Evolution of primates

Following the emergence of basal simians in Africa, the group split during the Eocene when New World monkeys dispersed to South America, presumably by rafting on mats of vegetation across the much narrower Atlantic Ocean.

The earliest known catarrhine is Kamoyapithecus from uppermost Oligocene at Eragaleit in the northern Kenya Rift Valley, dated to 24 million years ago.[6] Its ancestry is thought to be species related to Aegyptopithecus, Propliopithecus, and Parapithecus from the Faiyum depression, at around 35 million years ago.[7] In 2010, Saadanius was described as a close relative of the last common ancestor of the crown catarrhines, and tentatively dated to 29–28 million years ago, helping to fill an 11-million-year gap in the fossil record.[8] Notable species also include Nsungwepithecus gunnelli and Rukwapithecus fleaglei of the Oligocene.[9]

Reconstructed tailless Proconsul skeleton

In the early Miocene, about 22 million years ago, the many kinds of arboreally adapted primitive catarrhines from East Africa suggest a long history of prior diversification. Fossils at 20 million years ago include fragments attributed to Victoriapithecus, the earliest Old World monkey. Among the genera thought to be in the ape lineage leading up to 13 million years ago are Proconsul, Rangwapithecus, Dendropithecus, Limnopithecus, Nacholapithecus, Equatorius, Nyanzapithecus, Afropithecus, Heliopithecus, and Kenyapithecus, all from East Africa.

The presence of other generalized non-cercopithecids of middle Miocene age from sites far distant—Otavipithecus from cave deposits in Namibia, and Pierolapithecus and Dryopithecus from France, Spain and Austria—is evidence of a wide diversity of forms across Africa and the Mediterranean basin during the relatively warm and equable climatic regimes of the early and middle Miocene. The youngest of the Miocene hominoids, Oreopithecus, is from coal beds in Italy that have been dated to 9 million years ago.

Molecular evidence indicates that the lineage of gibbons (family Hylobatidae) diverged from Great Apes some 18–12 million years ago, and that of orangutans (subfamily Ponginae) diverged from the other Great Apes at about 12 million years; there are no fossils that clearly document the ancestry of gibbons, which may have originated in a so-far-unknown South East Asian hominoid population, but fossil proto-orangutans may be represented by Sivapithecus from India and Griphopithecus from Turkey, dated to around 10 million years ago.[10]

Some of the primates' vertebrate ancestors were tetrachromats, but their nocturnal mammalian ancestors lost two of their four cones during the mesozoic. Most modern primates, however, have evolved to be trichromats. All old world monkeys and apes are trichromats, but new world monkeys are polymorphic trichromats, meaning that males and homozygous females are dichromats while heterozygous females are trichromats (with the exceptions of howler monkeys and night monkeys, who have more and less advanced color vision respectively).

There are four prevailing theories as to what the evolutionary pressure was for primates to develop trichromatic vision. The Fruit Theory suggests that it was easier for trichromatic primates to find ripe fruit against a green background. While there is data supporting the Fruit Theory, there is some dispute about whether or not trichromacy was more advantageous for determining how ripe fruit was up close or spotting fruit from afar. The Young Leaf hypothesis suggests that primates with more advanced color vision could better spot younger and more nutritious leaves during fruit shortages, while there are also theories that suggest more advanced color vision was better for recognizing changes in skin tone, allowing primates to better determine the blood oxygen saturation of others. other theories indicate that primates' color vision evolved alongside their sense of smell, though research has shown that there is no direct correlation between concentration of olfactory receptors and acquisition of color vision.

Human evolution is the evolutionary process that led to the emergence of anatomically modern humans, beginning with the evolutionary history of primates – in particular genus Homo – and leading to the emergence of Homo sapiens as a distinct species of the hominid family, the great apes. This process involved the gradual development of traits such as human bipedalism and language.[11]

The study of human evolution involves many scientific disciplines, including physical anthropology, primatology, archaeology, paleontology, neurobiology, ethology, linguistics, evolutionary psychology, embryology and genetics.[12] Genetic studies show that primates diverged from other mammals about 85 million years ago, in the Late Cretaceous period, and the earliest fossils appear in the Paleocene, around 55 million years ago.[13]

Within the superfamily Hominoidea (apes), the family Hominidae diverged from the family Hylobatidae (gibbons) some 15–20 million years ago; African great apes (subfamily Homininae) diverged from orangutans (Ponginae) about 14 million years ago; the tribe Hominini (humans, Australopithecines and other extinct biped genera, and chimpanzee) parted from the tribe Gorillini (gorillas) between 9 million years ago and 8 million years ago; and, in turn, the subtribes Hominina (humans and biped ancestors) and Panina (chimpanzees) separated about 7.5 million years ago to 5.6 million years ago.[14]