Fascinating research explains why hominin brains grew large.
Two research teams, working independently, have identified the genes apparently responsible for the massive growth in hominin brains. Specifically, the genes involved, NOTCH2NLs, promote the number of neurons in the brain. The genes also appear in chimpanzees and gorillas but, there, they are not active. They did, however, appear in an active sense in Neanderthals and Denisovans. They work as follows. Stem cells in the brain normally divide to generate neurons. At that point, their job is done. NOTCH2NL instead leads to those stem cells dividing into more stem cells. With a greater number of stem cells, the brain is ultimately able to generate a greater number of neurons. Presumably, the skull then adapts to accommodate all the extra neurons. Hence, modern mankind.
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