Sunday, March 12, 2017

Human Ancestors: Vegetarians or Obligate Omnivores?

On July 23, 2012 Scientific American ran an editorial by biologist Rob Dunn with the title:
Although at the end of this opinion piece, he admits that his article doesn't really support the claim that human ancestors were nearly all vegetarians:

He supports his very misleading title choice by the claim that he used "the definition of vegetarian that most humans use" which according to him refers to someone who eats no meat in public but does eat meat in private.  Aside from the fact that he fails to provide any evidence that this is "the definition of vegetarian that most humans use," using the word "vegetarian" in the title with the assumption that this is the meaning most readers will assign to it is misleading click bait at best.  Many people who read his title want to believe that he is asserting that most human ancestors did not eat meat.

Nevertheless he retains the claim that our ancestors "tended to mostly eat vegetable matter."  He supported this claim by enlarging the pool of "our ancestors" to include pre-human primates.

In 2002 Hladik and Pasquet published, in the journal Human Evolution, their article "The human adaptations to meat-eating: a reappraisal," in which they argued that humans are unspecialized omnivorous frugivores:

In this paper, Hladik and Pasquet argued that starch-rich cooked tubers were the most likely source of increased caloric intake needed for evolution of the human brain:
In January of 2014, I published Powered by Plants (PBP) in which I attempted to provide further support for classifying humans as unspecialized, omnivorous frugivores with no specific adaptations to meat-eating.  Like Hladik and Pasquet, I also referred to Wrangham's team's 1999 paper "The Raw and the Stolen" to support the same conclusion that human brain evolution was more likely primarily supported by inclusion of cooked starch-rich plants in the diet, than by meat-eating.

However, as Hladik and Pasquet note, one main weakness of this argument is a paucity of strong evidence for controlled use of fire previous to 250,000 years ago.  Hladik and Pasquet think that this lack of evidence is not a strong argument against the use of cooking that long ago because the cooking methods used by contemporary Pygmy hunter-gatherers leave no trace within a matter of months:

Did Meat-Eating Make Ancestral Humans More Fecund?

On April 18 of 2012, Live Science published:

This article reports on a study comparing weaning ages of humans to other species.  The study found that humans wean their young at a proportionally much younger age than other primates.

Humans' natural weaning age is similar to that of carnivores that obtain at least 20 percent of their calories from meat:

To my fault, I did not take notice of this research in 2012-2014, when I was working on PBP.  This finding provides some support for the idea that regular consumption of fairly large amounts of meat (≥20 percent of calories) by prehistoric humans resulted in a natural selection favoring the reproduction of individuals having a lactation period proportionally shorter than that of other great apes and similar to that of carnivores. If so, this would be a specific adaptation to a carnivorous diet.

However, I do not see how we can rule out the possibility that this change in human weaning time was facilitated simply by increased caloric intake, which could have been supplied by either cooked starches, or a combination of cooked starches and meat.  It does not immediately strike as a characteristic that can only be supported by inclusion of meat in the diet because there is no reference to any nutrient uniquely or even predominantly provided by meat. 

As an aside: Is it really any wonder that people can get very confused about the natural human diet, when it looks like Scientific American endorses the claim that human ancestors were "nearly all vegetarians," yet other LiveScience headlines assert that prehistoric meat-eating made human ancestors more "fruitful"?

Revisiting the "Meat-Eating Fueled Brain Evolution" Hypothesis

On November 19 of 2012 LiveScience reported that meat-eating was necessary for the evolution of the human brain:
This report focuses on a study that calculated that early humans would not have been able to acquire enough dietary energy from a raw plant food diet to support the evolution of the human brain through the enormous increase in number of brain neurons that separates humans from other apes:

Human ancestors would have had to spend more than nine hours a day eating, in addition to the time required to acquire the foods.  Either eating more calorie-dense meat, or cooking the plant foods, would have been necessary to supply sufficient dietary energy to support addition of neurons to the brain over time.  Once again we're talking about energy (calories) which is not uniquely supplied by meat.  As Wrangham's team showed in their 1999 paper "The Raw and the Stolen" early humans would have gained substantially more calories by simply cooking their starchy underground storage organs and seeds than by switching from a wholly plant-based diet to one providing 60% of its energy in the form of raw meat.

