Explained: Are humans older than we thought? Explaining the study of the skeletal remains from South Africa

What is Australopithecus?

Australopithecus, meaning “southern ape”, was a group of hominins or now-extinct early humans, that was closely related to and almost certainly the ancestors of modern humans.

They inhabited the planet 4.4 million to 1.4 million years ago, likely encompassing a time period longer than our own genus, Homo. Their fossils have been found across sites in eastern, northern, central and southern Africa.

Australopithecus was originally defined by the anthropologist Raymond Dart in 1925, after the discovery of the first australopith fossil (a small child’s skull) in Tuang, South Africa. Through his research, Dart argued that early humans first evolved in Africa, challenging the conventional wisdom that they had done so in Europe and Asia.

Our early ancestors were bipedal in nature and travelled on the ground (but used trees for food and protection), had large teeth with thick enamel caps for chewing, and their brains were only slightly larger than apes. The facial and dental features suggest that they were able to consume tough foods, such as nuts, seeds, tubers and roots.

They stood at a height of around 3 ft 9 inches to 4 ft 11 inches, and likely weighed around 30 to 50 kg, with males almost double the size of females.

What are the Sterkfontein caves?

The “Cradle of Humankind” is a 47,000-hectare paleoanthropological site, declared a World Heritage Site by UNESCO. Located 40 km northwest of Johannesburg, it contains a complex system of limestone caves, where a significant number of hominin fossils have been found.

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Within this complex lies Sterkfontein, a complex system of caves that holds a long history of hominin occupation and contains the largest number of Australopithecus fossils in the world. This ancient site has been an invaluable resource for those tracing the evolution of humans and the environment over the past 4 million years.

Scholars first understood the historic importance of these limestone caves in 1936, when the palaeontologist Robert Broom discovered the first adult Australopithecus fossil within the site.

Since that pioneering discovery, hundreds of Australopithecus fossils have been found there. These include, “Mrs Ples”, the popular name for the most complete skull of an Australopithecus africanus ever to be found in South Africa, and “Little Foot”, a nearly complete Australopithecus skeleton.

While the Sterkfontein cave system is like a treasure trove for researchers, dating the fossils here can be rather difficult because of the unique topography of the site. Scientists previously used animal bones to determine the age of fossils or relied on calcite flowstone deposited in the cave.

However, flowing water that is rich in calcium carbonate can deposit layers of calcite and mix with older sediments. Bones and rocks can also shift and fall deeper into the cave, making it even more difficult for researchers.

What are the new findings?

To deal with these challenges, Darryl E. Granger and the other researchers involved in the study analysed the breccia, the concrete-like substance in which the fossils are embedded, to ascertain their age.

They found that all the Australopithecus remains in the Sterkfontein cave date back to 3.4 to 3.7 million years ago. This date places these fossils closer to the beginning of the Australopithecus era, instead of near the end of it.

Scientists had previously theorised the remains were 2-2.5 million years old, based on the study of faunal remains near the Australopithecus fossils. They had therefore argued that these South African Australopithecus were too young to have evolved into the genus Homo, which we belong to, and which first appeared around 3 million years ago.

This new research, therefore, shows that the South African Australopithecus had around a million years to evolve into our Homo ancestor, as reported by AFP.

According to the researchers Australopithecus africanus were not descendants of the Australopithecus afarensis from East Africa but were “contemporaneous” if not even older.

What is the significance of these findings?

Scholars had earlier considered East Africa to be the more likely place where early hominids had first evolved into the Homo genus, to which we belong. This was the home of the 3.2 million-year-old Lucy (also known as Dinkinesh), the most famous ancestor of modern humans, of the Australopithecus afarensis species.

By dating the Australopithecus africanus found in the Sterkfontein caves to 3.4 to 3.7 million years ago, these hominins would be even older than the famed Lucy.

“What our data does is resolve these controversies. It shows that these fossils are old – much older than we originally thought,” said Granger, in Purdue University’s press release.

This study also complicates the linear understanding of human evolution. The South African Australopithecus were not descendants of the hominins from East Africa like Lucy but were in fact contemporaries. This means the Mrs Ples and their relatives of the Sterkfontein caves, mingled with their eastern counterparts, and were possibly both the ancestors of early humans.

“Over a timeframe of millions of years, at only 4,000 kilometres (2,500 miles) away, these species had plenty of time to travel, to breed with each other… so we can largely imagine a common evolution across Africa,” said Laurent Bruxelles, one of the authors of the study cited by AFP.

The earlier date of the South African Australopithecus means that human evolution did not follow a simple line that emerged from one species alone. Instead, our ancestry is “more like a bush,” according to Bruxelles.

Rather than understanding our family tree as a single tree trunk that first emerged from the apes and led to the end point of Homo Sapiens, the present study presents human evolution more like a bush with various branches that interacted with one another.