Fossil discoveries rewrite our family history

Find shows humans’ direct ancestor existed 100,000 to 200,000 years earlier than previously thought

Undergraduate students participating in the Drimolen Field School in South Africa excavated fossils at an important paleoanthropological site. A new discovery from the Drimolen site is the earliest known representative of the species Homo erectus, a direct ancestor and the first early human to be broadly similar to modern humans in anatomy and behavior. (Photo courtesy David Strait)

An international team of researchers that includes anthropologists at Washington University in St. Louis has unearthed the earliest known skull of Homo erectus, the first of our ancestors to be nearly human-like in their anatomy and aspects of their behavior. The effort was led by La Trobe University in Australia.

David Strait

The 2-million-year-old fossil was reconstructed from more than 150 individual fragments excavated in South Africa over a five-year period.

Published today in Science, the findings are part of an international research excavation in the fossil-rich Drimolen cave system north-west of Johannesburg.

Washington University undergraduate students who participated in the Drimolen Paleoanthropology & Geoarchaeology Field School co-led by David Strait, professor of biological anthropology in Arts & Sciences, helped to unearth some of the fossils described in the paper.

“There is something very special about discovering a significant fossil human,” Strait said. “Fossil humans are rare, representing only a very small percentage of all of the fossil mammals discovered at any given paleontological site from this time period, so they are precious.

“In this case, the Homo erectus cranium that we have found is very delicate, very well preserved and once belonged to a child.

“The individual was probably only 2 or 3 years old when it died,” he said. “To discover a fossil like this is to open a window into the past, and it is very hard not to ask what this child’s life was like, and why it ended at such a young age.”

Project director and lead researcher Andy Herries of La Trobe said the age of the DNH 134 fossil shows that Homo erectus existed 100,000 to 200,000 years earlier than previously thought. The newly discovered fossil demonstrates that Homo erectus, our direct ancestor, clearly evolved in Africa.

Herries said that unlike the world today, where we are the only human species, two million years ago our direct ancestor was not alone.

“We can now say Homo erectus shared the landscape with two other types of humans in South Africa, Paranthropus and Australopithecus,” Herries said. “This suggests that one of these other human species, Australopithecus sediba, may not have been the direct ancestor of Homo erectus, or us, as previously hypothesized.”

Student archaeologist
Julia Praeger, a Washington University senior majoring in anthropology and psychological & brain sciences, was one of the students who discovered and excavated a specimen included in this study, identified as DNH 152, a cranium of Paranthropus robustus. (Photo courtesy of David Strait)

Researchers have been excavating at the Drimolen site for more than two decades.

Strait was invited to join the project in 2016. He runs the field school operated jointly by La Trobe, Washington University, and the University of Johannesburg’s Palaeo-Research Institute. He helps to describe and interpret the fossil humans discovered at the site and mentors graduate students who are also heavily involved in reconstructing and describing those fossils.

“From a purely scientific standpoint, this fossil pushes back in time the origin of one of our most important direct ancestors — Homo erectus,” Strait said.

“It speaks to the geographic location where that origin took place, and it documents important information about the evolution of brain size in Homo,” he said. “Our specimen has a brain that is smaller than those of later Homo erectus populations but larger than those of Australopithecus, the more ape-like early humans that shared the landscape with the earliest populations of Homo erectus.”

Herries said Homo erectus marks an important stage in human evolution in which our ancestors began accumulate many adaptations that made them increasingly human-like.

“However, as the last surviving human species, we should not think we are immune to the same fate as Australopithecus, who likely became extinct as a result of the changing climate two million years ago.”

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