Humans and chimps had a common ancestor 4-6 million years ago. Humans’ common ancestor with orangutans lived a far more distant 15 million years ago. This may be why chimps' personalities are like humans’ in many respects, and why orangs' personalities are like humans’ only in some.
Or not. How much like humans are chimps and orangs, anyway? Are they more similar to us than the puppies we dress in doll clothes so we can circulate cute pictures on the Internet? Are they more similar than cows that look pensive or chipmunks that “complain?”
Such are the questions that intrigued the University of Edinburgh's Alexander Weiss, lead author of a study in the journal Animal Behavior.