For the first time, scientists have revealed ancient gene mixing between chimpanzees and bonobos, humankind’s closest relatives, showing parallels with Neanderthal mixing in human ancestry.

Published in the journal Science, the study from scientists at the Wellcome Trust Sanger Institute and their international collaborators showed that one percent of chimpanzee genomes are derived from bonobos.

The study also showed that genomics could help reveal the country of origin of individual chimpanzees, which has strong implications for chimpanzee conservation.

Chimpanzees and bonobos are great apes found only in tropical Africa. They are endangered species and are supposedly fully protected by law, yet many chimpanzees and bonobos are captured and held illegally.

To aid the conservation effort, researchers analysed the whole genome sequences of 75 chimpanzees and bonobos, from 10 African countries, and crucially included 40 new wild-born chimpanzees from known geographic locations. They discovered that there was a strong link between the genetic sequence of a chimpanzee, and their geographic origin.

The study confirmed a main separation between chimpanzees and bonobos approximately 1.5 million years ago, and the presence of four chimpanzee subspecies in different regions. However, the researchers also found there were two additional gene flow events between the chimpanzee and bonobo populations, indicating that at least some individuals found their way across the river.

The study also included researchers from Spain, Copenhagen Zoo and the University of Cambridge and showed that there have been at least two phases of secondary contact, 200-550 thousand years ago and around 150 thousand years ago, mirroring what is believed to have happened during the last 100 thousand years of the evolution of humans.

Journal Reference: Science