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The improvement in the human brain could be the result of doubling a gene
Last reviewed: 30.06.2025
The increase (and improvement) of the human brain over the course of evolution may have resulted from the duplication of a gene that helps brain cells move from place to place.
At least twice in the last three million years, the SRGAP2 gene has been duplicated, says Megan Dennis of Washington State University, who and colleagues have shown that extra copies of the gene may be responsible for the thickening of the cerebral cortex.
The same team had previously found that SRGAP2 is one of 23 genes that only has a second copy in one primate species - humans. Ms Dennis concluded that an ancient form of the gene, located on chromosome 1, was partially duplicated on the same chromosome about 3.4 million years ago. This partial copy is responsible for producing a shortened version of the SRGAP2 protein.
Then, about 2.4 million years ago, a copy of that partial copy was made. It went into the short arm of chromosome 1.
But the extra copies don't necessarily mean the gene played an important role in evolution. So the researchers studied more than 150 people and found that the 3.4 million-year-old duplicate was missing from some, while the younger version was firmly entrenched in the human genome (in other words, everyone has it). A couple of million years and counting is a relatively short time for duplicate genes to become fixed, Ms. Dennis says. Such rapid assimilation could indicate the gene's great importance in evolution.
With the help of colleagues from other universities, the specialists discovered that a shortened version of the SRGAP2 protein prevents brain cells from creating filopodia, which they use to move. The reduction in the number of these pseudopodia prevented the cells from actively migrating and may have led to the appearance of new layers of the cerebral cortex.
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