Three species of hominids coexisted in South Africa two million years ago

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The discovery of fossils belonging to two different hominin species in South Africa reveals that the appearance of Homo erectus - one of the sapiens' direct ancestors - occurred earlier than previously thought.

The hills rising to the northwest of Johannesburg hide an impressive network of limestone caves. Crossroads of roads between the coast and the highlands of the interior of the continent, its rooms have served as a refuge for an impressive variety of hominids in different periods of prehistory: from archaic Australopithecus to beings very similar to modern Homo sapiens , passing through the enigmatic Homo naledi . Now, a new finding also testifies to the presence of Homo erectus more than two million years ago.

"During our practical classes at the Drimolen site , a student discovered a group of fragments," says Stephanie Baker of the Institute for Paleontological Research at the University of Johannesburg. " We saw that these were fragments of a skull, but at first the remains were not identifiable ." Such ancient fossils must be removed from the ground in fragments, which researchers then carefully reconstruct before they can identify their origin.

"During these field work new remains appeared; we began to assemble them but we did not finish seeing what exactly that piece could belong to, until we realized that we were before the bones of a hominid," he recalls. Baptized as DNH 134 , its morphology and brain cavity confirmed that it was a Homo erectus , specifically a boy of about three years. The finding is described in an article published this Thursday in Science , and also includes the discovery in the same site of a second skull, corresponding to a different member of the genus Homo , the Paranthropus robustus .

New chronology

Homo erectus was the longest-living species of our ancestors. It survived for more than 1.5 million years, adapting to climatic variations in multiple ecosystems on three different continents. With shorter arms and longer legs than the preceding members of the men's lineage, H. erectus could walk and run long distances.

Until now, no other specimen of the species has been discovered in South Africa, and the oldest have been found in Kenya - where it is believed to have appeared for the first time - and in Georgia, with an age of about 1.9 million years.

But the dating of the South African cave, carried out by the same team, shows that the skull and the rest of the fossils were older, dated between 2.04 and 1.95 million years old. "The age of DNH 134 shows that Homo erectus lived 150,000 or 200,000 years earlier than previously thought," says Andy Herries, co-director of the excavations and head of the Department of Archeology and History at La Trobe University in Australia.

Despite the fact that the finding delays the appearance of H. erectus , its discoverers do not believe that South Africa is the cradle of this species.

"The sudden appearance of Homo erectus at this location, coupled with the late presence of representatives of the Australopithecus africanus lineage, seem to suggest that both originated elsewhere and migrated to South Africa with other species," Herries notes. "There are other older Homo species similar to Homo habilis in this same location, so it is unlikely that it would emerge in South Africa," agrees Baker.

Since Homo erectus is one of the key species in evolution, the discovery has important implications. So, to verify their results, the team used all the available techniques: paleomagnetic dating, electronic paramagnetic resonance, uranium-lead dating, and dating of adjacent fauna. "We checked all the dates for each of these techniques and they confirmed that we were very precise in age," Baker insists.

Coexistence of three species

The nature of the coexistence between Homo erectus , Paranthropus and Australopithecus in the same place raises many questions. The three species had to use different resources of the territory to avoid competing with each other. "One of the most fascinating things about Drimolen is that it shows different species that coincide in time, adapting in completely opposite ways," says Herries. "It is a perfect example of different experiments in human evolutionary adaptation happening at the same time."

Of the three, H. erectus were the best prepared to survive. Tall and lean, compared to the other species, they ate easy-to-digest foods, such as fruits and berries. "We also know that they ate meat, but we are still not sure how they got it; it seems that these early Homo erectus were not hunting with weapons yet," says Baker. In comparison, Paranthropus robustus fed on roots and tubers. "They used their huge teeth to grind what we call circumstantial foods, especially very hard plants."

As the climate gradually changed, wooded landscapes became scarcer, forests were replaced by the savanna landscape seen today in many parts of Africa. Homo erectus , more mobile and social, was better adapted to the changes. "We know they were able to cover long distances, which was an advantage," says Baker.

"On the other hand, Paranthropus and Australopithecus had always evolved in hot, humid climates, but then the climate began to change and became cooler and drier."

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