[1] 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?

[4] 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

[7] 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

[10] 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

[13] 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

[16] 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.

[19] 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

[22] 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

[25] lengthening of the legs and flattening of the feet, which

facilitated upright walking.

Internet: (adapted)

Based on the text, it can be deduced that

living on the ground brought about new progress to human beings besides all the progress they had already achieved.