SCIENCE: The limits of intelligence

The human brain has virtually reached its evolutionary limits, say scientists. An analysis of the delicate balance between the billions of neurons in our skulls, and the need to supply the axons (which connect them like cables) with blood and fatty insulation shows we can only improve our data processing ability by 20 per cent at most.

The BT research, published in New Scientist, found that to expand our thinking ability, the 100 billion neurons in the brain would have to be larger, so they could pass signals more quickly. But that would in turn demand a greater blood supply - which, given the constricted size of the brain cavity, could only be achieved by limiting the growth of the neurons.

A larger skull might allow both more neurons and a bigger blood supply, but transmission of data would be slower.