Humans (species in the genus ''Homo'') are the only animals that cook their food, and Wrangham argues ''[[Homo erectus]]'' emerged about two million years ago as a result of this unique trait. [[Cooking]] had profound evolutionary effecteffects because it increased food efficiency, which allowed human ancestors to spend less time foraging, chewing, and digesting. ''H. erectus'' developed a smaller, more efficient digestive tract, which freed up energy to enable larger [[Human brain|brain]] growth. Wrangham also argues that cooking and control of fire generally affected species development by providing warmth and helping to fend off predators, which helped human ancestors adapt to a ground-based lifestyle. Wrangham points out that humans are highly evolved for eating cooked food and cannot maintain reproductive fitness with raw food.<ref name=":0" />
