Scientists May Have Found a Key Shift Between The Brains of Humans And Neanderthals

Key brain regions of the contemporary human take longer to mature than those of our long-extinct cousin, the Neanderthal, according to research on mice by scientists.

In this case, slow and steady wins out, much like with the hare and the tortoise. The additional time is brought on by protein variations that also seem to lessen chromosomal mistakes, ultimately leading to a population that is healthier and more robust.

The findings of the study suggest that this stage in human neocortex's development—the wrinkled outer layer responsible for higher order thinking—plays a role in defending us against sickness, a quality Neanderthals appear to lack.

Recent developments in genetics have made it possible for researchers to sequence DNA taken from prehistoric bones, providing extensive knowledge about how the genome of the Neanderthal differs from our own.

For instance, we are aware of around 100 amino acids, which are the building blocks of proteins, changing when modern humans split off from the branch that gave rise to Neanderthals and another near relative, the Denisovans.

It was unknown what functions altered between humans and Neanderthals as a result of amino acid substitutions, albeit these changes can have a big impact.

Six of the discovered alterations are found in proteins that are previously known to affect how chromosomes are distributed during cell division. As a result, experiments were carried out by a group of researchers under the direction of geneticist Felipe Mora-Bermdez of the Max Planck Institute of Molecular Cell Biology and Genetics in Germany to try and ascertain the potential significance of these amino acid changes for neocortex development.

Laboratory mice were used as the natural subject because they share those same six amino acids with Neanderthals (and apes) in the necessary proteins. The researchers replaced such amino acids with those found in contemporary humans using CRISPR Cas-9.

Additionally, they conducted the research in the reverse manner. Organoids of human brains were created from embryonic stem cells, replacing current human amino acids with Neanderthal/mouse/ape versions. These organoids are lumps of brain tissue that are not living or sentient.

The outcomes were astounding and captivating.

The three modern human amino acids in two of the proteins, according to Mora-Bermdez, "cause a longer metaphase, a phase where 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 like in modern humans.

In addition, the Neanderthalized human organoids' metaphase was briefer, which led to twice as many chromosomal separation mistakes as in the control organoids. This shows that, compared to Neanderthals, three amino acid alterations in modern humans account for less chromosomal distribution mistakes.

The findings imply that the alteration was advantageous for contemporary humans since mistakes in the number of chromosomes, known as polysomies, may cause significant illnesses as well as malignancies like leukemia and carcinoma. They also show that chromosomal abnormalities may have affected Neanderthal brain function more frequently than they do in contemporary people.

The researchers concluded in their report that contemporary humans may be less likely than Neanderthals, Denisovans, and primates to experience any negative impacts of chromosomal mis-segregation.

To address the significance of these impacts for qualities typical of modern people, more research is required.

The research has been published in Science.