Bonobos (Pan paniscus) are a species of chimp, closely related to their more common cousins, the “chimps” (Pan troglodytes*). The latter are the only species to be referred to as chimpanzees by the general public, despite the fact the term technically applies to the genus Pan and thus both “chimps” and bonobos.
However, this taxonomical misnomer isn’t a bonobo’s only claim to fame. That honour lies with their sexual behaviour, which is famously promiscuous. Indeed, I’d wager most other articles you’ll read about this story start by describing them as “the chimps oversexed cousin” or something similar.
Yet their sexual behaviour is just one small part of what makes bonobos unique. They’re also a lot less aggressive, have a less hierarchical society, are more playful and less politically conniving than regular “chimps”; amongst other things. Physically they’re more gracile than chimps, with a thinner upper body and head; although they are not smaller overall (despite often being referred to as pygmy chimps).
This obviously makes them very interesting to study since if we can uncover what it is that makes P. troglodytes and bonobos so different we may be able to work out the ultimate cause of those behaviours. If we figure out that some genetic change is responsible for their lack of aggression, for example, then perhaps chimpanzee aggression has a genetic basis. That might also have interesting implications for the source of human aggression, since we’re very closely related to both species.
However, attempts to figure out such interesting things have been hampered by the fact that only small parts of the bonobo genome have been sequenced do far. This work has provided some useful information, such as the fact that bonobos separated from the chimps because they were physically separated by the Congo River. This isolation allowed them to become more and more genetically distinct until they split into the two species we know and love between 1-2 million years ago.
Deciding that this lack of information needed to be rectified a team of geneticists, led by Kay Prüfer of the Max Plank Institute for Evolutionary Anthropology (quite what that blokes relationship is to EvoAnth I do not know), sequenced the bonobo genome. Whilst their data has yet to reveal anything quite as profound as the ultimate cause of aggressive behaviour it is still turning up some useful (and interesting) information.
For starters they found that the bits of the bonobo genome that have a corresponding sequence in chimps are 99.6% similar, which is what you’d expect given that they are very closely related. Further, bits of the bonobo genome with a corresponding human sequence are 98.7% similar. Again, this is what you’d expect given that they’re closely related to us but more closely related to chimps. As such the research is consistent with the typical tale of human evolution, lending it further credence (as if it needed it).
Secondly it shows that bonobos did indeed split from “chimps” ~1 million years ago and that there was no interbreeding between the two groups after this split. This is consistent with the Congo River being the driving cause of their speciation since neither species is a strong swimmer and so could not have crossed the river to interbreed after it had split them.
They also found that around 6% of the bonobo genome had been subject to incomplete lineage sorting (shortened to ILS by lazy bloggers like me). ILS is when an allele of a gene doesn’t follow the population history of a species. It might split from its genetic common ancestor before the species splits from its common ancestor. Alternatively an allele present in the common ancestor of bonobos, “chimps” and humans might only go into the human and bonobo lines by chance (perhaps dying out in the chimp lineage). If you’re still not quite sure what ILS is, P. Z. Myers gives a better explanation of ILS (with pictures!).