Cross-Species Interbreeding Discovered via DNA Analysis

A new study conducted by investigators at the University of Arizona, in the United States, demonstrates that modern and “archaic” humans interbred in Africa between 60,000 and 20,000 years ago. The behavior led to the transfer of small amounts of “old” genetic material into modern-day humans.

What the research implies is that each and every one of us carries at least some genetic material that originates in species of primitive humans that have long since disappeared. The exact locations at which these events occurred have not yet been determined precisely.

Evolutionary biologists, geneticists and mathematicians were all a part of the research team, which was coordinated by UA geneticist Michael Hammer. Details of the study appear in the latest issue of the esteemed journal Proceedings of the National Academy of Sciences (PNAS).

The investigation was funded by the Biological Anthropology Division at the US National Science Foundation (NSF), in Arlington, Virginia. This study was selected over others because it had the potential to be the first to demonstrate that separate human forms interbred in Africa.

Hammer's work is now the first to propose and confirm that this was indeed the case. “It appears some level of interbreeding may have occurred in many parts of the world at different times in human evolution,” the geneticist reveals.

In past studies on this topic, researchers focused their efforts on understanding the interactions between Homo sapiens and Neanderthals in Europe, or between different primitive humans in Asia. However, African interactions have been largely ignored because the continent is the cradle of humanity.

The reason why interbreeding is very possible in Africa is because numerous species of humans coexisted there for longer periods of time than they did in other parts of the world. In Europe, for example, the arrival of Homo sapiens coincided with the disappearance of Neanderthals.

“We estimate that the archaic DNA fragments that survive in modern African genomes come from a form or forms that diverged from the common ancestor of anatomically modern humans 700 thousand to 1 million years ago,” Hammer argues.

“This archaic genetic material is more prevalent in west-central African populations, possibly reflecting a hybridization event or process that took place in central Africa,” the investigator goes on to say.

“The populations that interbred were similar enough biologically so that they were able to produce fertile offspring, thus allowing genes to flow from one population to the other,” the scientist concludes.