Researchers theorize that the last common ancestor of modern humans and two of our extinct human cousins—Neanderthals and Denisovans—existed about 765,000 to 550,000 years ago. Where these ancestors first emerged, however, is still up for debate, and Moroccan fossils are moving the conversation forward.
An international team of researchers has analyzed hominin fossils—about 773,000 years old—found in a cave in Casablanca known as Grotte à Hominidés, according to a study published today in Nature. Hominins are a group made up of modern humans, bygone human species, and close ancestors. The fossils may shed light on the humans who roamed Africa long before known Homo sapiens existed.
Pinpointing the last common ancestor of modern humans, Neanderthals, and Denisovans would inform our understanding of subsequent lineages, Antonio Rosas, a researcher at the National Museum of Natural Sciences in Madrid who was not involved in the study, wrote in an accompanying News & Views article.
For decades, anthropologists lumped these ancient populations into a single species, Homo heidelbergensis, long believed to be the shared ancestor of modern humans and Neanderthals. But this theory is losing ground, as fossils from Africa and Europe point to multiple distinct lineages instead of just one.
Previous discoveries, like the species Homo antecessor found in Spain, suggest that this mysterious ancestor may have had early links to Europe. Part of the issue with determining this ancestor’s geographical origin, however, is the gap that exists in the African fossil record from around this time period.
Cue the Moroccan fossils, including a nearly complete adult mandible, half an adult mandible, a child mandible, a number of vertebrae, and teeth. Interestingly, a hominin femur bears evidence of having been gnawed on, suggesting that the fossils may have been the scraps of a scrumptious carnivore meal.
Earth’s magnetic field changes polarity every so often, leaving clear traces behind in sediments around the world. After studying the sediments surrounding the fossils, the team, including Jean-Jacques Hublin, an anthropologist with the Max Planck Institute for Evolutionary Anthropology, revealed that the remains date back to the last time Earth’s magnetic field switched, 773,000 years ago. Specifically, the sediments carrying the fossils in question formed exactly during the 8,000- to 11,000-year-long transition.
They’re around as old as Homo antecessor and feature both ancient characteristics present in Homo erectus—who existed between around 1.89 million and 110,000 years ago—as well as modern ones in Neanderthals and modern humans. For instance, while the shape of the mandible is similar to that of H. erectus and other African archaic humans, aspects of the molars recall those of early H. sapiens and Neanderthals.
Analysis of a dental structure known as the enamel-dentine junction “consistently shows the Grotte à Hominidés hominins to be distinct from both Homo erectus and Homo antecessor, identifying them as representative of populations that could be basal to Homo sapiens and archaic Eurasian lineages,” Matthew Skinner, a co-author also from the Max Planck Institute for Evolutionary Anthropology, said in a statement by the Max Planck Society. In other words, the fossils could represent populations close to the ancestors of modern humans and, more broadly, near the shared ancestry with Neanderthals and Denisovans. They might not necessarily be our last common ancestors, but they could be close predecessors.
“The fossils from the Grotte à Hominidés may be the best candidates we currently have for African populations lying near the root of this shared ancestry, thus reinforcing the view of a deep African origin for our species,” Hublin explained.
The team pinpoints “the H. sapiens lineage firmly within African populations derived from Homo erectus,” Rosas added in the News & Views article. According to the researcher, the study also supports the notion that our last common ancestor arose on the continent and indicates that modern humans may have split off the evolutionary tree earlier than researchers commonly think.
Source: Gizmodo