Homo erectus was outnumbered 10 to 1 by a big-toothed cousin 2 million years ago

A broken piece of an adult skull, pulled from a cave north of Johannesburg, confirms that Homo erectus, the first human species most researchers agree belongs in our own genus, was already living in southern Africa 2 million years ago. The fossil, catalogued DNH 127, is the first adult of the species found at Drimolen, and it is roughly 200,000 years older than adult Homo erectus fossils from anywhere else.

The surprise is the company it kept. Of 18 hominin fossils described in the new study, 14 belong to Paranthropus robustus, a heavy-jawed relative with a brain about the size of a chimpanzee’s. Only one belongs to Homo erectus. The lineage widely seen as leading toward us was, at this cave, the minority by more than ten to one.

That matters because the opening chapter of Homo erectus is still written from scraps. Until now, the case for the species at Drimolen rested on a single toddler’s cranium found at the same site. Children’s skulls lack many adult traits, so a child alone could not show what grown Homo erectus looked like this early in the species’ history. An adult fragment closes that gap.

“Homo erectus is the first species of hominin that researchers broadly agree fits within our own genus Homo and is likely directly ancestral to us,” said Jesse Martin, the La Trobe University archaeologist who led the work.

A straight seam and a small bump behind the ear

DNH 127 preserves parts of three bones from the right side of the head: a section of the temporal bone around the ear, part of the parietal bone on the side of the skull and part of the occipital bone at the back. All three meet near asterion, the junction where those bones come together behind the ear.

Two features rule out Paranthropus. The seam where the temporal and parietal bones meet runs straight, a trait typical of Homo erectus. And the mastoid process, the bony bump behind the ear that anchors neck muscles, is too small for the big-jawed robust species.

The team, from La Trobe University with colleagues at the University of Johannesburg, the University of the Witwatersrand and Washington University in St. Louis, worked through 18 previously undescribed hominin fossils from Drimolen Main Quarry. Most are small fragments of jaws, teeth and skulls, the kind of material that often sits unpublished in collections because no single piece looks spectacular. Read together, they show who lived at the site and how one species was changing.

The age comes from the cave deposits rather than the bone itself. Earlier work at Drimolen combined three independent methods: uranium-lead dating of flowstone, uranium-series electron spin resonance on fossil teeth, and palaeomagnetism, which reads the record of Earth’s magnetic field reversals locked into sediment. Together they place the main quarry deposit between about 2.04 and 1.95 million years ago.

Older than Dmanisi, and the robust cousin was evolving fast

For scale, the adult Homo erectus skulls from Dmanisi in Georgia, the site that showed early humans had already left Africa, are about 1.8 million years old. Turkana Boy, the most complete early skeleton of the species, found in Kenya, is roughly 1.5 million years old. DNH 127 sits about 200,000 years before the Dmanisi adults, which puts Homo erectus at the southern end of Africa close to the start of its known record.

The Paranthropus fossils tell a second story. Across roughly 200,000 years, between Drimolen and the younger site of Swartkrans at about 1.8 million years ago, Paranthropus robustus evolved larger teeth and bigger chewing muscles. The researchers link the change to climatic pressures that favoured tougher foods. The Drimolen population is classified as a distinct subspecies, Paranthropus robustus ukusa.

Homo erectus was moving the other way, toward larger brains and smaller molars, a shift often tied to eating more meat. Two strategies shared one landscape.

“While we know that Homo erectus and the lineage leading to us was ultimately the successful one, 2 million years ago P. robustus outnumbered Homo erectus at Drimolen by more than 10 to one,” Martin said.

Paranthropus died out around a million years ago. Homo erectus spread across Africa and Asia and survived on Java until a little over 100,000 years ago.

What one skull fragment cannot settle

DNH 127 is a fragment, not a skull. Its identification rests on two anatomical features, and partial crania invite argument over which traits are diagnostic. Drimolen still has no complete adult Homo erectus skull, so the face, brain size and jaw of the earliest southern African adults remain unknown.

The ten-to-one ratio is a count of fossils from one cave, not a census. What ends up in a cave depends on predators, on how bodies and bones washed in, and on which bones survive, so the ratio may partly reflect how the site formed rather than how many of each species lived nearby.

The “200,000 years older” figure also depends on which fossils count. A skull fragment from Koobi Fora in Kenya, dated close to 1.9 million years, has been assigned to Homo erectus by some researchers, but that attribution is debated. And at least one large Drimolen jaw, known as DNH 6, came from mining rubble, so its age is uncertain.

Common questions about Homo erectus at Drimolen

When did Homo erectus first appear?

The oldest fossils attributed to Homo erectus are about 2 million years old. Drimolen in South Africa now holds both a child and an adult of the species from that time, while widely accepted East African finds are slightly younger. The species lasted until roughly 110,000 years ago on the Indonesian island of Java.

Is Homo erectus a direct ancestor of modern humans?

Most researchers place Homo erectus in our genus and consider it likely ancestral to later humans, including Homo sapiens. The exact branching between Homo erectus, later species and our own lineage is still debated.

What was Paranthropus robustus?

Paranthropus robustus was a hominin that lived in southern Africa from about 2 million to about 1 million years ago. It had massive molars, powerful chewing muscles and a brain about the size of a chimpanzee’s. It is a relative, not an ancestor, and its lineage left no descendants.

Where is Drimolen?

Drimolen is a cave site about 40 kilometres north of Johannesburg, inside the Cradle of Humankind UNESCO World Heritage Site and around 6 kilometres from Sterkfontein. Excavations have recovered more than 100 hominin fossils there.

The missing piece is a full adult skull

Excavation at Drimolen began in 1992, and the 18 fossils in this study were dug up between then and 2019. The toddler cranium, DNH 134, was found in 2015 and described in 2020, when the team first argued that Homo erectus, Paranthropus and Australopithecus overlapped in South Africa around 2 million years ago. The new adult fragment, published in late September in Annals of Human Biology, turns that claim from one child into a population.

The decisive test is a more complete adult skull from the same deposit, with a face and a measurable braincase. Until one surfaces, the earliest adult Homo erectus in southern Africa is the side of a head and a seam that runs straight.

Reference: Martin et al., “New hominin cranial and mandibular remains from Drimolen Main Quarry, South Africa,” Annals of Human Biology, 2026. DOI: 10.1080/03014460.2026.2725046

Tags: archaeology, human evolution, Homo erectus, Cradle of Humankind, Drimolen, La Trobe University