Fossils discovered in cave reveal where our species emerged, until Earth’s magnetic field reversed

Where did our species first appear? Fossils discovered in Morocco dating back more than 773,000 years support the theory that Homo sapiens originally appeared in Africa, scientists say in a study Wednesday.

The oldest Homo sapien fossilsdating back more than 300,000 years ago, were discovered at Jebel Irhoud, northwest of Marrakech.

Our cousins Neanderthals lived primarily in Europe, while more recent additions to the family, the Denisovans, roamed Asia.

This has sparked a lingering mystery: who was the last common ancestor of Homo sapiens and our cousins, before the family tree split into different branches?

This divergence is thought to have occurred between 550,000 and 750,000 years ago.

So far, the main hominid fossils from this period have been found in Atapuerca, Spain.

They belonged to a species nicknamed “Homo antecessor,” dating back about 800,000 years, and exhibited characteristics that were a mix of the older Homo erectus and those more similar to Homo sapiens and our cousins.

This sparked a controversial debate over whether our species originally appeared outside of Africa, before returning there.

There is “a gap in the fossil record of Africa”, French paleoanthropologist and lead author of the study, Jean-Jacques Hublin, told AFP.

The search published in the journal Nature fills this gap by finally establishing a firm date for fossils discovered in 1969 in a cave in the Moroccan city of Casablanca.

For three decades, a Franco-Moroccan team unearthed hominid vertebrae, teeth and jaw fragments that intrigued researchers.

Researchers said a thigh bone found in the cave showed bite marks suggesting the person may have been killed or scavenged by a predator. The Reuters news agency reported.

“Only the femur shows clear evidence of carnivorous modifications – gnawing and tooth marks – indicating consumption by a large carnivore,” Hublin told Reuters. “However, the cave appears to have been primarily a carnivore den that hominids used only occasionally. The absence of tooth marks on the mandibles does not imply that other body parts were not consumed by hyenas or other carnivores.”

A thin lower jaw discovered in 2008 proved particularly puzzling.

“Hominids that lived half a million or a million years generally did not have small jaws,” Hublin said.

“We could clearly see it was something unusual – and we wondered how old it could be.”

However, many efforts to determine its age have failed.

When the Earth’s magnetic field reversed

The researchers then tried a different approach.

From time to time, the Earth’s magnetic field reverses. Until the last reversal – 773,000 years ago – our planet’s magnetic north pole was close to the geographic south pole.

Evidence of this change is still preserved in rocks around the world.

The Casablanca fossils were discovered in layers corresponding to the time of this reversal, allowing scientists to establish a “very, very precise” date, Hublin said.

This discovery eliminates “the absence of plausible ancestors” for Homo sapiens in Africa, he added.

Antonio Rosas, a researcher at Spain’s National Museum of Natural Sciences, said this adds “weight to the increasingly widespread idea” that the origins of our species and the last common ancestor of Homo sapiens and Neanderthals/Denisovians are in Africa.

“This work also suggests that the evolutionary divergence of the H. sapiens lineage may have begun earlier than conventionally assumed,” Rosas, who was not involved in the research, commented in Nature.

Like the ancestor of Homo, the Casablanca fossils display a mixture of characteristics of Homo erectus, ourselves and our cousins.

But although clearly closely related, the Moroccan and Spanish fossils are not the same, which Hublin says is a sign of “populations in the process of separating and differentiating.”

The Middle East is considered the main route for hominid migration out of Africa, but falling sea levels at certain periods could have allowed crossings between Tunisia and Sicily – or across the Strait of Gibraltar.

The Casablanca fossils therefore constitute “another piece of evidence to support the hypothesis of possible exchanges” between North Africa and southwest Europe, Hublin said.

The study was published just weeks after scientists said newly discovered fossils proved a Mysterious foot discovered in Ethiopia belongs to a little-known and recently named ancient human relative who lived alongside the famous Lucy’s species.