IANAEB*, but it seems really unlikely to me that mankind has been cooking food long enough for that to have evolutionary consequences. Looking at the geographical spread in the human fossil history, and the ranges and feeding behaviors of our nearest relatives, a simpler explanation is that our ancestors lived in areas where food that we could digest was plentiful. (Besides fruit–which the broken gene for vitamin C production suggests must have been a big part of our diet historically–insects, eggs, and certain types of meat and fish are clearly nutritionally valuable sans cooking.)
Our learning to harness fire was undoubtedly an early step in the process of expanding our range out of the tropical and subtropical zones into areas where edible raw food is less common. As well as in the process of eating less insects.
*I Am Not An Evolutionary Biologist