Tuesday, 6 September 2011

The Origins Of Archaic DNA

Michael Hammer with the skull of an ancient hominid
We know that Homo sapiens  appeared in Africa around 200,000 years ago with the oldest fossils dating to around 180,000 years old. These fossils, consisting of two craniums from the Omo River in southern Ethiopia, were definitely from our species. Yet when we studied our genome, we found two distinct factions; modern and archaic DNA. Genetic evidence suggests such a divide could have evolved as a result of interbreeding between Homo sapiens and more archaic forms of human such as Homo neanderthalensis.

A team from the Arizona Research labs led by Michael Hammer studied the interbreeding hypothesis by analysing the genomes of various populations of sub Saharans for traces of archaic DNA. By correlating the data, they created a simulation of history to look for patterns which matched real life. They found several prominent patterns of inheritance that could only have come from interbreeding between Homo sapiens and Homo neanderthalensis. 

By studying chromosomal DNA, they found that the divide appeared around 40,000 to 50,000 years ago, the time when humans left Africa and encountered Homo neanderthalensis in Ice Age Europe. This study has added to the growing pile of genetic evidence that humans and Neanderthals interbred. A previous blog posed used evidence from the gene diversity which controls the immune system.

The team are going to look for genes which would have given a selective advantage for humans in Africa and the Middle East if they had been transferred through interbreeding with other species of human. Such evidence is vital as it not only explains our origins, but also how Neanderthals could have died out; a long running palaeoanthropological mystery.