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Chimps and Bonobos Had a Fling in the Past

An adult female chimpanzee and her juvenile daughter rests on a fallen tree at Ngogo in Kibale National Park, Uganda. | Kevin Langergraber

A new genetic analysis of chimpanzees and bonobos reveals that these two great ape species likely interbred several hundred thousand years ago. The results, published in the 28 October issue of Science, will provide a better understanding of the genetic flow that plays a role in the evolution of great apes.

Tomas Marques-Bonet of the Universitat Pompeu Fabra noted that studying gene flow between ancient humans such as Neanderthals, Denisovans and the ancestors of modern humans has revealed numerous genes under selection that affect disease and an individual's traits. "Gene flow is then an important component in fully understanding speciation processes and particularly in the recent evolution of hominids," he said.

Great apes, or hominids, are a group of species that includes gorillas, humans, chimpanzees and bonobos, among others. Of this group, chimpanzees and bonobos are the closest living relatives to modern humans. While these two species are known to interbreed in captivity, historic genetic flow between the two species in the wild is less clear.

To gain more insights, Marques-Bonet and colleagues analyzed the complete genomes of 10 bonobos and 65 chimpanzees. They included more chimpanzees from various regions in Africa in their analysis, because previous genetic studies have suggested that four distinct geographical subspecies of chimpanzee exist.

"Our study is the first study to fully characterize the admixture signal in the genomes of chimpanzees and bonobos," said Marques-Bonet. "We do this by applying some known and novel techniques to estimate the amount and the timing of the gene flow events."

Based on their analyses, they estimate that gene flow between the two species occurred between 200,000 and 550,000 years ago. Central, eastern and Nigeria-Cameroon chimpanzees share significantly more genetic information with bonobos than western chimpanzees. What's more, similar to Neanderthal genetic patterns in humans, some bonobo genetic information has been deleted in the chimpanzee genome, suggesting that some bonobo genes may have been disadvantageous for chimpanzees.

Co-author Christina Hvilsom, a researcher at Copenhagen Zoo, said, "We have learned from the comparable studies of modern humans and Neanderthals that gene flow occasionally has an impact on parts of the genomes that provide some advantages for the admixed individuals. Our next step is to start exploring our dataset in the search of such patterns of selection, for new signatures of gene flow among chimpanzee subspecies."

Hvilsom noted that their comprehensive analyses of chimpanzee genomes revealed that the apes' genetic information can be used to determine from which country, and even which region, individual chimpanzees originated. Such information could be used to help identify hotspots for illegal trafficking of these animals, Hvilsom said, and to improve conservation efforts.