diets based on highly processed foods cannot be considered versions of the natural diet base.

 

The range of human diets is quite large, driven by variations in culture and food availability. Diets ranged from those with high levels of animal foods in very cold climates, to select diets in warmer climates that had high levels of plant foods. One occasionally hears claims in raw circles that humans evolved on strict raw vegan diets; these claims have no scientific merit and they are discussed below. 

 

Multiple lines of evidence for omnivory. That humans are naturally omnivorous is supported by multiple lines of well-documented scientific evidence. A partial list of the lines of evidence includes: a) the fossil record, b) isotope analysis of fossils, c) analysis of human gut morphology [form/structure], d) optimal foraging theory, e) historical and current evidence from hunter-gatherer societies, f) human metabolic adaptations. Data on non-human primates is of some relevance, as a comparison point in helping to clarify our knowledge of “natural” humans. As entry points into the scientific literature supporting the lines of evidence above, the following references are suggested: Stanford & Bunn (2001), Mann (2007), Nicholson (2008), Billings (2009). The primary focus of this paper will be on (f) metabolic adaptations; we add a new line of evidence: (g) genetics, and provide some new information on non-human primates.

 

Recent research pushes back the dates for omnivory in evolution. The earliest humans – Homo species - appeared, at the earliest, approximately 2.5 million years BP: Homo rudolphensis (Ungar et al. 2006). The oldest evidence of stone tools and animal bones showing cutmarks from tools dates to the same period, from archaeological sites in Gona, Afar, Ethiopia. Analysis of the cutmarks indicates the animals were hunted rather than scavenged. These sites yield no evidence of who (or what) made the stone tools; it may have been early Homo or another species, possibly Australopithecus - a predecessor of humans (Semaw et al. 2003, Dominguez-Rodrigo et al. 2005).  

 

Analysis of fossils of another prehistoric species, Ardipithecus ramidus, dated to ~4.4M (million) years BP, shows evidence of a more omnivorous diet than Australopithecus. The importance of the Ardipithecus findings for human evolution is the subject of active scientific discussion at this time (Lovejoy 2009, Suwa et al. 2009, Harrison 2010).  However the significance of the Gona and Ardipithecus findings is that they show that omnivory by our evolutionary predecessors was possible at earlier dates than was previously believed.

 

Recent research on non-human primates:  

so similar yet so different.

 

Recent research shows that chimpanzees exhibit many previously undocumented behaviors found in humans:

 

• Using stone hammers to crack nuts (Morgan & Abwe 2006, Mercader et al. 2007)
• Using tools to harvest underground storage organs (tubers, roots) of plants (Hernandez-Aguilar et al. 2007)
• Sheltering in caves to avoid heat (Pruetz 2007)
• Using pointed spears made from sticks to hunt for a small primate (bush babies: Galago senegalensis), a hunting behavior practiced primarily by females (Pruetz and Bertolani, 2007).

 

Using behavior as measure, there are many similarities between humans and chimps. In contrast to the above, recent research into the genomes for humans, chimpanzees, and the rhesus monkey shows many differences. Note that our current interpretation of genomic comparisons is constrained, in some cases, by our limited understanding of the function(s) of some genes. Also recognize that evolution is not limited to genes: “the footprints of evolutionary history are spread throughout the entire length of the whole genome…and are not limited to genes, introns [DNA regions that are not translated into proteins], or short, highly conserved, nongenic sequences that can be adversely affected by factors” (Sims et al., 2009, p. 17077).

 

Let’s first consider the genome of the rhesus macaque monkey, Macaca mulatta. The rhesus is an aggressive, opportunistic omnivore in areas of human settlement, but in wild areas its diet typically includes a significant fruit component (Primate Factsheet, 2010). Analysis of the rhesus genome shows that the rhesus monkey has many more copies of the PFKP gene than humans do. [In this context, copies refers to duplication of the PFKP gene within the genome.] The PFKP gene is involved in fructose metabolism, and this is considered to be an adaptation to fruit in the diet of the rhesus (Rhesus Consortium, 2007). Wild fruits generally contain more fructose than supermarket fruits (Milton 1999). Finally, for comparison purposes, note that human evolution is characterized by a burst in copy numbers of certain genes (Redon et al 2006, Marques-Bonet et al. 2009).

