Modern man meets Neanderthal

October 15, 2010

Well, they actually did it. And the whole world knows about it now, even if the news is tens of thousands of years old. It was, of course, a juicy story for the world’s media: Neanderthals mated with modern humans! But for Svante Pääbo, Department Director at the Max Planck Institute for Evolutionary Anthropology in Leipzig, this is not the most important aspect of his discovery.

Traces of Neanderthals also present in the genome of Asians

The time, money and hard work paid off. In February 2009, the team announced that it had achieved its objective, but this was all that was made public; the sequence wasn’t published as there was still more work to be done. “We had the feeling that we had to tell the world we had done it, as we had questions from journalists all the time,” says Pääbo. It took just under a year to perform the analysis of the data.

Johannes Krause und Anne Butthof from Svante Pääbo's team load a genome analyzer. It can analyze several samples simultaneously.

The results are impressive – a real milestone in the study of human evolution. Pääbo and his colleagues sequenced four billion base pairs, from which they were able to reconstruct more than 60 percent of the Neanderthal sequence by comparing their data with the human genome and the chimpanzee genome.

“We were able to sequence some of the positions in the sequence several times, and others we were not able to sequence at all,” says Johannes Krause, who has been working in Pääbo’s lab since 2005. To perform the analysis, the Leipzig researchers organized a consortium of groups, mainly in the US, involving more than 50 individuals.

It came as a surprise that there was a small amount of interbreeding between Neanderthals and humans – and the news made headlines around the globe. Between one and four percent of human DNA in people living outside Africa originates from Neanderthals. The researchers were even more surprised by the fact that our burly Ice Age ancestors left their genetic traces not only in Europe, but also in China and Papua New Guinea. “That was something we didn’t expect,” says Pääbo. Until now, there has been no proof whatsoever that Neanderthals ever lived in these regions. It follows, therefore, that there must have been sexual contact before early modern humans expanded into Eurasia from Africa.

The simplest explanation would be that there was an encounter between the two groups in the Middle East. Paleontological evidence proves that the two groups lived in the same region between 80,000 and 50,000 years ago. However, the possibility that the genetic traces entered the lineage by another route somewhere in Africa about 20,000 to 30,0000 years ago cannot be ruled out completely. It would, however, require a much more complicated scenario. Further work will clarify exactly how the Neanderthal contribution to present-day humans occurred.

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