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Javier E

Gains in DNA Are Speeding Research Into Human Origins - NYTimes.com - 0 views

www.nytimes.com/...search-into-human-origins.html

dna research human origins neanderthal denisovan interbreeding

shared by Javier E on 31 Jan 12 - No Cached
  • genetic analysis shows, modern humans encountered and bred with at least two groups of ancient humans in relatively recent times: the Neanderthals, who lived in Europe and Asia, dying out roughly 30,000 years ago, and a mysterious group known as the Denisovans, who lived in Asia and most likely vanished around the same time.
  • Their DNA lives on in us even though they are extinct. “In a sense, we are a hybrid species,
  • A third group of extinct humans, Homo floresiensis, nicknamed “the hobbits” because they were so small, also walked the earth until about 17,000 years ago. It is not known whether modern humans bred with them because the hot, humid climate of the Indonesian island of Flores, where their remains were found, impairs the preservation of DNA
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  • Comparing genomes, scientists concluded that today’s humans outside Africa carry an average of 2.5 percent Neanderthal DNA, and that people from parts of Oceania also carry about 5 percent Denisovan DNA. A study published in November found that Southeast Asians carry about 1 percent Denisovan DNA in addition to their Neanderthal genes.
  • as few as six couplings all those tens of thousands of years ago might have led to the current level of ancient immune alleles.
  • This means that our modern era, since H. floresiensis died out, is the only time in the four-million-year human history that just one type of human has been alive,
  • Were they romantic couplings? More likely they were aggressive acts between competing human groups, Dr. Stringer said. For a model, he pointed to modern hunter-gatherer groups that display aggressive behavior among tribes.
  • The value of the interbreeding shows up in the immune system, Dr. Parham’s analysis suggests. The Neanderthals and Denisovans had lived in Europe and Asia for many thousands of years before modern humans showed up and had developed ways to fight the diseases there
  • When modern humans mated with them, they got an injection of helpful genetic immune material, so useful that it remains in the genome today. This suggests that modern humans needed the archaic DNA to survive. The downside of archaic immune material is that it may be responsible for autoimmune diseases like diabetes, arthritis and multiple sclerosis, Dr. Parham said, stressing that these are preliminary results.
  • little is known about the Denisovans — the only remains so far are the pinky bone and the tooth, and there are no artifacts like tools. Dr. Reich and others suggest that they were once scattered widely across Asia, from the cold northern cave to the tropical south. The evidence is that modern populations in Oceania, including aboriginal Australians, carry Denisovan genes.
g-dragon

Early Humans Slept Around with More than Just Neanderthals - HISTORY - 0 views

www.history.com/...sovans-interbreeding-discovery

humans history Neanderthals Denisovans

shared by g-dragon on 31 May 18 - No Cached
  • It’s been known for some time that our modern human ancestors interbred with other early hominin groups like the Neanderthals. But it turns out they were even more promiscuous than we thought.
  • New DNA research has unexpectedly revealed that modern humans (Homo sapiens) mixed, mingled and mated with another archaic human species, the Denisovans, not once but twice—in two different regions of the ancient world.
  • Some Melanesians (who live in Papua New Guinea and other Pacific islands) were found to have around 5 percent of Denisovan ancestry, while some East and South Asians have around 0.2 percent. One particular gene mutation, which the Denisovans are thought to have passed to modern Tibetans, allows them to survive at high altitudes.
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  • Researchers assumed the Denisovan ancestry found in Asia was due to migration from Oceania, the larger region containing Melanesia.
  • What they found was a distinct set of Denisovan ancestry among some modern East Asians—particularly Han Chinese, Chinese Dai and Japanese—ancestry not found in South Asians or Papuans.
  • Browning and her colleagues assume that modern humans mixed with the Denisovans shortly after migrating out of Africa
  • While they’re not sure of the location, they believe the interbreeding occurred in at least two places: eastern Asia, and further south, in Indonesia or Australia.
  • While the new study confirms that modern humans interbred at least three times with ancient hominins—once with Neanderthals, and twice with the Denisovans
Javier E

Scientists find evidence of 'ghost population' of ancient humans | Science | The Guardian - 0 views

www.theguardian.com/...t-population-of-ancient-humans

human origins africa

shared by Javier E on 13 Feb 20 - No Cached
  • Arun Durvasula and Sankararaman obtained 405 genomes from four west African populations and used statistical techniques to work out whether an influx of genes from interbreeding was likely to have happened in the distant past. The analysis suggested that it had in every case.
  • The scientists went on to scour the African genomes for chunks of DNA that looked different to modern human genes. This allowed them to pull out sequences that most probably came from an ancient relative. By comparing these with genes from Neanderthals and Denisovans, they concluded that the DNA had to come from an unknown group of archaic humans.
  • “They seem to have made a pretty substantial impact on the genomes of the present day individuals we studied,” Sankararaman said. “They account for 2% to 19% of their genetic ancestry.” The four populations studied came from three countries: two from Nigeria, and one each from Sierra Leone and the Gambia.
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