carbohydrates are a food source rich in energy. after the agricultural revolution, human diet began to rely more on plant and animal domestication in place of hunting and gathering. this shift marked the beginning of a diet composed of 49% carbohydrates as opposed to the previous 35% observed in paleolithic humans. as such, starch became a staple of human diet. humans that contained amylase in the saliva would benefit from increased ability to digest starch more efficiently and in higher quantities.