London, Apr 21 (ANI): Archaic humans such as Neanderthals interbred with the ancestors of modern humans twice, leaving their genes within the DNA of people today, according to a genetic analysis of nearly 2,000 people from around the world.
The discovery adds important new details to the evolutionary history of the human species and it may help explain the fate of the Neanderthals, who vanished from the fossil record about 30,000 years ago.
"It means Neanderthals didn't completely disappear," Nature quoted Jeffrey Long, a genetic anthropologist at the University of New Mexico, as saying.
He insisted that there is a little bit of Neanderthal leftover in almost all humans.
The researchers arrived at that conclusion by studying genetic data from 1,983 individuals from 99 populations in Africa, Europe, Asia, Oceania and the Americas.
Sarah Joyce, a doctoral student working with Long, analyzed 614 microsatellite positions, which are sections of the genome that can be used like fingerprints.
She then created an evolutionary tree to explain the observed genetic variation in microsatellites.
The best way to explain that variation was if there were two periods of interbreeding between humans and an archaic species, such as Homo neanderthalensis or H. heidelbergensis.
"This is not what we expected to find," said Long.
Using projected rates of genetic mutation and data from the fossil record, the researchers suggest that the interbreeding happened about 60,000 years ago in the eastern Mediterranean and, more recently, about 45,000 years ago in eastern Asia.
Those two events happened after the first H. sapiens had migrated out of Africa, said Long.
However, his group failed to find evidence of interbreeding in the genomes of the modern African people included in the study.
The researchers suggest that the population from the first interbreeding went on to migrate to Europe, Asia and North America.
Then the second interbreeding with an archaic population in eastern Asia further altered the genetic makeup of people in Oceania.
The paleontological record also is producing fossils that complement such interbreeding theories.
The study was presented at the annual meeting of the American Association of Physical Anthropologists in Albuquerque, New Mexico. (ANI)