I have previously noted, see Convenient Darwinism, that the theory of natural selection is a flexible one that permits all kinds of odd arguments. For example, I would argue that we are genetically predisposed to crave meat. There is a biological basis for this argument. Scientific studies (see, e.g., here and here) suggest that the reason that the human brain evolved to its current size is because, at some point in the prehistoric past, the diets of human ancestors changed. These distant ancestors began to eat meat, and their brains grew. Indeed, some scientists conclude that the inclusion of meat in the diet, with its protein and high-caloric content, was essential to supporting the high-energy consumption qualities of the advanced human brain.
You could also argue that the theory of natural selection suggests that eating meat promoted bigger brains and keener intelligence for another reason. Eating plants doesn’t present much of an intellectual challenge. You see a plant, tear it out of the ground, and eat it. It is so unchallenging that the most tiny-brained creatures on Earth can do it. Eating meat, on the other hand, imposed much greater intellectual challenges. The animal from which the meat must be taken was desperately trying to avoid that fate, and therefore our ancestors needed to figure out how to track, trap, and kill the unwilling prey and then butcher and cook its meat. Those difficult tasks encouraged cooperation, language, social behavior, and the development of tools, among other things. The puny, weak-brained primates who couldn’t figure these challenges out were less likely to survive to reproduce; whereas the studly, brainy hunters thrived. And, from a social standpoint, the choices would be easy. If you were wandered across the savannah in Africa 2 million years ago, would you rather be a member of a dull-witted tribe that sat around munching dimly on grasses, ferns and brussel sprouts in a cold damp cave, or part of an active, fun-loving tribe that consumed sizzling haunches of meat around a roaring campfire and then, sated, talked animatedly about how to bring down that wild boar that had been seen around the neighborhood?
So, don’t listen to those who argue that our “natural” state requires a diet of vegetables. Stand up for bigger brains, social behavior, and tools! Stand up, and let your inner hunter/gatherer roar!