Did the first modern humans in Europe share a bed with nearby Neanderthals? Almost certainly not, according to a new analysis of 28,000 year old Cro-Magnon DNA.
The Cro-Magnons were the first modern Homo sapiens in Europe, living there between 45,000 and 10,000 years ago. Their DNA sequences match those of today's Europeans, says Guido Barbujani, an evolutionary anthropologist at the University of Ferrera, Italy, suggesting that "Neanderthal hybridisation" did not occur.
His team published similar findings in 2003, but that study left open the possibility that the Cro-Magnon DNA had been contaminated by the researchers' own genes.
Now, Barbujani's team has sequenced a section of DNA from everyone who handled the sample and found no trace of contamination.
"We knew we had a full and complete list of people who had potentially contaminated the specimen," he says. "In this case we are really sure that that sequence does not represent contamination."
Tom Gilbert, an expert on ancient DNA at the University of Copenhagen, Denmark, says the new tests convinced him of the Cro-Magnon DNA authenticity. "I was one of the guys who criticised it heavily the first time," he says.
Prehistoric family tree
The reanalysed Cro-Magnon DNA, which comes from maternally-inherited mitochondria, casts further doubt on the kinship between Neanderthals and humans, he says. However, the paucity of Cro-Magnon DNA samples – just a handful exist, with Barbujani's coming from a cave in southern Italy – still leaves the door ajar.
Barbujani agrees that mitochondrial DNA alone can't rule out the possibility that Cro-Magnons and Neanderthals bred, but nearly every ancient human skeleton recovered in Europe belongs to either Cro-Magnons or Neanderthals, not the hybrids that would be expected from interbreeding.
The only potential intermediate is a child's skull found in Portugal and dated to 24,500 years ago – after Neanderthals went extinct. However, other researchers have questioned the skeleton, suggesting it belonged to a "chunky" human child.