The bottom line, says Petrinovich, is that when you're hungry enough, ravenous really, and when all other food sources--including "inedible" things you'd rather not stomach such as shoes, shoelaces, pets, steering wheels, rawhide saddlebags, or frozen donkey brains--have been exhausted and expectations are sufficiently low, even the most recalcitrant moralist among us would shrug off the cannibalism taboo and savor the sweet meat of man ... or woman, boy or girl, for that matter. It's either that or die, and among the two choices, only one is biologically adaptive.
A behavior can be adaptive without being an inherited biological adaptation, of course. But because starvation occurred with such regularity in our ancestral past, and because the starving mind predictably relaxes its cannibalistic proscriptions, and because eating other people restores energy and sustains lives, and because the behavior is universal and proceeds algorithmically (we eat dead strangers first, then dead relatives, then live slaves, then foreigners, and so on down the ladder to kith and kin), there is reason to believe--for Petrinovich, at least--that anthropophagy is an evolved behavior. The taboo against cannibalism is useful in times of health and prosperity; groups wouldn't survive very long if members were eating one another up. Yet starvation has a way of releasing the cannibal within.
An Evolutionary Case For Cannibalism