this event is actually more recent: 4 million years ago. They studied the rate at which the DNA is changing, used a coalescent hidden Markov model for comparison, and assumed that organgutans split about 18 million years ago. The last divergence occurred more than 5 million years ago but they seem to imply that the split occurred more recently.
Well, this new result, if true, could make it 20% more understandable why some people think and behave the way they do. ;-)