Overview of speciation and hybridization within the genus Homo over the last two million years (vertical axis). The rapid "Out of Africa" expansion of H. sapiens is indicated at the top of the diagram, with admixture indicated with Neanderthals, Denisovans, and unspecified archaic African hominins.
Since the introduction of systematic names in the 18th century, knowledge of human evolution has increased drastically, and a number of intermediate taxa have been proposed in the 20th to early 21st century. The most widely accepted taxonomy groups takes the genus Homo as originating between two and three million years ago, divided into at least two species, archaic Homo erectus and modern Homo sapiens, with about a dozen further suggestions for species without universal recognition.
The genus Homo is placed in the tribeHominini alongside Pan (chimpanzees). The two genera are estimated to have diverged over an extended time of hybridization spanning roughly 10 to 6 million years ago, with possible admixture as late as 4 million years ago. A subtribe of uncertain validity, grouping archaic "pre-human" or "para-human" species younger than the Homo-Pan split is Australopithecina (proposed in 1939).
A proposal by Wood and Richmond (2000) would introduce Hominina as a subtribe alongside Australopithecina, with Homo the only known genus within Hominina. Alternatively, following Cela-Conde and Ayala (2003), the "pre-human" or "proto-human" genera of Australopithecus, Ardipithecus, Praeanthropus, and possibly Sahelanthropus may be placed on equal footing alongside the genus Homo. An even more radical view rejects the division of Pan and Homo as separate genera, which based on the Principle of Priority would imply the re-classification of chimpanzees as Homo paniscus (or similar).
Prior to the current scientific classification of humans, philosophers and scientists have made various attempts to classify humans. They offered definitions of the human being and schemes for classifying types of humans. Biologists once classified races as subspecies, but today anthropologists reject the concept of race and view humanity as an interrelated genetic continuum. Taxonomy of the hominins continues to evolve.
The discovery of the first extinct archaic human species from the fossil record dates to the mid 19th century, Homo neanderthalensis, classified in 1864. Since then, a number of other archaic species have been named, but there is no universal consensus as to their exact number. After the discovery of H. neanderthalensis, which even if "archaic" is recognizable as clearly human, late 19th to early 20th century anthropology for a time was occupied with finding the supposedly "missing link" between Homo and Pan. The "Piltdown Man" hoax of 1912 was the fraudulent presentation of such a transitional species. Since the mid-20th century, knowledge of the development of Hominini has become much more detailed, and taxonomical terminology has been altered a number of times to reflect this.
The introduction of Australopithecus as a third genus, alongside Homo and Pan, in the Hominini tribe is due to Raymond Dart (1925). Australopithecina as a subtribe containing Australopithecus as well as Paranthropus (Broom 1938) is a proposal by Gregory & Hellman (1939). More recently proposed additions to the Australopithecina subtribe include Ardipithecus (1995) and Kenyanthropus (2001). The position of Sahelanthropus (2002) relative to Australopithecina within Hominini is unclear. Cela-Conde and Ayala (2003) propose the recognition of Australopithecus, Ardipithecus, Praeanthropus, and Sahelanthropus (the latter incertae sedis) as separate genera.
The genus Homo has been taken to originate some two million years ago since the discovery of stone tools in Olduvai Gorge, Tanzania, in the 1960s. Homo habilis (Leakey et al., 1964) would be the first "human" species (member of genus Homo) by definition, its type specimen being the OH 7 fossils. However, the discovery of more fossils of this type has opened up the debate on the delineation of H. habilis from Australopithecus. Especially, the LD 350-1 jawbone fossil discovered in 2013, dated to 2.8 Mya, has been argued as being transitional between the two. It is also disputed whether H. habilis was the first hominin to use stone tools, as Australopithecus garhi, dated to c. 2.5 Mya, has been found along with stone tool implements. Fossil KNM-ER 1470 (discovered in 1972, designated Pithecanthropus rudolfensis by Alekseyev 1978) is now seen as either a third early species of Homo (alongside H. habilis and H. erectus) at about 2 million years ago, or alternatively as transitional between Australopithecus and Homo.