 

Putting the above information together, the possible inferences are:

1. Humans are less adapted to a fruit diet than a notoriously omnivorous monkey,
2. The lower numbers of PFKP genes in humans appears to be direct genetic evidence that humans are not “biologically adapted” to a high fruit diet (and, as a side note, not adapted to corn syrup either).

 

Analysis of the chimpanzee genome vs. humans shows major differences. The figure of 98.6% for “genetic similarity” between humans and chimps is commonly cited. However, a more accurate figure based on an analysis that includes data for insertions and deletions (of DNA strings) is 95% similarity (Britten 2002). As there is 90% commonality between the human and mouse genome, one concludes that the meaning of similarity-by-percentage is difficult to ascertain (Oxnard 2004).  Other major differences between humans and chimps include:

 

• Y-chromosomes are dramatically different (Hughes et al. 2010),
• Proteins – a major factor in phenotype differences – are 80% different (Glazko et al. 2005),
• Recombination hotspots – a major driver of evolution – are almost completely different (Winkler et al 2005; also see Paigen & Petkov 2010),
• Gene expression is significantly different (Nowick et al 2009).

 

The above shows that humans and chimps are very different indeed. However, important information can be obtained from comparison of the 2 genomes. For example, the genes for amino acid catabolism show acceleration in humans, compared to chimps. One interpretation of this is as an adaptation to higher protein diets in humans, when compared to chimps (Clark et al. 2003).

 

Significant protein sources in human evolution include animal foods, nuts, and seeds, but not sweet fruits which are usually low in protein. Greens are high in protein on a per-calorie basis but they are high in fiber and the human digestive system cannot handle large amounts of fiber.  The chimp genome researchers believe that increased animal food consumption by humans is the most likely explanation for the observed differences (Pennisi 2003).

 

Human adaptations to omnivory

 

Humans have multiple metabolic and genetic adaptations for omnivory. A few of the adaptations are described below.

 

Vitamin B-12 requirement. This is well-known so we mention it only briefly. B-12 is required for human nutrition, yet plant foods are not a reliable source. Certain insects, e.g., termites, a favored food for chimps, are a rich source of B-12 and were probably consumed by our evolutionary ancestors.

 

Enzyme: carnosinase. The human digestive system produces carnosinase, an enzyme to digest carnosine – a protein found only in animal tissue. The enzyme has a digestive function, and is found in other human tissues as well, as some carnosine is absorbed in intact form by intestinal cells (Sadikali et al. 1975, Lenney et al. 1985).

 

Enzyme: chitinase. The human digestive system can produce chitinase, an enzyme to digest chitin – found primarily in insects and shellfish. Ability to secrete the enzyme may depend on genetics or being recently descended from populations that consume insects and/or shellfish (Paoletti et al. 2006).

 

Enzyme: sucrase deficiency. Sucrase is the enzyme required to digest sucrose, aka white sugar, and also found in fruits, both wild and domesticated. Incidence rates of sucrase deficiency in Arctic Inuit range from 2-3% to as high as 10%; the latter is from a non-random sample and may be an overestimate (Draper 1977). The Inuit are a very young culture compared to others; they have been in the Arctic less than 4K years (Wrangham & Conklin-Britten 2003).  

 

Consider that fruit is allegedly the core of the human diet per raw vegan evolution beliefs, and retaining the ability to digest sucrose should not reduce reproduction. It follows that a rate of 2-10% for sucrase deficiency after only 4K years is hard to explain, as it contradicts the claims (by raw vegan evolution advocates) that evolutionary change in digestive processes was somehow “impossible” over more than 2 Million years of human evolution. From another perspective, this can be seen as an example of how quickly fundamental metabolic processes can start evolving in response to diet changes, even when the selective pressure is minimal.

