This ancient human may be the root of the Homo sapiens family tree
New fossils unearthed in Morocco could help solve the mystery of how Homo sapiens diverged from other ancient humans like Neanderthals.
Around 770,000 years ago, a small windswept cave overlooked grassy plains and trees in what today is southwest Casablanca in Morocco. The area abounded with gazelle, hyena, antelope, mongoose, bears, the now-extinct giant gelada baboons—and a hitherto unknown group of early humans.
In a paper published today in the journal Nature, researchers report the discovery of new hominin fossils from this cave, called Grotte à Hominidés, that date back to a critical period of human evolution when the ancestor to Homo sapiens was just beginning to split and diversify into different lineages that would later become Neanderthals and Denisovans. The remains strike at the heart of a debate about where our earliest ancestors come from, strongly pointing the finger toward northwest Africa as a contender for our original home.
“The fossils add a new piece to the puzzle of the origin of Homo sapiens,” says José María Bermúdez de Castro, a paleoanthropologist at the National Human Evolution Research Center in Spain who was not involved with the study. “This new research is excellent.”
Unearthing enigmatic ancestors
Prior genetic evidence suggested the earliest ancestor to modern Homo sapiens lived sometime between 765,000 to 550,000 years ago, but physical data from this time period are scarce. Bermúdez de Castro and his colleagues discovered the previous contender for our oldest common ancestor, which they named Homo antecessor, in Atapuerca, Spain and estimated it to be between 950,000 and 770,000 years old. The find led some to wonder if Homo sapiens developed the anatomical traits that set them apart from their evolutionary cousins in Europe, not Africa. But others consider that scenario less plausible because all uncontroversial early Homo sapiens specimens come from Africa.
(Homo antecessor may have also dabbled in cannibalism.)
The new work focuses on a handful of fossil specimens unearthed over the past three decades from a site with a rich hominin history known as Thomas Quarry—made famous in 1969 when an amateur collector uncovered a human mandible fragment within Grotte à Hominidés. The quarry includes a 1.3-million-year-old archaeological site that contains the first definitive evidence of human stone toolmaking in northwest Africa, as well as a younger area that includes Grotte à Hominidés where the newer fossils were found. In total, the new remains include two jaw fragments from adults, one from a child, and several associated teeth and vertebrae.
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“What struck me immediately was the unexpected gracility of the adult mandible,” says Jean-Jacques Hublin, a paleoanthropologist at the Max Plank Institute for Evolutionary Anthropology in Germany and lead author of the research. “Even before any formal analysis, it felt like something that did not quite fit the established narrative of human evolution in this part of the world.”
Based on microCT scans, Hublin and his colleagues found that the remains are distinct from Homo antecessor, lacking features in the teeth and jaws that would connect them to Neanderthals in Europe while maintaining more “primitive” features that keep them linked to Africa. The fossils also share some similarities with modern Homo sapiens and could represent an early version of our species, but the researchers argue the most plausible interpretation is that they belong to an isolated group of Homo erectus, an even more ancient species, that was in the process of diverging from older populations elsewhere. Either way, the team’s analysis suggests Homo antecessor and the new remains likely each come from a more ancient population, with the Moroccan remains later leading to Homo sapiens.
Magnetic minerals
Further analysis revealed that the ancient soils surrounding the fossils contained key signatures associated with the reversal of the Earth’s magnetic pole, a rare event that happens sporadically every 450,000 or so years. Because rocks contain magnetized minerals that align with the direction of Earth’s polarity, scientists can pinpoint these reversals by measuring the differences in how magnetized minerals settled in buried sediments.
“We were able to identify a major event in Earth’s history: the last major reversal of the geomagnetic field,” says Hublin. “Remarkably, the hominin remains are embedded in sediments recording this very transition.”
Rock layers worldwide suggest that the shift—called the Matuyama-Brunhes transition—occurred around 773,000 years ago, making the new fossils some of the most precisely dated and oldest human-like ancestors yet discovered, edging out the Spanish Homo antecessor, and placing the divergence of human species firmly in Africa.
(Inside the last days of the Neanderthals.)
A critical stage in human evolution
The researchers are “appropriately cautious” in their placement of the specimens near the base of Homo sapiens lineage, says Chris Stringer, a paleoanthropologist at the Natural History Museum in London who was not involved in the research. It’s possible the remains belong to a very early Homo sapiens ancestor, he says, lacking some of the characteristics we would later evolve. For now, there’s not enough evidence to make a definitive claim.
Despite the significance of the new remains, there is still much to learn regarding the split between Homo sapiens, Neanderthals, and Denisovans. “The period between one million years ago to 300,000 years ago is often referred to as the ‘muddle in the middle’,” says Michael Petraglia at Griffith University in Australia who was not involved with the research. While the new fossils are “of great interest,” they cannot by themselves “solve the puzzle of our evolution.”
While Hublin agrees that more work needs to be done, he can’t help but reflect on the “profoundly moving experience” of uncovering the fossils themselves. “Beyond their scientific importance,” he says, “such remains confront us with the physical presence of a human being who once lived, moved, and died—someone who belonged to a world now irretrievably lost.”
