(Update 10/16/2014: Sorry. I just discovered this video has been removed from Youtube by the owner. I regret that very much, because it was a good one.)
The bonobo was the last of the great apes to be discovered. And even then, it was thought for a long time to be just a smaller variety of chimpanzee. It was, in fact, known as the “dwarf chimpanzee” for many years.
Eventually, with further study, it was realized that bonobos and chimps are separate species which separated from each other around 2 million to 3 million years ago. They are both our closest relatives in the animal kingdom. Our ancestors separated from their ancestors around 6 million to 7 million years ago. We are evolutionarily closer to both chimps and bonobos than they are to gorillas.
It is interesting — and undoubtedly informative — that bonobos have their forests all to themselves, with no other apes to contend with. Much fruit falls to the ground where they can collect it at their leisure.
Chimpanzees, on the other hand, have to contend with gorillas in the best parts of their range. The giant gorillas rule the ground and monopolize fallen fruit, while the chimps are forced to remain mostly in the trees. Life is much harder for them, and this may very well account for most of the differences that have developed between the two species.