Ardipithecus lived in the Afar Depression of Ethiopia between about 5.8 and 4.4 million years ago, more than a million years before Lucy, and may be an early member of the human family. Most of what is known comes from one partial skeleton of the species Ardipithecus ramidus, a female nicknamed Ardi. Her brain was about the size of a female chimpanzee’s and her big toe could grip branches, yet her pelvis and leg bones point to walking upright on the ground. That mix puts her at the centre of the question of how walking on two legs began, and the studies of her bones disagree.
Fifteen years to rebuild her
A team led by White found the first fossils of the species at Aramis, in the Middle Awash valley, between 1992 and 1994, and named it from Afar words: ardi for ground or floor, ramid for root. Ardi was found in 1994, in about 125 pieces, in such poor condition that excavating, rebuilding and analysing her took 15 years. She was announced only in 2009.
She stood about 120 cm tall and is usually said to have weighed about 50 kg, though published estimates start at about 32 kg. Her canine teeth are small and diamond-shaped, with no sign of sharpening, and differ little between the sexes. Some researchers read that as little aggression between males, an inference the fossils cannot confirm.
What kind of climber?
In 2009 her discoverers described a species that clambered carefully along branches on flat palms and, on the ground, walked upright in a way more primitive than Australopithecus. They found none of the features typical of hanging below branches, vertical climbing or knuckle-walking, and concluded that the last common ancestor of humans and chimpanzees probably differed substantially from any living African ape. Her pelvis combines short, broad upper blades, like those of Lucy’s species, with a large lower part suggesting massive climbing muscles, and with such flat feet she probably could not walk or run far.
Later studies moved her closer to the African apes. In 2019 Prang found her foot most like those of chimpanzees and gorillas. A 2021 study of her hand, across 53 primate species, found it most similar to those of chimpanzees, bonobos and orangutans, and suited to hanging and climbing. In 2025 Prang’s team reported that her ankle bone also resembles those of chimpanzees and gorillas, with added features for a stronger push-off in walking. Prang called this a correction of the first interpretation, not a claim that humans evolved from chimpanzees.
Others disagree, in both directions. In 2011 Sarmiento and Meldrum argued from her proportions that she mostly went on all fours on the ground and climbed little. A 2019 study of fossils from Gona, led by Simpson, found an ankle and big toe better suited to upright walking than previously recognised, though he still called Ardipithecus “a lousy biped”. The Smithsonian notes that the pelvis was rebuilt from crushed fragments and, to some scientists, only suggests upright walking.
Woodland or savanna
Her discoverers describe a largely woodland home, and the fossils found with her include fig, palm and hackberry, leaf-eating monkeys, kudu and peafowl. The Smithsonian takes this as evidence against the old idea that upright walking began as grasslands spread. In 2010 Cerling’s team challenged it: carbon isotopes and microscopic grass fossils suggested that dense trees covered only 5 to 25 per cent of the area, so Ardi may have lived in a thin wooded strip within a savanna. White’s team answered that no reliable method can estimate savanna there, and that shallow groundwater and springs laid down the fossils, with no sign of an ancient river or lake.
An older species and an uncertain branch
Ardipithecus kadabba is known from far less: 11 specimens from at least five individuals in the Smithsonian’s count, most of them 5.6 to 5.8 million years old. The only evidence of upright walking is one toe bone, 5.2 million years old, found about 16 km from the rest. Its canines still project beyond the tooth row, and in 2008 Wood and Lonergan cited them in doubting its place on the human line.
The discoverers of Ardipithecus ramidus think it was ancestral to Australopithecus. Sarmiento argued that the genus shares no feature exclusive to humans, while later studies of its hand, skull base and tooth roots argue for the human line. There is no evidence of any cultural traits, and nothing is known of its skin or hair.
