Skull fragment puts Homo erectus in South Africa 2 million years ago

A skull fragment from South Africa has strengthened the evidence that Homo erectus, one of our direct ancestors, was living in southern Africa 2 million years ago, about 200,000 years earlier than traditionally believed.

Archaeologists from La Trobe University in Australia have described 18 newly published hominin fossils from Drimolen Main Quarry, in South Africa's Cradle of Humankind, one of the richest sites in the world for the remains of ancient human relatives. The research was published in the Annals of Human Biology.

An adult at last

The fossils include the first known adult Homo erectus fossil from Drimolen, catalogued as DNH 127. At about 2 million years old, it is roughly 200,000 years older than adult Homo erectus fossils found elsewhere, including those from Dmanisi in Georgia, which date to about 1.8 million years ago.

"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 the lead researcher, Dr Jesse Martin.

Drimolen had already produced evidence of Homo erectus 2 million years ago, but the original fossil, DNH 134, belonged to a child aged between two and four, leaving uncertainty about what adults looked like. "This paper publishes a new adult fossil attributed to Homo erectus, DNH 127, providing further confirmation that this species first appeared in southern Africa 2 million years ago," Dr Martin said.

Two paths

The fossils also include remains of Paranthropus robustus, a very different human relative that lived in the same landscape.

While Homo erectus was developing a larger brain and smaller molars, possibly because it was eating more meat, P. robustus kept a brain only slightly larger than a chimpanzee's. Instead, it evolved enormous molars and powerful chewing muscles, suited to grinding tough, hard foods "much like a mortar and pestle".

"These two human species shared the same landscape and are both preserved in Drimolen cave," Dr Martin said. "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. During this time period, it was our ancestors that looked like the outside long-odds chance to survive."

Evolution in action

Because Drimolen has produced so many fossils, the researchers could compare populations of P. robustus about 200,000 years apart. Between around 2 million and 1.8 million years ago, the species developed even larger teeth and stronger chewing muscles, apparently adapting to changing environments and climate.

"Hominin fossils are so rare that generally the differences between them are huge, and researchers are left to make educated guesses," Dr Martin said. The Drimolen collection allows "an unprecedented insight into the micro-evolutionary changes that shaped human ancestors".

A long-studied site

Drimolen was discovered in 1992 and excavated until 2019, but many of its fossils had never been formally described. The new work involved scientists from La Trobe University, the University of Johannesburg, the University of the Witwatersrand and Washington University in the United States.

Why Homo erectus matters

Homo erectus was the first human relative with body proportions much like ours, and the first known to have spread out of Africa, reaching as far as Georgia, China and Indonesia. It survived for well over a million years, making it one of the most successful human species ever to have lived.