Like lipstick on a collar, new DNA evidence is pointing to ancient affairs between bonobos and chimpanzees.
Chimps carry a small percentage of bonobo DNA, researchers report in the Oct. 28 Science. The conclusion comes from analysis of the genetic instruction books, or genomes, of 63 wild-born chimps, two captive chimps named Clint and Donald, and 10 wild-born bonobos. The apes came from 10 African countries.
Although chimps (Pan troglodytes) and bonobos (Pan paniscus) became separate species 1.6 million to 2 million years ago, they are still closely related enough to interbreed occasionally.
Finding bonobo genetic variants in chimp DNA suggests at least two past periods of interspecies intimate relations. Between about 550,000 and 200,000 years ago, bonobos mated with the ancestors of eastern and central chimp subspecies.
Subsequent mating between chimp subspecies probably carried some bonobo DNA into the Nigeria-Cameroon chimpanzee subspecies. Central chimps and bonobos interbred again about 100,000 to 200,000 years ago, giving modern central chimps more bonobo DNA than their sister subspecies.
Even with the extra dose of interbreeding, individual chimps have inherited less than 1 percent of their genomes from bonobos. That and other evidence suggests that bonobo DNA is an evolutionary disadvantage for chimps, evolutionary geneticist Marc de Manuel of Pompeu Fabra University in Barcelona and colleagues report.
Bonobos may also possess some chimp DNA, but most of the gene flow researchers can detect appears to have been from bonobos into chimps.
DNA evidence has shown that humans mixed with now-extinct cousins, including Neandertals, Denisovans and possibly other unknown hominids (SN Online: 10/21/16). But until now, signs of hybridization between humans’ closest living relatives have been lacking.