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Humans and chimpanzees might have one more thing in common: they both seem to have benefitted from sex with a closely related species.

During the last decade, geneticists have reported that our species interbred with ancient humans including the Neanderthals and Denisovans. They have also found tantalising signs that we benefitted from doing so, gaining DNA that may have boosted our immune systems or made us better able to survive at high altitude or in the frigid Arctic.

Now comes evidence that something similar has been going on in , following episodes of interbreeding with their close relatives during the last 500,000 years.

Three of the four subspecies of chimpanzee carry sections of bonobo DNA in their genomes. This prompted at Pompeu Fabra University in Barcelona, Spain and her colleagues to investigate whether the bonobo DNA has benefitted the chimps.

Bonobo DNA everywhere

It seems it has. Certain chunks of bonobo DNA are unusually common in chimp populations, suggesting they have spread because they are useful.

Different segments of bonobo DNA seem to have been favoured in the different chimp subspecies. That鈥檚 a surprise, says Nye. It suggests there is a complex interplay between genetics and the environment each chimp subspecies occupies, meaning each subspecies has gained in a unique way from the bonobo DNA.

For example, there are signs that the immune systems of have been upgraded by bonobo DNA. This mirrors evidence that our species got an immune system boost from breeding with Neanderthals.

However, the chimp finding doesn鈥檛 quite make sense. Supposedly, humans benefitted so much from Neanderthal immune system DNA because the Neanderthals occupied Eurasia and had evolved to fight the pathogens living there 鈥� pathogens that our species, with its African roots, had never seen before. But eastern chimps and bonobos live in the same corner of Africa, and in theory are exposed to most of the same pathogens. 鈥淭heir territories are both close and similar,鈥� says Nye.

My bonobo brain

What鈥檚 more, it seems benefitted from bonobo DNA involved in brain function and nervous system development. This hints that this chimp subspecies might have an unusually bonobo-like brain.

The bonobo brain gains volume at a slower rate through childhood than the chimp brain, and bonobos retain 鈥渃hild-like鈥� characteristics into adulthood: for instance, they play more than chimps. Bonobo society is also more peaceful than chimp society, and dominated by females rather than males.

So far there is no evidence that the Nigeria-Cameroon chimpanzee displays such bonobo-like traits, but it鈥檚 a poorly-known subspecies. 鈥淔ew studies into their natural behaviour exist,鈥� says Nye.

at the Copenhagen Zoo in Denmark was part of the team that published in 2016. He says understanding these differences between chimp subspecies could help us conserve them. .

The apes may also help us understand how our species benefitted from interbreeding with ancient humans 鈥� because unlike Neanderthals and their ilk, bonobos are still with us.

鈥淚t would be incredibly interesting to observe if recipients have gained any [traits] that evoke some characteristic of the living donor,鈥� says at the University of Tartu, Estonia.