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Neanderthal, Denisovan Hybrid Teen Sheds Light On Interbreeding Among Different Human Species

Aug 23, 2018 01:29 AM EDT
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Meet, Denny. Scientists are stunned to find that this 90,000-year-old hybrid teenager is the child of an interspecies relationship between a Neanderthal and Denisovan.

It is the first time scientists have ever confirmed a first-generation hybrid with parents of two different human species.

Tracing Denny's Unconventional Roots

Researchers from the Max Planck Institute for Evolutionary Anthropology only had a single bone of Denny from Denisova Cave in Russia, but it's enough for a genetic analysis that has great implications on the study of ancient humans.

The bone fragment's mitochondrial DNA was initially analyzed, which is genes that's only passed from the mother to child. It revealed the Neanderthal maternal roots of Denny, but did not identify the father.

It's the nuclear DNA that is inherited from both parents and can reveal the lineage of both mother and father.

When the results of the analysis came, it was so surprising that study author and paleogeneticist Viviane Slon assumed she made a mistake, according to National Geographic. However, tests on six other samples saw consistent results that identify Denny's parentage: a Neanderthal mother and a Denisovan father.

"We knew from previous studies that Neandertals and Denisovans must have occasionally had children together", Slon says in a statement. "But I never thought we would be so lucky as to find an actual offspring of the two groups."

Furthermore, Denny had extremely high heterozygosity, which means there is incredible diversity found in his genome. With parents of two different species, this is to be expected in her DNA.

More Revealed On Ancient Humans

While Denny's parentage is the most groundbreaking finding from the 90,000-year-old genome, the study published in the journal Nature were able to discover key details about early hominin ancestry.

From analyzing Denny's genome, the scientists were able to determine that the mother was genetically closer to Neanderthals from western Europe than those who lived earlier in Denisova Cave. This means the species migrated from western to eastern Eurasia tens of thousands of years before they went extinct.

On the other hand, Denny's genome also revealed that her father had hints of Neanderthal ancestry as well. It suggests that interactions between Denisovans and Neanderthals may be more common than previously believed.

Interbreeding Between Neanderthals, Denisovans

Neanderthals and Denisovans are related homonins, diverging from a common ancestor about 390,000 years ago. The two species are believed to have lived until around 40,000 years ago.

Kelley Harris, a population geneticist at the University of Washington, tells Nature that sexual encounters between Neanderthals and Denisovans may have been common, especially since the number of pure Denisovan bones that have been uncovered are few and far in between.

However, it's also strange that — if interbreeding were indeed common — the two species never merged and remained totally genetically distinct over hundreds of thousands of years of co-existing. Harris suggests that one reason for this could be infertility or biologically unfitness of any offspring between the two.

On the other hand, lead author of the study Svante Pääbo believed encounters between the two species would have been rare, since Neanderthals were known to live across western Eurasia, while Denisovans have mostly stuck to their cave in Russia, as far as scientists currently know.

Both Neanderthals and Denisovans are long extinct, but their lineage has made it into modern humans. Most Europeans and Asians have 2 percent of Neanderthal DNA, while modern Melanesians have Denisovans to thank for 4 to 6 percent of their genoms.

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