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Homo (humans)

    Both Sahelanthropus and Orrorin existed during the estimated duration of the ancestral chimpanzee-human speciation events, within the range of eight to four million years ago (Mya). Very few fossil specimens have been found that can be considered directly ancestral to genus Pan. News of the first fossil chimpanzee, found in Kenya, was published in 2005. However, it is dated to very recent times—between 545 and 284 thousand years ago.[12] The divergence of a "proto-human" or "pre-human" lineage separate from Pan appears to have been a process of complex speciation-hybridization rather than a clean split, taking place over the period of anywhere between 13 Mya (close to the age of the tribe Hominini itself) and some 4 Mya. Different chromosomes appear to have split at different times, with broad-scale hybridization activity occurring between the two emerging lineages as late as the period 6.3 to 5.4 Mya, according to Patterson et al. (2006),[13] This research group noted that one hypothetical late hybridization period was based in particular on the similarity of X chromosomes in the proto-humans and stem chimpanzees, suggesting that the final divergence was even as recent as 4 Mya. Wakeley (2008) rejected these hypotheses; he suggested alternative explanations, including selection pressure on the X chromosome in the ancestral populations prior to the chimpanzee–human last common ancestor (CHLCA).[14]

Most DNA studies find that humans and Pan are 99% identical,[15][16] but one study found only 94% commonality, with some of the difference occurring in noncoding DNA.[17] It is most likely that the australopithecines, dating from 4.4 to 3 Mya, evolved into the earliest members of genus Homo.[18][19] In the year 2000, the discovery of Orrorin tugenensis, dated as early as 6.2 Mya, briefly challenged critical elements of that hypothesis,[20] as it suggested that Homo did not in fact derive from australopithecine ancestors.[21] All the listed fossil genera are evaluated for:

  1. probability of being ancestral to Homo, and
  2. whether they are more closely related to Homo than to any other living primate—two traits that could identify them as hominins.

Some, including Paranthropus, Ardipithecus, and Australopithecus, are broadly thought to be ancestral and closely related to Homo;[22] others, especially earlier genera, in

Most DNA studies find that humans and Pan are 99% identical,[15][16] but one study found only 94% commonality, with some of the difference occurring in noncoding DNA.[17] It is most likely that the australopithecines, dating from 4.4 to 3 Mya, evolved into the earliest members of genus Homo.[18][19] In the year 2000, the discovery of Orrorin tugenensis, dated as early as 6.2 Mya, briefly challenged critical elements of that hypothesis,[20] as it suggested that Homo did not in fact derive from australopithecine ancestors.[21] All the listed fossil genera are evaluated for:

Some, including Paranthropus, Ardipithecus, and Australopithecus, are broadly thought to be ancestral and closely related to Homo;[22] others, especially earlier genera, including Sahelanthropus (and perhaps Orrorin), are supported by one community of scientists but doubted by another.[23][24]

List of known hominin species