Friday, 24 April 2020

Human Evolution News - Icelanders' Neanderthal Ancestors


Models of male and female Neanderthals in the Neanderthal Museum, Mettmann, Germany.
Photo: UNiesert / Frank Vincentz (assembly: Abuk Sabuk) /
Wikimedia Commons / CC-BY-SA-3.0 / GFDL
Icelandic DNA puzzle gives new knowledge about Neanderthals

A new study into the Neanderthal component in the genomes of modern Icelanders has raised a couple of interesting questions:
  1. Did anatomically modern humans breed with Neanderthals and Denisovans when they first entered Eurasia from Africa?
  2. Or had Neanderthals and Denisovans interbred before hand so denisovan DNA was widespread in the Neanderthal population moderns interbred with.

This question is raised by the finding from examining the genomes of 27,566 Icelanders whose genome is in the deCODE database.

The finding is presented in a paper published in Nature last Wednesday for which the copyright holder, Springer, require a ridiculously high fee for publishing the abstract here. It is the work of an international team using a technique developed by Laurits Skov, from the Bioinformatics Research Centre (BiRC) at Aarhus University. It can be read about in the Aarhus University press release.

What was surprising in this study was that Denisovan DNA was found scattered throughout the Icelanders' genomes along with that of Neanderthals. Previously, Denisovan DNA had only been found in the genomes of Australian Aborigines, East Asians and people in Papua New Guinea. Finding it in Icelanders, whose ancestors came from Western Europe, was unexpected and can only be explained by one or both of the above possibilities.

The analysis also shows that the Neanderthal women living 100,000 – 500,000 years ago on average became mothers at a later age than the contemporary Homo-Sapien women living in Africa. On the other hand, Neanderthal men fathered at a younger age than their Homo-Sapien cousins in Africa.

The team also found that the mothers of anatomically modern humans who interbred with Neanderthals were older than mothers from Homo sapiens in Africa and the Neanderthal fathers were younger than H. sapiens fathers in Africa. There are several possible explanations for this - possibly Neanderthal females were slower to reach maturity or slower to reach the menopause, or possibly that sex was not always consensual as is often the case with an invading people.

We have previously thought that many of the Neanderthal variants previously been found in modern human DNA were associated with an increased risk of diseases. However, our study shows that the human gene variants located directly beside the Neanderthal genes are better explanations for the risk. We have also found something that can only be explained by Neanderthal genes, but this doesn’t mean that much.

Mikkel Heide Schierup, co-author
One significant finding was that the Neanderthal DNA was not strongly associated with beneficial genes. Previous studies had suggested that incoming H. sapiens acquired beneficial genes from the Neanderthals who had been evolving them for hundreds of thousands of years in the harsh northern environment, but this study suggests otherwise.

What we have in this study is further confirmation that for much of our history, humans co-existed with other hominins with whom they could interbreed, albeit with varying degrees of success, behaving much like some ring species today and illustrating evolution in progress as different populations evolved and diverged with incomplete speciation across a large geographical area and varying environments.

For our unfortunate Bible literalist, creationist friends, the problem is that not only was there never a founding couple, there was not even a founding species!

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