Hominin

See also: Evolution of hominin intelligence; Hominin intelligence

The term Hominin refers to primates in the Tribe Hominini which is a relatively recent classification under which it is proposed would fall all of the fossil and living bipedal apes including the Australopithecines, fossil members of the genus Homo and living humans. It is generally replacing the term hominid in the scientific literature.

The taxonomic classification of humans

Traditional classification

In the traditional Linnaean system of classification humans are categorized as firstly Animalia, then Chordata because humans have a backbone; Mammalia because humans have hair and suckle their young; Primates because humans share with apes, monkeys and lemurs certain morphological characters; Hominidae because, among a few other criteria, humans are separated from the other apes by being bipedal; Homo being our generic classification as human; and finally sapiens a species name meaning, rightly or wrongly, “wise”. The Linnaean system also recognizes such groupings as “Superfamilies” and “Subfamilies” and in the case of the human lineage, the most often recognized superfamily is the Hominoidea (hominoids) which includes all of the living apes.

The traditional view of scientists has been to recognize three families of hominoid: the Hylobatidae, the Hominidae and the Pongidae. The Hylobatidae includes the so-called lesser apes of Asia - the gibbons and siamangs. The Hominidae includes living humans and typically fossil apes that possess a suite of characters such as bipedalism, reduced canine size and increasing brain size such as the australopithecines. The Pongidae includes the remaining African great apes and the orang-utan recognizing this groups “ape-ness” in being large-bodied, quadrupedal, arboreal primates.

A modern approach to human classification

New evolutionary evidence largely driven by genetic research suggests that despite the morphological differences, we humans are in fact more closely related to the common chimpanzee and bonobo (often referred to as the pygmy chimpanzee) than either species is to the gorilla. We share approximately 95 - 98 percent of our genes in common with chimps, indicating that humans share a common ape ancestor with the chimpanzees. Divergence times between the two groups based on a molecular clock suggest that the chimpanzee/human split occurred between 4 and 7 million years ago. In turn, the African apes, including humans, are more closely related to each other than any are to the orang-utan. Thus humans, chimps, gorillas and orang-utans are in turn, more closely related to each other than they are to the gibbons and siamangs. In recognition of these genetic relationships some scientists argue that the present morphologically based classification system must be replaced with one that is more representative of the true evolutionary relationships as evinced by our genes.

The application of the term hominin

Under most “new” proposed classification models the human family tree would appear as follows: Hominoids would be a primate superfamily, as has always been the case. Underneath this hominoid umbrella would fall orang-utans, gorillas, chimps and humans all in the Family Hominidae. In recognition of their genetic divergence some 11-13 million years ago, the orangutans would be placed in the sub-family Ponginae and the African apes, including humans, would all placed together in the Subfamily Homininae. The bipedal apes, namely all of the fossil species as well as living humans, would fall into the Tribe Hominini (thus hominin). It is this tribe that all of the fossil genera such as Australopithecus, Ardipithecus, Kenyanthropus and Homo would be placed within. A few more evolutionary biologists propose to include humans and chimpanzees within the same genus - the genus Homo.

Hominid vs. Hominin

The terms Hominin and Hominid are both used frequently by scientists in publications. It is still being debated as to which term is correct for the classification of humans and ancestral bipedal apes. This is due to the fact that while the genetic interpretation - which favors use of the term Hominini - has many advantages in its precision and its recognition of biological reality that moves beyond physical morphology, it is difficult to test genetic relationships in fossils-thus leaving room for error.