However, this report also refers to an archaeological find providing evidence that "meat must have been an integral, and not sporadic, element of the prehuman diet more than 1 million years ago."

Presumably if raw wild plants provided plenty of iron, folate and B12, this child would not have had this malnutrition condition.  While wild plants may provide plenty of folate, they lack B12 and have non-heme iron that is poorly absorbed.  Relevant here is the fact that childhood iron-deficiency is world-wide one of the most common mineral deficiencies and it is most common in nations having cereal and legume based diets where meat intake is low.

Source:  Zimmermann et al.

This find  was separately reported on by LiveScience on October 3, 2012 [orginal article in PLO One].  As stated, the remains consist of a toddler's skull showing that the toddler suffered from porotic hyperostosis, a bone condition associated with low iron, folate, and vitamin B12 status.

Now we are in the realm of neural nutrients that are for practical purposes and particularly in the context of the paleolithic era uniquely supplied by meat.  Wild plants may have traces of B12, but they simply are not sufficient sources of B12 for lactating women or growing children; for practical purposes B12 was a nutrient exclusively provided by meat in human prehistory.  While plants provide iron, they don't provide heme iron and as documented above, we know that even contemporary children in populations subsisting on cooked plant-based diets with very low meat intakes are highly prone to iron deficiency. Cooking underground storage organs just won't add to their B12 or iron value.

Are Humans Obligate Carnivores?

Thus, this finding of porotic hyperostosis in a child 1.5 million years ago provides evidence that before 1 million years ago the human lineage had already been molded by natural selection to require during childhood intakes of iron and B12 that only regular consumption of meat could provide.

It is very significant that both the weaning data and this case of ancient porotic hyperostosis pertain to reproductive efficiency.  The nutritional needs of pregnant and lactating women and their children are increased in comparison to adults, particularly adult men, who are not pregnant or lactating.  During pregnancy, lactation, and childhood growth, the faults of a diet become apparent.  This evidence indicates that human ancestors 1.5 million years ago could not successfully reproduce without eating meat.

This interpretation is further supported by the finding by Beasley et al 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." Most likely, an need to eat microbe-laden meat imposed on our ancestors a naturally selection that favored the survival and reproduction of those who produced a gastric pH of 1.5, sufficient to protect them from deadly meat-borne pathogens.

What would you call an animal that in its natural environment eats both plants and animals, but has a specific biological adaptation to meat-eating (gastric pH of 1.5) because its ancestors were in their natural habitat compelled to eat animal flesh in order to get adequate nutrition, survive and reproduce?

I would like to call such an animal an obligate carnivore, because this term literally means "compelled meat-eater."  If the animal must eat meat to meet nutrient needs, survive and reproduce then it is certainly compelled to eat meat.

However, biologists use this term to refer only to animals like the felines that in their natural habitats are restricted to meat-eating and virtually never eat plants. 

Zoologists classify animals that are capable of but not restricted to meat-eating facultative carnivores.  This is essentially another term for omnivores: animals that in their natural habitats can and do eat both plants and animals

These terms fail to capture the nutritional adaptations of some omnivorous animals, such as wolves, because neither of these terms connotes nutritional dependence on meat-eating.  Although wolves are omnivores, they can't survive in the wild unless they eat meat.

I suggest the term obligate omnivore to refer to animals that in their natural environment, without the aid of modern agriculture or food processing, need to eat both plants and animals in order to survive and reproduce.  Since an obligate omnivore has a dietary requirement for animal flesh, every obligate omnivore is also an obligate carnivore in the literal sense discussed above: a "compelled meat-eater," compelled to eat meat by dietary requirements, even if it can also eat plants.

