A South African quarry skull put Africa at the centre of human origins
In 1924 lime-quarry workers at Taung unearthed the skull of a three-year-old who had walked upright. Raymond Dart named it Australopithecus africanus, the southern ape, and argued it was a human ancestor. The genus lasted for millions of years in Africa, and our own genus Homo grew out of it.
Australopithecus is an extinct genus of early hominins that lived in Africa through the Pliocene and Early Pleistocene. Its earliest known species, A. anamensis, appears in eastern Africa around 4.2 million years ago; the last members vanished about 1.9 million years ago. Homo branched off somewhere between 3 and 2 million years ago, and Paranthropus and Kenyanthropus also descend from Australopithecus species. A fossil from Chad, A. bahrelghazali, hints that the genus ranged far wider than its bones reveal.
Dart, an Australian anatomist at the University of the Witwatersrand, reported the Taung Child in Nature in February 1925. Later finds added weight. A trackway at Laetoli in Tanzania, 3.6 million years old, holds the earliest evidence of fully bipedal hominins, with prints strikingly like ours. In 1997 the Sterkfontein caves yielded Little Foot, an almost complete skeleton about 3.7 million years old, and in 2008 the same caves produced A. sediba.
Anatomy and genes show the slow drift toward humanity. Australopithecus carried two duplicated versions of a gene called SRGAP2, one of which later helped boost the number and migration of neurons in the human brain. Hands start to change in later A. afarensis about 3 million years ago, with fingers shortening relative to the thumb.
Classification is a tangle. In 1950 Ernst Mayr wanted every bipedal ape placed in Homo, but J. T. Robinson's opposing view of 1954 won out. Because some Australopithecus species are closer to humans than others, the genus is paraphyletic: a tidy grouping would have to swallow Homo too. Proposals keep coming, from reviving a genus called Praeanthropus in 2003, largely dismissed, to moving A. africanus into Paranthropus, and there is debate over whether A. bahrelghazali is a separate species at all.
Source: Australopithecus