 

Enzyme: AGT. Alanine:glyoxylate aminotransferase (AGT) is a metabolic enzyme that is targeted in animals to different subcellular units - peroxisomes or mitochondria - with variation in targets differing by diet classification categories that are crude/approximate, i.e., the diet vs. target - association is not strict (Danpure et al. 1994, Holbrook et al 2000, Birdsey et al 2004). Raw vegan advocates have claimed that AGT is proof that humans are “metabolic herbivores”. That claim is an inaccurate oversimplification of a complex issue, and reflects the extremely poor scholarship and black-and-white thinking found in raw vegan advocacy.

 

AGT contains a polymorphism (genetic variation) - Pro11Leu - that would be advantageous to someone eating animal foods. This suggests the hypothesis: human populations that have higher traditional consumption of animal foods should have a higher incidence of this polymorphism. A comparative study of multiple populations confirmed the hypothesis, and suggested that it is probably due to dietary selective pressures (Caldwell et al. 2004).

 

 “The human, in fact, is remarkable because, after having lost the ability to target AGT to mitochondria…some individuals have reacquired the ability to target a small amount of their AGT back to mitochondria” (Birdsey et al. 2005). AGT targeting to mitochondria has an association with omnivorous and carnivorous diets. The retargeting in humans is via a polymorphism that creates a complex new AGT target sequence, comprised of multiple amino acids. The interpretation here is that AGT targeting in humans is in fact evolving towards the targets associated with omnivory.

 

Gene: apolipoprotein E ɛ3 allele (written as apoE3).  The ɛ3 allele (version) of the apolipoprotein E gene evolved around 226K years BP; this is before the appearance of anatomically modern humans around 195K years BP (McDougall et al. 2005). A detailed analysis by Finch et al. (2004) provides extensive evidence that apoE3 was an evolutionary adaptation to increased consumption of animal foods, i.e., a “meat-adaptive” gene. The apoE3 allele also reduces the risk of Alzheimer’s and vascular diseases. The same paper identifies additional genes that may have changed as a result of increased animal food consumption in evolution, including genes that support the brain, gut, hair and skin, bone maturation, and growth.

 

Other nutrition-related human genes subject to positive selection in evolution

 

The following genes are mentioned to document that many nutrition-related genes have changed over the course of human evolution.

• Cytochrome P450 genes involved in detoxification of plant compounds and the MGAM gene involved in starch digestion; this may be due to changes in plant food consumption that started in the agricultural revolution (Nielsen et al. 2007, Kosiol et al. 2008).
• TCN1 (transcobalamin) gene involved in transport of vitamin B-12 into cells (Kosiol et al. 2008).
• Also: genes involved in the senses of taste and smell; other genes involved in carbohydrate metabolism, e.g. glycolysis [energy metabolism] and lactose digestion; processing of fat including catabolism; amino-acid catabolism; calcium signaling (Blekhman et al. 2008, Voight et al. 2006, Haygood et al. 2007, Kosiol et al. 2008).

 

The evidence of positive selection for genes involved in nutrition from both plant and animal sources provides genetic evidence that humans are omnivores.

 

Human culture:

the most powerful evolutionary selective pressure of all

 

The culture-evolution link is important because, for 2 million years, humans have followed “cultural” omnivorous diets. Until recently, much of the research on the interaction between human culture and genes/evolution was theoretical and highly mathematical and statistical; see Boyd & Richerson (1985) for an example. Advances in genome research are now validating some of the mathematical models of culture-gene interaction.

 

Culture-evolution interaction can create extremely strong evolutionary selective pressures, as well as buffer or block some selective pressures (Varki et al. 2008). “Gene-culture dynamics are typically faster, stronger and operate over a broader range of conditions than conventional evolutionary dynamics, leading some practitioners to argue that gene-culture co-evolution could be the dominant form of human evolution” Laland et al. (2010, p. 137). Cultural practices are disseminated by teaching and learning, processes that can spread much faster than human reproduction. A cultural practice that enhances reproductive success is an extremely powerful evolutionary selective pressure. Culture may even explain the evolution of human longevity (Caspari & Lee 2005).

