The Evolutionary History of the Brain

The devel­op­ment of the human brain is intric­ately linked with almost every moment of our evol­u­tion from sea-dwell­ing anim­als to advanced, social prim­ates. That is the the over­whelm­ing theme from New Sci­ent­ist’s brief his­tory of the brain.

The enga­ging art­icle ends with a look at the con­tin­ued evol­u­tion of the human brain (“the visu­al cor­tex has grown lar­ger in people who migrated from Africa to north­ern lat­it­udes, per­haps to help make up for the dim­mer light”), and this on why our brains have stopped grow­ing:

So why did­n’t our brains get ever big­ger? It may be because we reached a point at which the advant­ages of big­ger brains star­ted to be out­weighed by the dangers of giv­ing birth to chil­dren with big heads. Or it might have been a case of dimin­ish­ing returns.

Our brains are pretty hungry, burn­ing 20 per cent of our food at a rate of about 15 watts, and any fur­ther improve­ments would be increas­ingly demand­ing. […]

One way to speed up our brain, for instance, would be to evolve neur­ons that can fire more times per second. But to sup­port a 10-fold increase in the “clock speed” of our neur­ons, our brain would need to burn energy at the same rate as Usain Bolt’s legs dur­ing a 100-metre sprint. The 10,000-calorie-a-day diet of Olympic swim­mer Michael Phelps would pale in com­par­is­on.

Not only did the growth in the size of our brains cease around 200,000 years ago, in the past 10,000 to 15,000 years the aver­age size of the human brain com­pared with our body has shrunk by 3 or 4 per cent. Some see this as no cause for con­cern. Size, after all, isn’t everything, and it’s per­fectly pos­sible that the brain has simply evolved to make bet­ter use of less grey and white mat­ter. That would seem to fit with some genet­ic stud­ies, which sug­gest that our brain’s wir­ing is more effi­cient now than it was in the past.

Oth­ers, how­ever, think this shrink­age is a sign of a slight decline in our gen­er­al men­tal abil­it­ies.

via @mocost

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