Bonobos were identified as separate species from common chimps only by 1929. They are not as small compared to common chimps as their name (pygmy) implies. They are less aggresive and more human-like in their behavior than their cousins (Pan troglodytes). This, together with the fact that they share between 99.0% and 99.6% of their genetic code with humans, has made some people believe that they are "closer", phylogenetically, to us -- sort of "between" us and common chimps. This is not necessarily true. Another possibility is that bonobos and common chimps evolved from a common ancestor, who in turn evolved from another common ancestor of both theirs and humans.
The above picture was taken at the Cincinnati zoo, in May 2001. Lots of people had gathered in front of the bonobos' area, so these two took a comfortable position and started watching curiously at us.
The following picture is from the same place, showing a young member of the same family, sleeping.
Life on Earth