Wood and Richmond (2000) proposed that Gray's tribe Hominini ("hominins") be designated as comprising all species after the chimpanzee-human last common ancestor by definition, to the inclusion of Australopithecines and other possible pre-human or para-human species (such as Ardipithecus and Sahelanthropus) not known in Gray's time. In this suggestion, the new subtribe of Hominina was to be designated as including the genus Homo exclusively, so that Hominini would have two subtribes, Australopithecina and Hominina, with the only known genus in Hominina being Homo. Orrorin (2001) has been proposed as a possible ancestor of Hominina but not Australopithecina.
Designations alternative to Hominina have been proposed: Australopithecinae (Gregory & Hellman 1939) and Preanthropinae (Cela-Conde & Altaba 2002);
At least a dozen species of Homo other than Homo sapiens have been proposed, with varying degrees of consensus. Homo erectus is widely recognized as the species directly ancestral to Homo sapiens. Most other proposed species are proposed as alternatively belonging to either Homo erectus or Homo sapiens as a subspecies. This concerns Homo ergaster in particular. One proposal divides Homo erectus into an African and an Asian variety; the African is Homo ergaster, and the Asian is Homo erectus sensu stricto. (Inclusion of Homo ergaster with Asian Homo erectus is Homo erectus sensu lato.) There appears to be a recent trend, with the availability of ever more difficult-to-classify fossils such as the Dmanisi skulls (2013) or Homo naledi fossils (2015) to subsume all archaic varieties under Homo erectus.
A subspecies cannot be recognized independently: a species will either be recognized as having no subspecies at all or at least two (including any that are extinct). Therefore, the designation of an extant subspecies Homo sapiens sapiens only makes sense if at least one other subspecies is recognized. H. s. sapiens is attributed to "Linnaeus (1758)" by the taxonomic Principle of Coordination.William Stearn (1959) in a "passing remark" argued that Linnaeus "must stand as the type of his Homo sapiens". Since Linnaeus describes H. s. europaeus as having blue/green (caerulus) eyes but himself had brown eyes, he cannot have included himself in H. s. europaeus, Linnaeus would therefore have to be classified as H. sapiens sapiens, as not matching any of the descriptions of his five subspecies, and so would stand as the lectotype both for H. sapiens, and for H. s. sapiens within his own subspecies nomenclature.
During the 19th to mid-20th century, it was common practice to classify the major divisions of extant H. sapiens as subspecies, following Linnaeus (1758), who had recognized H. s. americanus, H. s. europaeus, H. s. asiaticus and H. s. afer as grouping the native populations of the Americas, West Eurasia, East Asia and Sub-Saharan Africa, respectively, besides H. s. ferus (for the "wild" form which he identified with feral children) and two further "wild" forms for reported specimens now considered part of cryptozoology, H. s. monstrosus and H. s. troglodytes.
Homo sapiens neanderthalensis was proposed by King (1864) as an alternative to Homo neanderthalensis. There have been "taxonomic wars" over whether Neanderthals were a separate species since their discovery in the 1860s. Pääbo (2014) frames this as a debate that is unresolvable in principle, "since there is no definition of species perfectly describing the case."Louis Lartet (1869) proposed Homo sapiens fossilis based on the Cro-Magnon fossils.
By the 1980s, the practice of dividing extant populations of Homo sapiens into subspecies declined. An early authority explicitly avoiding the division of H. sapiens into subspecies was Grzimeks Tierleben, published 1967–1972.
A late example of an academic authority proposing that the human racial groups should be considered taxonomical subspecies is John Baker (1974). The trinomial nomenclature Homo sapiens sapiens became popular for "modern humans" in the context of Neanderthals being considered a subspecies of H. sapiens in the second half of the 20th century. Derived from the convention, widespread in the 1980s, of considering two subspecies, H. s. neanderthalensis and H. s. sapiens, the explicit claim that "H. s. sapiens is the only extant human subspecies" appears in the early 1990s. This is only true if the nomenclature derived from Linnaeus is rejected. Based on Linnaeus (1758), there are at least six subspecies, with H. s. sapiens catching those specimens not included in any other.
