Scientists may have found a major transformation between the brains of humans and Neanderthals

Scientists conducting experiments on mice have found evidence that key parts of the modern human brain take longer to develop than those of our long-extinct cousin, Neanderthals.

Like the hare and the tortoise, slow and steady is the winner here. The extra time is caused by protein differences that also seem to reduce chromosomal errors, ultimately resulting in a healthier and stronger population.

The study results suggest that this step in the development of the neocortex (the outer, wrinkled layer responsible for higher-order thinking) plays a role in protecting us from disease, a feature that Neanderthals seem to be missing.

In recent years, advances in genetics have allowed scientists to sequence DNA extracted from ancient remains, revealing detailed information about how the Neanderthal genome compares and contrasts with ours.

We know, for example, about 100 amino acids — the compounds that make up proteins — that changed when modern humans diverged from the branch that gave rise to Neanderthals and another close cousin, Denisovans.

Amino acid substitution could have significant effects, but it was not clear what functions these substitutions changed among humans and Neanderthals.

Six of the identified substitutions are located in proteins already known to play a role in chromosomal distribution during cell division. So a team of researchers led by geneticist Felipe Mora-Bermudes of the Max Planck Institute for Molecular Cell Biology and Genetics in Germany conducted experiments to see if they could determine what role these amino acid changes might play in the development of the neocortex.

The natural subject was lab mice, which happened to share with Neanderthals (and apes) the same six amino acids within related proteins. Using CRISPR-Cas9, the researchers replaced those amino acids with those found in modern humans.

They also took the search in the opposite direction. They have grown human brain organoids from embryonic stem cells – clumps of brain tissue that are neither living nor conscious – and replaced modern human amino acids with Neanderthal/mouse/ape variants.

The results were amazing and wonderful.

Mora-Bermúdez explained that three modern human amino acids in two proteins cause a longer anaphase, a phase in which chromosomes are prepared for cell division, and this leads to fewer errors when distributing daughter chromosomes. neural stem cell cells, just as in modern humans.”

In addition, metaphase in Neanderthal human organelles was shorter, resulting in twice the number of chromosome segregation errors compared to control organelles. This indicates that three modern human amino acid substitutions are responsible for fewer chromosomal distribution errors compared to Neanderthals.

Since errors in the number of chromosomes, known as polysomies, can lead to serious disorders, as well as cancers such as leukemia and cancer, the results suggest that the change has been in favor of modern humans. They also suggest that brain function in Neanderthals may have been affected by chromosomal disorders at a higher rate than we see in modern humans.

“Current data indicate that the potential for such adverse effects of chromosomal mis-segregation may be lower in modern humans than in Neanderthals, Denisovans and apes,” the researchers wrote in their paper.

“More work is needed to address the importance of these effects to the hallmarks of modern humans.”

The search was published in Sciences.

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