Primitive Homo sapiens and Neanderthals didn't produce children together despite swaths of shared DNA, some scientists say, casting doubt in a new study on a contentious idea about the origin of modern humans.

Anthropologists who found that humans with non-African lineage shared up to four per cent of their DNA with the long-extinct Neanderthals concluded in 2010 that the link was likely due to hybridization — or sex between the two hominid species.

But researchers at the University of Cambridge said this week that computer models simulating the last 500,000 years of population migration offered a different interpretation of how we came to share DNA with our ancient cousins.

The researchers say the DNA crossover is actually a remnant from a common ancestor from half a million years ago, not a result of Homo sapiens and Neanderthals interbreeding.

This common ancestor lived in parts of Africa and Europe, but divided into separate populations in Europe and Africa around 300,000 to 500,000 years ago, according to the latest study.

2 divergent groups from common ancestor

The researchers theorize that once both ancient groups were geographically isolated, the African population evolved into Homo sapiens while the European range eventually became Neanderthals.

Homo sapiens were believed to have emerged from Africa around 70,000 years ago.

Based on the computer models, Cambridge evolutionary biologists Dr. Anders Eriksson and Dr. Andrea Manica concluded there was no compelling evidence to suggest any sort of fling between Neanderthals and Homo sapiens.

"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," Manica said in a news release.

"So, if any hybridization occurred — it's difficult to conclusively prove it never happened — then it would have been minimal and much less than what people are claiming now."

That hasn't put the debate to rest, however. David Reich, a Harvard Medical School professor of genetics who co-authored the 2010 study supporting hybridization, argued that population diversity isn't enough to explain the shared genes.

Last week, Reich and his colleagues even published a draft paper that further analyzed the genetic variants shared between Neanderthals and non-African humans.

The analysis put the introduction of Neanderthal DNA at just a few tens of thousands of years ago. If the dates are correct, that would mean that the emergence of the DNA was so recent it could only have showed up after modern humans migrated from Africa, and after the origin of Neanderthals 320,000 years ago.

The paper supporting interbreeding is scheduled for publication in the journal PLoS Genetics, while the University of Cambridge study is published in the latest edition of the journal Proceedings of the National Academy of Science.