Apply heat to food and it becomes easier to digest and better tasting. Why?
Well, we need to understand digestion first. To digest food, you need to break down carbohydrates into simple sugars, proteins into their constituent amino acids, large globules of fat into smaller ones. Then these simpler nutrients can be absorbed by the small intestine.
Typically this breakdown process is done in the mouth and stomach, and it can be really time and energy consuming. Chimps spend several hours a day chewing. Cows chew the cud for even longer. But at some point hundreds of thousands of years ago, humans figured out a trick to make their food easier to digest: heating.
Applying heat breaks down tough, complex molecules into simpler ones. It's essentially an external digestive system that makes your stomach's job easier.
There is archaeological evidence to show that as we learnt to cook, we lost the ability to make the most of the tough, raw food that most animals have to consume. Evolution made our jaws weaker, intestines shorter, and stomachs smaller as we increasingly became dependent on cooked food.