Why was the evolution of a large brain important to human evolution?
This is an absolutely huge question! It would help if you could let us know a little about the aim of your work, or at least the subject & level. As a basic guide, the growth of the human brain allowed for language acquisition, problem solving, tool usage, social communication and hierarchy maintenance, logical reasoning, forward planning... all of the higher cognitive functions we have that apes and other animals don’t have. Think of the reptilian brain, mammalian brain and then the neocortex. Each stage brings with it more complexity. Then look at the convolutions of the human neocortex versus the great apes. Where we needed more surface area, more convolutions were needed. The activation of specific areas (see fMRI research for examples) show functions that have arisen as a result of our bigger brains, in comparison to little or no activation in those areas in other apes. I hope this helps you to start forming an answer.
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