A publication of the Archaeological Institute of America
Will an extinct genome reveal what makes us human?
An argument that began 150 years ago with a stunning discovery in Germany's Neander valley may soon come to an end in an ultra-sterile lab at the Max Planck Institute for Evolutionary Anthropology in Leipzig. Genetic anthropologist Svante Pääbo is teasing the genetic secrets out of bones that have lain buried as glaciers advanced and retreated over Europe. Today, the building is sweltering, the air conditioning is out, but Pääbo is coolly confident that he has found a way to reassemble the genetic code of a Neanderthal who lived in Croatia 45,000 years ago and who may provide answers to some important questions: Were Neanderthals a separate species from us? Did they interbreed with modern humans? Do their genes survive in modern humans?
"The big picture is that modern humans came out of Africa and replaced Neanderthals," says Pääbo, a bristly browed Swede with a penchant for wearing sandals and goofy socks. "The really important question is what the mutations are that became fixed in [modern] humans. What are these things that are unique to us with respect to Neanderthals?"
Finding these unique mutations could reveal the biological basis for the way that modern human brains developed, and how we acquired language and art. It may also settle the long-running debate between scientists who believe that anatomically modern humans came from Africa and gradually forced the Neanderthals into extinction, an idea called the Out-of-Africa theory, and those who believe that Neanderthals were among the archaic human species with whom anatomically modern humans interbred as they moved across the globe, an idea called Multi-Regional Evolution.
Nuclear DNA, the prize for genetic sequencing, contains the Neanderthal's full genetic code. Some of Pääbo's earlier work focused on retrieving mitochondrial DNA from Neanderthal bones. (Mitochondria are the microscopic organelles that provide energy to our cells.) Those studies supported the Out-of-Africa theory by showing that no strains of Neanderthal mitochondria survive in modern humans. Because each cell has several mitochondria and only one set of nuclear DNA, mitochondrial DNA is much easier to find, but it only contains a small portion of the Neanderthal's genes. A new sequencing technique is allowing researchers to piece together the elusive nuclear DNA.
Finding Neanderthal nuclear DNA is like alchemy, only better. A small piece of Neanderthal bone is drilled out and dissolved into a test-tube solution. The sample is flown to a company called 454 Life Sciences in Branford, Connecticut. It is then poured into a machine that sifts through every miniscule fragment of DNA, discarding the 95 percent of recovered genetic material that comes from contaminants such as bacteria or people who have handled the bone. The process is like picking millions of needles out of billions of haystacks.
Even so, Pääbo may have the entire Neanderthal genome sequenced in the next 18 months. As the pieces fall into place the biological differences between modern humans and Neanderthals will come into focus. One interesting marker is a gene labeled FOXP2, which researchers suspect plays a role in the development of language. By comparing the Neanderthal FOXP2 gene to the modern human and chimpanzee versions of the gene, Pääbo believes he can determine whether Neanderthals were capable of developing complex languages, and that could help scientists determine whether language gave modern humans enough of a survival advantage to doom Neanderthals to extinction.
Michael Dumiak is a freelance science writer based in Berlin, Germany.