What Is a Hominin Reassessing our Ancient Family Tree

Over the last few years, the word hominin has crept into the public news stories about our human ancestors. This is not a misspelling for hominid; this reflects an evolutionary change in the understanding of what it means to be human. But it is admittedly confusing to scholars and students alike. Up until the 1980s, paleoanthropologists generally followed the taxonomic system developed by the 18th-century scientist Carl Linnaeus, when they spoke of the various species of humans. After Darwin, the family of Hominoids devised by scholars by the middle of the 20th century included two subfamilies: the subfamily of Hominids (humans and their ancestors) and that of Anthropoids (chimpanzees, gorillas, and orangutans). Those subfamilies were based on morphological and behavioral similarities in the groups: thats what the data had to offer, comparing skeletal differences. But debates as to how closely related our ancient relatives were to us heated in paleontology and paleoanthropology: all scholars had to base those interpretations on was morphological variations. Ancient fossils, even if we had complete skeletons, were made up of myriad traits, often shared across species and genus. Which of those traits should be considered significant in determining relatedness of species: tooth enamel thickness or arm length? Skull shape or jaw alignment? Bipedal locomotion or tool use? New Data But all that changed when new data based on underlying chemical differences began to arrive from laboratories like the Max Planck Institutes in Germany. First, molecular studies in the late 20th century showed that shared morphology does not mean shared history. At the genetic level, humans, chimpanzees, and gorillas are more closely related to one another than we are to orangutans: in addition, humans, chimps and gorillas are all African apes; orangutans evolved in Asia. More recent mitochondrial and nuclear genetic studies have also supported a tripartite division of our family group as well: Gorilla; Pan and Homo; Pongo. So, the nomenclature for analysis of human evolution and our place in it had to change. Splitting Up the Family To better express our close relationship to the other African apes, scientists split the Hominoids into two subfamilies: Ponginae (orangutans) and Homininae (humans and their ancestors, and chimps and gorillas). But, we still need a way to discuss humans and their ancestors as a separate group, so researchers have proposed a further breakdown of the Homininae subfamily, to include Hominini (hominins or humans and their ancestors), Panini (pan or chimpanzees and bonobos), and Gorillini (gorillas). Roughly speaking, then--but not exactly--a Hominin is what we used to call a Hominid; a creature that paleoanthropologists have agreed is human or a human ancestor. Species in the Hominin bucket include all of the Homo species (Homo sapiens, H. ergaster, H. rudolfensis, includinging Neanderthals, Denisovans, and Flores), all of the Australopithecines (Australopithecus afarensis, A. africanus, A. boisei, etc.) and other ancient forms like Paranthropus and Ardipithecus. Hominoids Molecular and genomic (DNA) studies have been able to bring most scholars to consensus about many of the previous debates about living species and our closest relatives, but strong controversies still swirl around the placement of Late Miocene species, called hominoids, including ancient forms like Dyropithecus, Ankarapithecus, and Graecopithecus. What you can conclude at this point is that since humans are more closely related to Pan than gorillas, Homos and Pan probably had a joint ancestor who probably lived between 4 and 8 million years ago, during the late Miocene. We just havent met her yet. Family Hominidae The following table is adapted from Wood and Harrison (2011). Subfamily Tribe Genus Ponginae -- Pongo Hominiae Gorillini Gorilla Panini Pan Homo Australopithecus,Kenyanthropus,Paranthropus, Homo Incertae Sedis Ardipithecus,Orrorin,Sahelanthropus Family Hominidae Finally... Fossil skeletons of hominins and our ancestors are still being recovered around the world, and there is no doubt that new techniques of imaging and molecular analysis will continue to provide evidence, supporting or refuting these categories, and always teaching us more about the early stages of human evolution. Meet the Hominins Toumaà ¯ (Sahelanthropus tchadensis)Lucy (Australopithecus afarensisSelam (Australopithecus afarensis)Ardipithecus ramidusFlores man (Homo floresiensis Guides to Hominin Species AustralopithecusDenisovansNeanderthalsHomo erectus and Homo egaster Sources Agustà  J, Siria ASd, and Garcà ©s M. 2003. Explaining the end of the hominoid experiment in Europe. Journal of Human Evolution 45(2):145-153.Cameron DW. 1997. A revised systematic scheme for the Eurasian Miocene fossil Hominidae. Journal of Human Evolution 33(4):449-477.Cela-Conde CJ. 2001. Hominid Taxon and Systematics of the Hominoidea. In: Tobias PV, editor. .Humanity from African Naissance to Coming Millennia: Colloquia in Human Biology and Palaeoanthropology Florence; Johannesburg: Firenze University Press; Witwatersrand University Press. p 271-279.Krause J, Fu Q, Good JM, Viola B, Shunkov MV, Derevianko AP, and Paabo S. 2010. The complete mitochondrial DNA genome of an unknown hominin from southern Siberia. Nature 464(7290):894-897.Lieberman DE. 1998. Homology and hominid phylogeny: Problems and potential solutions. Evolutionary Anthropology 7(4):142-151.Strait DS, Grine FE, and Moniz MA. 1997. A reappraisal of early hominid phylogeny. Journal of Human Evolution 32(1):17-82 .Tobias PV. 1978. The earliest Transvaal members of the genus Homo with another look at some problems of hominid taxonomy and systematics. Zeitschrift fà ¼r Morphologie und Anthropologie 69(3):225-265.Underdown, Simon. How the word hominid evolved to include hominin. Nature 444, Nature, December 6, 2006.Wood, Bernard. The evolutionary context of the first hominins. Nature volume 470, Terry Harrison, Nature, February 16, 2011.