To me, the archaeological evidence produced by Dominguez-Rodrigo along with the finding that humans have stomach acid stronger than many other carnivores and similar to scavengers indicates that humans evolved as omnivorous obligate carnivores: a species that was in its natural habitat and evolution compelled to eat meat in order to obtain nutrients required to successfully reproduce.

In Powered by Plants I (in retrospect, foolishly) argued against the idea that humans are obligate omnivores.  If this research is valid – and it seems to be – I stand both embarrassed and corrected.

I would say that I made the very common mistake of rejecting the idea that humans are obligate omnivores because some modern humans can live for extended periods of time without eating meat.
The problem with this is that even if it is in modern circumstances possible for some people to avoid eating meat to some extent by eating plant foods that weren't available to our preagricultural ancestors, or by extensive processing of plants (fermentation, refining, etc.), or by taking iron or B12 supplements, etc., this does not change the fact that without these technological innovations, in nature, human ancestors could not successfully reproduce without eating meat.

Just as the fact that some people succeed in feeding dogs completely plant-based diets does not prove that the dogs are not obligate carnivores, the fact that some people seem to get along without eating animal foods does not prove that humans did not evolve as obligate omnivores. Just as a dog is an obligate carnivore without human technological intervention, human ancestors lacking modern agriculture, food processing technologies and dietary supplements were obligate carnivores (in my preferred sense of the term).

If humans evolved as obligate omnivores, this would certainly explain why people self-identifying as vegetarians or vegans comprise no more than 3% and 0.8% of the population, respectively.  Some researchers estimate that no more than 0.1% of the population is strictly vegan or vegetarian (i.e. never eating meat).  The rarity of strict vegetarians makes perfect sense if humans have an evolved drive and genetic requirement for meat-eating.

Research shows that while 3% of people self-identify as vegetarians, 66% of these people report eating red meat, poultry, and fish on follow-up challenges; only 0.9% of the total study population both self-defined as vegetarian and provided dietary recalls that included no animal flesh. Why would they misrepresent themselves?  This reminds me of how priests trying to suppress their biological drive for procreation often get caught engaging in sexual abuse behind closed doors. If humans have a strong innate biological drive to eat meat then it is really no surprise to find that most people who attempt to eat meat-free diets are unable to consistently maintain a meat-free diet, or that deception of self or others is common among self-identified meat-avoiders. 

The fact that at least 84% of people who attempt meat-free diets eventually return to eating meat (see also Hal Herzog's article on this topic) also supports the conclusion that humans are not adapted to meat-free diets and have an innate biological drive to eat meat.

None of these facts makes sense if humans have no biological drive or requirement for meat-eating.

Nature always has the last word.  Biology will always trump ideology.

The Natural Selection and Survivor Bias of Successful Vegetarians and Vegans 

A vegetarian or vegan diet itself exerts a natural selection on populations.  Among people who attempt meat-free diets, only the small fraction who have greater genetic, biological capacity to survive or thrive on such diets will stick to them for long.  The fact that some individuals are able to do so doesn't prove that all individuals can do so, any more that the fact that some individuals can thrive in professional basketball proves that all individuals can do so.

People vary in their nutritional requirements.  Even well-planned vegetarian diets tend to be marginal in choline and zinc.  The Linus Pauling Institute notes that "Strict vegetarians, who consume no meat, milk, or eggs, may be at risk for inadequate choline intake" and "The requirement for dietary zinc may be as much as 50% greater for strict vegetarians whose major food staples are grains and legumes, because high levels of phytic acid in these foods reduce zinc absorption."

