Human taxonomy is the classification of the human species (systematic name Homo sapiens, Latin: "wise man") within zoological taxonomy. The systematic genus, Homo, is designed to include both anatomically modern humans and extinct varieties of archaic humans. Current humans have been designated as subspecies Homo sapiens sapiens, differentiated, according to some, from the direct ancestor, Homo sapiens idaltu (with some other research instead classifying idaltu and current humans as belonging to the same subspecies). 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 and early 21st centuries. The most widely accepted taxonomy grouping 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 tribe Hominini 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 extreme view rejects the division of Pan and Homo as separate genera, which based on the Principle of Priority would imply the reclassification of chimpanzees as Homo paniscus (or similar). Categorizing humans based on phenotypes is a socially controversial subject. Biologists originally classified races as subspecies, but contemporary anthropologists reject the concept of race as a useful tool to understanding humanity, and instead view humanity as a complex, interrelated genetic continuum. Taxonomy of the hominins continues to evolve. History Human taxonomy on one hand involves the placement of humans within the taxonomy of the hominids (great apes), and on the other the division of archaic and modern humans into species and, if applicable, subspecies. Modern zoological taxonomy was developed by Carl Linnaeus during the 1730s to 1750s. He named the human