They usually move slowly and deliberately using all four limbs. They cannot swim. Most descend to the ground only when there is no other way to get to another tree. Then they walk on all fours with clenched fists and not on their knuckles. Large males, in particular, may be less arboreal because few branches can take their weight.
Males can be twice as big as females.
One young born, twins are rare, gestation 260-270 days, no specific breeding season, female does not mate until her last baby is 3 years old. Relying on fruiting trees, they are found in dense primary rainforests, mangroves, swamps, to deciduous forests and mountain forests up to 1,500m. The only species in the family Pongidae, with 2 subspecies. Fossils suggest that a giant race of Orangs existed half a million years ago. When walking on the ground, they walk on all fours, clenching their feet or bending them inwards.