Neanderthal brain

This article was originally published on July 29, 2022.

Faster isn’t always better, especially when it comes to growing brains—or the pace of development of the human brainFor this question.

When neuron cells divide, they duplicate their own DNA, and molecular ropes drag one copy to each daughter cell. Rushing the process can cause genetic mishaps, whether it’s leaving behind bits of DNA or dragging too many copies into a single cell. According to a a new studyafter diverging from Neanderthals, humans have developed three unique protein mutations that slow cell division during brain development. The steady pace, the authors say, prevents chromosomal errors.

“The discoveries […] suggest that Neanderthal brain function may have been more affected by chromosomal errors than that of modern humans,” says co-author Wieland Hüttner of the Max Planck Institute for Molecular Cell Biology and Genetics in press release.

Neanderthal brain versus human brain growth

Since we split from the Neanderthals, our species has evolved 100 changes from ours amino acids — the building blocks of proteins — that nearly all of us share. Six of these changes affect the mechanisms of cell division. The researchers tested whether these half-dozen mutations slowed the process and prevented errors.

To “humanize” the developing brains of mice, researchers genetically edited them to our version of the genes. Then, to test an ancestral brain, they created a brain-like organoid grown from human cell culture and edited in versions of a Neanderthal gene. If their hypothesis is correct, the mice’s human brains should slow down cell division, while the ancestral, artificial human brain should speed it up.


Read more: How much Neanderthal DNA do humans have?


Both predictions came true. The humanized mice had slower periods of metaphase, the point of division when chromosomes line up in the center of a dividing cell. Normal mice spend 4.6 minutes in metaphase, but humanized mice spend 5.8 minutes in it. Meanwhile, the ancestral genes sped up metaphase in artificial human brains from 9.2 to seven minutes.

The slow pace reduces chromosome separation errors. Cells inherit the incorrect number of chromosomes half as often in the humanized mice compared to the normal ones. They also do so twice as often in ancestral organoids as compared to normal ones.

Harmonious brain function

Incorrect segregation of chromosomes can affect human health, especially during early development. Protoneurons duplicate rapidly and aberrant cells pass their incorrect number of chromosomes to offspring as they proliferate. Down the line, a defective cell can excess or underproduction of proteins, increase the risk of cancer or to open and die.

Therefore, our brains appear to be uniquely protected from erroneous cell division compared to Neanderthal brains. This likely affects the way our neurons develop and organize, the authors say. But in terms of the evolution of the human brain, it remains unknown whether it contributes to the cognitive abilities that make us uniquely human.

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