StonyArabia
09-23-2011, 04:43 AM
A 90-year-old tuft of hair has yielded the first complete genome of an Aboriginal Australian, a young man who lived in southwest Australia.
He, and perhaps all Aboriginal Australians, the genome indicates, descend from the first humans to venture far beyond Africa more than 60,000 years ago, and thousands of years before the ancestors of most modern Asians trekked east in a second migration out of Africa.
"Aboriginal Australians are descendents of the first human explorers. These are the guys who expanded to unknown territory into an unknown world, eventually reaching Australia," says Eske Willerslev, a palaeogeneticist at the University of Copenhagen, Denmark, who led the study. It appears online today in Science.
Hanging on a hair
The oldest human remains in Australia date to around 50,000 years ago, and yet older stone tools found in India and elsewhere hint at an early southern migration of anatomically modern humans out of Africa and through India and Southeast Asia.
However, genetic studies of contemporary Asians and Oceanians haven't always told the same story. The most comprehensive genetic analysis carried out so far pointed to a single migration that spawned all Asian populations, including Aboriginal Australians. But estimated times of the separation of European and Asian ancestors in this population does not chime well with the archaeological evidence for the continuous settlement of Australia from much earlier times.
A complete genome from an Aboriginal Australian would settle this debate, Willerslev says. Many contemporary Aboriginal Australians also descend from Europeans because of recent interbreeding between Aboriginals and Australian colonists. To get a better picture of the ancient history of Aboriginals, Willerslev wanted to sequence the genome of someone who did not descend from Europeans.
About a year ago, his team obtained a hair sample originally collected by the British ethnologist Alfred Cort Haddon. Historical records suggest that Haddon got the hair from a young Aboriginal man in the early 1920s while on a train journey from Sydney to Perth.
Willerslev believes that the man offered his hair to Haddon willingly, and a Danish bioethics review board saw no problem with sequencing his genome. Willerslev later received the blessing of a committee that represents Aboriginal people in the region where the man probably lived.
An analysis of his genome indicates that his ancestors started their journey more than 60,000 years ago, branching off from humans who left Africa. The ancestors of contemporary Europeans and most other Asians probably went their separate ways less than 40,000 years ago, according to Willerslev's team.
Ancient relations
Like other populations outside Africa, the Australian Aboriginal man owes small chunks of his genome to Neanderthals4. More surprisingly, though, his ancestors also interbred with another archaic human population known as the Denisovans. This group was identified from 30,000–50,000-year-old DNA recovered from a finger bone found in a Siberian cave. Until now, Papua New Guineans were the only modern human population whose ancestors were known to have interbred with Denisovans.
A second study incorporating genomic surveys from different Aboriginal Australians paints an even clearer picture of their ancestors' exploits with the Denisovans. Researchers led by Mark Stoneking at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, calculated the portion of Denisovan ancestry found in the genomes of 243 people representing 33 Asian and Oceanian populations. Patterns of Denisovan interbreeding in human populations could reveal human migration routes through Asia, reasoned the team. The paper is published today in the American Journal of Human Genetics.
This comparison revealed a patchwork in which some populations, including Australian Aboriginals, bore varying levels of Denisovan DNA, while many of their neighbours, like the residents of mainland Southeast Asia, contained none.
Stoneking says that this pattern hints at at least two waves of human migration into Asia: an early trek that included the ancestors of contemporary Aboriginal Australians, New Guineans and some other Oceanians, followed by a second wave that gave rise to the present residents of mainland Asia. Some members of the first wave (though not all of them) interbred with Denisovans. However, the Denisovans may have vanished by the time the second Asian migrants arrived. This also suggests that the Denisovan's range, so far linked only to a cave in southern Siberia, once extended to Southeast Asia and perhaps Oceania.
"Put together, these two papers make an overwhelming case for multiple waves of migration," says David Reich, a population geneticist at Harvard Medical School in Boston, an author on the second study.
Alan Redd, a biological anthropologist at the University of Kansas in Lawrence, says that the peopling of Australia may have been more complicated than either paper suggests. Dingoes, for instance, were brought to the island continent by humans who arrived in the last 5,000 years. "It's certainly possible that people were trickling in at different times," he says.
http://www.nature.com/news/2011/1109...11.551.html#B1
http://www.sciencemag.org/content/333/6050/1689
Table S2 from the paper (pdf) gives the Denisova admixture as a fraction of the Papuan New Guinea highlander Denisova admixture. It seemed almost certain to me that Australian aboriginals would register such admixture, as they have often been described, on physical anthropological grounds, as closer to Papuans than to any other human population. But, it is nice to see the evidence (or lack thereof) for Denisova admixture quantified in various groups described as "Negrito" or "Australoid" by traditional physical anthropology.
