The jawbone of an ancient hominin found at Grotte à Hominidés in Morocco
Hamza Mehimdate, Programme Préhistoire de Casablanca
Fossils nearly three-quarters of a million years old, discovered in North Africa, may belong to a common ancestor of Neanderthals, Denisovans and modern humans that lived shortly before the three hominin lineages split.
It is thought that the last common ancestor of modern humans, Neanderthals and Denisovans lived sometime between 765,000 and 550,000 years ago. But exactly when and where it lived remain two of the great questions of human evolution.
The new fossils may not be the last common ancestor of the three human species, says Jean-Jacques Hublin at the Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany, but they are certainly close to the point at which ancient human lineages diverged.
Hublin and his colleagues analysed several fossils found in a cave called Grotte à Hominidés on the outskirts of Casablanca, Morocco, including two adult jawbones, a child’s jawbone and several vertebrae. One of the adult jawbones was reported in a previous study in 1969, but the rest have been described for the first time.
The fossilised molars are similar to those of early Homo sapiens and Neanderthals, but the jaw shape resembles older African humans, like Homo erectus.
Fortuitously for the scientists, the Moroccan hominins lived at around the same time as a shift in the Earth’s magnetic field, which is recorded in the geological layer in which the fossils were found, allowing them to be dated to around 773,000 years ago.
Hublin says the discoveries fill a “major gap” in the African hominin record between 1 million and 600,000 years ago. Paleogenetic studies indicate that this is when the ancestors of Neandertals and Denisovans branched off the lineage that led to H. sapiens. Neanderthals went on to dominate Europe for hundreds of thousands of years. Denisovans travelled as far as East Asia, and H. sapiens are thought to have continued to evolve in Africa.
The newly described fossils were near contemporaries of a Spanish population of hominins called Homo antecessor, which has previously been considered as a possible common ancestor between H. sapiens and Neanderthals.
Jean-Paul Raynal et Fatima Zohra Sihi-Alaoui work on the excavation that led to the discovery of the fossils in Morocco
R. Gallotti, Programme Préhistoire de Casablanca
Both H. antecessor and the Moroccan hominins display a “comparable mosaic of primitive and derived traits”, says Hublin, meaning there may have been connections and genetic exchanges between the populations across the Strait of Gibraltar. However, there are also clear differences between the fossils from the two regions, with the Spanish fossils appearing more Neanderthal-like.
“The last common ancestor of these lineages was likely present on both sides of the Mediterranean at that time and was already diverging,” says Hublin. “This supports a deep African ancestry for Homo sapiens and argues against Eurasian origin scenarios that have been proposed by some authors.”
Julien Louys at Griffith University in Brisbane, Australia, says he is struck by the differences in physical characteristics among early Pleistocene hominins that are closely related to or ancestral to our own species.
“The important point raised is that these differences appear to have arisen before Homo antecessor made it to Spain, implying this species was one of potentially several that arose across northern Africa, but then somehow crossed the straits,” Louys says.
Chris Stringer at the Natural History Museum in London says a study on Chinese hominin fossils published last year, to which he contributed, suggested the last common ancestor of H. sapiens, Neanderthals and Denisovans could have lived more than 1 million years ago.
“It was unclear on which continent that common ancestor lived,” says Stringer. “However, even if the last common ancestor lived outside of Africa, our analyses indicated that the later evolution of Homo sapiens still took place in Africa, so in that case there would have been an early migration into Africa to continue that evolution.”
The new Moroccan fossils may even represent an early sapiens ancestor in Africa, he says, but there aren’t enough pieces of the skeleton to assign it to a species.
He is keen to compare the new fossils with the ones he has already studied to determine where they might fit.
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