South African Human Fossils More Than a Million Years Older Than Previously Thought

This undated photo made available by the National Park Service in September 2021 shows fossilized human footprints at the White Sands National Park in New Mexico. (NPS via AP Photo)

Fossils of early human ancestors that were found in a cave in South Africa are now thought to be a million years older than originally estimated, thereby shaking the current scientific understanding of human evolution and its origins.

Fossils from the Sterkfontein Cave, belonging to the genus Australopithecus, were initially thought to have been from 2 to 2.6 million years ago. But researchers who used a new technique to date the fossils found them to be from 3.4 to 3.6 million years ago, according to a recent study published in the Proceedings of the National Academy of Sciences (PNAS) on June 27.

The new dating makes these fossils older than the famed Lucy fossil from Ethiopia, which was dated to 3.2 million years.

The fossils are from “Member 4” infill of Sterkfontein which contains the richest deposit of Australopithecus fossils anywhere in the world. The first Australopithecus fossil was discovered in the caves back in 1936, with hundreds being excavated since then.

Previous dating methods of Member 4 fossils were based on calcite flowstone deposits discovered in the cave fill. But careful observation revealed that the method underestimates the age of fossils. The new study used radioactive decay of rare isotopes like beryllium-10 and aluminum-26 in the mineral quartz to date the fossils.

“These radioactive isotopes, known as cosmogenic nuclides, are produced by high-energy cosmic ray reactions near the ground surface, and their radioactive decay dates when the rocks were buried in the cave when they fell in the entrance together with the fossils,” said Darryl Granger of Purdue University in the United States, lead author on the paper, in a June 27 news release published at EurekaAlert.

Human Evolution Chronology

The new dating has important implications for the theory of hominin evolution. Hominin is a term used to refer to members of the Hominini zoological tribe, of which only one species exists at present—the Homo Sapiens or current human beings.

Younger hominins like Homosapiens and Paranthropus are dated to about 2 to 2.8 million years. Based on earlier dates, the South African Australopithecus was seen as too young to be their ancestors. Homosapiens and Paranthropus are thought to have more likely evolved in East Africa.

With the new dating pushing back the South African Australopithecus by a million years, this chronology comes into question.

The discovery will “undoubtedly re-ignite the debate over the diverse characteristics of Australopithecus at Sterkfontein, and whether there could have been South African ancestors to later hominins,” Granger said in the news release.