May 7, 2010

Some Of Us Have Genetic Ties To The Neanderthal

According to a genetic study, researchers have found that Neanderthals and modern humans interbred, most likely at the time when early humans first began to migrate from Africa.

In Friday's issue of the journal Science, researchers report that people of European, Asian and Australian origin all have Neanderthal DNA. They discovered, however, that people from Africa have no traces of the ancient genome.

Researchers believe the study will help resolve a long-lasting debate over whether Neanderthals and modern humans did more than just coexist with each other throughout the Middle East and Europe.

Study leader, Svante Paabo of the Max Planck Institute in Munich, Germany, said: "Those of us who live outside Africa carry a little Neanderthal DNA in us."

"The proportion of Neanderthal-inherited genetic material is about 1 to 4 percent. It is a small but very real proportion of ancestry in non-Africans today," Dr. David Reich of Harvard Medical School in Boston told Reuters.

Paabo said that the findings show no identifying traits of Neanderthal in modern humans. "As far as we can tell these are just random pieces of DNA," he added.

Whole genome sequencing was used by researchers to examine DNA from Neanderthal bones found in Croatia, Russia, Germany and Spain. New methods were implemented to gather, distinguish and sequence the DNA. Paabo said that most of the bones are from more than 30,000 years ago and contain very little preserved DNA. 97 percent of the DNA the team did extract was from bacteria and fungi, he said.

The Neanderthal DNA they were able to extract was compared to DNA sequences from five people from Europe, Asia, Papua New Guinea and Africa.

Results of the comparison in genomes between the Neanderthal and modern humans paint an intimate portrait of two very distinct cultures coexisting and interacting with each other, and give researchers insight into a people that no longer exist.

"It certainly is an indication of what went on socially when Neanderthals and modern humans met," Paabo said.

"There was interbreeding at some little level. I would prefer to leave it to others who want to quarrel over whether to call us separate species or not," he added. "They were not genetically very distinct from us."

The DNA sequences date back some 80,000 years, when modern humans moving through the Middle East on their way out of Africa would have encountered the southernmost populations of Neanderthals.

Five genes were identified that were unique to the Neanderthals, including three skin genes. "This suggests that something in the physiology or morphology of the skin has changed in humans," Paabo told Reuters.

After human origins were traced from Africa into the Middle East, they then spread through to other parts of the world. The genetic relationship with Neanderthals was found in people from Europe, China and Papua New Guinea, but not from people from Africa.

More Africans should be sampled, suggested Todd Disotell, an anthropologist at New York University. "My guess is, as we sample more Africans we're going to find some of these old lineages in Africa," he said.

Disotell noted that the researchers looked at the genomes of a West African and a South African, but not someone from northeast Africa, where he said the mixture would be more likely to have occurred.

Paabo agreed that the findings do not mean that only people from outside Africa have Neanderthal biology. More studies might prove that Africans do have some of that DNA as well.

Neanderthals existed from about 400,000 years ago to about 30,000 years ago before becoming extinct. They coexisted with modern humans for 30,000 to 50,000 years in Europe and western Asia.

Although modern humans and Neanderthals are both hominids, the fossil record showed us long ago that we differ physically from Neanderthals, in a variety of ways. But by genetic codes and proteins, the new research reveals that we hardly differ at all. It also shows that we both -- Neanderthals and modern humans -- differ from chimps in virtually identical ways.

"The astonishing implication of the work we've just published," says Prof. Gregory Hannon, Ph.D., of Cold Spring Harbor Laboratory (CSHL), "is that we are incredibly similar to Neanderthals at the level of the proteome, which is the full set of proteins that our genes encode."

Image Courtesy NASA


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