Approximately 550,000-year-old fossils discovered in North Africa potentially belong to a shared ancestor of Neanderthals, Denisovans, and modern humans, existing right before these three significant hominin lineages diverged.

Neanderthals and Denisovans, the final common ancestors of modern humans, are believed to have thrived between 765,000 and 550,000 years ago. However, key questions about their existence and habitats still challenge our understanding of human evolution.

Recent fossil discoveries suggest that researchers, including Jean-Jacques Hublin from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, are nearing the pivotal moment of divergence in ancient human lineages.

Hublin and his team examined various fossils, including two adult jawbones, one juvenile jawbone, and several vertebrae unearthed from a cave referred to as the Cave of Mankind near Casablanca, Morocco. One of the adult jawbones had been detailed in a 1969 study, while the remaining specimens are presented for the first time.

The fossilized molars share similarities with early Homo sapiens and Neanderthals, yet their jaw structures resemble ancient African Homo erectus.

Fortunately, these Moroccan hominids existed around the same period as changes in Earth’s magnetic field, recorded within the geological formations containing the fossils, allowing for precise dating to approximately 773,000 years ago.

Hublin described the find as filling a “significant gap” in the African human fossil record dating back to between one million and 600,000 years ago. Paleogenetic studies reveal that the ancestors of Neanderthals and Denisovans diverged around this time, while H. sapiens evolved independently in Africa.

The newly identified fossils are contemporaneous with a hominid population in Spain, previously hypothesized to serve as a common ancestor between Homo sapiens and Neanderthals.

Both Homo ancestors and Moroccan hominins exhibit “a mosaic of primitive and derived features,” Hublin notes, suggesting possible genetic exchanges across the Strait of Gibraltar. However, notable distinctions exist between the fossils from both areas, with Spanish specimens appearing more Neanderthal-like.

“The last common ancestor likely inhabited both sides of the Mediterranean during that era, indicating a deep African lineage for Homo sapiens opposed to the Eurasian origin theories proposed by some,” Hublin states.

Julian Lewis, a professor at Griffith University in Brisbane, Australia, expresses intrigue over the physical differences in early Pleistocene hominids closely related to our species.

“The key takeaway is that these differences have been developing for a substantial period,” Lewis concluded, alluding to the arrival of the Homo ancestor in Spain, indicating it may represent one of several species across North Africa that eventually crossed over to Europe.

Chris Stringer from the Natural History Museum in London has also contributed to this discussion. His research, including findings from human fossils in China published last year, suggests that the last common ancestor of Homo sapiens, Neanderthals, and Denisovans could date back over a million years.

“The specific continent for that common ancestor’s existence remains unknown,” Stringer remarked. “Yet even if it lived outside Africa, our analysis indicates that the evolution of Homo sapiens predominantly took place in Africa, suggesting a potential early migration back into Africa for continued evolution.”

These newly identified Moroccan fossils may even represent early specimens of Homo sapiens, though sufficient skeletal fragments are lacking for definitive classification.

Ongoing comparisons with previously studied fossils will help ascertain their evolutionary positioning.