We have spent years searching for what made us human. We finally found the answer

 We have spent years searching for what made us human.  We finally found the answer
we have spent years searching for what made us human.

There are not so many differences between the brains of Neanderthals and those of modern humans. At least, that is what we believe. Because it is true that, today, we cannot exactly reconstruct the form, function or organization of the cortical layers of the Neanderthal brain; but if we closely examine the fossils we realize that we are both very close and very far. What exactly is it that made us human, that brought us here?

Diving into the genome to understand history. That same question was asked by Svante Pääbo and Wieland Huttner, two scientists of great prestige in their respective fields. The first was a pioneer in the study and sequencing of human ancestral genomes (and, very especially, in the Neanderthals); the second was also a pioneer, but in the study of the development of the embryonic brain and its unique aspects in the human being. Together they had an idea that could turn the question around.

And it is that, although we do not have access to the living tissues of Neanderthals to examine them, we do have the genome. Examining it, the team of these two researchers realized that modern humans differ from apes and Neanderthals by a single amino acid change: a single amino acid in the so-called TKTL1, abundant in the embryonic human cerebral cortex, especially, in the frontal lobe.

Could the key be there? Can such a simple change lead to so much? “To study the effect of this difference in the development of the embryonic cerebral cortex, the authors overexpressed modern or ancient TKTL1 in mouse (with a small, smooth cortex) and ferret (with a large, folded cortex) embryos. They verified that, in both cases, the modern TKTL1, but not the old one, increased the abundance of bRG cells, a very special type of cortical progenitor cell with a great capacity to produce cortical neurons”, explained Víctor Borrell Franco, a researcher at the SMC CSIC at the Institute of Neurosciences (Alicante).

In the ferret, in fact, the changes very strikingly modified the size and pattern of the cortical folds. This is especially remarkable because, as we believe, (as it happens with other apes) the structure of the cortical folds is what separates us from them the most. Furthermore, the researchers have proposed a mechanism of action that would make such a small change have such a significant impact.

A small change with huge results. Thus, the results of this study suggest that this small change could be behind the characteristic expansion of the frontal lobe in modern humans. It is possible that TKTL1 itself influences the amount and pattern of folding of the cortex (something that, as Borrell Franco reminds us, “is essential in cognitive performance”), but further research is needed to reach this conclusion.

The genetic accident that made us human? That’s what the researchers plan. However, many of his classmates are skeptical of him. For example, Emiliano Bruner of the National Center for Research on Human Evolution said that “the brain is an incredibly complex organ and the cognitive process is much more so, because it also encompasses all kinds of environmental factors. It seems very reductionist to me to reach conclusions as important only as a result of a single gene and a cell culture or expression experiment.

Be that as it may, we will soon know because this genetic adventure has only just begun.

Image | Jolly Crawford

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Brian Adam
Professional Blogger, V logger, traveler and explorer of new horizons.