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Wednesday, February 17, 2016

Complex Human DNA Trail Provides Some Interesting Surprises

Neanderthals & humans interbred 100,000 years ago
At least 5 different species of humans found
By Rebecca Morelle, Science Correspondent, BBC News

Neanderthal recreation   Image copyright ELISABETH DAYNES/SCIENCE PHOTO LIBRARY
Neanderthals may have been breeding with modern humans much earlier than was thought

Traces of human DNA found in a Neanderthal genome suggest that we started mixing with our now-extinct relatives 100,000 years ago.

Previously it had been thought that the two species first encountered each other when modern humans left Africa, about 60,000 years ago.

The research is published in the journal Nature.

Dr Sergi Castellano, from the Max Planck Institute for Evolutionary Anthropology, in Germany, said: "It is significant for understanding the history of modern humans and Neanderthals."

The Neanderthal remains were found in a cave in Siberia copyright BENCE VIOLA

The ancient remains of a female Neanderthal, found in a remote cave in the Altai Mountains in Siberia, are the source of these revelations about the sex lives of our ancestors.

A genetic analysis reveals that portions of human DNA lie within her genome, revealing an interspecies mingling that took place 100,000 years ago.

We really don't know how widespread Neanderthals and early modern 
humans might have been in the regions between Arabia and China at this time

Prof Chris Stringer, Natural History Museum

Earlier research suggested that humans started interbreeding with our heavy-browed, stocky relatives when they migrated out of Africa and began to spread around the world.

As they left the continent, they met - and mingled with - the Neanderthals, who lived across Europe and Asia.

Neanderthal genes from these encounters are found in humans today, and recent studies have shown that these portions of DNA play an integral role in everything from our immune system to our propensity to diseases.

But the latest finding of a flow of genes in the opposite direction, from humans to Neanderthals, suggests such mating was happening thousands of years earlier.

It is not yet clear what impact these genes had on Neanderthals. "The functional significance of this is unclear at the moment," said Dr Castellano.

Neanderthal genes in the humans are found in many Europeans and Asian populations Science Photo Library

However, the findings do shed more light on the history of human migration.

At the moment we simply don't know how these matings happened
Prof Chris Stringer, Natural History Museum

If early humans were having sex with Neanderthals 100,000 years ago, then they must have been doing so outside of Africa because our close relatives were not found there. And this means that they had left Africa before the larger dispersal that took place at least 40,000 years later.

This adds to the idea that early forays out of the continent took place. Other recent evidence includes early human fossils found in Skhul and Qafzeh in Israel, and recent research that suggests people were living in China at least 80,000 years ago.

Commenting on the study Prof Chris Stringer, research leader in human origins, from the Natural History Museum in London, said: "I think that anywhere in southern Asia could theoretically have been the location of this early interbreeding, since we really don't know how widespread Neanderthals and early modern humans might have been in the regions between Arabia and China at this time."

He added: "At the moment we simply don't know how these matings happened and the possibilities range from relatively peaceful exchanges of partners, to one group raiding another and stealing females (which happens in chimps and some modern hunter-gatherers), through to adopting abandoned or orphaned babies.

"Eventually, geneticists should be able to show if the transfer of DNA in either direction was mainly via males, females, or about equal in proportion, but it will need a lot more data before that becomes possible."

Altai Mtns, Siberia/Mongolia

The cave in the Altai Mountains of Siberian in the photo above is actually famous for having housed not only Neanderthals and humans, but also another extinct species called Denisovans. Their history just adds a whole nuther level of confusion to the human genome. This from Wikipedia:

Denisovan or Denisova hominin (pronunciation: /dᵻˈniːsəvə/ dɛ-nee-sə-və) is an extinct species of human in the genus Homo. The species is sometimes given the name Homo sp. Altai, and Homo sapiens ssp. Denisova. In March 2010, scientists announced the discovery of a finger bone fragment of a juvenile female who lived about 41,000 years ago, found in the remote Denisova Cave in the Altai Mountains in Siberia, a cave which has also been inhabited by Neanderthals and modern humans. Two teeth belonging to different members of the same population have since been reported. In November 2015, a tooth fossil containing DNA was reported to have been found and studied.

Genetically distinct DNA

Analysis of the mitochondrial DNA (mtDNA) of the finger bone showed it to be genetically distinct from the mtDNAs of Neanderthals and modern humans. Subsequent study of the nuclear genome from this specimen suggests that Denisovans shared a common origin with Neanderthals, that they ranged from Siberia to South-East Asia, and that they lived among and interbred with the ancestors of some modern humans, with about 3% to 5% of the DNA of Melanesians and Aboriginal Australians deriving from Denisovans. 

Yet another human species

DNA discovered in Spain suggests that Denisovans at some point resided in Western Europe, where Neanderthals were previously thought to be the only inhabitants. A comparison with the genome of a Neanderthal from the same cave revealed significant local interbreeding with local Neanderthal DNA representing 17% of the Denisovan genome, while evidence was also detected of interbreeding with an as yet unidentified ancient human lineage.

This probably has nothing to do with the discovery of 'hobbits', another human species, on an island in Indonesia. Consequently, that means that there were at least 5 different humanoid species in existence at some time or another.

Similar analysis of a toe bone discovered in 2011 is underway, while analysis of DNA from two teeth found in layers different from the finger bone revealed an unexpected degree of mtDNA divergence among Denisovans. In 2013, mitochondrial DNA from a 400,000-year-old hominin femur bone from Spain, which had been seen as either Neanderthal or Homo heidelbergensis, was found to be closer to Denisovan mtDNA than to Neanderthal mtDNA.