Answer by Adriana Heguy:
Humans are not carnivores, but omnivores. We do not have the gut structure that a carnivore, such as cat has. Our digestive juices are not the same as carnivores’. Carnivores can actually digest bones up to a certain extent. We did not evolve from carnivores, but from apes. So it’s not like we had the capacity to eat raw meat and then we “devolved” it. No ape is a strict carnivore. Most apes are frugivores or herbivores. Even for chimps, who eat meat fairly regularly, meat is a very small portion of their diet, and when they eat meat, they eat it fresh. We can digest raw meat (think steak tartare), but we get less nutrients from raw than cooked meats. Cooking food in general, not only meats, make them more digestible and more calories can be extracted from cooked food.
Raw meat can make people ill if the meat is contaminated with bacteria. If we were to kill an animal and immediately consume its flesh without storing it, we would not get sick. But in modern meat processing plants, the meat can become contaminated with fecal matter from the hapless animal; the same goes with eggs from factory farms. So it is best to cook meat and eggs, rather than eating them raw, not just for digestibility but also to kill the bacteria. Carnivores tolerate eating more bacteria than us because of the amounts of acid their stomachs contain, about 10 times higher than those of a non-carnivore. Their shorter guts also make for quick passage of the food so there is no time for rotting.
In other words, we did not evolve the capacity to eat cooked foods. We evolved as omnivores, not carnivores. And once we hit on the fact that cooking foods makes us able to extract more calories and kill bacteria, we stuck with it.