A new whole-genome analysis of chimpanzees and bonobos reveals that these two great ape species likely interbred several hundred thousand years ago. A better understanding of the genetic flow between humans' closest living relatives could shed light on processes that might have played a recurring role in great ape evolution. While chimpanzees and bonobos are known to interbreed in captivity, the historic genetic flow between the two species in the wild is less clear. To gain better insights into possible historical gene flow between them, Marc de Manuel et al. analyzed the complete genomes of 10 bonobos and 65 chimpanzees. Significantly, more chimpanzees were included in their analysis, and from various regions in Africa, because previous genetic studies have suggested that four distinct species of chimpanzee exist. Following their analysis, the researchers observed clear evidence for gene flow between the two species, occurring between 200 and 550 thousand years ago, they estimate. Central, eastern, and Nigeria-Cameroon chimpanzees share significantly more genetic information with bonobos than do western chimpanzees, they report. What's more, similar to Neanderthal genetic patterns in humans, some background bonobo genetic information has been deleted in the chimpanzee genome, suggesting that some bonobo genes may have been disadvantageous for chimpanzees. The researchers also found that their genetic analysis could be used to determine from which country, and even which region, the various chimpanzees evaluated originated. Such information could be used to help identify hotspots for illegal trafficking of these animals, the authors say, and to improve conservation efforts. A Perspective by A. Rus Hoelzel provides more context.