Vegetarian ancestors

Most primates have the capacity for eating sugary fruit, the capacity for eating leaves and the capacity for eating meat. But meat is a rare treat, if eaten at all. Sure, chimpanzees sometimes kill and devour a baby monkey, but the proportion of the diet of the average chimpanzee composed of meat is small. And chimps eat more mammal meat than any of the other apes or any of the monkeys. The majority of the food consumed by primates today–and every indication is for the last thirty million years–is vegetable, not animal. Plants are what our apey and even earlier ancestors ate; they were our paleo diet for most of the last thirty million years during which our bodies, and our guts in particular, were evolving. In other words, there is very little evidence that our guts are terribly special and the job of a generalist primate gut is primarily to eat pieces of plants. We have special immune systems, special brains, even special hands, but our guts are ordinary and for tens of millions of years those ordinary guts have tended to be filled with fruit, leaves, and the occasional delicacy of a raw hummingbird.

Human Ancestors Were Nearly All Vegetarians