New research from the University of Cambridge says that the theory that humans and Neanderthals interbred may not be correct. Researchers say that the similarities found between humans and Neanderthals are due to a common ancestor and not due to inbreeding.

Previous studies had shown that Neanderthals and people with a European-Asian (Eurasian) descent share between 1 and 4 percent of their DNA while people with African descent do not share any portion of their DNA with Neanderthals. These studies had said that hybridization between Neanderthals (living in Europe) and the modern humans might explain the shared DNA.

New research says that this is not true and provides and alternative theory to explain the shared genetics. The research team used computer simulations to assess the probability of the shared genome arising out of inbreeding and from that of a common ancestor.

Researchers concluded that the similarities in the DNA are due to common ancestry and that Neanderthals and modern humans weren't inbreeding.

"Thus, based on common ancestry and geographic differences among populations within each continent, we would predict out of Africa populations to be more similar to Neanderthals than their African counterparts - exactly the patterns that were observed when the Neanderthal genome was sequenced; but this pattern was attributed to hybridization," Dr. Andrea Manica, from the University of Cambridge, lead author of the study.

Researchers say that about half a million years ago, an ancestor of both modern human and Neanderthal lived across Africa and Europe. The populations of this ancestor weren't mixed but were genetically distinct from each other due to limited migration.

When the ranges of Africa and Europe separated about 300-350 thousand years ago, the European range evolved to become Neanderthals while the African range became the modern humans.

The modern human retained some genetic variants of the common ancestor. When these modern humans expanded from Africa about 70 thousand years ago, they bought their share of genetic variations along with them making people in Europe and Asia more genetically similar to Neanderthals.

"Our work shows clearly that the patterns currently seen in the Neanderthal genome are not exceptional, and are in line with our expectations of what we would see without hybridization. So, if any hybridization happened - it's difficult to conclusively prove it never happened - then it would have been minimal and much less than what people are claiming now," Manica added.

The study was published in the Proceedings of the National Academy of Sciences.