Human evolution: Neanderthal Y chromosome (Introduction)

by David Turell , Friday, September 25, 2020, 12:49 (1518 days ago) @ David Turell

Somewhat of mystery:

https://www.sciencemag.org/news/2020/09/how-neanderthals-lost-their-y-chromosome?utm_ca...

"Neanderthals have long been seen as uber-masculine hunks, at least compared with their lightweight human cousins, with whom they competed for food, territory, and mates. But a new study finds Homo sapiens men essentially emasculated their brawny brethren when they mated with Neanderthal women more than 100,000 years ago. Those unions caused the modern Y chromosomes to sweep through future generations of Neanderthal boys, eventually replacing the Neanderthal Y.

"The new finding may solve the decade-old mystery of why researchers have been unable to find a Neanderthal Y chromosome. Part of the problem was the dearth of DNA from men: Of the dozen Neanderthals whose DNA has been sequenced so far, most is from women, as the DNA in male Neanderthal fossils happened to be poorly preserved or contaminated with bacteria.

***

"The best scenario to explain the Y pattern is that early modern human men mated with Neanderthal women more than 100,000 but less than 370,000 years ago, according to the team’s computational models. Their sons would have carried the modern human Y chromosome, which is paternally inherited. The modern Y then rapidly spread through their offspring to the small populations of Neanderthals in Europe and Asia, replacing the Neanderthal Y, the researchers report today in Science. Interestingly, the modern human mates were not ancestors to today’s H. sapiens—but were likely part of a population that migrated early out of Africa and then went extinct. Traces of Neanderthal DNA in living humans were inherited from a separate mixing event between 50,000 and 70,000 years ago.

"Researchers aren’t sure exactly why the replacement happened. Natural selection may have favored the H. sapiens Y chromosome, because Neanderthals had more deleterious mutations across their genomes, Kelso says. Neanderthals had smaller populations than moderns, and small populations tend to accumulate deleterious mutations, especially on the X and Y sex chromosomes. Modern humans, with their bigger, more genetically diverse ancestral populations, may have had a genetic advantage. Another possibility is that once Neanderthals had inherited a modern human mtDNA, their cells might have favored interaction with the modern human Y, says computational biologist Adam Siepel of Cold Spring Harbor Laboratory, who was not part of the study."

Comment: Still sorting out our evolution. Note the bold about deleterious mutations in small populations an opposite point to small populations creating punctuated equilibrium. Lots of Darwin theory is just supposition.