Homo erectus since its introduction in 1892 has been divided into numerous subspecies, many of them formerly considered individual species of Homo. None of these subspecies have universal consensus among paleontologists.
^J. E. Gray, "An outline of an attempt at the disposition of Mammalia into Tribes and Families, with a list of genera apparently appertaining to each Tribe", Annals of Philosophy, new series (1825), pp. 337–344.
^Introduced for the Florisbad Skull (discovered in 1932, Homo florisbadensis or Homo helmei). Also the genus suggested for a number of archaic human skulls found at Lake Eyasi by Weinert (1938). Leaky, Journal of the East Africa Natural History Society (1942), p. 43.
^Villmoare B, Kimbel H, Seyoum C, Campisano C, DiMaggio E, Rowan J, Braun D, Arrowsmith J, Reed K. (2015). Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia. Science. doi:10.1126/science.aaa1343. Some paleoanthropologists regard the H. habilis taxon as invalid, made up of fossil specimens of Australopithecus and Homo. Tattersall, I. & Schwartz, J.H., Extinct Humans, Westview Press, New York, 2001, p. 111.
^Antón, S. C. (2003). "Natural history of Homo erectus". Am. J. Phys. Anthropol. 122: 126-170. doi:10.1002/ajpa.10399. PMID14666536. By the 1980s, the growing numbers of H. erectus specimens, particularly in Africa, led to the realization that Asian H. erectus (H. erectus sensu stricto), once thought so primitive, was in fact more derived than its African counterparts. These morphological differences were interpreted by some as evidence that more than one species might be included in H. erectus sensu lato (e.g., Stringer, 1984; Andrews, 1984; Tattersall, 1986; Wood, 1984, 1991a, b; Schwartz and Tattersall, 2000) ... Unlike the European lineage, in my opinion, the taxonomic issues surrounding Asian vs. African H. erectus are more intractable. The issue was most pointedly addressed with the naming of H. ergaster on the basis of the type mandible KNM-ER 992, but also including the partial skeleton and isolated teeth of KNM-ER 803 among other Koobi Fora remains (Groves and Mazak, 1975). Recently, this specific name was applied to most early African and Georgian H. erectus in recognition of the less-derived nature of these remains vis à vis conditions in Asian H. erectus (see Wood, 1991a, p. 268; Gabunia et al., 2000a). It should be noted, however, that at least portions of the paratype of H. ergaster (e.g., KNM-ER 1805) are not included in most current conceptions of that taxon. The H. ergaster question remains famously unresolved (e.g., Stringer, 1984; Tattersall, 1986; Wood, 1991a, 1994; Rightmire, 1998b; Gabunia et al., 2000a; Schwartz and Tattersall, 2000), in no small part because the original diagnosis provided no comparison with the Asian fossil record.
^Confirmed H. habilis fossils are dated to between 2.1 and 1.5 million years ago. This date range overlaps with the emergence of Homo erectus. Schrenk, Friedemann; Kullmer, Ottmar; Bromage, Timothy (2007). "The Earliest Putative Homo Fossils". In Henke, Winfried; Tattersall, Ian (eds.). Handbook of Paleoanthropology. 1. In collaboration with Thorolf Hardt. Berlin, Heidelberg: Springer. pp. 1611-1631. doi:10.1007/978-3-540-33761-4_52. ISBN978-3-540-32474-4.DiMaggio, Erin N.; Campisano, Christopher J.; Rowan, John; et al. (March 20, 2015). "Late Pliocene fossiliferous sedimentary record and the environmental context of early Homo from Afar, Ethiopia". Science. 347 (6228): 1355-1359. Bibcode:2015Sci...347.1355D. doi:10.1126/science.aaa1415. ISSN0036-8075. PMID25739409. Hominins with "proto-Homo" traits may have lived as early as 2.8 million years ago, as suggested by a fossil jawbone classified as transitional between Australopithecus and Homo discovered in 2015.
