"Humans, unlike other animals, have a built-in need for supplemental energy, such as firewood, or fossil fuel energy. Over one million years ago, pre-humans figured out how to cook part of their food. Because of this cooked food, their jaws and digestive apparatus could shrink in size. The improved food supply allowed their brains to improve in complexity. Also, cooked food greatly reduced the time required for chewing, allowing more time for toolmaking and crafts. Heat is also important for killing pathogens in water."