A skull fragment from an adult Homo erectus, about 2 million years old, has been found in the Drimolen cave in South Africa. It is about 200,000 years older than adult specimens of the species known from other sites, such as Dmanisi in Georgia, which are about 1.8m years old. The find backs up an earlier discovery from the same cave and rests on a single piece of bone.
The fragment, numbered DNH 127, is made up of parts of the temporal, parietal and occipital bones of the skull. A team from La Trobe University led by Jesse Martin described it, along with 18 hominid fossils from Drimolen, in the journal Annals of Human Biology. Hominids are humans and their close ancestors. Homo erectus is the first species that scientists almost unanimously place in our genus and regard as a direct forerunner of modern humans.
Of the 18 fossils, 14 belong to Paranthropus robustus, a heavily built relative with huge molars, not to Homo erectus. Martin says that two million years ago Paranthropus was more than ten times as common as Homo erectus at Drimolen.
The child's skull DNH 134 and the adult DNH 127
The first find of the species at Drimolen was the skull DNH 134, from a young child. In 2020 a team led by Gary Schwartz of Arizona State University put it together from more than 150 fragments and put the child's age at 3 to 6 years. The skull was dated to between 2.04 and 1.95m years ago using three methods: uranium-lead dating of flowstone, electron spin resonance on teeth, and palaeomagnetism of sediments.
The child's skull left open what an adult looked like, because children's bones grow and change. DNH 127 is the first adult specimen assigned to the species at Drimolen. Martin says it "provides additional confirmation" that the species appeared in South Africa two million years ago.
The team assigns it to the species on two features: the suture between the temporal and parietal bones is straight, and the bony projection behind the ear, the mastoid process, is relatively small. The researchers say a number of traits rule out Paranthropus.
A small fragment and an imprecise date
The fragment does not show what the face looked like or how large the brain was, so the authors cautiously classify it as Homo erectus in the broad sense. There is still no complete, well-preserved adult skull.
Reports of the find give "about 2 million years", while the journal article mentions 1.98m years for the species' presence in South Africa. The available materials do not say which methods were used on DNH 127 itself. The claim also rests on the earlier dating of the whole quarry, which falls in the same range.
The 10-to-1 ratio is not a measure of real population size. It only shows what survived in one cave, and it may be skewed by how the bones piled up and survived. In East Africa there is a fragment that may be Homo erectus and may be 1.9m years old, but the finds there that are confidently identified are about 1.6m years old. Martin compares current knowledge to looking through a "pinhole" instead of a window.
Three hominid species in one place
At Drimolen the two species lived side by side, and their fossils span about 100,000 years. Martin describes Homo erectus as something that "looked like an underdog with little chance of survival". Homo erectus developed a bigger brain and smaller molars, probably because it ate more meat, while Paranthropus kept a brain slightly larger than a chimpanzee's. Australopithecus sediba, a third hominid species, also lived in the area.
Schwartz writes that it is not known whether the species met directly, but their presence in one place suggests they shared land and resources.
Martin notes that huge parts of West and Central Africa remain unexcavated.