Temporal range: 7–0 Ma
|Skull of Sahelanthropus tchadensis, described as the earliest member of the hominin line, but this is debated.|
The Hominini is a taxonomical tribe of the subfamily Homininae; it comprises three subtribes: Hominina, with its one genus Homo; Australopithecina, comprising at least three extinct genera (see inset at bottom right[clarification needed]); and Panina, with its one genus Pan, the chimpanzees (see the evolutionary tree below). Members of the human clade, that is, the subtribe Hominina, include only the genus Homo; it is the "human" branch as depicted in an evolutionary tree chart (see below). Homo and those species of the australopithecines that arose after the split from the chimpanzees, are called hominins. Not all hominins are directly related to the emergence of early Homo.
Researchers proposed the taxon Hominini on the basis that the least similar species of a trichotomy should be separated from the other two. The common chimpanzee and the bonobo of the genus Pan are the closest living evolutionary relatives to humans, sharing a common ancestor with humans about four to seven million years ago. Research by Mary-Claire King in 1973 found 99% identical DNA between humans and chimpanzees; later research modified that finding to about 94% commonality, with some of the difference occurring in noncoding DNA.
The human clade, the subtribe Hominina, contains only Homo; it is the "human" branch as depicted in a tree of life. One community of scientists and scholars identifies a speciation of proto-chimpanzees from proto-humans as having occurred sometime after about eight million years ago (Mya). This community applies the term hominins to Homo and those species of australopithecines and other genera that arose after the split from the line to chimpanzees. The earliest hominins included lines, whether australopithecines or other genera, that arose after speciating from the ancestors of chimpanzees but then went extinct without developing into Homo; thus, not all hominins are ancestral to the emergence of early Homo.
All the listed, fossil genera (see classification infobox, "Genera") currently are being, or have been, evaluated 1) for probability of being ancestral to Homo, and 2) whether they are more closely related to Homo than to any other living primate—two values that could identify them as hominins. Some, including Paranthropus, Kenyanthropus, Ardipithecus, and Australopithecus, are broadly thought to be ancestral and closely related to Homo; others, especially earlier genera, including Sahelanthropus (and perhaps Orrorin), are supported by one community of scientists/ scholars but doubted by another.
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); see CHLCA. So one or both of these specimens may yet prove to be "hybrid" (see ..hybridization), and thereby ancestral to both Pan and Homo—or to Pan instead of Homo. Very few fossil specimens have been found on the Pan 'side' of the split from the common ancestral line. 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 radiometric (kyr).
In the proposal of Mann and Weiss (1996), the tribe Hominini includes Pan as well as Homo, but within separate subtribes. Homo and (by inference) all bipedal apes are referred to the subtribe Hominina, while Pan is assigned to the subtribe Panina. Wood (2010) discusses the different views of this taxonomy.
Complex speciation and hybridization
A source of confusion in determining the exact age of the Pan–Homo split is evidence of a complex speciation process rather than a clean split between the two lineages. Different chromosomes appear to have split at different times, possibly over as much as a four-million-year period, indicating a long and drawn out speciation process with large-scale hybridization events between the two emerging lineages as late as 6.3 to 5.4 million years ago according to Patterson et al. (2006).
The assumption of late hybridization was in particular based on the similarity of the X chromosome in humans and chimpanzees, suggesting a divergence as late as some 4 million years ago. This conclusion was rejected as unwarranted by Wakeley (2008), who suggested alternative explanations, including selection pressure on the X chromosome in the populations ancestral to the chimpanzee–human last common ancestor (CHLCA).
Cladogram of the superfamily Hominoidea
This cladogram shows the clade of superfamily Hominoidea and its descendent clades; it features the hominids, which is the family Hominidae. The hominids comprise the orangutans, gorillas, and the clade of the tribe Hominini—which groups the chimpanzees, the extinct subtribe Australopithecina (australopithicenes), and the subtribe Hominina (humans).
