Our ancestors, Homo sapiens, cohabited the Earth with others from the Homo genus, including Neanderthals. Now there is more evidence to suggest the two species mated.
Researchers think it is possible that humans of European or Asian decent may have between 1 and 4 percent of Neanderthal DNA. Others even suggest that this DNA might be the cause of some basic traits (hair, skin) or even modern diseases like Crohn's.
It has never been completely clear how Homo sapiens inherited this DNA. Two hypotheses have floated around. According to the Verge:
"The first hypothesis puts forth that idea that certain human populations — those that went on to become modern Eurasians — evolved in isolated patches in Africa that allowed them to stay genetically similar to Neanderthals after they split from their shared common ancestor. The interbreeding hypothesis, on the other hand, states that bouts of human-Neanderthal reproduction would have occurred after humans migrated out of Africa."
A team of European scientists used statistics and an evolutionary model to test both hypotheses, and their conclusion adds great certainty to the interbreeding hypothesis. Co-authors Konrad Lohse and Laurent A. F. Frantz published their findings yesterday in the scientific journal Genetics.
To test the two hypotheses the scientists split the genome into short blocks and used them to compute the possibility of each scenario. According to Genetics, "We apply this likelihood scheme to triplets of human and Neandertal genomes and compare the relative support for a model of admixture from Neandertals into Eurasian populations after their expansion out of Africa against a history of persistent structure in their common ancestral population in Africa."
Their conclusion contradicts a 2012 study that was published in Proceedings of the National Academy of Sciences, and provides more certainty that the species mated. According to co-author Laurent Frantz of the Wageningen University in the Netherlands, "When we tested two hypotheses, we got a high support for a scenario where humans and Neanderthals interbred." The scientists can't completely discount hypothesis one, but say that their evidence shows that it is not the sole reason for the genetic similarities.
What does this mean in terms of evolution? Well, if anything, the mating between the two species complicates questions about how the two species interacted.
Many argue over the fate of Neanderthals. The species died out 30,000 years ago. Some speculate that it was a violent end. "Some think that we outcompeted [other hominins] or that they were killed by humans," Frantz said according to the Verge. "But now we can see that it's not that simple."