All seven species of great apes share the following characteristics: no tail, a large skull with a large brain, a curved spine and an opposable or prehensile thumb. Like the chimpanzee, which is at home in central Africa and known for its often aggressive behavior.

The Bonobo, or pygmy chimpanzee, is a really peaceable ape. "Make love, not war" is its motto. Bonobos use frequent sex to ease tension in the group; they are also into French kissing and oral sex. Bonobos only live in the Democatic Republic of Congo.

There are two species of orangutans: one lives on the island of Borneo, the other on Sumatra. Both live on trees, have very long arms and hand-like feet that they use for climbing. Bornean orangutans are squat, they are heavier than their cousins on Sumatra, and their fur is darker and longer.

The Sumatra orangutan's fur is more reddish than that of the Borneo orangutan, the males' cheek pads are less pronounced and often covered in white hair. Sumatra orangutans also spend less time on the ground than their Bornean cousins. Experts suspect the reason to stay aloft may be the Sumatra tiger, which also preys on orangutans.

Gorillas are subdivided into two subspecies, the Eastern and the Western gorilla. The Eastern gorilla is bigger, its fur is darker, and the species is subdivided even further into the Eastern lowland and the Mountain gorilla (photo).

The Western gorilla is also subdivided, into the Western lowland (photo) and the profoundly endangered Cross River gorilla. Almost all gorillas in zoos are Western lowland gorillas. In the wild, there are far more Western gorillas than the Eastern species. The former also live in smaller groups.

Is there a great ape missing? Right: We, too are great apes. We humans are more closely related to chimpanzees and bonobos than the chimps are to gorillas. But we're the only great ape species that isn't threatened by extinction.