 

A recent analysis of a major genetic database - the HapMap SNP database - has shown that human evolution has accelerated dramatically in the last 40K years BP, with adaptive evolution in the last 10K years BP occurring at a rate >100 times the rate that prevailed in most of human evolution (Hawks et al. 2007, Hawks 2007). There are two primary drivers for this phenomenon: 1) the major increase in human population caused by the agricultural revolution – a larger population base allows for a larger number of genetic mutations, 2) diversity in human cultures – diets, environments – created numerous environments with different selective pressures to filter the mutations.

 

The preceding suggests that more human evolution has occurred in the time since the agricultural revolution began, ~10K years BP,  than in the 1 million years that preceded the date 40K BP. The conclusion here is that humans are still evolving, and very rapidly, i.e., we are very much a “work in progress” in evolutionary terms.

 

Additional adaptations of interest

 

The practice of wearing shoes started approximately 28K years BP, which caused a decline in the “robustness” – size – of human foot bones (Shipman 2008). While not a dietary adaptation, it is an example of a morphological adaptation driven by a cultural practice. [Note that substantial changes in human morphology can evolve in only a few thousand years (Henneberg 2006).]

 

Starch digestion enzymes. Amylase is an enzyme secreted in saliva that digests starch. A study of the copy numbers of the salivary amylase gene (AMY1) in humans revealed that: a) salivary amylase protein levels are correlated with number of copies of the gene, b) individuals from populations whose traditional diet is high-starch, have more copies of the gene than individuals whose traditional diet is low starch.  The increase in copies of AMY1 is estimated to have occurred within the last 200K years BP. The analysis concludes that the number of copies of AMY1 is an adaptation to diet, in at least some populations (Perry et al. 2007).

 

Supplementary note: Chimps have 1/3 as many copies of the gene as humans and the gene is present but appears to be nonfunctional in bonobos. The study notes that “AMY1 copy number was probably gained in the human lineage, rather than lost in chimpanzees” (Perry et al. 2007, p. 3).

 

Lactose digestion enzymes. Lactase is the enzyme that digests lactose, a sugar found in milk. A large part of the adult population cannot produce lactase, hence are lactose-intolerant. However, genetic evolutionary changes have allowed at least two populations to continue to produce lactase: Northern Europeans and select West African pastoralists. These are populations that consumed dairy and herded cattle. The relevant genetic changes are in different parts of the genome, indicating that the trait evolved multiple times.

 

The ability to produce lactase evolved within the last 7K years for Africans. For Europeans, dates inferred via genetic analysis suggest that the trait evolved within the last 2-20K years. However, genetic analysis of ancient European skeletons suggests that the trait evolved from low incidence rates to near universality in the target population within the last 5-8K years (Tishkoff et al. 2006, Ingram et al. 2007, Berger et al. 2007). This example proves that cultural behaviors can drive genetic evolution.

 

Supplementary note: A genetic study of milk cattle in Europe shows evidence that cattle milk protein genes co-evolved in association with human milk consumption and the selective breeding of cattle for higher milk production (Beja-Pereira et al. 2003, Evershed et al. 2008). This is symmetry: human-controlled breeding of cattle for higher milk production inducing changes in cattle genes, and in the same period the human genetic structure evolves to allow more adult humans to digest lactose.

 

Raw Vegan Evolution Claims: a brief assessment

 

Given the extensive scientific evidence in support of human omnivory, the statement (often attributed to Carl Sagan) applies here: “Extraordinary claims require extraordinary evidence.” That is, promoters of raw vegan evolution need to present extraordinary evidence to support their claims. However, the lack of substantive evidence to support their claims is glaringly obvious. Instead of “extraordinary evidence,” raw vegan evolution advocates:

• Play diversionary word games, e.g., the terms omnivore and frugivore
• Demonstrate bad logic: black-and-white thinking applied to subtle, complex topics
• In some cases, they appear to not even read (or understand) the full text of scientific articles they quote
• Rely on short, out of context quotes in a way that can be misleading

 

and in general provide examples of pseudoscience.

