Our most direct human ancestor is older than what was previously thought

Discovered in a cave in South Africa the oldest fossils of 'Homo erectus', the first human species to walk completely upright.

homo-erectus
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A child’s skull in South Africa’s Drimolen cave was discovered and reveals that Homo erectus lived two million years ago with other more primitive human species such as Australopithecus sediba and Paranthropus robustus. It is the oldest fossil of Homo erectus ever found, the first human species to walk fully upright and also the first to leave Africa about 1.8 million years ago. This discovery completely changes the debate about where this successful species evolved.

Three hominids coexisting in southern Africa

Thus, Homo erectus could have lived between 150,000 and 200,000 years earlier than what was previously thought, showing that members of three different hominid lines grouped in southern Africa about two million years ago. However, it is not clear whether the three ancient populations inhabited the region at exactly the same time.

These findings indicate a major transition in hominid evolution in southern Africa. During this period of time, climatic and habitat fluctuations led to the extinction of the Australopithecus species. H. erectus and P. robustus withstood these ecological challenges, possibly outperforming Australopithecus because of limited resources, the researchers speculate.

Paleoanthropologists at the La Trobe University in Melbourne, Australia, found two fossil skulls, one of Homo erectus (a child) and another of Paranthropus robustus (an adult). Both findings date from 1.95 million to 2.04 million years ago, according to their study published in the magazine Science and leave open the interaction of H. erectus with Paranthropus and Australopithecus. Mind you, without DNA evidence it will be very difficult to determine whether the three species could have crossed.

homo-erectus2
Andy Herries, Jesse Martin and Renaud Joannes-Boyau

Analysing the fossils

Considering that Homo erectus was the first species that we know of whose body form is most similar to modern humans, indicating a complete adaptation to life on the ground, it also appears to have survived nearly two million years on Earth, spreading across much of the world, a dispersion so wide that it raises many questions about its evolution.

The team dated the fossil cranial boxes at Drimolen using two techniques to calculate the time since sediments formed just below and above where the specimens were found, including paleo-magnetic dating, by resonance electron spin, uranium-lead and faunal. Evidence of previously dated reversals of the Earth’s magnetic field in the Drimolen sediment helped to confirm age estimates for the fossils. The researchers estimated that the skull of the smallest individual, DNH 134’s, brain capacity was too large for it to be an Australopitechus child and that he was only two to three years old when he died. He was a Homo erectus.

After all, and because Homo erectus is one of modern human’s direct ancestors (the last Homo erectus lived until 117,000 years ago), the current discovery has implications for the origins of modern humans.

"Until this discovery, we always assumed that Homo erectus originated in East Africa. But DNH 134 shows that Homo erectus possibly comes from Southern Africa. That would mean they later moved north into East Africa. From there they went through North Africa to populate the rest of the world,” explains Stephanie Baker, co-author of the paper.

Reference: A.I.R. Herries el al., "Contemporaneity of Australopithecus, Paranthropus, and early Homo erectus in S. Africa," Science (2020). science.sciencemag.org/cgi/doi … 1126/science.aaw7293

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