Our earliest ancestors may have been less like chimpanzees than assumed
A study of Ardipithecus ramidus, a hominin from roughly 4.4 million years ago, argues that it looked and perhaps behaved more like a gentle bonobo than an aggressive chimpanzee. If right, chimpanzee traits evolved after the split from our line, and using chimps as a stand-in for early humans misleads.
The authors point to a skull resembling that of young chimpanzees, a sign of juvenile features retained into adulthood, and to small differences between males and females, as in bonobos. They suggest early hominins may have domesticated themselves, with growing maternal care and female mate choice, and that many basic human traits arose in the forests and woodlands of late Miocene and early Pliocene Africa. It is one argument in a crowded field, not settled fact.
The deeper backstory stretches far. Primates split from other mammals around 85 million years ago, and early primate-like animals such as Plesiadapis in North America and Archicebus in China lived in the warm Paleocene and Eocene. Fossil beds in Egypt's Faiyum depression, southwest of Cairo, preserve the tropical population that gave rise to every living primate, from Madagascar's lemurs to monkeys and apes. The oldest known catarrhine, Kamoyapithecus from Kenya, dates to 24 million years ago.
Apes then diversified widely. East Africa held Proconsul and many relatives during the Miocene, while Dryopithecus lived in Europe, and Oreopithecus, the youngest Miocene hominoid, survives in Italian coal beds dated to 9 million years ago. Gibbons branched off some 18 to 12 million years ago and orangutans around 12. Molecular evidence says gorillas and then chimpanzees parted from the human line between 8 and 4 million years ago; human DNA is about 98.4 percent identical to chimp DNA on single-letter comparisons. Acidic rainforest soils dissolve bone, leaving great ape fossils scarce.
Candidates for the earliest members of our lineage include Sahelanthropus at about 7 million years and Orrorin at about 6, followed by Ardipithecus. Australopithecus arose in eastern Africa around 4 million years ago and died out about 2 million years ago. The oldest documented Homo is the Ledi jaw, dated to 2.75 to 2.8 million years ago, arguably the earliest species with positive evidence of stone tools.
Source: Human evolution
