All are monogamous. The songs are inflexible and seem to be innate, not learned. There are three subspecies of lar gibbon. Ours are probably H. l. entelloides from Thailand, based on their song characteristics. Evidence from healed bone fractures show that gibbons do sometimes fall.
Gibbons are absolutely dependent upon old growth tropical forests.
Repeated exposure of the continental shelf, during the last million years of the Pleistocene and subsequent isolation of animal populations following rises in sea level, resulted in speciation throughout Southeast Asia. Since gibbons will not cross water, major rivers separate the different species. The absence of strong sexual dimorphism is possibly the result of an evolutionary trend favoring the brachiating mode of locomotion, which selected for small size and great agility. Fossil evidence suggests that the gibbons diverged from the great apes prior to the separation of great apes and humans Gibbon-like remains are known from the Oligocene and Miocene of Africa, the Miocene of Europe, and the upper Pliocene and Pleistocene of Asia. It is uncertain whether this represents a direct relationship or parallel evolution.