^Curnoe, Darren (June 2010). "A review of early Homo in southern Africa focusing on cranial, mandibular and dental remains, with the description of a new species (Homo gautengensis sp. nov.)". HOMO - Journal of Comparative Human Biology. 61 (3): 151-177. doi:10.1016/j.jchb.2010.04.002. ISSN0018-442X. PMID20466364. A species proposed in 2010 based on the fossil remains of three individuals dated between 1.9 and 0.6 million years ago. The same fossils were also classified as H. habilis, H. ergaster or Australopithecus by other anthropologists.
^Haviland, William A.; Walrath, Dana; Prins, Harald E.L.; McBride, Bunny (2007). Evolution and Prehistory: The Human Challenge (8th ed.). Belmont, CA: Thomson Wadsworth. p. 162. ISBN978-0-495-38190-7.H. erectus may have appeared some 2 million years ago. Fossils dated to as much as 1.8 million years ago have been found both in Africa and in Southeast Asia, and the oldest fossils by a narrow margin (1.85 to 1.77 million years ago) were found in the Caucasus, so that it is unclear whether H. erectus emerged in Africa and migrated to Eurasia, or if, conversely, it evolved in Eurasia and migrated back to Africa.
^Formerly dated to as late as 50,000 to 40,000 years ago, a 2011 study pushed back the date of its extinction of H. e. soloensis to 143,000 years ago at the latest, more likely before 550,000 years ago.
Indriati E, Swisher CC III, Lepre C, Quinn RL, Suriyanto RA, et al. 2011 The Age of the 20 Meter Solo River Terrace, Java, Indonesia and the Survival of Homo erectus in Asia.PLoS ONE 6(6): e21562. doi:10.1371/journal.pone.0021562.
^The type fossil is Mauer 1, dated to ca. 0.6 million years ago.
The transition from H. heidelbergensis to H. neanderthalensis between 300 and 243 thousand years ago is conventional, and makes use of the fact that there is no known fossil in this period. Examples of H. heidelbergensis are fossils found at Bilzingsleben (also classified as Homo erectus bilzingslebensis).
^Muttoni, Giovanni; Scardia, Giancarlo; Kent, Dennis V.; Swisher, Carl C.; Manzi, Giorgio (2009). "Pleistocene magnetochronology of early hominin sites at Ceprano and Fontana Ranuccio, Italy". Earth and Planetary Science Letters. 286 (1-2): 255-268. Bibcode:2009E&PSL.286..255M. doi:10.1016/j.epsl.2009.06.032.
^Dirks, P.; et al. (9 May 2017). "The age of Homo naledi and associated sediments in the Rising Star Cave, South Africa". eLife. 6: e24231. doi:10.7554/eLife.24231. PMID28483040.
^Bischoff, James L.; Shamp, Donald D.; Aramburu, Arantza; et al. (March 2003). "The Sima de los Huesos Hominids Date to Beyond U/Th Equilibrium (>350 kyr) and Perhaps to 400-500 kyr: New Radiometric Dates". Journal of Archaeological Science. 30 (3): 275-280. doi:10.1006/jasc.2002.0834. ISSN0305-4403.
The first humans with "proto-Neanderthal traits" lived in Eurasia as early as 0.6 to 0.35 million years ago (classified as H. heidelbergensis, also called a chronospecies because it represents a chronological grouping rather than being based on clear morphological distinctions from either H. erectus or H. neanderthalensis). There is a fossil gap in Europe between
300 and 243 kya, and by convention, fossils younger than 243 kya are called "Neanderthal".
D. Dean; J.-J. Hublin; R. Holloway; R. Ziegler (1998). "On the phylogenetic position of the pre-Neandertal specimen from Reilingen, Germany". Journal of Human Evolution. 34 (5). pp. 485-508. doi:10.1006/jhev.1998.0214.
