Cooking food made possible a larger or . . .
. . more resilient human population, because the process detoxifies many plant foods.
Non-human primates are very reluctant to move from feeding on one tree to another because even within the same species toxicity varies significantly. Usually the more marginal members of the clan are "encouraged" to try out a new tree before the main group moves to it.
Particularly cyanide toxins (a common plant biological defense) are driven off by cooking, but many others as well. Also, relatively indigestible plant materials are rendered digestible and nutritious by cooking.
Of course overcooking vegetables (see England and Germany) has a deleterious effect on both flavor and nutrition.
