There is not much difference between the brains of Neanderthals and the brains of modern humans. At least we believe that. Because it is true that today we have not been able to fully reconstruct the form, function or organization of the cortical layers of the Neanderthal brain; but if we examine the fossils closely, we realize that we are both very close and very far away. What exactly is it that makes us human, that brings us here?

Diving into the genome to understand history. The same question was asked by Svante Pääbo and Wieland Huttner, two scientists of great prestige in their fields. First, he was a pioneer in researching and sequencing the genomes of human ancestors (and especially Neanderthals); the latter was also a pioneer, but in studies of the development of the embryonic brain and its unique aspects in humans. Together they had an idea that could turn the question around.

And while we don’t have access to living tissues of Neanderthals to study them, we do have the genome. Studying this, the team of two researchers realized that modern humans differed from apes and Neanderthals by a single amino acid change: A single amino acid, called TKTL1, is abundant in the embryonic human cerebral cortex, particularly in the frontal lobe. .

Could the key be there? Could such a simple change lead to so much? To examine the effect of this difference in the development of the embryonic cerebral cortex, the authors overexpressed modern or ancient TKTL1 in mouse (small, smooth cortex) and ferret (large, folded cortex) embryos. In both cases, modern TKTL1 has increased the abundance of bRG cells, a very specific type of cortical progenitor cell capable of generating cortical neurons, not the old one,” explained Víctor Borrell Franco, researcher at SMC CSIC at the Institute of Neurosciences (Alicante).

In the ferret, in fact, the changes changed the size and pattern of the cortical folds very dramatically. This is particularly striking because, as we believe (as in other monkeys), the structure of the cortical folds is what most distinguishes us from them. Also, the researchers proposed a mechanism of action that would allow such a small change to have such a significant impact.

A small change with big results. Therefore, the results of this study suggest that this small change may be behind the characteristic enlargement of the frontal lobe in modern humans. It is possible that TKTL1 itself affects the amount and pattern of folding of the cortex (as Borrell Franco reminds us, it is “essential in cognitive performance”), but more research is needed to reach this conclusion.

Is it the genetic accident that makes us human? That’s the researchers’ plan. However, many of his colleagues are skeptical. Emiliano Bruner of the National Research Center for Human Evolution, for example, explains that “the brain is an incredibly complex organ, and the cognitive process is much more complex because it also encompasses all kinds of environmental factors. It seems very reductionist to me. It’s just a single gene and a cell culture or achieve significant results as a result of the expression experiment.

Regardless, we’ll find out soon because this genetic adventure has only just begun.

Image | jolly Crawford