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The DNA from the caves

Genome of Neanderthal man brings clues about our origin


The Vindija cave housed for 38 thousand years the fossil now sequencedJOHANNES KRAUSE, MAX PLANK-INSTITUTE E EVOLUTIONARY ANTHROPOLOGY

38 thousand years ago, there lived in present-day Eastern Europe a man who would not remotely imagine that he would become history. In 1980, archeologists found in a Vindija cave, in Croatia, one of his femurs, whose genome is now being sequenced by two teams of geneticists, one in the United States and the other in Germany. The first results of the two groups are, respectively, in the scientific magazines Science and Nature (November 16 and 17). Only a fraction of the work is ready, but it is already enough to estimate when two sister species – Homo sapiens and Homo neanderthalensis – became distinct and how similar their DNAs are. The complete sequence of the Neanderthal genome is promised for two years from now. Researchers believe that it can clarify the origin of characteristics of anatomy and behavior that define modern man.

The team led by Edward Rubin is working at the Lawrence Berkeley National Laboratory, in California, United States. The group decoded 65 thousand base pairs, the units that make up DNA. There is a lot missing, as the genome of the modern man has around 3 billion base pairs. And the two humans are genetically very similar: Rubin’s sample indicates a 99.5% similarity. The group does not see evidence of crossbreeding between the two species – a hypothesis recently aired by other researchers, such as Bruce Lahn and colleagues in an article published in the PNAS also in November – and calculates that the two species separated 370 thousand years ago.

The German team, coordinated by Svante Päabo, of the Max Planck Institute for Evolutionary Anthropology, has analyzed more DNA, 1 million base pairs, and calculated a more distant date for the separation between the two species: 516 thousand years ago. But, as there is a large margin of error, it is not yet known whether the difference between the two estimates is relevant. The data does not indicate a mixture of genes of the two species: if there was crossbreeding, it was limited and involved above all male homo sapiens and female homo neanderthalensis.

The work of the two groups is a technical feat. Subject for thousands of years to bad weather, the degraded genetic material is extracted from the fossils in tiny fragments. The jigsaw puzzle can only be put together using as a framework the genome of the modern man. Moreover, the old DNA comes mixed with the DNA of intruders, like the DNA of bacteria and present-day humans. In spite of the challenges, the researchers involved in the project say that they have the technology to complete the sequencing.

The Neanderthal men lived in Europe and in the west of Asia between 400 thousand and 30 thousand years ago. According to the fossil records, they became extinct after the arrival of  Homo sapiens in the region, from Africa. Archeological artifacts indicate that there may have been a cultural exchange between the two hominids, although they may not have lived together pacifically. Many researchers believe that the competition between the two species caused the extinction of the Neanderthal man. The victorious species not only lived, but spread over the world, originating the man that today occupies from deserts to megalopolises.