|MadSci Network: Evolution|
It's often said that the chimpanzee is our closest living relative. As you astutely noted, however, the bonobo shares some traits with humans that chimps do not. The genetic studies I've seen indicate, though, that chimps and bonobos are both descended from a common ancestor that split from the human ancestral line about five million years ago. So both are equally closely related to humans, genetically, and the relative closeness of one or the other that we might perceive are due to the chances and pressures of evolution.
One trait of the bonobo that you didn't mention is their communication ability. At least one bonobo, named Kanzi, has shown a remarkable ability to communicate with human language. His mentor is Dr. Sue Savage- Rumbaugh, and you can find mention of him in this discussion of communication, and a longer mention in this review of her book. For a more thorough discussion, of course, you should pick up her book, titled "Kanzi: The Ape at the Brink of the Human Mind."
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