Ape - Biology

Biology

The "lesser apes" are the gibbon family, Hylobatidae with sixteen medium-sized species. Their major differentiating characteristic is their long arms, which they use to brachiate through the trees. As an evolutionary adaptation to this arboreal lifestyle, their wrists are ball and socket joints. The largest of the gibbons, the siamang, weighs up to 14 kg (31 lb). In comparison, the smallest "great ape" is the bonobo at 34 to 60 kg (75 to 132 lb).

The "great apes" were formerly treated as the family Pongidae. As noted above, this definition makes the Pongidae paraphyletic, and does not show that orangutans, gorillas, chimpanzees and humans are all more closely related to one another than any of these four groups are to gibbons. Further, current evidence implies that humans share a common extinct ancestor with the chimpanzee line, from which we separated more recently than the gorilla line.

The superfamily Hominoidea falls within Catarrhini, which also includes the Old World monkeys of Africa and Eurasia. Within this group, both families (Hylobatidae and Hominidae) can be distinguished from Old World monkeys by the number of cusps on their molars (hominoids have five—the "Y-5" molar pattern, Old World monkeys have only four in a bilophodont pattern). Hominoids have more mobile shoulder joints and arms due to the dorsal position of the scapula, broad ribcages that are flatter front-to-back, and a shorter, less mobile spine compared to Old World monkeys, with caudal (tail) vertebrae greatly reduced, resulting in complete tail loss in living species. These are all anatomical adaptations to vertical hanging and swinging locomotion (brachiation), as well as better balance in a bipedal pose. However, there are also primates in other families that lack tails, and at least one (the pig-tailed langur) that has been known to walk significant distances bipedally. The front skull is characterised by its sinuses, fusion of the frontal bone and post-orbital constriction.

Although the hominoid fossil record is far from complete, and the evidence is often fragmentary, there is enough to give a good outline of the evolutionary history of humans. The time of the split between humans and other living hominoids used to be thought to have occurred 15 to 20 million years ago. Some species occurring within that time period, such as Ramapithecus, used to be considered as hominins, and possible ancestors of humans. Later fossil finds indicated that Ramapithecus was more closely related to the orangutan, and new biochemical evidence indicated that the last common ancestor of humans and other hominins occurred between 5 and 10 million years ago, and probably in the lower end of that range.