A new genetic study of nearly two thousand people from around the world suggests that some of our ancestors bred with other species of humans, such as Neanderthals, at least twice. "The researchers suggest the interbreeding happened about 60,000 years ago in the eastern Mediterranean and, more recently, about 45,000 years ago in eastern Asia," Nature News reports from the annual meeting of the American Society of Physical Anthropologists in Albuquerque, New Mexico.
     The researchers arrived at that conclusion by analyzing over 600 genetic markers, called microsatellites, from 1,983 individuals from 99 populations in Africa, Europe, Asia, Oceania and the Americas. As humans began fanning out from Africa, between 50 and 100,000 years ago, these markers changed, allowing researchers to determine the relationship between different populations and to estimate when they split from one another.
     If humans bred only with other humans, all these markers would create a neat phylogenetic tree, showing that human genetic diversity can be traced to a single population that existed in Africa in the last 100,000 years. Instead, a team led by Jeffrey Long, at the University of New Mexico, found evidence that some of the markers looked far too old to have come from humans. Inbreeding with other ancient species is the likeliest explanation. "It means Neanderthals didn't completely disappear," he told Nature.
     Last month, a team at the Max Planck Institute for Evolutionary Anthropology in Leipzig Germany recovered hominin DNA in Mongolia from a 30-50,000-year-old finger bone that appears to be neither Neanderthal nor human. Its ancestors, or another yet-to-be-discovered kind of archaic hominin, could have bred with humans.
     Previous studies of small parts of the Neanderthal genome have found no evidence for interbreeding.
     
Sources: Nature News (20 April 2010), News Scientist (21 April 2010)