New study explains how human brains evolved differently from Neanderthals

Experiments on mice have helped scientists identify some key differences in brain development in modern humans and our closest relative, Neanderthals. After our ancestors split from the Neanderthals, about a hundred amino acids underwent changes and spread to almost all modern humans. The reason behind this change had puzzled scientists all along. However, six of the amino acid changes were found to have occurred in the three proteins that play a role in the distribution of chromosomes or the carriers of genetic material to the daughter cells during cell division in our body.

To dig deeper into the cause, researchers at the Max Planck Institute for Molecular Cell Biology and Genetics in Germany and the Max Planck Institute for Evolutionary Anthropology introduced modern human variants into mice. The six amino acid positions are the same in both mice and Neanderthals.

Therefore, the mice gave the scientists a model to study the development of the human brain. “We found that three modern human amino acids in two of the proteins cause a longer metaphase, a phase in which chromosomes are prepared for cell division, and this results in fewer errors when the chromosomes are distributed to the daughter cells of the neural stem cells, just as with the modern humans,” explains geneticist Felipe Mora-Bermúdez, the lead author of the study published in Scientific progress.

Exploring whether the sequence of amino acids in Neanderthals had the opposite effect, researchers introduced ancestral amino acids into brain organoids. These are small organ-like structures that can be grown in the laboratory with human stem cells in cell culture dishes. Brain organoids mimic aspects of early human brain development.

In this case, the team noted that the metaphase was shorter, while the number of errors in the chromosome distribution was also greater. Mora-Bermúdez described that the amino acids in modern humans were responsible for fewer errors in the chromosome distribution. “Having errors in the number of chromosomes is usually not a good idea for cells, as seen in conditions such as trisomies and cancer,” Mora-Bermudez said.

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