The finding of the 3.8 million years old skull contradicts the long-held notion of anagenesis in hominins, whereby one species disappears and gives rise to the next in a linear fashion.

By Ian Horswill

Posted on August 29, 2019

A nearly complete 3.8 million-year-old skull of an early ape-like human ancestor is challenging the theory of how the first humans evolved from ape-like ancestors.

The amazing discovery at the Woranso-Mille research site in Miro Dora, Afar Regional State, Ethiopia on 10 February, 2016 is a rare and remarkably complete specimen.

At the Woranso-Mille research site, approximately 12,600 fossil specimens including 230 hominin fossils have been discovered. The team was working a mere 35 miles (56 km) away from Hadar, the region in which the famous ‘Lucy’ specimen, of the Australopithecus afarensis, was found.

Upon arrival at the location of the jaw discovery, Professor Yohannes Haile-Selassie saw something globular less than 10 feet away from where he was standing. Getting closer, he realised that it was a tiny brain case and hoped that it would fit with the jaw. He picked it up and sure enough, the two pieces seamlessly clicked together like puzzle pieces.

An analysis of the new specimen challenges ideas about how the first humans evolved from ape-like ancestors. Photo: Dale Omori, Cleveland Museum of Natural History

“I couldn’t believe my eyes when I spotted the rest of the cranium,” Haile-Selassie says of this incredibly rare find. “It was a eureka moment and a dream come true,” said Haile-Selassie, who is affiliated to Cleveland Museum of Natural History in Ohio.

Researchers who discovered the skull say the skull belongs to a species called Australopithecus anamensis, and it provides scientists with their first good look at the face of this hominin, which includes orang utans, gorillas, chimpanzees and humans. This species though is thought to precede the Lucy species, Australopithecus afarensis, Nature stated.

Lucy, the first afarensis skeleton discovered in 1974, is regarded as “the first ape to have walked”. However, this new discovery suggests that Australopithecus anamensis shared the prehistoric Ethiopian landscape with Lucy’s species, for at least 100,000 years.

This finding contradicts the long-held notion of anagenesis in hominins, whereby one species disappears and gives rise to the next in a linear fashion.

“This is a game changer in our understanding of human evolution during the Pliocene,” said Haile-Selassie.

The almost intact 3.8 million years old Australopithecus anamensis specimen skull that contradicts the thinking of the evolution of humans. Photo: Cleveland Museum of Natural History

Carol Ward, a palaeoanthropologist at the University of Missouri in Columbia who wasn’t involved in the analysis, said: “Fossil hominin crania are exceptionally rare treasures. This to me is the specimen we have been waiting for.”

Cleveland Museum of Natural History brought in experts from across the globe to try to properly date the specimen and conduct extensive comparative analyses with other previously discovered and examined specimens.

Dr Beverly Saylor, of Case Western Reserve University, in Cleveland, and her colleagues first determined the age of the fossil to be 3.8 million years by dating minerals in layers of volcanic rocks nearby. They also combined field observations with analysis of microscopic biological remains to reconstruct the landscape, vegetation, and hydrology in the area where MRD died.

“MRD lived near a large lake in a region that was dry,” says Dr Naomi Levin, a co-author on the study from the University of Michigan. “We’re eager to conduct more work in these deposits to understand the environment of the MRD specimen, the relationship to climate change, and how it affected human evolution, if at all.”