Wednesday, April 21, 2010

Good News for Inter-Species Sex!

I always felt it a tragedy that the Neanderthals disappeared without a trace. So I'm overjoyed to find that they didn't go away. Modern humans mated at least twice with them and remnants of Neanderthals live on in our genome! Here's a bit from an article by Rex Dalton in Science magazine:
Archaic humans such as Neanderthals may be gone but they're not forgotten — at least not in the human genome. A genetic analysis of nearly 2,000 people from around the world indicates that such extinct species interbred with the ancestors of modern humans twice, leaving their genes within the DNA of people today.

The discovery, presented at the annual meeting of the American Association of Physical Anthropologists in Albuquerque, New Mexico, on 17 April, adds important new details to the evolutionary history of the human species. And it may help explain the fate of the Neanderthals, who vanished from the fossil record about 30,000 years ago. "It means Neanderthals didn't completely disappear," says Jeffrey Long, a genetic anthropologist at the University of New Mexico, whose group conducted the analysis. There is a little bit of Neanderthal leftover in almost all humans, he says.

The researchers arrived at that conclusion by studying genetic data from 1,983 individuals from 99 populations in Africa, Europe, Asia, Oceania and the Americas. Sarah Joyce, a doctoral student working with Long, analyzed 614 microsatellite positions, which are sections of the genome that can be used like fingerprints. She then created an evolutionary tree to explain the observed genetic variation in microsatellites. The best way to explain that variation was if there were two periods of interbreeding between humans and an archaic species, such as Homo neanderthalensis or H. heidelbergensis.

"This is not what we expected to find," says Long.

Using projected rates of genetic mutation and data from the fossil record, the researchers suggest that the interbreeding happened about 60,000 years ago in the eastern Mediterranean and, more recently, about 45,000 years ago in eastern Asia. Those two events happened after the first H. sapiens had migrated out of Africa, says Long. His group didn't find evidence of interbreeding in the genomes of the modern African people included in the study.
I'm betting this new finding will help close the gap in an old debate. Twenty years ago there were two camps on human origins: (a) out of Africa and (b) the candelabra theory of simultaneous evolution. The best evidence for the candelabra theory was the strange connection between local homo erectus traits and modern traits, specifically the shovel-toothed denture of Orientals (see here). I have no knowledge, but I'm guessing that this unusual denture is explicable by the interbreeding 45,000 years ago in eastern Asia. I will have to wait to see if my wild stab is confirmed by the evidence or shown to be complete hooey.

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