The specific gene is not present in chimps, and allowed for a dramatic rise in the number of neurons in a crucial brain region. The gene has only been discovered in modern humans, Neanderthals and Denisovans, another branch of extinct humans, writes Tia Ghose for Live Science.
Human brain: Increasing number of neurons
Scientists now believe that the gene allows the neocortex to contain a greater number of neurons, laying the foundations for the expansion of the human brain relative to chimpanzees.
“It is so cool that one tiny gene alone may suffice to affect the phenotype of the stem cells, which contributed the most to the expansion of the neocortex,” claimed Marta Florio, lead author of the study and a doctoral candidate in molecular and cellular biology and genetics at the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden, Germany.
Florio and her team discovered that the gene, known as ARHGAP11B, is highly activated in human neural progenitor cells, but is found at all in mouse cells. The section of DNA is only 804 genetic bases long, making it a tiny but crucial fragment.
Laboratory tests on mice
It was once part of a longer gene but was somehow duplicated and later put into the human genome. In order to test their theory the scientists inserted the DNA snippet into the brains of mice, and sure enough those mice with the additional DNA seemingly developed larger neocortex regions.
The fact that Neanderthals and Denisovans also had this gene, and chimpanzees do not, would seem to suggest that the gene emerged soon after we separated from chimpanzees.
Florio was quick to acknowledge that the gene is probably not the only genetic differentiation which makes the human brain special, and predicts that there are probably many more that we still have not discovered.
The study was published on Thursday in the journal Science.