It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Thank you.
Some features of ATS will be disabled while you continue to use an ad-blocker.
As modern humans migrated out of Africa, they encountered many new environmental conditions, including greater temperature extremes, different pathogens and higher altitudes. These diverse environments are likely to have acted as agents of natural selection and to have led to local adaptations. One of the most celebrated examples in humans is the adaptation of Tibetans to the hypoxic environment of the high-altitude Tibetan plateau1, 2, 3. A hypoxia pathway gene, EPAS1, was previously identified as having the most extreme signature of positive selection in Tibetans4, 5, 6, 7, 8, 9, 10, and was shown to be associated with differences in haemoglobin concentration at high altitude. Re-sequencing the region around EPAS1 in 40 Tibetan and 40 Han individuals, we find that this gene has a highly unusual haplotype structure that can only be convincingly explained by introgression of DNA from Denisovan or Denisovan-related individuals into humans. Scanning a larger set of worldwide populations, we find that the selected haplotype is only found in Denisovans and in Tibetans, and at very low frequency among Han Chinese. Furthermore, the length of the haplotype, and the fact that it is not found in any other populations, makes it unlikely that the haplotype sharing between Tibetans and Denisovans was caused by incomplete ancestral lineage sorting rather than introgression. Our findings illustrate that admixture with other hominin species has provided genetic variation that helped humans to adapt to new environments
Studies have linked their altitude adaptation to several genes including EPAS1, part of the system that helps the body react to low levels of oxygen. The Tibetan version of EPAS1 came from ancestors of the Nepalese Sherpa people and spread rapidly through the population 30,000 years ago, suggesting it is beneficial.
Now Rasmus Nielsen of the University of California, Berkeley, and his colleagues have compared Tibetan genomes with populations from around the world. No other modern group carries the Tibetan variant of EPAS1.
But they found the same gene variant in the genome of a Denisovan, an extinct species of human known only from a cave in the Altai mountains in east-central Asia.
"The study shows that one of the most spectacular cases of [genetic] adaptation in humans has its roots in Denisovans," says Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. "It is very satisfying to see that gene flow from Denisovans, an extinct group of archaic humans that we discovered only four years ago, is now found to have had important consequences for people living today."
The Tibetan EPAS1 probably got there by interbreeding, but more evidence is needed to confirm which archaic humans were the source, says David Reich of Harvard Medical School in Boston. "There is no proof in the paper that the origin of the [DNA] is Denisovan." He says it could just as easily have come from Neanderthals, whose EPAS1 looks similar to the Tibetans'. That might make more sense as they were common on mainland Asia, whereas the Denisovan heartland seems to have been in South-East Asia.
The Tibetan EPAS1 probably got there by interbreeding, but more evidence is needed to confirm which archaic humans were the source, says David Reich of Harvard Medical School in Boston. "There is no proof in the paper that the origin of the [DNA] is Denisovan." He says it could just as easily have come from Neanderthals, whose EPAS1 looks similar to the Tibetans'. That might make more sense as they were common on mainland Asia, whereas the Denisovan heartland seems to have been in South-East Asia.
Denisovans are one of at least two extinct hominin species that humans mated with, the other being Neanderthals. Many of us carry bits of DNA from these other species.
The new finding adds to the evidence that this interbreeding had significant effects on our evolution. For instance, Neanderthal DNA is particularly common in genes relating to keratin, a protein found in hair, skin and nails. Another Neanderthal gene found in modern Eurasians may increase the risk of type 2 diabetes.
Humans interbred with Neanderthals soon after moving out of Africa, when we were ill-equipped to cope with Eurasian diseases. However Neanderthals had been hanging out in Europe and Asia for much longer, so their immune systems had adapted. There is evidence that humans snagged some of the Neanderthals' immunity genes when the two mated, perhaps helping us to spread across the planet.
originally posted by: punkinworks10
a reply to: Kratos40
If I've read the paper correctly, the gene is not found in any other modern population.
Whether or not the Andean people are represented in the worldwide samples, but he fact that the Han have it and it is not found in the new world suggests that native Americans split off before this admixture event.
The Andean people have adapted to the high altitude via very definitive physiological adaptations, like larger lungs and slower heartbeats.