The inference, by the authors, that Denisova admixture took place in Southeast Asia itself makes sense to me. This admixture may have been variable to begin with, but it was reduced in Southeast Asia itself as the number of modern humans in it grew, absorbing the Denisova-admixed early inhabitants, with the latest episode taking the form of the arrival of East Eurasian populations (traditional Mongoloids) that seem to lack this admixture altogether.
The interesting question now seems to be: with Denisovans spread from the Altai to Southeast Asia, how did the ancestors of East Asians avoid having any?
UPDATE: Figure 1 from the paper shows Denisovan admixture as a fraction of that in New Guineans:
One of the most interesting findings of the paper is that the extent of Denisova admixture is strongly correlated with the extent of Near Oceanian (Australian-Papuan) admixture.
An interesting question is to what extent does Denisova admixture contribute to the differentiation between Australasians and other modern humans? The following admixture graph gives an idea:
You can see that 7% Denisova introgression into the ancestors of Australians/New Guineans is inferred to have been "diluted" by roughly 50-50 admixture with Denisova-deficient modern humans, leading to the ~4% figure of Denisova admixture in extant Australians/New Guineans. This was further diluted in populations like Mamanwa, by admixture with East Asians.
It seems likely that inter-population differentiation within the species H. sapiens may be driven, at least in part, by admixture with archaic humans, and is not only the result of isolation post-Out of Africa. If Franz Weidenreich were alive, he would probably be smiling.
UPDATE II: A possible reason why East Asians lack Denisovan admixture is given by Mark Stoneking, as quoted in Nature:
Stoneking says that this pattern hints at at least two waves of human migration into Asia: an early trek that included the ancestors of contemporary Aboriginal Australians, New Guineans and some other Oceanians, followed by a second wave that gave rise to the present residents of mainland Asia. Some members of the first wave (though not all of them) interbred with Denisovans. However, the Denisovans may have vanished by the time the second Asian migrants arrived. This also suggests that the Denisovan's range, so far linked only to a cave in southern Siberia, once extended to Southeast Asia and perhaps Oceania.
Given that the Denisova hominin is about 41ka old, that would imply that East Asian ancestors moved through their territory after that date, when the Denisovans were already extinct, partially absorbed by first-wave "Australasian-like" people.
We must also consider the possibility that the Denisovans themselves may have been intrusive to Siberia; could the Altai Denisovans be remnants of a Southeast Asian population that fled out of the way of the modern humans that migrated to Australasia? If that is the case, then East Asian ancestors may lack Denisovan admixture because they had already reached the far east when Denisovans started moving north.
I, for one, can't wait until we start getting ancient DNA from Upper Paleolithic H. sapiens, who knows what new surprises are in store for us?
The American Journal of Human Genetics, 22 September 2011
doi:10.1016/j.ajhg.2011.09.005
Denisova Admixture and the First Modern Human Dispersals into Southeast Asia and Oceania
David Reich et al.
It has recently been shown that ancestors of New Guineans and Bougainville Islanders have inherited a proportion of their ancestry from Denisovans, an archaic hominin group from Siberia. However, only a sparse sampling of populations from Southeast Asia and Oceania were analyzed. Here, we quantify Denisova admixture in 33 additional populations from Asia and Oceania. Aboriginal Australians, Near Oceanians, Polynesians, Fijians, east Indonesians, and Mamanwa (a “Negrito” group from the Philippines) have all inherited genetic material from Denisovans, but mainland East Asians, western Indonesians, Jehai (a Negrito group from Malaysia), and Onge (a Negrito group from the Andaman Islands) have not. These results indicate that Denisova gene flow occurred into the common ancestors of New Guineans, Australians, and Mamanwa but not into the ancestors of the Jehai and Onge and suggest that relatives of present-day East Asians were not in Southeast Asia when the Denisova gene flow occurred. Our finding that descendants of the earliest inhabitants of Southeast Asia do not all harbor Denisova admixture is inconsistent with a history in which the Denisova interbreeding occurred in mainland Asia and then spread over Southeast Asia, leading to all its earliest modern human inhabitants. Instead, the data can be most parsimoniously explained if the Denisova gene flow occurred in Southeast Asia itself. Thus, archaic Denisovans must have lived over an extraordinarily broad geographic and ecological range, from Siberia to tropical Asia.
read more: http://dienekes.blogspot.com/2011/09/widespread-denisovan-admixture-reich-et.html
if you want to look at the graphs and such
He, and perhaps all Aboriginal Australians, the genome indicates, descend from the first humans to venture far beyond Africa more than 60,000 years ago, and thousands of years before the ancestors of most modern Asians trekked east in a second migration out of Africa.
