A foot shakes up the theory of human evolution: "It's a different species than Lucy"

BarcelonaThe night that American paleoanthropologist Donald Johanson unearthed the oldest hominid skeleton in present-day Ethiopia was playing in the background Lucy in Sky with Diamonds by the Beatles. The year was 1974, and researchers named the most famous fossil after that song. The discovery of Lucy marked a turning point in evolutionary history: it showed that they Australopithecus afarensis, who lived approximately 3.2 million years ago, walked upright long before the emergence of the genus Homo. But for a decade it has been suspected that Lucy and her peers were not alone and that they are not the only candidates to be our direct bipedal ancestors.

A study published this Wednesday in Nature It defends the coexistence of this species with a more recent – and less recognized – one, theAustralopithecus deyiremeda. The proof: the association of new remains with a 3.4-million-year-old fossilized foot found in the same region years ago, exhibiting different patterns of adaptation to locomotion. A discovery that challenges what we know so far about our origins.

In 2009, scientists led by paleoanthropologist Yohannes Haile-Selassie discovered eight foot bones belonging to an ancient human ancestor within 3.4-million-year-old layers of sediment in the Afar Rift, a geological scar that runs for nearly 5,000 kilometers. The fossil, called the Burtele foot, was found at the Woranso-Mille site and was announced in a scientific article in 2012. "We knew it was different from Lucy's species," says Haile-Selassie, who is the director of the InstitutE'HOR and the Institute of Human and Social Change at Arizona State University. The rest was anatomically more primitive, but the researchers hesitated to give it a name and assign it to a specific species.

The fossil showed a foot with an opposable big toe, which, in the eyes of paleoanthropologists, made it more similar to that of a primate than a human. This feature would have facilitated climbing trees, but would not have prevented them from walking on two legs. Unlike modern humans, this species probably propelled itself with its second toe, says Haile-Selassie, which must have resulted in a less stable footprint. "We are discovering that bipedalism in early hominins did not have a single form. There were different ways of walking on two legs before the more modern pattern appeared," he observes.

Teeth reveal a different diet

Haile-Selassie's group described the existence of theA. deyiremeda –day-ihreme-dahmeansclose relativein the Afar language of the area—but he didn't want to link the foot to it until he had more solid evidence. Validity always comes from skulls, jaws, or teeth. Now, however, they claim to have been able to confirm that the remains are associated with the new species.

In the article a NatureThey have announced the discovery of new hominid fossils at the Woranso-Mille site in the central Afar region, dating back approximately 3.4 million years. These include fragments of a pelvis, skull, and a jawbone with 12 teeth from a child of about four years old, some still milk teeth, found in the same stratigraphic section of soil as the foot fossil.

Woranso-Mille is currently the only place where it has been clearly demonstrated that two hominid species coexisted in the same time and place 3.4 million years ago. Researchers believe that understanding how they divided territory, diet, and mobility can provide clues about how diversity evolves in our own evolutionary lineage.

By analyzing the dental enamel of the teeth found, the team has concluded thatA. deyiremeda It fed mainly on resources from trees and shrubs, as did earlier hominids such as theArdipithecus ramidus or theA. anamensisIn contrast, Lucy and her contemporaries began to incorporate tropical herbs and seeds into their diet. "This indicates that both species occupied distinct ecological niches, which could explain their coexistence without direct competition," they stated in a press release.