By DISCOVER MAGAZINE
Added: Fri, 08 Aug 2008 23:00:00 UTC

Thanks to SPS for the link.

http://blogs.discovermagazine.com/80beats/2008/08/08/neanderthal-dna-shows-they-rarely-interbred-with-us-very-different-humans/

Neanderthal DNA Shows They Rarely Interbred With Us Very Different Humans

For the first time, scientists have sequenced the mitochondrial DNA of a Neanderthal. Researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, analyzed the genetic material from a 38,000-year-old leg bone found in Croatia and published their findings today in Cell.

The mitochondria are only passed down the female line, so can be used to trace the species back to an ancestral "Eve", the mother of all Neanderthals. The team analysed the DNA of 13 genes from the Neanderthal mitochondria and found they were distinctly different to modern humans, suggesting Neanderthals never, or rarely, interbred with early humans. The genetic material shows that a Neanderthal "Eve" lived around 660,000 years ago, when the species last shared a common ancestor with humans [Guardian].

It's difficult to know exactly when one species diverges into two—the sceintists estimated their date by comparing the Neanderthal DNA to that of modern humans, chimps, and bonobos. Starting with the commonly-held idea that chimps and humans diverged six to eight million years ago, and factoring in the rate of mitochondrial DNA evolution, the team dated Neanderthal separation from humans back 660,000 years.

According to John Hawks, a University of Wisconsin-Madison biologist not involved in the study, the work further dispels the idea that modern humans are closely related to Neanderthals. "Comparing the complete mitochondrial DNA genomes of a Neandertal and many recent humans presents a very different picture," Hawks says. "Humans are all more similar to each other, than any human is to a Neandertal. And in fact the Neandertal sequence is three or more times as different, on average, from us as we are from each other" [Science News].

However, much remains to be learned about Neanderthal DNA: The mitochondrion — a structure often dubbed the cell's powerhouse — contains a mere 16,565 DNA letters that code for 13 proteins, whereas the nucleus holds more than 3 billion letters that produce more than 20,000 proteins [New Scientist]. Still, study leader Richard Green says he hopes to be well on the way to a complete Neanderthal genome by year's end.

TAGGED: EVOLUTION, GENETICS