Three or four million years ago, the ancestors of humans developed genes that allowed the human cerebral cortex to reach its present size.
During embryonic development, a group of genes allows the neocortex to reach the dimensions that characterize the human being. This layer is the outermost of the brain; it is the last to have developed during evolution. The structure of the neocortex occupies about 80% of the surface of the brain. This discovery is the result of 5 years of research. It was published in the journal Cell on May 31, 2018.
These genes are three in number. They are very similar to each other because they all come from the duplication of the same gene, NOTCH2NL, which is on chromosome 1.
The Californian team at the origin of the study first tried to understand how these genes developed during evolution. To do this, the researchers compared the DNA of different species of primates. It seems that in the ancestor common to humans, chimpanzees and gorillas, part of the NOTCH2NL gene has duplicated itself, ie a copy of this fragment has been inserted into the nearby DNA of the original gene.
In large apes, this DNA fragment does not allow the production of a functional protein. On the other hand, in humans, successive mutations have caused the duplicated fragment to produce an active protein inside the cell. This gene was then duplicated to give rise to two other functional copies.
According to the researchers, these events occurred three to four million years ago, a period that corresponds to the development of the human cerebral cortex.