I tracked my intake of both of these nutrients for several years on a calorie adequate animal-free whole foods plant based diet, and I never met the full requirement for either nutrient on any day I analyzed.  My choline intake almost always fell below 50% of the recommended intake of 550 mg per day for men.    When you look at the top sources of choline it is obvious why this is the case:

Source: Linus Pauling Institute
The plant foods richest in choline are very poor sources.  I found it difficult to consistently obtain the 17 mg zinc recommended daily for vegan men.  Again a look at food sources of zinc indicates why this is the case: the zinc content of even the best plant-food sources is very low and variable on top of having low bioavailability due to phytates and other inhibitors.

Source: Linus Pauling Institute
Plant-based diets do not provide any long-chain omega-6 or omega-3 fats, which are likely required dietary nutrients for people of European and Asian ancestry.  Vegan and vegetarian diets will naturally select people who have lower than average dietary requirements for arachidonic acid, long-chain omega-3 fats (EPA and especially DHA), choline, zinc, and iron.

Just as basketball leagues select for people who are genetically suited to excel in basketball, with the result that people who don't excel at basketball defect to other sports, vegetarian diets select for people who are more suited to such diets, while those who don't do well on such diets just quit them.   This in turn means that vegetarian and vegan communities are always dominated and led by survivors of the selection process imposed by the restriction of animal products, and these people will tend to believe that since they survived and perhaps even thrive on the diet, everyone else should be able to as well.  This is known as survivor bias.

Unfortunately, this bias enables and emboldens a tiny minority population of more or less strict vegans and vegetarians to believe that they both have proven that everyone can thrive without meat-eating and have the "moral authority" to demand that everyone else give up eating meat.

But if as the evidence indicates evolution gave humans a biological drive, specific adaptations and nutritional requirements for meat, no moral question exists.  In this case, telling people they must never eat meat is like telling them they must never have sex.  No one can be required to behave in a way contrary to genuine biological drives and needs. Any attempt to enforce restrictions on biological drives will only result in physical and mental dis-ease and dysfunction in most people; very few will get away with it.

Eurasians' Neanderthal Ancestors Were Top-Level Carnivores

On March 14, 2016, Science Daily posted this report:

According to this report, not only Neanderthals, but also more recent Stone Age humans subsisted on predominantly meat-based diets:

In fact this is not new information.  Ten years earlier, in 2002 MP Richards reviewed the evidence for Paleolithic and Neolithic subsistence.  Neanderthals were found by stable collagen isotope studies to have been "all top-level carnivores who derived the vast majority of their protein from animal sources, likely to be large herbivores."  For upper Paleolithic Europeans "the main source of dietary protein was animal-based, and most likely herbivore flesh."  The evidence clearly indicated high animal protein diets for Stone Age Europeans.  Unlike Africans, Europeans and Asians are descended from "top level carnivores" who occupied cold northern habitats that had long winters. 

Neanderthal Descendants Have Top-Level IQs

While mulling over these findings, I recalled the evidence that Europeans and Asians have a very limited activity of the enzymes required to produce long-chain neural fatty acids arachidonic acid,  and DHA from plant-derived precursors linoleic acid and alpha-linolenic acid, compared to people of East Indian or African descent.  To adapt to northern climates, due to the relative paucity and seasonality of edible Eurasian plants during the ice ages, Eurasians were required to eat meat-based diets, which would have naturally selected for the survival of individuals having either mere tolerance for or outright dependence on nutrients exclusively or primarily supplied by meat.  It would have also selected against individuals who were genetically highly dependent on highly plant-based diets. 

What I find very interesting is that Europeans and Asians rank highest in the world for average IQ.  Ethnic Indians (who appear to have a specific adaptation to vegetarian diets) have a mean IQ of 82; most African nations have mean IQs below 80, and Africans also possess the SNP that facilitates conversion of LA and LNA to AA and DHA respectively.  Meanwhile, all European and Asian nations have mean IQs above 90, with many having mean IQs 98 or above. 

If you think these IQ disparities are only a result of technological development, note that Mongolians have only very recently adopted some technological modernization but have a mean IQ of 101, equal to Iceland and Switzerland.  Meanwhile, the mean IQ in Kenya, home of the pastoral Masai, is only 80.  These IQ differences have a biological and genetic basis.

