Interbreeding and the Human Family Tree
Scientists may have come a step closer to uncovering the human family tree. Interestingly, interbreeding with now-extinct human races seems to have been key components in the differentiation of Eurasians from Africans and South Asians from Eurasians.
BBC NewsBy Pallab Ghosh22 December 2010
Professor Chris Stringer: “It’s nothing short of sensational – we didn’t know know how ancient people in China related to these other humans”
Scientists say an entirely separate type of human identified from bones in Siberia co-existed and interbred with our own species.
The ancient humans have been dubbed “Denisovans” after the caves in Siberia where their remains were found.
There is also evidence that this population was widespread in Eurasia.
A study in Nature journal shows that Denisovans co-existed with Neanderthals and interbred with our species – perhaps around 50,000 years ago.
An international group of researchers sequenced a complete genome from one of the ancient hominins (human-like creatures), based on nuclear DNA extracted from a finger bone.
According to the researchers, this provides confirmation there were at least four distinct types of human in existence when anatomically modern humans (Homo sapiens sapiens) first left their African homeland.
DNA from a tooth (pictured) and a finger bone show the Denisovans were a distinct group
Along with modern humans, scientists knew about the Neanderthals and a dwarf human species found on the Indonesian island of Flores nicknamed “The Hobbit”. To this list, experts must now add the Denisovans.
The implications of the finding have been described by Professor Chris Stringer of the Natural History Museum in London as “nothing short of sensational”.
Scientists were able to analyse DNA from a tooth and from a finger bone excavated in the Denisova cave in southern Siberia. The individuals belong to a genetically distinct group of humans that were distantly related to Neanderthals but even more distantly related to us.
The finding adds weight to the theory that a different kind of human could have existed in Eurasia at the same time as our species.
Researchers have had enigmatic fossil evidence to support this view but now they have some firm evidence from the genetic study carried out by Professor Svante Paabo of the Max Planck Institute in Leipzig, Germany.
“A species of early human living in Europe evolved,” according to Professor Paabo.
“There was a western form that was the Neanderthal and an eastern form, the Denisovans.”
The study shows that Denisovans interbred with the ancestors of the present day people of the Melanesian region north and north-east of Australia. Melanesian DNA comprises between 4% and 6% Denisovan DNA.
David Reich from the Harvard Medical School, who worked with Svante Paabo on the study, says that the fact that Denisovan genes ended up so far south suggests they were widespread across Eurasia: “These populations must have been spread across thousands and thousands of miles,” he told BBC News.
One mystery is why the Denisovan genes are unique in modern Melanesians and are not found in other Eurasian groups that have so far been sampled.
Professor Stringer believes it is because there may have been only a fleeting encounter as modern humans migrated through South-East Asia and then on to Melanesia.
The remains were excavated at a cave site in southern Siberia
“It could be just 50 Denisovans interbreeding with a thousand modern humans. That would be enough to produce this 5% of those archaic genes being transferred,” he said.
“So the impact is there but the number of interbreeding events might have been quite small and quite rare.”
No one knows when or how these humans disappeared but, according to Professor Paabo, it is very likely something to do with modern people because all the “archaic” humans, like Denisovans and Neanderthals disappeared sometime after Homo sapiens sapiens appeared on the scene.
“It is fascinating to see direct evidence that these archaic species did exist (alongside us) and it’s only for the last few tens of thousands of years that is unique in our history that we are alone on this planet and we have no close relatives with us anymore,” he said.
The study follows a paper published earlier this year by by Professor Paabo and colleagues that showed there was interbreeding between modern humans and Neanderthals as they emerged from Africa 60,000 years ago.
Sandra Bullock: A Woman for Our Time
Sandra Bullock is People magazine’s Woman of the Year!
Having trouble remembering Bullock’s devastating and sensitive filmic performance from this past year? Or even which movie she was in?
Well, according to IMDb, Bullock appeared in a total of … ZERO roles for the entirety of 2010.
Was there some mistake?
No. According to People,
For Sandra Bullock, 2010 was the year that changed everything: She became a mother to son Louis, ended her five-year marriage to Jesse James and reached new career heights with her emotional Oscar win for The Blind Side.
So, after being embraced by her peers for portraying a Southern Christian woman who brings a 300-pound Black into her family home and neglects her biological children on his behalf, Sandra got divorced, and then became a single mother by adopting an African orphan.
This may be the first time a major magazine has given someone an award for living a politically correct private life.