Lowland gorillas are familiar to us as the star attractions of the zoo scene and are the only gorillas to have been studied in captivity. Females are smaller and weigh only about half as much. Like the other apes, gorillas have no tails. They usually travel along on all fours with their weight on their feet and on the knuckles of their hands. Their bodies are adapted to this gait, with an armspan that greatly exceeds their standing height.
Mountain gorillas have longer, silkier hair than the lowland varieties.
Mature males are called silverbacks because the hair across their backs becomes silver with age. High crowns or skull crests, which are more pronounced in mountain gorillas, also identify older males. Gorillas live in close-knit groups often consisting of a dominant silverback, one or two other males, several females and young. Silverbacks are known to show off by hooting, standing erect, throwing plants around, beating their chests, and making loud barking vocalizations. Such displays have certainly fueled the gorilla's reputation for ferocity but generally serve to frighten away intruders and reinforce the dominant male's position as leader without further need for aggression.