Disturbing Behaviors of the Orangutan; June 2002; Scientific American Magazine; by Anne Nacey Maggioncalda and Robert M. Sapolsky; 6 Page(s)

The orangutan is one of humankind's closest relatives. One of the four great apes (the other three are gorillas, chimpanzees and bonobos), Pongo pygmaeus is exquisitely adapted for life in the forest canopies of the Southeast Asian islands of Borneo and Sumatra. With their long arms and hooklike hands, orangutans are adept at swinging from tree to tree in search of tropical fruits. They are among the most solitary of large primates and the only great apes found outside Africa. Orangutans are also notable for the striking size difference between males and females: the average weight of an adult male (about 90 kilograms, or 198 pounds) is more than twice that of a female.

An adult male orangutan is an impressive sight. The animal has a pair of wide cheek pads, called flanges, and a well-developed throat sac used for emitting loud cries known as long calls. The mature male also has long, brightly colored hair on its body and face. These are secondary sexual characteristics, the flamboyant signals that male orangutans flaunt to proclaim their fertility and fitness to the opposite sex. The features emerge during orangutan adolescence: males reach puberty at around seven to nine years of age, then spend a few years in a far-from-impressive "subadult" stage, during which they are about the same size as mature females. The males reach their adult size and develop secondary sexual traits by ages 12 to 14. Or at least that's what primate researchers used to think.