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The human brain is six times as large as that of other mammals of a similar size. Why are we so brainy? So far, the favoured hypothesis was that brain growth was driven by social pressures, such as the need to communicate, cooperate, and compete with others. But recent research suggests that the key factors may instead be ecological; those challenges that come from the environment around us, such as finding food. Mauricio González-Forero and Andy Gardner of the University of St Andrews have developed a mathematical model of human brain evolution. By using this model, the pair aim to accurately predict the consequences of various proposed theories, which can then be compared with the facts to work out which theory is the most likely. The model is based on the assumption that brains require a lot of energy, but that a bigger brain will help an animal to get more energy. It then predicts that human brains evolved when the challenges faced were 60% ecological, 30% cooperation-based, and 10% related to inter-group competition. This is partly because, whilst environmental challenges do not change with brain size, certain social challenges do change. For example, it might be harder to get ahead if those around you are getting smarter and are capable of lying and cheating. Thus, they argue, social challenges may sometimes favour a smaller brain.

Ecological challenges on the other hand are predicted to favour bigger brains—but only when an increase in brain power delivers a relatively big reward. For example, once an animal has evolved the brainpower to open an oyster, further brain growth may not help it to eat any more oysters, so there would be no evolutionary pressure for it to grow a larger brain. However, if subsequent improvements in the design of spears helps to catch more and more fish, this can be an evolutionary incentive for continuous brain growth. This phenomenon is amplified in an advanced culture where cooperation and communication leads to individuals sharing skills which help them tackle environmental pressures. Therefore, the same environmental pressure (such as the need to find food) may result in brain growth in some species, but not in others. However, other scientists, such as David Geary of the University of Missouri, though finding this research interesting, are wary of drawing conclusions too soon and still favour a mainly social explanation for human brain growth. 

Students applying for Biology, Natural Sciences, or Anthropology may be interested in learning about the conflicting hypotheses surrounding various elements of our human evolution. They should consider how these hypotheses can be tested, and evaluate which option they find most convincing.

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