A cluster of genes found only in humans might have had a key role in the evolution of the unusually bulky Homo sapiens brain.
Frank Jacobs at the University of Amsterdam, David Haussler at the University of California, Santa Cruz, and their colleagues found that members of a gene family called NOTCH2NL are active in humans — but not in apes. The researchers say that the genes arose in their current form roughly 3–4 million years ago, after the human lineage split from the branch that led to the great apes. When the team deleted the genes from human brains growing in lab dishes, the resulting organs were smaller than controls that had normal NOTCH2NL gene activity.
In an independent result, Pierre Vanderhaeghen at the Free University of Brussels and his colleagues found that NOTCH2NL genes are active in progenitor cells that give rise to neurons. The group also found that increasing the activity of one NOTCH2NL gene boosts the number of human stem cells that give rise to neurons in the cortex — and thereby boosts neuron production. This suggests that NOTCH2NL helps to drive the enlargement of the brain during fetal development.