New Scientist tracks the evolution of our brain from its origin in ancient seas to its dramatic expansion in one ape – and asks why it is now shrinking.

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. Simon Laughlin at the University of Cambridge compares the brain to a sports car, which burns ever more fuel the faster it goes.

One way to speed up our brain, for instance, would be to evolve neurons that can fire more times per second.

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