"Aboriginal Australians are descendents of the first human explorers. These are the guys who expanded to unknown territory into an unknown world, eventually reaching Australia," says Eske Willerslev, a palaeogeneticist at the University of Copenhagen, Denmark, who led the study. It appears online today in Science.
Hanging on a hair
The oldest human remains in Australia date to around 50,000 years ago, and yet older stone tools found in India and elsewhere hint at an early southern migration of anatomically modern humans out of Africa and through India and Southeast Asia.
However, genetic studies of contemporary Asians and Oceanians haven't always told the same story. The most comprehensive genetic analysis carried out so far pointed to a single migration that spawned all Asian populations, including Aboriginal Australians. But estimated times of the separation of European and Asian ancestors in this population does not chime well with the archaeological evidence for the continuous settlement of Australia from much earlier times.
A complete genome from an Aboriginal Australian would settle this debate, Willerslev says. Many contemporary Aboriginal Australians also descend from Europeans because of recent interbreeding between Aboriginals and Australian colonists. To get a better picture of the ancient history of Aboriginals, Willerslev wanted to sequence the genome of someone who did not descend from Europeans.
About a year ago, his team obtained a hair sample originally collected by the British ethnologist Alfred Cort Haddon. Historical records suggest that Haddon got the hair from a young Aboriginal man in the early 1920s while on a train journey from Sydney to Perth.
Willerslev believes that the man offered his hair to Haddon willingly, and a Danish bioethics review board saw no problem with sequencing his genome. Willerslev later received the blessing of a committee that represents Aboriginal people in the region where the man probably lived.
An analysis of his genome indicates that his ancestors started their journey more than 60,000 years ago, branching off from humans who left Africa. The ancestors of contemporary Europeans and most other Asians probably went their separate ways less than 40,000 years ago, according to Willerslev's team.
Ancient relations
Like other populations outside Africa, the Australian Aboriginal man owes small chunks of his genome to Neanderthals4. More surprisingly, though, his ancestors also interbred with another archaic human population known as the Denisovans. This group was identified from 30,000–50,000-year-old DNA recovered from a finger bone found in a Siberian cave. Until now, Papua New Guineans were the only modern human population whose ancestors were known to have interbred with Denisovans.
A second study incorporating genomic surveys from different Aboriginal Australians paints an even clearer picture of their ancestors' exploits with the Denisovans. Researchers led by Mark Stoneking at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, calculated the portion of Denisovan ancestry found in the genomes of 243 people representing 33 Asian and Oceanian populations. Patterns of Denisovan interbreeding in human populations could reveal human migration routes through Asia, reasoned the team. The paper is published today in the American Journal of Human Genetics.
This comparison revealed a patchwork in which some populations, including Australian Aboriginals, bore varying levels of Denisovan DNA, while many of their neighbours, like the residents of mainland Southeast Asia, contained none.
Stoneking says that this pattern hints at at least two waves of human migration into Asia: an early trek that included the ancestors of contemporary Aboriginal Australians, New Guineans and some other Oceanians, followed by a second wave that gave rise to the present residents of mainland Asia. Some members of the first wave (though not all of them) interbred with Denisovans. However, the Denisovans may have vanished by the time the second Asian migrants arrived. This also suggests that the Denisovan's range, so far linked only to a cave in southern Siberia, once extended to Southeast Asia and perhaps Oceania.
"Put together, these two papers make an overwhelming case for multiple waves of migration," says David Reich, a population geneticist at Harvard Medical School in Boston, an author on the second study.
Alan Redd, a biological anthropologist at the University of Kansas in Lawrence, says that the peopling of Australia may have been more complicated than either paper suggests. Dingoes, for instance, were brought to the island continent by humans who arrived in the last 5,000 years. "It's certainly possible that people were trickling in at different times," he says.
http://www.nature.com/news/2011/1109...11.551.html#B1
http://www.sciencemag.org/content/333/6050/1689
Table S2 from the paper (pdf) gives the Denisova admixture as a fraction of the Papuan New Guinea highlander Denisova admixture. It seemed almost certain to me that Australian aboriginals would register such admixture, as they have often been described, on physical anthropological grounds, as closer to Papuans than to any other human population. But, it is nice to see the evidence (or lack thereof) for Denisova admixture quantified in various groups described as "Negrito" or "Australoid" by traditional physical anthropology.
