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Fossils in South African cave reignite debate on origins of humankind

A photograph released by the French National Center for Scientific Research shows a South African dig site around caves in Sterkfontein, northwest of Johannesburg. (Laurent Bruxelles/AFP/Getty Images)

Fossils of early human ancestors in a cave in South Africa are a million years older than researchers previously thought, according to a study published this week that gives insight into the history of humankind.

The study of fossils from the Sterkfontein Caves, which yielded the near-complete skull of a cave woman nicknamed Mrs. Ples, found they date back 3.4 million to 3.6 million years.

The findings suggest hominins in South Africa existed around the same time as others in East Africa, such as the renowned 3.2-million-year-old skeleton Lucy, which was discovered in 1974 in Ethiopia. East Africa was long-considered the more likely origin of the earliest hominin that eventually evolved into the Homo genus we belong to, so this study reignites the debate on the origins of modern humans.

Hundreds of Australopithecus fossils of human ancestors have been found at the Sterkfontein Caves, at a UNESCO World Heritage site known as the Cradle of Humankind. The site, northwest of Johannesburg, was home to the discovery of the first adult Australopithecus, an ancient hominin, in 1936.

The caves that tell the story of humankind, including the latest, Homo naledi

The caves have more Australopithecus fossils than anywhere else in the world, according to Darryl Granger, an author of the new study published in the peer-reviewed journal Proceedings of the National Academy of Sciences.

“But it’s hard to get a good date on them,” Granger, a professor at Purdue University who specializes in dating geologic deposits, said in a statement. His team’s findings show that “these fossils are old — much older than we originally thought,” he added.

The researchers, including experts from Johannesburg and France, examined radioactive decay in rocks buried at the same time as the fossils, whereas earlier estimates were based on calcite flowstone deposits.

The age of the fossils helps scientists understand “how and where humans evolved, how they fit into the ecosystem, and who their closest relatives are and were,” Purdue University said in an announcement on the study.

The study indicates that the South African hominins, which had been considered “too young” to be ancestors of the Homo genus, were actually “contemporaries” of those in East Africa and had the time to evolve, said Dominic Stratford, director of research at the caves and one of the paper’s authors.

“This important new dating work pushes the age of some of the most interesting fossils in human evolution research, and one of South Africa’s most iconic fossils, Mrs. Ples, back a million years to a time when, in East Africa, we find other iconic early hominins like Lucy,” he said.