31 Aug 2012

Scientists assemble first complete genome from early man

Researchers have recovered the entire genetic code from a 50,000 year old fossil of a human predecessor found in a Siberian cave. It’s a step that could revolutionise the study of early humans.

Fingerbone fossil found in Siberian cave used to sequence first complete genome from early man (Max Planck Institute for Evolutionary Anthropology)

The entire DNA sequence, as complete as that from a living human, was extracted from a tiny fragment of bone from a little finger and two teeth.

The analysis reveals they belonged to a girl, who had brown skin, brown eyes and brown hair. Her closest living descendants are aboriginal people living in modern day Australia and melanesian groups in South East Asia, though they share just a few percent of their DNA. This suggests that mixing between her kind and early modern humans happened for only a short period, many tens of thousands of years ago.

Until now only fragmentary sequences of DNA have been extracted from fossils of modern humans and our ancient cousins, the neanderthals. This new research, published in the journal Science, uses a new technique to recover nearly all the genetic code from very damaged fragments of genetic material.

“We can now know as much about someone’s DNA who lived 50 thousand years ago as someone who is still alive today,” said Matthias Meyer of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany who devised the new technique.

Denisova cave in Siberia (Max Planck Institute for Evolutionary Anthropology)

The fossil fragments were discovered in the Denisova cave in southern Siberia in 2010, near to remains of neanderthals and early modern humans. But who these new “Denisovan” humans were, or how they were related to us, was not clear.

The new genetic sequence shows the Denisovans were much more closely related to neanderthals than our ancestors were. They also know, by looking at the DNA the girl inherited from each of her parents, that Denisovans had much lower genetic diversity than modern humans.

As the genome is studied in more detail it will shed new light on this particular human ancestor. But the power to extract entire genetic sequences from samples of DNA degraded over millennia is a major breakthrough in the study of human origins.

By comparing the ancient DNA sequence with our own, the researchers identified about 100,000 changes in the genome that have occurred since we split from the Denisovans. Many of the changes affect genes involved in brain function and nerve development.

“This research will help determining how it was that modern human populations came to expand dramatically in size as well as cultural complexity while archaic humans eventually dwindled in numbers and became physically extinct”, says Svante Pääbo, who led the research team at the Max Planck Instiute.

The team are already using the technique to decode the entire genome of a neanderthal, and hope it could be used to shed new light on other important fossils too. They also suggest the technique could improve forensic science, where investigators are often working with very small amounts of damaged DNA from a crime scene.

(Pictures courtesy of Max Planck Institute for Evolutionary Anthropology)