|Richard Leakey with skull of Australopithecus (left) and Homo habilis (right). Photo from fotosimagenes.org|
Let me start with this: if you're a vegetarian, and enjoy good health on your diet, that's fine with me. Everybody should have a diet that works for them, and if you've found it, I won't discourage you from following it.
That said, evolution doesn't support human vegetarianism--unless you go back to Australopithecus (see photo). While doing a bit of research, I came across an odd quote attributed to paleoanthropologist Richard Leakey:
"[y]ou can’t tear flesh by hand, you can’t tear hide by hand … We wouldn’t have been able to deal with food source that required those large canines” (although we have teeth that are called “canines,” they bear little resemblance to the canines of carnivores).
It shows up on several vegan and vegetarian websites and articles, but with no source cited. I call it an odd quote because from what I've read in evolutionary anthropology books such as Cro Magnon: How the Ice Age Gave Birth to the First Modern Humans by Brian Fagan, Catching Fire: How Cooking Made us Human by Richard Wrangham and Evolution of the Human Diet by Peter S. Ungar--not just books or web sites promoting any sort of diet--the idea of humans as meat eaters seems well established based on tools, cut marks, human anatomy and carbon isotope analysis of human bones and isn't a matter of controversy. If Leakey took the position that humans have been evolving as vegetarians, he'd be going against the mainstream views, and quite a bit of evidence, in his field.
Some searches through Google and Amazon finally revealed where this quotation came from: The Power of Your Plate--Eating Well for Better Health--20 Experts Tell you How by Neal D. Barnard, page 171. I don't have the book and can't see the whole page in the Amazon view, but I can repeat some other Leakey quotes from the book.
"If you faced a narrowing of your dietary base, dessication, whatever," Leakey said, "then the only way to maintain yourself would be to change your feeding strategy. One of the options seems to have been to increase the amount of meat."
Leakey goes on to hypothesize that early humans were scavengers of meat; Barnard writes,
Patterns of scratches on [animal] bones have revealed that stone tools were scraped over the bones after carnivorous teeth had cut into them, suggesting that the bones had been carnivores' prey which were then scraped clean by human scavengers....."About two and a half million years ago, you suddenly find evidence of tools: sharp stones, stones that have been broken and have sharp edges," Leakey said. These are invariably associated with bones of animals, suggesting meat in the diet in one form or another. That evidence coincides with the first appearance of an enlarged and modified brain shape."...."Remember that the eating of meat on the African savannah," Leakey said, "although it's in big packages, and you can share it, still accounts for a relatively small part of your diet. Even with the successful scavengers and successful hunters, meat is a rather small part of the diet, except in places like the Arctic..." page 170-174
I can't see where the reference is from in the Amazon preview and I don't know when it's from--Leakey has been writing books since the 1970s. However, I have in front of me Leakey's book Origins Reconsidered, published in 1992, three years before The Power of Your Plate.
With the origin of the Homo lineage, the trend toward bigger grinding molars became reversed, not to fruit-processing teeth again, but to the teeth of omnivores, animals that may have included meat in their diet. This we see in Homo erectus. (page 54)
Prominent in the mix is the enlarged brain, expanding in an evolutionary punctuation from close to 500 cc in australopithecines to more than 700 cc in early Homo. An almost 50 percent expansion in brain size in creatures of roughly the same body size is a biological signal about as dramatic as can be imagined. As significant to me is the concomitant shift in life history. And, as our earlier sketch of australopithecine and Homo troop life implies, there was also an important change in subsistence. Here the new constituent is meat, not as a rare item in the diet, but for the first time a substantial component. Is it a coincidence that we see stone tools enter the archeological record at about the same time as we judge Homo to have evolved, some 2.5 million or more years ago? I think not. I think we are seeing here the elements of an evolutionary package that in time led to Homo sapiens. (page 163).
Two and a half million years ago--when the stone tools suddenly appeared--was the start of the first of several ice ages, bringing about a change in climate and habitat that would have pushed our ancestors into meat eating and tool making. Leakey continues,
The expansion [of diet] involved making meat an important food source, not just an occasional items, as it was with earlier hominids and is still for baboons and chimpanzees. Although some anthropologists argue that regular meat eating was a late development in human history, I believe they are wrong. I see evidence for the expansion of the basic omnivorous hominid diet in the fossil record, in the archaeological record, and, incidentally, in theoretical biology. Bob Martin points out what all good biologists know: the brain is an expensive item to maintain. It constitutes only 2 percent of the body bulk, yet consumes almost 20 percent of total energy. Bob extends the argument, saying that the brain not only is expensive to maintain, but is expensive to build.....Part of Bob Martin's thesis about a species' ability to afford a large brain is that it must have a stable environment, stable in terms of food supply. Stable and nutritionally rich. The robust australopithecines managed to stabilize their food supply in the new prevailing environment 2.5 million years ago, but their rough plant foods were not rich nutritionally. By broadening the diet to include meat, early early Homo achieved both stability and rich nutrition. Meat represents high concentrations of calories, fat and protein. This dietary shift in Homo drove the change in pattern of tooth development and facial shape. The links in the chain join up yet more closely....Primates have great difficulty in getting at the meat of large, tough-skinned animals. With a sharp stone flake, however, even the toughest hide can be sliced through, literally opening up a new nutritional world. (pages 165-166)
We don't need big teeth to eat meat--we started using stone tools around 2.5 million years ago and started cooking around two million years ago, according to Catching Fire. Watch hunter Shawn Woods butcher a deer with a homemade obsidian stone tool.
The evidence that includes stone tools and cut marks makes more sense to me than Barnard's book, which states on page 168, "On their diet of fruits and vegetation, chimps remain amazingly healthy, free of most of the diseases that plague humans." Well, yes, because they're eating their native diet. If I ever have a chimp to feed, I'll make sure it has plenty of fruits and vegetation.