Humans are omnivores

I keep running into people who–not satisfied with their own dietary choices and the need to declare them as the true, correct, path with all others being wrong–claim that humans are “natural herbivores.” As one person put it, “our ancestors were herbivores.  Meat eating was a mistake that came much later.”

Put simply, that’s ridiculous.

Let’s take that “our ancestors were herbivores.” Really?  When?  As far back as anthropologists have been able to find, humans and proto-humans have included meat in their diet.  Early finds include such things as stone tools used for cracking open bones to extract the marrow (said bones also being found at the same site).

For that matter, our nearest relatives, chimpanzees (pan troglodytes) and bonobos (pan paniscus), eat meat when it’s available.  They will, when they can, kill other animals for the meat.  The “our ancestors were herbivores” require our ancestors to, sometime after the split from our common ancestor with chimps and bonobos (the “pan” group) have stopped eating meat, become completely herbivorous, and then, by the time the fossil record picks up with australopithecines, they started eating meat again.  Alternately, perhaps the common ancestor was a pure or nearly pure herbivore (gorillas are much closer to herbivores than our closer relatives–or perhaps not) and chimpanzees, bonobos, and he ancestors to humans made the same “mistake” of adding meat to their diet.

As an aside, the truth is, many herbivores will eat meat when it’s available:

Even if either of those scenarios held, and even leaving aside the herbivores do eat meat when available factor, the fact remains that the ancestors of humans were eating meat and using tools to help them with the eating of meat, more than 3 million years ago and over a period where we went from Australopithecus afarensis through (possibly) Kenyanthropus platyops, other australopithecines, through homo habilis, homo erectus, and finally to homo sapiens.  Evolution through multiple species and even genuses?  Is that not enough to consider it “normal”for homo sapiens sapiens? It certainly took far less for pandas to go the other way.

It certainly seems that humans are adapted to eating meat as part of their diet.  There are a number of nutrients that are difficult to impossible for humans to get from a purely plant based diet.  Some particular ones to note are Vitamin B-12, required for producing red-blood cells and for nerve and brain function, and DHA–docosahexanoic acid.

DHA, an important Omega 3 fatty acid, is particularly important in that it’s critical for brain function and development.  About 18% of the brain is DHA.  It participates in the formation of myelin, the “white matter” that insulates brain circuits.  It serves in the blood-brain barrier to help protect the brain from undesirable outside influences.  And it is vital for the development of the cortex–the part of the brain involved in “thinking.”

DHA only comes form animal fat.  Why, after all, would plants have it?  None of the functions it provides exist in plants.  They don’t need it.  Humans, however, are a different matter.  We need it.  And you know who especially needs it?  Young children whose brains are still growing.

Plants do have ALA, Alpha Lineolic Acid which is a precursor that can, in principle be converted into the fatty acids the body need including DHA.  However, the conversion rate is extremely low.  Studies show a conversion rate of less than 10% between ALA and DHA.  Some studies report the conversion rate as zero. So to meet the body’s needs of DHA you would have to eat, at best, foods containing ten times as much ALA.  And it may well be that no amount of plant-based foods will provide the required DHA.

This is part of why some scientists are coming to the conclusion that an omnivorous diet allowed proto-humans to grow the large brains that led to the evolution of homo sapiens sapiens.  The brain uses a remarkably large fraction of the human bodies energy expenditures, and in particular its development relies on having sufficient fat in the diet, animal fat.

If a person chooses to saddle themselves with the handicaps of an all-plant diet, carefully balancing various plant foods one against the other to ensure they get a complete protein (another factor which I haven’t gone into here), supplement things like vitamin B12, accept the lesser utility of plant sourced vitamin D2 instead of animal-sourced d3, and so on then more power to them.  I applaud them in their perseverance in their whimsy.  But if they claim that this is “natural” and what is the “really, truly best diet for humans”?  Well…

I laugh in their general direction.