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Why is Neanderthal Genetic material Found in only Small amount in Genomes of Modern Humans?

The scientists estimated that these gene variations were able to persist in Neanderthals because Neanderthals had a much smaller population size than humans

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FILE - A model of an adult Neanderthal male head and shoulders by artist John Gurche on display in the Hall of Human Origins in the Smithsonian Museum of Natural History in Washington, D.C. VOA
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New York, November 9, 2016: Neanderthal genetic material is found in only small amount in the genomes of modern humans because, after inter-breeding, natural selection removed large numbers of weakly deleterious Neanderthal gene variants, says a study.

Humans and Neanderthals inter-bred tens of thousands of years ago, but today, Neanderthal DNA makes up only one to four per cent of the genomes of modern non-African people.

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“For a while now we have known that humans and Neanderthals hybridised. Many Europeans and Asians – along with other non-African populations – are the descendants of those hybrids,” said Ivan Juric from the University of California, Davis in the US.

“Previous work has also shown that, following hybridisation, many Neanderthal gene variants were lost from the modern human population due to selection. We wanted to better understand the causes of this loss,” Juric noted.

To understand how modern humans lost their Neanderthal genetic material and how humans and Neanderthals remained distinct, the researchers developed a novel method for estimating the average strength of natural selection against Neanderthal genetic material.

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They found that natural selection removed many Neanderthal alleles from the genome that might have had mildly negative effects.

The scientists estimated that these gene variations were able to persist in Neanderthals because Neanderthals had a much smaller population size than humans.

Once transferred into the human genome, however, these alleles became subject to natural selection, which was more effective in the larger human populations and has removed these gene variants over time.

“Our results are compatible with a scenario where the Neanderthal genome accumulated many weakly deleterious variants, because selection was not effective in the small Neanderthal populations. Those variants entered the human population after hybridisation,” Juric said.

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“Once in the larger human population, those deleterious variants were slowly purged by natural selection,” Juric noted.

These findings, published in the journal PLOS Genetics, shed new light on the role of population size on losing or maintaining Neanderthal ancestry in humans. (IANS)

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Neanderthals And Sapiens Both Faced Risks

But the new study is not the final word on Neanderthal trauma

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Neanderthal
A 3D-printed model of a Neanderthal man stands at the stand of FIT AG during a media presentation at the international fairs FabCon 3.D and Rapid.Tech, Germany. VOA

Life as a Neanderthal was no picnic, but a new analysis says it was no more dangerous than what our own species faced in ancient times.

That challenges what the authors call the prevailing view of our evolutionary cousins, that they lived risky, stressful lives. Some studies have suggested they had high injury rates, which have been blamed on things like social violence, attacks by carnivores, a hunting style that required getting close to large prey, and the hazards of extensive travel in environments full of snow and ice.

While it’s true that their lives were probably riskier than those of people in today’s industrial societies, the vastly different living conditions of those two groups mean comparing them isn’t really appropriate, said Katerina Harvati of the University of Tuebingen in Germany.

Neanderthal model
Neanderthal model. Reconstruction of a Neanderthal (Homo neanderthalensis) based on the La Chapelle-aux-Saints fossils. Neanderthals inhabited Europe and western Asia between 230,000 and 29,000 years ago. They did not use complex tools but had mastery of fire and built shelters. It is thought that they had language and a complex social structure, living in small family groups and hunting for food. It is not known why Neanderthals became extinct, but one theory is that they were outcompeted by modern humans (Homo sapiens). Reconstruction by Elisabeth Daynes of the Daynes Studio, Paris, France.

A better question is whether Neanderthals faced more danger than our species did when we shared similar environments and comparable lifestyles of mobile hunter-gatherers, she and study co-authors say in a paper released Wednesday by the journal Nature.

To study that, they focused on skull injuries. They reviewed prior studies of fossils from western Eurasia that ranged from about 80,000 to 20,000 years old. In all they assessed data on 295 skull samples from 114 individual Neanderthals, and 541 skull samples from 90 individuals of our own species, Homo sapiens.

Injury rates turned out to be about the same in both species.

Also Read: Neanderthal Genes Helped Early Humans Beings to Fight Flu, Hepatits

That questions the idea that the behavior of Neanderthals created particularly high levels of danger, Marta Mirazon Lahr of Cambridge University wrote in an accompanying commentary.

But the new study is not the final word on Neanderthal trauma, she wrote. It didn’t include injuries other than to the skull. And scientists still have plenty of work to do in seeking the likely cause of injuries and evidence of care for the injured, which could give insights into the behavior of both Neanderthals and ancient members of our species, she wrote. (VOA)