The scientist/ scholar community has not reached a consensus re adopting a formal taxon label for the early close connection of the subtribes Hominina and Australopithecina—hence the blank space (*) after the tribe-label "Hominini". However, the community has informally adopted a name to refer to humans and their closest biological relatives. These comprise the several Homo genera—only one of which is not extinct—plus those australopithecines that rose after the splitting of the lineage of chimpanzees from the common ancestors. These humans and australopithecines collectively are called hominins.
Morphological and geological/ radiometric analyses indicate that hominids, the most recent common ancestors (MRCA) of the subfamily Homininae, lived until at least about 14 million years ago (Mya), that is, prior to the ancestors of orangutans speciating from the common ancestors. Previously, the common ancestors of hominids had speciated from the superfamily Hominoidae between 20 to 15 million years ago. Recent molecular analyses have refined some paleo-chronological dates for the emergence of specific clades.
||It has been suggested that Chimpanzee–human last common ancestor be merged into this article. (Discuss) Proposed since December 2015.|
- Fuss, J; Spassov, N; Begun, DR; Böhme, M (2017). "Potential hominin affinities of Graecopithecus from the Late Miocene of Europe". PLoS ONE. 12 (5).
- "Chimps and Humans Very Similar at the DNA Level". News.mongabay.com. Retrieved 2009-06-06.
- Mary-Claire King (1973) Protein polymorphisms in chimpanzee and human evolution, Doctoral dissertation, University of California, Berkeley.
- Minkel JR (2006-12-19). "Humans and Chimps: Close But Not That Close". Scientific American.
- Bradley, B. J. (2006). "Reconstructing Phylogenies and Phenotypes: A Molecular View of Human Evolution". Journal of Anatomy. 212 (4): 337–353. PMC . PMID 18380860. doi:10.1111/j.1469-7580.2007.00840.x.
- Wood and Richmond.; Richmond, BG (2000). "Human evolution: taxonomy and paleobiology". Journal of Anatomy. 197 (Pt 1): 19–60. PMC . PMID 10999270. doi:10.1046/j.1469-7580.2000.19710019.x.
Thus human evolution is the study of the lineage, or clade, comprising species more closely related to modern humans than to chimpanzees. Its stem species is the so-called ‘common hominin ancestor’, and its only extant member is Homo sapiens. This clade contains all the species more closely-related to modern humans than to any other living primate. Until recently, these species were all subsumed into a family, Hominidae, but this group is now more usually recognised as a tribe, the Hominini.
- Cameron, D. W. (2003). "Early hominin speciation at the Plio/Pleistocene transition.". HOMO - Journal of Comparative Human Biology. 54 (1): 1–28. PMID 12968420. doi:10.1078/0018-442x-00057.
- Coyne, Jerry A. (2009) Why Evolution Is True, pp.197-208, 244, 248. ISBN 978-0-670-02053-9(hc), ISBN 978-0-14-311664-6(pbk). Penguin Books Ltd, London. "Anthropologists apply the term hominin to all the species on the "human" side of our family tree after it split from the branch that became modern chimps." (p.197)
- Coyne, Jerry A. (2009) Why Evolution Is True, pp.202-204. ISBN 978-0-670-02053-9(hc), ISBN 978-0-14-311664-6(pbk). Penguin Books Ltd, London. "After A. afarensis, the fossil record shows a confusing melange of gracile australopithecine species lasting up to about two million years ago. … [T]he late australopithecines, already bipedal, were beginning to show changes in teeth, skull, and brain that presage modern humans. It is very likely that the lineage that gave rise to modern humans included at least one of these species."
- Potts, Richard and Sloan, Christopher. “What Does It Mean to Be Human?”, pp. 31-42. ISBN 978-1-4262-0606-1. National Geographic Society, Washington.
