The Cradle of Humankind, the Sterkfontein Caves in South Africa are also known as the Cradle of Humankind. Hundreds of fossils of one of the first hominids have been found. And they now turn out to be even older than expected. Didn’t the first people come from the east, but from the south of Africa?

The fossils in the Sterkfontein Caves, northwest of Johannesburg, span nearly 4 million years of human evolution. The first remains of the hominid Australopithecus were discovered in 1936 and in 1947 the first complete human skull, Mrs. Pleas. It was only after studying these fossils that it was discovered that the Australopithecus africanus was not a species of monkey but more of a humanoid. Partly because he could stand upright. Nowhere in the world are there so many fossils of the Australopithecus found as in Sterkfontein. It makes the caves world famous.

Cradle of Mankind

The Cradle of Mankind refers to an area about 30 kilometers northwest of Johannesburg in South Africa, where fossils of the very first hominids have been found. The area is a UNESCO World Heritage Site and consists of the three sites Kromdraai, Swartkrans and Sterkfontein, of which the limestone caves of Sterkfontein are the most important. About five hundred fossils have been uncovered from the Australopithecus, one of the oldest humanoids. This makes it the richest site of this species in the world and offers interesting insights into the evolution from ape to man. The biggest find is that of Mrs. Ples in 1947: an ancient skull between 2.6 and 2.8 million years old. It is the most complete skull ever discovered from the Australopithecus africanus. Another important discovery was that of Little Foot in 1997. This is a nearly complete skeleton, named after the foot, which was the first to be found.

Older than expected
The South African University of Witwatersrand has been researching the cave for decades, but all the while the age of the fossils has been debated. According to some, the excavations are ‘only’ 2 million years old, making them younger than our own species Homo† Others estimate the age of the fossils at 3 million years earlier.

Four different Australopithecus skulls found in the Sterkfontein Caves. Photo: Jason Heaton and Ronald Clarke, in collaboration with the Ditsong Museum of Natural History

Radioactive decay

In research that in scientific magazine PNAS popped up, researchers are using a new technique to determine the age of the fossils in specific areas of the caves. Their conclusion? The fossils are even older than thought. “The new dates range from 3.4 to 3.6 million years ago. This indicates that the hominids were contemporaries of other early Australopithecus-species, such as the afarensis in East Africa,” said Professor Dominic Stratford, the caves research director and one of the authors of the paper.

The new dates are based on the radioactive decay of the rare cosmogenic isotopes aluminum-26 and beryllium-10 in the quartz mineral. “These radioactive isotopes are created by high-energy cosmic radiation reactions near the ground surface. Their radioactive decay began when the rocks invaded through the cave entrance along with the fossils and were buried,” said study leader Professor Darryl Granger of Purdue University.

More time

Previously, the dates were determined based on calcite rock deposits found in the cave. But close observations showed that this rock is younger than what lay further in the cave. As a result, the age of the fossils was underestimated. “This revision of the age of the Sterkfontein fossils has important implications for South Africa’s role on the stage of human evolution. Younger humanoids like our own Homo appeared between 2.8 and 2 million years ago. If you look at the old data, the South African Australopithecus could never have been their ancestor, so it was thought that the Homo and also the paranthopus developed in East Africa,” said Stratford. However, the new data show that the Australopithecus almost a million years before Homo and paranthropus made his appearance. So there was more time for human evolution in South Africa. This puts Sterkfontein’s hominins at the center of early human evolution.

South African Ancestry

“The most interesting fossils in evolutionary research and one of South Africa’s most iconic fossils, Mrs. Ples, turn out to be a million years older. This puts them at the same time as other iconic humanoids in East Africa, such as Lucy,” concludes Stratford. “This new dating of the Australopithecusfossils in the caves are no doubt rekindling the debate about the different traits of the hominins at Sterkfontein and whether there are South African ancestors of later hominids,” Granger said.


The Australopithecus (literally: southern monkey) is one of the oldest hominins and lived between 4.3 and 2 million years ago. It was only after the discovery of fossils in Sterkfontein in 1947 that scientists decided that it had to be a human, partly because evidence was found that they walked on two legs and that the teeth resembled that of a human rather than a monkey. However, the limited brain size was more reminiscent of a chimpanzee. So it was for the first time a species that was more or less somewhere between man and ape. In addition, it was much older than fossils found so far. It is generally believed that our gender Homo descended from the Australopithecusalthough that is still a matter of debate.