The inference, by the authors, that Denisova admixture took place in Southeast Asia itself makes sense to me. This admixture may have been variable to begin with, but it was reduced in Southeast Asia itself as the number of modern humans in it grew, absorbing the Denisova-admixed early inhabitants, with the latest episode taking the form of the arrival of East Eurasian populations (traditional Mongoloids) that seem to lack this admixture altogether.
The interesting question now seems to be: with Denisovans spread from the Altai to Southeast Asia, how did the ancestors of East Asians avoid having any?
UPDATE: Figure 1 from the paper shows Denisovan admixture as a fraction of that in New Guineans:
One of the most interesting findings of the paper is that the extent of Denisova admixture is strongly correlated with the extent of Near Oceanian (Australian-Papuan) admixture.
An interesting question is to what extent does Denisova admixture contribute to the differentiation between Australasians and other modern humans? The following admixture graph gives an idea:
You can see that 7% Denisova introgression into the ancestors of Australians/New Guineans is inferred to have been "diluted" by roughly 50-50 admixture with Denisova-deficient modern humans, leading to the ~4% figure of Denisova admixture in extant Australians/New Guineans. This was further diluted in populations like Mamanwa, by admixture with East Asians.
It seems likely that inter-population differentiation within the species H. sapiens may be driven, at least in part, by admixture with archaic humans, and is not only the result of isolation post-Out of Africa. If Franz Weidenreich were alive, he would probably be smiling.
UPDATE II: A possible reason why East Asians lack Denisovan admixture is given by Mark Stoneking, as quoted in Nature:
Stoneking says that this pattern hints at at least two waves of human migration into Asia: an early trek that included the ancestors of contemporary Aboriginal Australians, New Guineans and some other Oceanians, followed by a second wave that gave rise to the present residents of mainland Asia. Some members of the first wave (though not all of them) interbred with Denisovans. However, the Denisovans may have vanished by the time the second Asian migrants arrived. This also suggests that the Denisovan's range, so far linked only to a cave in southern Siberia, once extended to Southeast Asia and perhaps Oceania.
Given that the Denisova hominin is about 41ka old, that would imply that East Asian ancestors moved through their territory after that date, when the Denisovans were already extinct, partially absorbed by first-wave "Australasian-like" people.
We must also consider the possibility that the Denisovans themselves may have been intrusive to Siberia; could the Altai Denisovans be remnants of a Southeast Asian population that fled out of the way of the modern humans that migrated to Australasia? If that is the case, then East Asian ancestors may lack Denisovan admixture because they had already reached the far east when Denisovans started moving north.
I, for one, can't wait until we start getting ancient DNA from Upper Paleolithic H. sapiens, who knows what new surprises are in store for us?
The American Journal of Human Genetics, 22 September 2011
doi:10.1016/j.ajhg.2011.09.005
Denisova Admixture and the First Modern Human Dispersals into Southeast Asia and Oceania
David Reich et al.
It has recently been shown that ancestors of New Guineans and Bougainville Islanders have inherited a proportion of their ancestry from Denisovans, an archaic hominin group from Siberia. However, only a sparse sampling of populations from Southeast Asia and Oceania were analyzed. Here, we quantify Denisova admixture in 33 additional populations from Asia and Oceania. Aboriginal Australians, Near Oceanians, Polynesians, Fijians, east Indonesians, and Mamanwa (a “Negrito” group from the Philippines) have all inherited genetic material from Denisovans, but mainland East Asians, western Indonesians, Jehai (a Negrito group from Malaysia), and Onge (a Negrito group from the Andaman Islands) have not. These results indicate that Denisova gene flow occurred into the common ancestors of New Guineans, Australians, and Mamanwa but not into the ancestors of the Jehai and Onge and suggest that relatives of present-day East Asians were not in Southeast Asia when the Denisova gene flow occurred. Our finding that descendants of the earliest inhabitants of Southeast Asia do not all harbor Denisova admixture is inconsistent with a history in which the Denisova interbreeding occurred in mainland Asia and then spread over Southeast Asia, leading to all its earliest modern human inhabitants. Instead, the data can be most parsimoniously explained if the Denisova gene flow occurred in Southeast Asia itself. Thus, archaic Denisovans must have lived over an extraordinarily broad geographic and ecological range, from Siberia to tropical Asia.
read more: http://dienekes.blogspot.com/2011/09/widespread-denisovan-admixture-reich-et.html
if you want to look at the graphs and such