A new study by researchers at Durham University in the UK looks at the evolution of the brain of primates relative to other monkeys. The lead researcher suggests that the prior thinking about the evolution of apes’ brains may have been wrong. That is, scientists were focusing too much on the neocortex, which is the folded outer part of the brain which makes human brains particularly distinct. The researchers found that early monkeys’ brains may have experienced simultaneous growth in the neocortex and the cerebellum. But this may have changed 25 million years ago, when apes suddenly experienced accelerated growth in the cerebellum compared to growth in the neocortex. This could well have propelled higher IQ in apes relative to other species of primates.
There are several theories as to why this may be the case. Some scientists have posited that the sudden acquisition of technical abilities have have triggered the supernormal growth of the cerebellum. The cerebellum of an ape contains significantly more neurons than the cerebellum of a monkey, even when the monkey’s brain is scaled to match the size of an ape. In fact, it is reported that apes have on average 16 billion more neurons than monkeys. This figure equates to the entire amount of neurons contained in the cerebellum of a human brain.
So higher IQ in apes may have been the result of acquiring new technical skills such as swinging from trees, and eventually the ability to even learn how to use tools in hunter / gathering activities.
Higher IQ in apes: cerebellum or neocortex?
But the neocortex and the cerebellum work together. As the brain’s cerebellum might have expended as a result of acquiring new activities, the neocortex would have needed to expand and play catch up in order to be able to synthesize information, reactions and reflexes.
There are potentially parallels to be drawn from humans. Higher IQ in apes, acquired out of developing new skills, is not dissimilar to higher IQs in humans (and their offspring) who have higher levels of education and more intellectually challenging professional jobs. In humans, it is estimated that 60% of IQ is heritable, while the rest is environmental. Heritability is a key trait of IQ, and it would be interesting to understand whether humans have also experienced continued growth in their cerebellums since the industrial revolution, or whether the growth in the neocortex and cerebellum occurred in tandem.
But whether cerebellum or neocortex led, higher IQ in apes seems to have been the result of acquiring new skills (a form of education).
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