Humans (species in the genus ''homoHomo'') 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 effect 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>{{cite news|url=https://www.nytimes.com/2009/05/27/books/27garn.html?ref=books |title=Why Are Humans Different From All Other Apes? It's the Cooking, Stupid |work=New York Times |date=2009-05-26 |accessdate=2009-06-12 | first=Dwight | last=Garner}}</ref>
