Control of fire by early humans
The cooking of meat, as can be seen from burned and blackened mammal bones, makes the meats easier to eat. It is also easier to get the nutrition from proteins because the meat itself is easier to digest. The amount of energy needed to digest cooked meat is less than that needed for raw meat, and cooking gelatinizes collagen and other connective tissues as well, it "opens up tightly woven carbohydrate molecules for easier absorption." Cooking also kills parasites and food poisoning bacteria.