I.

Introduction

Ape, any of 13 species of large, highly intelligent primates, including chimpanzees, gorillas, gibbons, and orangutans. Apes are sometimes confused with monkeys, but unlike their smaller primate counterparts, apes do not have tails and their arms are usually longer than their legs. Apes live in tropical woodlands and forests of Africa and Asia. Despite sharing similar habitats, different ape species show striking differences in behaviors and ways of life.

At one time, apes were classified as a single group of primates, but today most zoologists divide them into two distinct families: the lesser apes, or gibbons, and the great apes. Gibbons are similar to monkeys, with lithe, slender bodies and extremely agile movements. Gibbons spend all of their lives in trees, using their hands like hooks to swing arm-over-arm between branches. Known as brachiation, this method of locomotion is so fast that gibbons can easily overtake a person running on the forest floor.

The great apes include the gorilla, the orangutan, and two species of chimpanzee: the common chimp and the bonobo (sometimes called the pygmy chimpanzee). Great apes are bigger than gibbons and also much less acrobatic. However, they are still good climbers. While orangutans spend most of their life in trees, where they use their long arms and dexterous hands and feet to grasp branches and vines, chimpanzees frequently come to the ground to feed. Gorillas are primarily terrestrial, but even fully grown adult males have been observed clambering among tree branches more than 15 m (49 ft) high. Chimpanzees and gorillas—the apes that spend the most time on the ground—normally walk on all fours, clenching their hands so that their knuckles take their weight.

From physical and fossil evidence, biologists know that apes and humans share a common ancestry. In recent years, biochemical analysis has shown just how close this link is—chimpanzees and humans differ significantly in only 2 percent of their genes. This evidence suggests that they diverged from a common ancestor around five to seven million years ago.