The Hominini (hominins) form a taxonomic tribe of the subfamily Homininae (hominines). They comprise two extant genera: Homo (humans) and Pan (chimpanzees and bonobos), and in standard usage exclude the genus Gorilla (gorillas), which is grouped separately within the subfamily Homininae.
The term Hominini was originally introduced by Camille Arambourg (1948), who combined the categories of Hominina and Simiina pursuant to Gray's classifications (1825).
Taxonomic classification of the superfamily Hominoidea (hominoids), emphasizing the tribe Hominini. 𝄪 Tribe Hominini (lower left in graphic) comprises two genera, Homo and Pan; while gorillas are classified as separate from these—as the single genus Gorilla of tribe Gorillini; all of subfamily Homininae.
Traditionally, chimpanzees, gorillas and orangutans were grouped together, excluding humans, as pongids. Since Gray's classifications, evidence accumulating from genetic phylogeny confirmed that humans, chimpanzees, and gorillas are more closely related to each other than to the orangutan.[3] The orangutans were reassigned to the family Hominidae (great apes), which already included humans; and the gorillas were grouped as a separate tribe (Gorillini) of the subfamily Homininae.[3] Still, details of this reassignment remain contested, and of publishing since (on tribe Hominini), not every source excludes gorillas and not every source includes chimpanzees.
Humans are the only extant species in the Australopithecine branch (subtribe), which also contains many extinct close relatives of humans.
Concerning membership, when Hominini is taken to exclude Pan, Panini ("panins")[4] may refer to the tribe containing Pan as its only genus.[5][6] Or perhaps place Pan with other dryopithecine genera, making the whole tribe or subtribe of Panini or Panina together. Minority dissenting nomenclatures include Gorilla in Hominini and Pan in Homo (Goodman et al. 1998), or both Pan and Gorilla in Homo (Watson et al. 2001).
By convention, the adjectival term "hominin" (or nominalized "hominins") refers to the tribe Hominini, whereas the members of the subtribe Hominina (and thus all archaic human species) are referred to as "homininan" ("homininans").[7][8][9] This follows the proposal by Mann and Weiss (1996), which presents tribe Hominini as including both Pan and Homo, placed in separate subtribes. The genus Pan is referred to subtribe Panina, and genus Homo is included in the subtribe Hominina (see below).[10]
The alternative convention uses "hominin" to exclude members of Panina: for Homo; or for human and australopithecine species. This alternative convention is referenced in e.g. Coyne (2009)[11] and in Dunbar (2014).[6] Potts (2010) in addition uses the name Hominini in a different sense, as excluding Pan, and uses "hominins" for this, while a separate tribe (rather than subtribe) for chimpanzees is introduced, under the name Panini.[5] In this recent convention, contra Arambourg, the term "hominin" is applied to Homo, Australopithecus, Ardipithecus, and others that arose after the split from the line that led to chimpanzees (see cladogram below);[12][13] that is, they distinguish fossil members on the human side of the split, as "hominins", from those on the chimpanzee side, as "not hominins" (or "non-hominin hominids").[11]
Cladogram
This cladogram shows the clade of superfamily Hominoidea and its descendant clades, focused on the division of Hominini (omitting detail on clades not ancestral to Hominini). The family Hominidae ("hominids") comprises the tribes Ponginae (including orangutans), Gorillini (including gorillas) and Hominini, the latter two forming the subfamily of Homininae. Hominini is divided into Panina (chimpanzees) and Australopithecina (australopithecines). The Hominina (humans) are usually held to have emerged within the Australopithecina (which would roughly correspond to the alternative definition of Hominini according to the alternative definition which excludes Pan).
Genetic analysis combined with fossil evidence indicates that hominoids diverged from the Old World monkeys about 25 million years ago (Mya), near the Oligocene-Miocene boundary.[14] The most recent common ancestors (MRCA) of the subfamilies Homininae and Ponginae lived about 15 million years ago. The best-known fossil genus of Ponginae is Sivapithecus, consisting of several species from 12.5 million to 8.5 million years ago. It differs from orangutans in dentition and postcranial morphology.[15] In the following cladogram, the approximate time the clades radiated newer clades is indicated in millions of years ago (Mya).
