The thumb is rather short and stubby, but manipulative ability is greater than in chimpanzees or orang-utans. The gait is quadrupedal, with the weight of the forequarters carried on the backs of the knuckles. With long arms and short legs, the gorilla's intermembral index is high - 117. Arm-swinging never takes place except in infancy. I have also observed an infant clinging to her mother's arms or legs while the mother walks quadrupedal.
All races are extremely large.
Mature females are approximately half the weight of males. Groups are very cohesive and generally peaceable. There is little overt dominance among females, but access to the breeding females is the prerogative of the silverback male. As a young male matures and becomes a silverback at about 11-13 years of age, he may not be tolerated by the dominant males, and may be forced to emigrate from the troop. He lives a solitary life as a lone male, probably traveling some distance, until an opportunity occurs to start a group of his own by luring maturing females from other groups.