It has long been a fascinating puzzle to scientists: Why did our apelike ancestors come down from the trees and develop brains many times larger than they actually needed? Many theories have been discussed, most of which revolve around social cooperation; big brains would have helped our ancestors develop language, make better tools, plan hunting strategies, and pass on complex culture to the next generation.

However, some scientists have pointed out that other animals — chimpanzees and crows, for example — are also able to make and use tools, can communicate adequately to suit their purposes, and live within a matrix of socially intricate relationships. Yet these animals do not possess the enormous brains that humans do, relative to their body size. Therefore, some other factor must have led to our runaway brain growth, and in his 2009 book Catching Fire, biological anthropologist Richard Wranghamm makes a case for cooking. It is not currently known when early hominids began controlling fire and the first discovery of fire was likely accidental.

While it is unclear whether these early fires were used to cook food, fire would have kept predators at bay, allowing our vulnerable ancestors to sleep on the ground, rather than in trees as other apes do. This ground living could explain some of the anatomical changes early hominids eventually underwent, such as the loss of climbing efficiency, and the lengthening of the legs and flattening of the feet, which facilitated upright walking.

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