| Hominids | ||||||||||
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Pongo (orangutans)
Gigantopithecus - extinct Pan (chimpanzees) Gorilla (gorillas) Subfamily Homininae Orrorin - extinct Ardipithecus - extinct Kenyanthropus - extinct Australopithecus - extinct Paranthropus - extinct Homo (humans) | ||||||||||
Originally the group was restricted to humans and their extinct relatives, with great apes being placed in a separate family, the Pongidae. However, the Pongidae are paraphyletic, whereas most taxonomists nowadays encourage monophyletic groups. Thus many biologists consider Hominidae to include the Pongidae, or restrict the latter to the orangutan and extinct relatives like Gigantopithecus.
Especially close human relatives form a subfamily, the Homininae. Some researchers go so far as to include chimpanzees and gorillas in the genus Homo along with humans, but recent genetic evidence suggests that the human relationship to these species is not as close as previously thought.
The exact criterion for membership in the Homininae is not clear, but usually includes the species who share more than 97% of their DNA with the modern human genome, and requires the capacity for language and for simple cultures beyond the family or band. A theory of mind providing the capacity to lie convincingly is a controversial criterion distinguishing the adult human alone among the hominids. Humans acquire this capacity at about four and a half years of age in our cultures whereas the bonobo, gorilla and chimpanzee never seem to do so. However, without the ability to test whether early members of the Homininae such as australopithecines, Homo erectus, or Neanderthals had a theory of mind, it is irrational to ignore similarities seen in their living cousins. Despite an apparent lack of real culture and significant physiological differences, some say that the orangutan may also satisfy these criteria. These scientific debates take on political significance for advocates of Great Ape personhood, who some believe have influenced the debates in order to refer to "ape genocide".
In 2002, a 6-7 million year old fossil skull nicknamed Toumaļ by its discoverers, and formally classified as Sahelanthropus tchadensis, was discovered in Chad and is possibly the earliest hominid fossil ever found. In addition to its age, Toumaļ, unlike the 3-4 million year younger Australopithecine dubbed "Lucy", has a relatively flat face without the prominent snout seen on other pre-Hominoid hominids. Some researchers have made the suggestion that this previously unknown species may in fact be a direct ancestor of modern humans (or at least closely related to a direct ancestor). Others contend that one fossil is not enough to make such a claim because it would overturn the conclusions of over 100 years of anthropological study. A report on this finding was published in the journal Nature on July 11, 2002. While some scientists claim that it is merely the skull of a female gorilla, others have called it the most important hominid fossil since Australopithecus.