Chimpanzee–human last common ancestor

The chimpanzee–human last common ancestor, or CHLCA, is the last common ancestor shared by the extant Homo (human) and Pan (chimpanzee and bonobo) genera of Hominini. Due to complex hybrid speciation, it is not possible to give a precise estimate on the age of this ancestral population. While 'original divergence' between populations may have occurred as early as 13 million years ago (Miocene), hybridization may have been ongoing until as recently as 4 million years ago (Pliocene).In effect, there is now no a priori reason to presume that human-chimpanzee split times are especially recent, and the fossil evidence is now fully compatible with older chimpanzee–human divergence dates [7 to 10 Ma... The chimpanzee–human last common ancestor, or CHLCA, is the last common ancestor shared by the extant Homo (human) and Pan (chimpanzee and bonobo) genera of Hominini. Due to complex hybrid speciation, it is not possible to give a precise estimate on the age of this ancestral population. While 'original divergence' between populations may have occurred as early as 13 million years ago (Miocene), hybridization may have been ongoing until as recently as 4 million years ago (Pliocene). The taxon 'tribe Hominini' was proposed on basis of the idea that, regarding a trichotomy, the least similar species should be separated from the other two. Originally, this produced a separated genus Homo, which, predictably, was deemed 'most different' from the other two genera, Pan and Gorilla. However, later discoveries and analyses revealed that Pan and Homo are closer genetically than are Pan and Gorilla; thus, Pan was referred to the tribe Hominini with Homo. Gorilla now became the separated genus and was referred to the new taxon 'tribe Gorillini'. Mann and Weiss (1996), proposed that the tribe Hominini should encompass Pan as well as Homo, but grouped within separate subtribes. They would classify Homo and all bipedal apes to the subtribe Hominina and Pan to the subtribe Panina. (Wood (2010) discusses the different views of this taxonomy.) The 'human-side' descendants of the CHLCA species are specified as members of the tribe Hominini, that is to the inclusion of the genus Homo and its closely related genus Australopithecus, but to the exclusion of the genus Pan — meaning all those human-related genera of tribe Hominini that arose after speciation from the line with Pan. Such grouping represents 'the human clade' and its members are called 'hominins'. A 'chimpanzee clade' was posited by Wood and Richard, who referred it to a 'Tribe Panini', which was envisioned from the family Hominidae being composed of a trifurcation of subfamilies. Sahelanthropus tchadensis is an extinct hominine with some morphology proposed (and disputed) to be as expected of the CHLCA; and it lived some 7 million years ago — close to the time of the chimpanzee–human divergence. But it is unclear whether it should be classified as a member of the Hominini tribe, that is, a hominin, as a direct ancestor of Homo and Pan and a potential candidate for the CHLCA species itself, or simply a Miocene ape with some convergent anatomical similarity to much later hominins. Richard Wrangham (2001) argued that the CHLCA species was very similar to the common chimpanzee (Pan troglodytes) — so much so that it should be classified as a member of the genus Pan and be given the taxonomic name Pan prior. However, no fossil has yet been identified as a probable candidate for the CHLCA or the taxon Pan prior. An estimate of TCHLCA at 10 to 13 million years was proposed in 1998, and a range of 7 to 10 million years ago is assumed by White et al. (2009):.mw-parser-output .templatequote{overflow:hidden;margin:1em 0;padding:0 40px}.mw-parser-output .templatequote .templatequotecite{line-height:1.5em;text-align:left;padding-left:1.6em;margin-top:0} The Ardipithecus probably branched off of Pan in the middle Miocene Messinian. Few fossil specimens on the 'chimpanzee-side' of the split have been found; the first fossil chimpanzee, dating between 545 and 284 kyr (thousand years, radiometric), was discovered in Kenya's East African Rift Valley (McBrearty, 2005). All extinct genera listed in the taxobox are ancestral to Homo, or are offshoots of such. However, both Orrorin and Sahelanthropus existed around the time of the divergence, and so either one or both may be ancestral to both genera Homo and Pan.