 

Raw vegan evolution advocates often claim that omnivorous diets are “cultural diets” and this label somehow makes them immune to evolution. The growing evidence of a powerful culture-gene evolutionary linkage contradicts that claim. They claim that evolutionary change as adaptation to diet was impossible over 2 million years of evolution; the scientific evidence contradicts them yet again. (Given the fact that the human brain showed major evolution in the period, the raw vegan claim can be restated as “the brain can evolve but the stomach cannot”).

 

Raw vegan evolution advocates contradict themselves when they say that eating animal foods, by necessity, promotes disease (meaning it is a strong negative evolutionary selective pressure), yet no adaptations to animal foods occurred over 2 million years of evolution (meaning it is not a selective pressure at all, and can be interpreted as proof that animal foods are part of the natural diet range). A rational assessment of raw vegan evolution theories reveals that such theories are, to paraphrase the queen from Alice in Wonderland, “one of the impossible things to believe before breakfast.”

 

Humans are natural omnivores:

does that mean I should eat animal products?

 

That is a personal decision – it is your life and your diet. However, as a vegetarian since 1970, my suggestion would be: not unless there are major, compelling reasons to leave the vegan or vegetarian paradigm. The animal foods humans consumed over evolution were – until the agricultural revolution – wild animals. Today’s modern animal foods are dramatically different:

 

• Factory-farmed – with antibiotics, pesticides, fungicides, and other chemicals, terrible cruelty to the animals, social issues (low prices paid to farmers, low wages for workers), and extremely negative environmental impacts.
• Significantly higher in fat and cholesterol than wild animals (for example, “marbled” meat). Feedlot meats also have a less favorable omega-6/omega-3 fatty acid ratio.
• Animal foods were consumed in the raw state prior to the advent of cooking. The date when cooking started is controversial; estimates range from as recent as 40,000 years ago to 1.9 million years ago. Perhaps the date with the strongest evidence is approximately 300,000 years ago: cooking softens foods, and human dental structures have been slowly decreasing in size since that date (Lucas 2004).
• People today eat mostly muscle tissue – this increases protein consumption and it is easy to eat too much protein.
• Muscle tissue is extremely tough and requires pre-processing: pounding, cooking, or aging. Raw, wild animal meat is tough and difficult to chew without pre-processing. The dental reduction described above suggests that at least some kinds of pre-processing of meat became common 300,000 years ago. Our Paleolithic ancestors would eat the whole animal, including internal organs.
• Epidemiological evidence indicates that diets high in modern feedlot meats are often unhealthy in that they have higher incidence rates of certain diseases. To contrast: some hunter-gatherer populations have excellent health on diets with high levels of wild animal foods (O’Dea 1991). However you probably don’t exercise like a hunter-gatherer, and have limited access to wild animal foods.

 

The bottom line: modern animal foods are a poor substitute for wild, and the earth does not produce enough wild foods – animal or plant - to support us all. There are many good reasons to be vegan or vegetarian, and to eat lots of raw/unprocessed foods.

 

An overdose of vitamin N aka naturalism?

 

Idealistic “most natural” evolutionary diets are not feasible options for most of us at the present time, due to the limited supply of wild foods and uncertainty regarding the level of individual adaptation to agricultural diets. Instead, whatever diet one chooses will be – at best – an approximation (or compromise) based on available foods.

 

Most of us have freedom of choice and many options to consider when selecting a diet, whether   raw or cooked, vegan, vegetarian or non-vegetarian. Your choice may be influenced by vegan/vegetarian ideals, naturalism, or other factors relevant to you. It should be noted here that one does not need to believe fallacious raw vegan evolution theories to follow a raw, vegan, or vegetarian diet. In fact, letting go of such nonsense and seeing and accepting the world as it is, without blinders or dogma, can be mentally refreshing and very liberating.

 

The fact that so many in the raw/veg community cling fervently to invalid claims that their diet is ”most natural” or “species-specific” leads us to the 4th and last question: why is it so incredibly important to some in the raw vegan/vegetarian community that their diet be considered “most natural” rather than  “most compassionate” or “healthy and sustainable”?  In my opinion, that is the most interesting question of all, and unfortunately it cannot be addressed in this article.  I hope that you will think about the 4^th question, and I wish you all good health.

 

 

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