Some modern humans carry immune genes that originated in Neanderthals and a related species. But these genes may have come at a price
One question seemed to hang in the air more than any other when scientists first turned the powerful techniques of modern genetics on the fragile and damaged remains of ancient humans: did we or didn't we? Have sex with them, that is.
The answer came after years of painstaking work, when material extracted from the leg of a Neanderthal and the fingerbone of a Denisovan, an apparent sister species, yielded readable DNA. It turned out that most of us have some of their genes. The Neanderthals contributed up to 4% of modern Eurasian genomes, while the Denisovans contributed roughly 4-6% of modern Melanesian genomes. That doesn't happen by holding hands.
And so the scene was set. Hundreds of thousands of years ago, early humans in Africa split into several groups, among them Homo sapiens, Neanderthals and their apparent sister species, the Denisovans. The Neanderthals headed for West Asia and Europe, the Denisovans to East Asia. Our ancestors left Africa much later, and arrived in Eurasia where the others had set up home. Cue amorous encounters, and surely a fair amount of less than amorous contact.
But the question of whether our ancestors mated with these other human-like groups was always just the starting point for a line of inquiry. With interbreeding now well-established the intriguing question is, what came of it? How did our ancestors' antics shape the people we are today?
A glimpse of the legacy of those ancient encounters is revealed in a study reported today in the US journal, Science. An international team of scientists, led by Stanford University, scoured the Neanderthal and Denisovan genomes for gene variants that are central to the immune system. These genes belong to a group known as the HLA class I genes, which govern the body's ability to recognise and destroy dangerous pathogens.
By comparing the HLA genes of modern human populations with those from Denisovans and Neanderthals, the scientists identified a handful that could be traced back to ancient sexual encounters between the groups. One variant, known as HLA-B*73, likely arose in modern humans after cross-breeding with Denisovans. The variant is most common in West Asian populations, the region where the mating probably happened.
The Neanderthals contributed a string of HLA gene variants, or alleles, to the modern Eurasian population's gene pool, the study found.
There was good reason for Neanderthal and Denisovan immune system genes to have spread through the populations of modern humans who encountered them. Both Neanderthals and Denisovans had established themselves long before modern humans arrived. Their immune systems had adapted to the threats of the local environment. When those genes crossed into modern humans, they conveyed an advantage. Natural selection took care of the rest.
But the scientists think there was a downside. Inheriting Denisovan or Neanderthal immunity genes will have helped modern humans to fight the diseases of the day, but beyond the age of reproductive maturity they might have a more harmful effect, turning our immune systems on ourselves.
Paul Norman, a co-author on the paper, put it like this: "There's enormous genetic variation in people's immune systems and that can control how different people fight different diseases. This could go some way to explaining why some people are better at fighting some infections than others, but we think it also goes some way to explaining why some people are susceptible to autoimmune diseases."
Autoimmune diseases are conditions that arise when the immune system turns its firepower on the body, usually when it mistakenly identifies the body's tissues as foreign, and so potentially dangerous.
"The vast majority of autoimmune diseases have been shown by genome-wide association studies to be associated with particular HLA alleles and we find a couple of those in Denisovans," Norman added. "So it looks to me like modern humans have acquired these alleles, but we weren't kind of prepared for them, we hadn't grown up with them, and in some circumstances, they can start to attack us as well as the viruses and other pathogens."
The group is now investigating a gene variant called HLA-B51, which came from cross-breeding with Neanderthals and has already been linked to Behcet's disease, a rare and chronic inflammatory condition.
How else might immune genes inherited from Neanderthals and Denisovans affect the health of modern humans? The question is intriguing and will differ from population to population. Here, at least, is a worthy successor to the question of "did we or didn't we?"
http://www.guardian.co.uk/science/blog/2011/aug/25/neanderthal-denisovan-genes-human-immunity>
Showing posts with label Denisovans. Show all posts
Showing posts with label Denisovans. Show all posts
Friday, August 26, 2011
Thursday, December 23, 2010
Ancient humans, dubbed 'Denisovans', interbred with us (via Dawn Holloway)
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 group 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.
'Sensational' find
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.
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 belonged 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.
'Fleeting encounter'
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.
"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 Professor Paabo and colleagues that showed there was interbreeding between modern humans and Neanderthals as they emerged from Africa 60,000 years ago.
By Pallab Ghosh
Science correspondent, BBC News
http://www.bbc.co.uk/news/science-environment-12059564
The ancient humans have been dubbed Denisovans after the caves in Siberia where their remains were found.
There is also evidence that this group 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.
'Sensational' find
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.
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 belonged 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.
'Fleeting encounter'
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.
"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 Professor Paabo and colleagues that showed there was interbreeding between modern humans and Neanderthals as they emerged from Africa 60,000 years ago.
By Pallab Ghosh
Science correspondent, BBC News
http://www.bbc.co.uk/news/science-environment-12059564
Ancient humans, dubbed 'Denisovans', interbred with us (via Dawn Holloway)
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 group 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.
'Sensational' find
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.
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 belonged 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.
'Fleeting encounter'
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.
"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 Professor Paabo and colleagues that showed there was interbreeding between modern humans and Neanderthals as they emerged from Africa 60,000 years ago.
By Pallab Ghosh
Science correspondent, BBC News
http://www.bbc.co.uk/news/science-environment-12059564
The ancient humans have been dubbed Denisovans after the caves in Siberia where their remains were found.
There is also evidence that this group 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.
'Sensational' find
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.
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 belonged 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.
'Fleeting encounter'
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.
"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 Professor Paabo and colleagues that showed there was interbreeding between modern humans and Neanderthals as they emerged from Africa 60,000 years ago.
By Pallab Ghosh
Science correspondent, BBC News
http://www.bbc.co.uk/news/science-environment-12059564
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