Neanderthal DNA sequences are 99.95% identical to modern human DNA sequences
Researchers have sequenced DNA from the leg bone of a Neanderthal man who died 38,000 years ago and said on Wednesday it shows the Neanderthals are truly distant relatives of modern humans who interbred rarely, if at all, with our own immediate ancestors.
They estimate that modern humans and Neanderthals split from a common ancestor at least 370,000 years ago, and possibly 500,000 years ago, although we share 99.95 percent of our DNA.
"We see no evidence of mixing 40,000, 30,000 years ago in Europe. We don't exclude it, but see no evidence," Edward Rubin of the U.S. Department of Energy Joint Genome Institute in Walnut Creek, California, who led one study, told reporters.
This conflicts with some evidence from other researchers, including a team who said earlier this month that humans may have inherited a brain gene from Neanderthals.
The researchers reported their findings jointly in the journals Nature and Science.
Rubin's team used one method to isolate and sequence part of the Neanderthal's DNA, while another team, led by Svante Paabo of the Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany, used a separate method to sequence a much larger amount.
Paabo was the first scientist to find and sequence Neanderthal DNA, in 1997, and first suggested that Neanderthals did not mix with modern humans.
"I think the sequence data will serve as a DNA time machine that will tell us about biology and aspects that we will never be able to get from their bones and a limited number of associated artifacts," Rubin said.
Neanderthals and modern humans are both descended from Homo erectus, which left Africa and spread around the world about 1.5 million years ago.
Neanderthals lived in Europe and the Middle East until about 30,000 years ago. Cro-Magnon people, the ancestors of modern humans, started a second wave of migration out of Africa about 10,000 years earlier.
One huge question is how closely they interacted. Paabo's and Rubin's genetic analysis both suggest there was little sexual contact, at least according to the genes from this one male found at the back of a cave in Croatia.
Paabo's team sorted through 70 Neanderthal specimens before they found a bone well-preserved enough to provide DNA. They took the tiniest samples they could to preserve the valuable bones.
They know it was a male because the DNA has a Y chromosome. Females have two X chromosomes.
Paabo's team used a gene sequencer made by 454 Life Sciences Corporation, a majority-owned subsidiary of CuraGen Corporation. He said they have refined their methods and hope to have a complete genetic sequence within two years.
They said the Neanderthal sequences are 99.95 percent identical to human DNA sequences. This compares to about a 98 percent similarity between humans and chimpanzees, who split from a common ancestor 6 million to 7 million years ago.
Three-way comparisons among the human, chimpanzee and Neanderthal genomes should shed light on what makes modern humans unique, experts agreed.
Rubin and other experts stressed that while full sequences of the human genome are available, very little is understood about what the code actually means.
"We have the book but we haven't yet read it," Rubin said.
They found, for instance, sequences linked with eye color but cannot read the code to tell what color Neanderthal eyes were.
Neanderthal DNA reveals human divergence
Neanderthal DNA will help to unlock the secrets of humanity
Neandertal DNA Partially Mapped, Studies Show
New Methods Let Scientists Analyze Neanderthal DNA
New Machine Sheds Light on DNA of Neanderthals