Humans are the only species that cook their food and Wrangham argues [[Homo erectus]] emerged about two million years 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 via a smaller, more efficient digestive tract which freed up energy to enable larger 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=http://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 |publisher=New York Times |date=2009-05-26 |accessdate=2009-06-12 | first=Dwight | last=Garner}}</ref>
