May 31, 2018
Clive Cookson, Science Editor | Financial Times 

Research teams discover family of genes called NOTCH2NL that shaped intelligence

Three international research teams have solved a genetic mystery of evolution: how human brains got to be so big.

Two groups of scientists have discovered a family of genes called NOTCH2NL, found only in humans, that played a critical role in the evolutionary expansion that made human intelligence and behaviour possible. Their findings appear in the journal Cell.

A third team discovered how the brain maintained a healthy balance between different types of neuron as it more than doubled in size. Adult brains grew almost threefold between 3m years ago, when our Australopithecine ancestors were alive, and 200,000 years ago, when Homo sapiens (modern humans) emerged in Africa.

The effect of the NOTCH2NL genes is to increase the production of neural stem cells, while delaying the stem cells’ development into mature neurons. Slowing down the growth process gives more time for neurons to build up in the neocortex, the brain’s outer layer that hosts higher cognitive functions such as language and reasoning.

This process fits the pattern of delayed maturation in humans in comparison with apes and other animals, said Professor David Haussler of the University of California, Santa Cruz, who led one of the research teams. “Now we are seeing molecular mechanisms supporting this evolutionary trend even at a very early stage of brain development,” he said.

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