- Brunet, Michel; Guy, F; Pilbeam, D; MacKaye, H. T.; Likius, A; Ahounta, D; Beauvilain, A; Blondel, C; Bocherens, H; Boisserie, JR; De Bonis, L; Coppens, Y; Dejax, J; Denys, C; Duringer, P; Eisenmann, V; Fanone, G; Fronty, P; Geraads, D; Lehmann, T; Lihoreau, F; Louchart, A; Mahamat, A; Merceron, G; Mouchelin, G; Otero, O; Pelaez Campomanes, P; Ponce De Leon, M; Rage, J. C.; et al. (July 2002), "A new hominid from the Upper Miocene of Chad, Central Africa", Nature, 418 (6894): 145–151, PMID 12110880, doi:10.1038/nature00879,
Sahelanthropus is the oldest and most primitive known member of the hominid clade, close to the divergence of hominids and chimpanzees.
- Wolpoff, Milford; Senut, Brigitte; Pickford, Martin; Hawks, John (October 2002), "Sahelanthropus or 'Sahelpithecus'?", Nature, 419 (6907): 581–582, Bibcode:2002Natur.419..581W, PMID 12374970, doi:10.1038/419581a,
Sahelanthropus tchadensis is an enigmatic new Miocene species, whose characteristics are a mix of those of apes and Homo erectus and which has been proclaimed by Brunet et al. to be the earliest hominid. However, we believe that features of the dentition, face and cranial base that are said to define unique links between this Toumaï specimen and the hominid clade are either not diagnostic or are consequences of biomechanical adaptations. To represent a valid clade, hominids must share unique defining features, and Sahelanthropus does not appear to have been an obligate biped.
- McBrearty, Sally; Nina G. Jablonski (2005). "First fossil chimpanzee". Nature. 437 (7055): 105–108. Bibcode:2005Natur.437..105M. PMID 16136135. doi:10.1038/nature04008.
- Mann, Alan; Mark Weiss (1996). "Hominoid Phylogeny and Taxonomy: a consideration of the molecular and Fossil Evidence in an Historical Perspective". Molecular Phylogenetics and Evolution. 5 (1): 169–181. PMID 8673284. doi:10.1006/mpev.1996.0011.
- B. Wood (2010). "Reconstructing human evolution: Achievements, challenges, and opportunities". Proceedings of the National Academy of Sciences. 107: 8902–8909. Bibcode:2010PNAS..107.8902W. PMC . PMID 20445105. doi:10.1073/pnas.1001649107.
- Patterson N, Richter DJ, Gnerre S, Lander ES, Reich D; Richter; Gnerre; Lander; Reich (June 2006). "Genetic evidence for complex speciation of humans and chimpanzees". Nature. 441 (7097): 1103–8. Bibcode:2006Natur.441.1103P. PMID 16710306. doi:10.1038/nature04789.
- Wakeley J (March 2008). "Complex speciation of humans and chimpanzees". Nature. 452 (7184): E3–4; discussion E4. Bibcode:2008Natur.452....3W. PMID 18337768. doi:10.1038/nature06805. "Patterson et al. suggest that the apparently short divergence time between humans and chimpanzees on the X chromosome is explained by a massive interspecific hybridization event in the ancestry of these two species. However, Patterson et al. do not statistically test their own null model of simple speciation before concluding that speciation was complex, and—even if the null model could be rejected—they do not consider other explanations of a short divergence time on the X chromosome. These include natural selection on the X chromosome in the common ancestor of humans and chimpanzees, changes in the ratio of male-to-female mutation rates over time, and less extreme versions of divergence with gene flow. I therefore believe that their claim of hybridization is unwarranted."
- Andrew Hill; Steven Ward (1988). "Origin of the Hominidae: The Record of African Large Hominoid Evolution Between 14 My and 4 My". Yearbook of Physical Anthropology. 31 (59): 49–83. doi:10.1002/ajpa.1330310505.
- Dawkins R (2004) The Ancestor's Tale.
- "Query: Hominidae/Hylobatidae". Time Tree. 2009. Retrieved December 2010. Check date values in:
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