Neanderthal Genome Mapping Our Similarities, Differences

"The rough draft of the Neanderthal genome is complete. Using 38,000-year-old bone fragments and new shotgun sequencing technology, researchers have sequenced 3.7 billion base pairs of Neanderthal DNA. That's more than the 3 billion base pairs expected in the final draft of the genome, but many of the snippets of genetic code are repeats. At this stage scientists have just 63 percent of the hominid genome completely sequenced. Still, even with a rough draft, scientists can begin to isolate the genetic variations that are uniquely, irreducibly human. "The first big goal of this project, which is really about understanding our evolution, is this catalog of [evolutionary] changes," said the project leader, Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. "The second goal is finding evidence of positive selection, of where something changed in our ancestors that really made a difference in how we reproduce and survive."

Neanderthals are our closest relatives on the hominid family tree. We split from them about 500,000 years ago and for the next 475,000 years or so, modern humans and Neanderthals coexisted on the planet and sometimes even in the same region. The relationship between humans and our cousins has inspired lots of ideas about sex and war. Recent scientists have speculated that Neanderthals and humans in Europe could have interbred, while others have speculated that humans killed off the Neanderthals.

The draft genome does not yet provide enough evidence to answer some of the big questions about the relationship between humans and our cousins, but already little details are emerging. For example, last year the team revealed that a gene known to be important in the development of speech was present in the Neanderthal genome. "There's no reason to think they [couldn't] articulate as we do, although there are many more genes related to speech," Pääbo told reporters at the AAAS annual meeting in Chicago, which runs through Monday.

We also know that Neanderthals were sophisticated toolmakers and were highly intelligent, although that remains a subject of debate. The question becomes, then, what switch was thrown that allowed modern humans to surpass all previous hominid species and become the world-dominating predator that we are? "Why are Neaderthals so important to us and why do we want to know about their genome? Because the Neaderthals represent the last divergent branch of the human evolutionary bush," said Jean-Jacques Hublin, who studies evolution at the Planck Institute. "Studying the Neanderthal genome tells us what makes modern humans really modern and really human."

In small ways, studying the Neanderthal genome tells us something about Neanderthals, too. For example, Pääbo revealed that Neanderthals didn't possess a mutation often found in humans that allows us to metabolize lactose, which lets cow's milk do a body good. "We can start looking at interesting genes to start seeing what Neaderthals might have been like," he said.

With the draft completed, the researchers will try to collect more DNA and sequence it faster to get a "deeper" read on the genome, increasing its accuracy and filling in the gaps. They now have five archaeological sites from which they can recover genetic fragments, including a new excavation in Spain that is taking precautions to prevent destroying or contaminating the fragile genes. The more complete and redundant sequencing effort will allow the scientists to isolate genes unique to the Neanderthals, not just variations on human genes. By sequencing 15 or 20 times as many base pairs as exist in the Neanderthal genome, the researchers will be able to separate mistakes from unique genes. "We're going to sequence things much deeper, get 15 to 20 times coverage," Pääbo said. "Then, we'll be able to believe things that are Neanderthal-specific." But don't get your hopes up for creating a Neanderthal clone, a real-life Encino Man meets Jurassic Park. Researchers say that will remain technically impossible."

- Alexis Madrigal, http://blog.wired.com/wiredscience/2009/02/rough-draft-of.html