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DNA hints at African cousin: profiles suggest existence of now-extinct human relative.

Researchers have found the genetic signature of a sister species to Homo sapiens buried in the genetic blueprints of 15 African hunter-gatherers. Its DNA apparently jumped into the Homo sapiens gene pool through interbreeding with modern humans about 30,000 to 70,000 years ago, when other modern humans and Neandertals were mixing in the Middle East. Researchers report the genetic findings in the Aug. 3 Cell.

The evidence for past interbreeding is convincing, says Richard "Ed" Green, a genome biologist at the University of California, Santa Cruz. "There is a signal that demands explanation, and archaic admixture seems to be the most reasonable one at this point," he says.

Scientists have discovered that some people with ancestry outside Africa have DNA inherited from Neandertals or from Denisovans, a mysterious group known only through DNA derived from a fossil finger bone found in a Siberian cave (SN.. 6/5/10, p. 5; SN: 1/15/11, p. 10).

Those researchers had DNA from fossils to guide them. This time, researchers led by Sarah Tishkoffat the University of Pennsylvania in Philadelphia didn't have fossil DNA, or even fossils.

Tishkoff's group took DNA donated by 15 African hunter-gatherers--five Pygmies from Cameroon and five Hadza and five Sandawe from Tanzania--and compiled complete genetic blueprints for each person. Population geneticist Joshua Akey of the University of Washington and his colleagues helped analyze the data. Using a statistical analysis, the team determined that about 2 percent of the DNA from the hunter-gatherers came from an unknown species of hominid that split from modern human ancestors about 1.1 million years ago. These long-lost human cousins must have then interbred with modern humans sometime before the common ancestral lineage of the three hunter-gatherer groups separated about 30,000 to 70,000 years ago, Akey says.

Other researchers aren't convinced that the DNA remnants identified are the genetic remains of a new species of human cousin. The DNA could have come from a genetically distinct group of modern humans that has since died out due to changes in the environment, diseases or confrontations with rival groups of people, says Jean-Jacques Hublin, a paleoanthropologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

Relatively recent interbreeding isn't the only explanation for the presence of this newly discovered DNA, says anthropological geneticist Paul Verdu of Stanford University. He thinks the DNA may be the genetic stamp left by a common ancestor of modern humans and another species. The DNA may have morphed so much in non-African groups, just by chance, that it is now unrecognizable.
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Title Annotation:Humans
Author:Saey, Tina Hesman
Publication:Science News
Geographic Code:60AFR
Date:Sep 8, 2012
Words:428
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