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‘sÂ 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. [â€¦]
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.