Although in prehistoric times there were orang-utans on the Asian mainland, today they are found in just a few restricted areas of the islands of Borneo and Sumatra. Orang-utans diverged from the other apes between 16 million and 10 million years ago. One of their recent ancestors was the largest known primate, called Gigantopithecus blacki. Compared to Asia's lesser apes, the orang-utan is one of the slowest land mammals on the continent.
Life is generally very unhurried for orang-utans.
Orang-utans are described as having four hands, rather than four feet. They tend to use their arms to grip branches rather than standing on branches for support. They move their arms and legs in whatever order circumstances dictate, being equally at home hanging sloth-like under a branch or spreading their weight over several slender supports. This means that in a female's reproductive life time she may only produce three or four offspring. The youngster is solely dependent on its mother until her next baby is born.