Life › Human evolution › Hominins: the human branch begins
Australopithecus
c. 4.2–2 million years ago· Organism or group· Human ancestors & us
Well establishedStrong fossil, genetic or geological evidence.
A group of small-brained, upright-walking hominins that lived in eastern and southern Africa about 4.2–2 million years ago.
See it on the Life map →What happened
The name means 'southern ape', given by Raymond Dart in 1925 to the Taung Child skull from South Africa. Species include A. anamensis, A. afarensis (Lucy's species), A. africanus and A. sediba. Australopiths walked upright on the ground but kept long arms and curved fingers for climbing. Their brains were about 400–550 cubic centimeters (cc), close to a chimpanzee's, and their large teeth suited a tough, mostly plant diet.
Why it matters
Australopiths proved that upright walking came long before big brains, overturning early 20th-century expectations, and one of them probably gave rise to our genus, Homo.
The evidence (fossils, genes, rocks)
Hundreds of fossils from East African sites such as Hadar and Laetoli, dated by volcanic ash, and from South African caves such as Sterkfontein and Taung, which are harder to date.
Still debated
How many species there were, which one led to Homo, and whether South Africa's 'Little Foot' skeleton is really 3.67 million years old are all debated.
Inside this (2)
Connections (5)
▸Ardipithecus ramidus ('Ardi') may be ancestral to AustralopithecusDebated
The connection
Ardipithecus is older and more apelike than Australopithecus, which appears about 4.2 million years ago in the same region. Its finders think Ardi's kind, or a close cousin, evolved into the earliest Australopithecus, A. anamensis, which walked more efficiently and relied less on climbing.
When and how
Middle Awash, Ethiopia: Ardipithecus at Aramis about 4.4 million years ago, and Australopithecus anamensis at nearby Asa Issie about 4.2–4.1 million years ago.
How sure are we?
Both appear in the same valley a few hundred thousand years apart and share some tooth traits. But no fossil shows the actual transition.
Debates and open questions
Some researchers see Ardi as a side branch, or even doubt it is a hominin at all. With so few fossils, the exact ancestor of Australopithecus is unknown.
▸Lucy (Australopithecus afarensis) is the most famous AustralopithecusWell established
The connection
Lucy belongs to Australopithecus afarensis, the best-known species in the genus. Her skeleton, about 40% complete, gave the first clear picture of a small-brained, upright-walking hominin, and her species became the yardstick for comparing all other australopiths.
When and how
Hadar, Ethiopia, on 24 November 1974, by Donald Johanson and Tom Gray; the species was named in 1978 from her bones and fossils from Laetoli.
The evidence
Hundreds of afarensis fossils from Hadar, Laetoli and Dikika, including the 'First Family' group and the child 'Selam', match her anatomy.
Debates and open questions
Whether afarensis gave rise to later australopiths and Homo, and how it relates to other species living at the same time, such as Kenyanthropus and A. deyiremeda.
▸Laetoli footprints were probably made by AustralopithecusStrong evidence
The connection
The only hominin fossils known from Laetoli at that time belong to Australopithecus afarensis, Lucy's species, so the footprint makers are usually identified as afarensis. The prints suggest small, upright walkers of different sizes moving together across the ash.
When and how
Laetoli, Tanzania: afarensis jaws and teeth were found there in the 1970s in the same rock layers as the trails.
How sure are we?
The match of age, place and foot shape with afarensis foot bones from Hadar is strong but circumstantial; footprints carry no bones or DNA.
Debates and open questions
A 2021 restudy of a separate Laetoli trail (site A), once thought to be a bear's, argued that a second, different hominin also walked there.
▸Australopithecus probably gave rise to The genus HomoStrong evidence
The connection
Homo appears about 2.8 million years ago, while australopiths were still widespread. A jaw from Ledi-Geraru, Ethiopia, mixes australopith and Homo traits, suggesting that one australopith population, perhaps A. afarensis or a relative, evolved smaller teeth, bigger brains and greater reliance on tools.
When and how
East Africa, about 3–2.5 million years ago; the Ledi-Geraru jaw (LD 350-1), about 2.8 million years old, was found in 2013 and published in 2015.
How sure are we?
Fossils of intermediate form and their timing support the link, but the fossil record between 3 and 2.5 million years ago is thin.
Debates and open questions
Which australopith was the ancestor is debated: A. afarensis in East Africa, A. africanus or A. sediba in South Africa, or a species not yet found.
▸Australopithecus probably also gave rise to Paranthropus: the robust homininsStrong evidence
The connection
Paranthropus appears about 2.7 million years ago, likely from an East African australopith. It took a different path from Homo: instead of bigger brains and tools, it evolved huge chewing teeth and jaw muscles for tough plant food. The two lines lived side by side for over a million years.
When and how
East Africa from about 2.7 million years ago (the 2.5-million-year-old 'Black Skull', West Turkana, Kenya, found 1985); South Africa about 2 million years ago.
How sure are we?
Skull and tooth features shared with earlier australopiths, especially A. afarensis, and its appearance in the fossil record soon after them.
Debates and open questions
Did East and South African robust forms descend from one ancestor, or evolve big jaws separately? The answer decides whether Paranthropus is one true group.