They also climb and leap. On the ground they walk bipedally with their arms held out to their sides. Their forearms are much longer than their hindlimb. When upright, Gibbons stand more erect than any other primate except for man. Lone indivduals are either old, or young animals attempting to leave the nest and start their own family.
Gibbons show no signs of sexual dimorphism that is common in many other primates.
This is due to the relationships they form socially that pair males and females for life.