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Mating With Neanderthals And Denisovans Helped Ancient Humans Survive Outside Africa

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A new study has argued that modern humans have accrued many strengths and qualities from the sexual contacts their ancestors had with other forms of humans, like Neanderthals and Denisovans, in the process of exploring the world outside Africa several thousands of years ago.

The study mentions specific genetic traits that came as gifts of cross breeding and now present in varying proportions within the human genomes of different ethnic groups.

It says hybridization with archaic humans gave humans and the descendants enhanced means of survival including efficient adaptation to the environments and skin properties.

Gainful Encounters

Published in Current Biology, the study gives details of the beneficial aspects of interbreeding with Neanderthals and others.

The study identifies 126 different places in the genome where genes of archaic humans are ingrained at a high frequency around the world.

Listing the traits, the study says strong immune systems and skin pigmentation are major gains that came down from the long-extinct hominid relatives.

"Our work shows that hybridization was not just some curious side note to human history, but had important consequences and contributed to our ancestors' ability to adapt to different environments as they dispersed throughout the world," said Joshua Akey, professor of genome Sciences at the University of Washington School of Medicine in Seattle.

Case Of Non-Africans

While unveiling the sequences inherited from archaic ancestors, the study shows non-African individuals have inherited nearly 2 percent of genomes from Neanderthals.

Similarly, the Denisovan genome content in people of Melanesian ancestry is in the range of 2 to 4 percent from ancestors.

Nevertheless, the study is less clear on the influence of DNA sequences on human biology, traits and evolutionary history.

The study examined many samples and included 500 individuals each from Europe, East Asia and South Asia.

Genomes of individuals from Melanesia covering the region of Indonesia, Fiji, Vanuatu and New Guinea were also analyzed.

In some samples, surviving Neanderthal and Denisovan sequences were at low frequencies of less than 5 percent.

However, the study also noted that in 126 places in our genomes, archaic sequences were at a higher frequency and touched 65 percent.

The study asserts that the genetic strength in the immune system was a gift of the Neanderthals or Denisovans who helped humans in combating hard environments.

Adaptive Introgression

Meanwhile, geneticists Fernando Racimo, Davide Marnetto and Emilia Huerta-Sanchez also put forth a postulate that interbreeding with archaic human forms has been beneficial and promoted "adaptive introgression."

According to the lead author, Racimo, the latter is a trait by which a piece of genetic material radiates into a vast population.

"Nobody has yet done a systematic survey of adaptive introgression around the world," said Racimo, a geneticist at the New York Genome Center.

The study, published in the journal Molecular Biology and Evolution said beneficial genetic variants inherited are related to immune response, skin pigmentation, respiration, fat storage, liver function and keratin production.

During the study, Racimo and colleagues developed many models for scanning human genomes across the world and showed that many groups bear resemblance to the DNA of archaic humans, other than Homo sapiens.

The best example of adaptive introgression has been about Tibetans whose genome carries 5 percent of Denisovan traits.

As a mountainous society, their genetic variant helps them breathe at high altitudes. The study notes that trait is closely related to a Denisovan gene, which is completely absent in the genomes of nearby Han Chinese individuals.

Photo: Paul Hudson | Flickr

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