^Détroit, F.; Mijares, A. S.; Corny, J.; Daver, G.; Zanolli, C.; Dizon, E.; Robles, E.; Grün, R.; Piper, P. J. (2019). "A new species of Homo from the Late Pleistocene of the Philippines". Nature. 568 (7751): 181-186. doi:10.1038/s41586-019-1067-9.
^"as far as I know, there is no type material for Homo sapiens. To be fair to Linnaeus, the practice of setting type specimens aside doesn't seem to have developed until a century or so later." Bob Ralph, "Conforming to type", New Scientist No. 1548 (19 February 1987), p. 59.
^"ICZN glossary". International Code of Zoological Nomenclature. 4th ed., article 46.1: "Statement of the Principle of Coordination applied to species-group names. A name established for a taxon at either rank in the species group is deemed to have been simultaneously established by the same author for a taxon at the other rank in the group; both nominal taxa have the same name-bearing type, whether that type was fixed originally or subsequently."
Homo sapiens sapiens is rarely used before the 1940s. In 1946, John Wendell Bailey attributes the name to Linnaeus (1758) explicitly: "Linnaeus. Syst. Nat. ed. 10, Vol. 1. pp. 20, 21, 22, lists five races of man, viz: Homo sapiens sapiens (white -- Caucasian) [...]", This is a misattribution, but H. s. sapiens has since often been attributed to Linnaeus. In actual fact, Linnaeus, Syst. Nat. ed. 10 Vol. 1. p. 21 does not have Homo sapiens sapiens, the "white" or "Caucasian" race being instead called Homo sapiens Europaeus. This is explicitly pointed out in Bulletin der Schweizerische Gesellschaft für Anthropologie und Ethnologie Volume 21 (1944), p. 18 (arguing not against H. s. sapiens but against "H. s. albus L." proposed by von Eickstedt and Peters): "die europide Rassengruppe, als Subspecies aufgefasst, [würde] Homo sapiens eurpoaeus L. heissen" ("the Europid racial group, considered as a subspecies, would be named H. s. europeaeus L.").
See also: John R. Baker, Race, Oxford University Press (1974), 205.
^Stearn, W. T. 1959. "The background of Linnaeus's contributions to the nomenclature and methods of systematic biology", Systematic Zoology 8 (1): 4-22, p. 4
^"It is certain that Linnaeus was present when he wrote this description and that he regarded himself as included in Homo sapiens. That he is not part of any of his subgroups is clear from the descriptions, in particular he is certainly not part of Homo sapiens europaeus since this subspecies is described as 'Pilis flavescentibus, prolixis. Oculis caeruleis' whereas Linnaeus has brown hair and eyes (Tullberg, 1907). He is therefore included in the type series of Homo sapiens sapiens (Article 220.127.116.11). There was, however, no single person recognised as the type until 1959, when Professor William Stearn, in a passing remark in a paper on Linnaeus' contributions to nomenclature and systematics wrote that 'Linnaeus himself, must stand as the type of his Homo sapiens'. This was enough to designate Linnaeus as a lectotype (Article 74.5), the single name bearing type specimen for the species Homo sapiens and its subspecies Homo sapiens sapiens."
David Notton and Chris Stringer, "Who is the type of Homo sapiens?", International Commission on Zoological Nomenclature (2011).
See e.g. John Wendell Bailey, The Mammals of Virginia (1946), p. 356.;
Journal of Mammalogy 26-27 (1945), p. 359.;
J. Desmond Clark (ed.), The Cambridge History of Africa, Cambridge University Press (1982), p. 141 (with references).
^ abIn the 1970s a tendency developed to regard the Javanese variety of H. erectus as a subspecies, Homo erectus erectus, with the Chinese variety being referred to as Homo erectus pekinensis. See: Sartono, S. Implications arising from Pithecanthropus VIII In: Paleoanthropology: Morphology and Paleoecology. Russell H. Tuttle (Ed.), p. 328.
^Emanuel Vl?ek: Der fossile Mensch von Bilzingsleben (= Bilzingsleben. Bd. 6 = Beiträge zur Ur- und Frühgeschichte Mitteleuropas 35). Beier & Beran, Langenweißbach 2002.