Gorillas (Gorilla gorilla) inhabit the forests of Central Africa and are the largest and most powerful of all primates. Adult males stand 6 ft (1.8 m) upright (an unnatural position for a gorilla) and weigh up to 450 lb (200 kg), while females are much smaller. Gorillas live to about 44 years and mature males (those usually over 13 years), or silverbacks, are marked by a band of silver-gray hair on their backs.

Gorillas live in small family groups of several females and their young, led by a dominant silverback male. The females comprise a harem for the silverback, who holds the sole mating rights in the troop. Like humans, female gorillas produce one infant after a gestation period of nine months. The large size and great strength of the silverback are advantages in competing with other males for leadership of the group and in defending the group against outside threats.

During the day...