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.[16] 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),[17] 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).[18]
Most DNA studies find that humans and Pan are 99% identical,[19][20] but one study found only 94% commonality, with some of the difference occurring in non-coding DNA.[21] It is most likely that the australopithecines, dating from 4.4 to 3 Mya, evolved into the earliest members of genus Homo.[22][23] In the year 2000, the discovery of Orrorin tugenensis, dated as early as 6.2 Mya, briefly challenged critical elements of that hypothesis,[24] as it suggested that Homo did not in fact derive from australopithecine ancestors.[25]
All the listed fossil genera are evaluated for two traits that could identify them as hominins:
probability of being ancestral to Homo, and
whether they are more closely related to Homo than to any other living primate.
Some, including Paranthropus, Ardipithecus, and Australopithecus, are broadly thought to be ancestral and closely related to Homo;[26] others, especially earlier genera, including Sahelanthropus (and perhaps Orrorin), are supported by one community of scientists but doubted by another.[27][28]
^ abMcNulty, K. P. (2016). "Hominin Taxonomy and Phylogeny: What's In A Name?". Nature Education Knowledge. 7 (1): 2. However, overwhelming genetic evidence has since demonstrated that humans, chimpanzees, and gorillas are much more closely related to each other than to the orangutan ... Thus, there is no genetic support for grouping the great apes together in a distinct group from humans. For this reason, many researchers now place all species of great ape and human within a single family, Hominidae – making them all proper 'hominids'.
^ abDunbar, Robin (2014). Human evolution. Pelican. ISBN978-0-14-197531-3. Conventionally, taxonomists now refer to the great ape family (including humans) as 'hominids', while all members of the lineage leading to modern humans that arose after the split with the [Homo-Pan] LCA are referred to as 'hominins'. The older literature used the terms hominoids and hominids respectively.
^Diogo, Rui; Wood, Bernard (2015). "Origin, Development, and Evolution of Primate Muscles, with Notes on Human Anatomical Variations and Anomalies". Developmental Approaches to Human Evolution. pp. 167–204. doi:10.1002/9781118524756.ch8. ISBN978-1-118-52475-6.
^Worthington, Steven (2012). New approaches to late Miocene hominoid systematics: Ranking morphological characters by phylogenetic signal (Thesis). ProQuest1038821782.
^ abCoyne, Jerry A. (2009). Why evolution is true. London: Penguin Books. pp. 197–208, 244, 248. ISBN978-0-670-02053-9. 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)
^Wood; Richmond, B. G. (2000). "Human evolution: taxonomy and paleobiology". Journal of Anatomy. 197 (Pt 1): 19–60. doi:10.1046/j.1469-7580.2000.19710019.x. PMC1468107. PMID10999270. 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.
^Wakeley, J. (March 2008). "Complex speciation of humans and chimpanzees". Nature. 452 (7184): E3–4, discussion E4. Bibcode:2008Natur.452....3W. doi:10.1038/nature06805. PMID18337768. S2CID4367089. 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.
^King, Mary-Claire (1973). Protein polymorphisms in chimpanzee and human evolution (Thesis). OCLC923094595.
^Coyne, Jerry A. (2009). Why evolution is true. London: Penguin Books. pp. 202–204. ISBN978-0-670-02053-9. 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.
^Reynolds, Sally C.; Gallagher, Andrew (2012). African genesis: perspectives on hominin evolution. Cambridge University Press. ISBN978-1-107-01995-9. The discovery of Orrorin has ... radically modified interpretations of human origins and the environmental context in which the African apes/hominoid transition occurred, although ... the less likely hypothesis of derivation of Homo from the australopithecines still holds primacy in the minds of most palaeoanthropologists.
^Wolpoff, Milford; Senut, Brigitte; Pickford, Martin; Hawks, John (October 2002). "Sahelanthropus or 'Sahelpithecus'?". Nature. 419 (6907): 581–582. Bibcode:2002Natur.419..581W. doi:10.1038/419581a. hdl:2027.42/62951. PMID12374970. S2CID205029762. 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.
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