European and Asian nations are composed of people who, unlike Africans, have ~3-5% exclusively Neanderthal genes, which control genetic expression in many important ways.  They are descended from people who had to have the wits to adapt to very cold ice age habitats and who hunted very large game animals to survive.

In other words, Eurasian ancestors had to outwit animals, understand laws of nature, and develop technologies in order to thrive in a habitat that is much more demanding and unforgiving than Africa and other tropical and subtropical regions.  It appears that this may have selected not only for dependence on dietary AA and DHA, but also for a significantly higher mean IQ in European and Asian populations.

So the higher mean IQs found in Europe and Asia are associated with Neanderthal ancestry, ancestral diets very rich in meat, and a probable biological dependence on animal sourced dietary long-chain fatty acids (and perhaps other neurologically important nutrients).  Think about that.

No doubt there will continue to be conflicting information about optimum human nutrition.  We will also see new information emerge as research continues into the future.  Each individual will need to make his or her own decisions about what to eat.  One thing seems certain to me: humans are not the creators of the universe or of human nature and do not have the knowledge or competence required to decide that it should be remade to fit their preferences. Very often acting on our desire to "improve" the world has resulted in unintended consequences and disasters producing suffering far greater than that which we sought to avoid by "improving" things.  For a simple example, agricultural and medical technology have been applied to reduce childhood infectious disease mortality, resulting in overpopulation and consequent suffering from starvation and ecological devastation.  I am reminded of Chapters 29 and 19 of the Tao Te Ching:

Do you think you can take over the universe and improve it?
I do not think it can be done.

The universe is sacred.
You cannot improve it.
If you try to change it, you will ruin it.
If you try to hold it, you will lose it.

Give up sainthood, renounce wisdom,
And it will be a hundred times better for everyone.

Give up kindness, renounce morality,
And men will rediscover filial piety and love.

Give up ingenuity, renounce profit,
And bandits and thieves will disappear.

These three are outward forms alone; they are not sufficient in themselves.
It is more important
To see the simplicity,
To realize one's true nature,
To cast off selfishness
And temper desire.

1 comment:

Joel W said...

I think the whole "did our ancestor eat this or that?" discussion is just a red herring used by the animal rights NAZIs to distract. Who gives a damn who ate what? In actuality though, considering the brain is made up of saturated fat & cholesterol, common sense (scary thought) dictates we should and probably always have eaten meat. Why do we have incisors if we weren't meant to eat meat? And take a look at most, if not all vegetarians and vegans. They are some of the most unhealthy looking people on earth. Especially vegans. They fall into two main categories. The ultra waifs (usually men) with beige skin, OBVIOUSLY due to the lack of ALL essential amino acids (sorry the incomplete protein in broccoli does not cut it, as it is just converted to sugar) and complete lack of iron, so they seems to have muscle wasting syndrome. Then there are the land whale vegans who obviously make up for the caloric intake a fruit/veggie cannot supply with bread and other quick carbs. And most seem (at least to me - watch any Snowflake video) to being entirely mentally deficient, due to the lack of saturated fats & cholesterol (brain food, as mentioned earlier). Then there is the pesky fact that there is exactly ZERO clinical evidence to back up a single vegan claim. Now some do it, and do it right. Fine that's there choice but it does not work for everybody. I recently saw an ad for supplements marketed specifically to vegans, to make up for lack of nutrients in a vegan diet. To me that says it all. I'm not against vitamins & supplements, I take them. But ONLY to supplement what I am already consuming. I went well over a decade with none. ZERO health problems. I'm just getting a bit older now and am trying to age gracefully, without complications of age-related illness/disease. The ONLY time I would recommend a vegan diet is to somebody with cancer, since it HAS been clinically proven that meat (esp red meat) can feed cancer. Other than that, pass the bacon & eggs (fried in bacon grease please).

On top of it all, meat is just plain delicious