Generally accepted theories of hybridization— or the concept that modern humans and Neanderthals interbred at some point in the development of the current human race—have been debunked by a new study conducted by University of Cambridge researchers, according to the University of Cambridge Research News.

According to the study, published in the most recent edition of the Proceedings of the National Academy of Sciences of the United States of America (PNAS), a common ancestry is responsible for the 1-4 percent DNA shared between Eurasian (European and Asian) populations and Neanderthals, rather than hybridization. By contrast, Cambridge says African populations do not share any DNA similarities with Neanderthals—previously explicated by theories that interbreeding occurred when African populations moved into Eurasia.

Rather than a genetic difference based on hybridization, scientists say the new study shows that common ancestry was in fact the reason for genetic similarity.  The common ancestor shared by Africa and Eurasia approximately half a million years ago is the same population that produced both anatomically modern humans and Neanderthals, according to the study.

Researchers cite numerous genetic and archaeological studies as saying populations at the time were structured according to the amount of exchange possible within the population—that is, those populations with limited traveling capabilities remained distinct in terms of genetics and morphology.

The study says when the European and African range split, European populations evolved into Neanderthals while African populations evolved into anatomically modern humans. Cambridge scientists say the African population retained more of the ancestral DNA, including the small amount shared with Neanderthals, throughout their evolution. Therefore, Cambridge says the similarities between Eurasians and Neanderthals would have already been present upon the migration of African (modern human) populations into Europe and Asia.

The University of Cambridge study, led by Dr. Andrea Manica, is based upon a model focused on discovering whether differences in genetic code were attributable to the proximity of modern human populations. Scientists say the model used modern human similarities in genetic makeup to infer the distinct characteristics of proximal populations within a continent. The Cambridge study model then simulated the evolution of populations over the last half a million years and estimated similarities between Neanderthals and modern African and Eurasian humans.

“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,” says Dr. Manica.

The Cambridge scientist added that the populations coming out of Africa is more closely aligned with Neanderthals than their African counterparts. Dr. Manica said she hopes the study will provoke more interest in the topic and further research.

“Hopefully, everyone will become more cautious before invoking hybridization, and start taking into account that ancient populations differed from each other probably as much as modern populations do.”