Neanderthals genome contained harmful mutations making them 40% less reproductively fit than modern humans: Research

According to a new genetic research, Neanderthals genome included dangerous mutations, making them nearly 40% less reproductively fit in comparison to present day humans; and non-Africans received some of the genetic burden when they interbred with the extinct cousins.

The research findings suggested that such harmful gene variants have been decreasing the fitness of few populations existing today. The research has also been linked to the management of endangered species.

Earlier researches of DNA extracted from Neanderthal remnants disclosed that the Eurasian hominids were quite more inbred and less genetically diverse in comparison to the present day humans.

The Neanderthal population size stayed small for thousands of years and interbreeding apparently became common.

Thereafter, around 50,000-100,000 years back, groups of anatomically modern humans shifted from Africa to the homelands of their far away Neanderthal cousins. Both the groups interbred, and mingled their formerly distinct genomes.

Though today a little fraction of the genome of non-African populations is Neanderthal, they have uneven genetic contribution. In the human genome, Neanderthal sequences are concentrated in many specific parts, but is absent in other areas.

Study leader Kelley Harris, said, “Whenever geneticists find a non-random arrangement like that, we look for the evolutionary forces that caused it”.

Harris along with her colleague theorized that the questioned force was natural selection. According to them, in small populations, such as that of the Neanderthals, natural selection was less effective and chance had more influence.

As a result of this, weakly harmful mutations persisted, instead of being weeded out over the generations. But when these mutations were again introduced into a larger population, like modern humans, they would come in touch with the surveillance of natural selection and ultimately will get lost.

A report published in New Kerala revealed, “The results suggest that these harmful gene variants continue to reduce the fitness of some populations today. The study also has implications for management of endangered species.”

Previous studies of DNA extracted from Neanderthal remains revealed that these Eurasian hominids were much more inbred and less genetically diverse than modern humans. For thousands of years, the Neanderthal population size remained small, and mating among close relatives seems to have been common.

Then, 50,000-100,000 years ago, groups of anatomically modern humans left Africa and moved to the homelands of their distant Neanderthal cousins. The two groups interbred, mingling their previously distinct genomes.

“The two groups interbred, mingling their previously distinct genomes. But though a small fraction of the genome of non-African populations today is Neanderthal, their genetic contribution is uneven. Neanderthal sequences are concentrated in certain parts of the human genome, but missing from other regions,” according to a news report published by Sci-News.

This allows weakly harmful mutations to persist, rather than being weeded out over the generations. But once such mutations are introduced back into a larger population, such as modern humans, they would be exposed to the surveillance of natural selection and eventually lost.

To quantify this effect, the scientists used computer programs to simulate mutation accumulation during Neanderthal evolution and to estimate how humans were affected by the influx of Neanderthal genetic variants.

“To assess the fitness effects of Neanderthal introgression on a genome-wide scale, we used forward-time simulations incorporating linkage, exome architecture, and population size changes to model the flux of deleterious mutations across hominin species boundaries,” the scientists said.

According to a story published on the topic by Vice, “Nearly 100,000 years ago, a resolute group of Homo sapiens left Africa for the unknown. The impetus and timing of their exodus into the Arabian Peninsula remains controversial, but there’s one thing paleoanthropologists know for sure: We weren’t the only human species to have colonized Eurasia.”

A new study published in the journal GENETICS proposes that harmful mutations in Neanderthals’ genome not only made the hominin 40 percent less evolutionarily fit than modern humans, but also endowed some of us with that same genetic burden.

“Neanderthals are fascinating to geneticists because they provide an opportunity to study what happens when two groups of humans evolve independently for a long time—and then come back together,” said lead author Kelley Harris in a statement. “Our results suggest that inheriting Neanderthal DNA came at a cost.”

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