Fossil find pushes back birth of modern humans

The discovery of modern human remains dating to 300,000 years ago looks set to overturn many current models of the evolution and migration of Homo sapiens.

The dating of the human bones, found in Morocco, was completed by a team led by Jean-Jacques Hublin of the Max Planck Institute for Evolutionary Anthropology in Germany, and Abdelouahed Ben-Ncer of the National Institute for Archaeology and Heritage in Rabat, Morocco. The results are published in Nature.

Dr. Jean-Jacques Hublin pointing to a crushed human skull found at Jebel Irhoud, whose orbits are visible just beyond his finger tip. Credit: Shannon McPherron, MPI EVA Leipzig

The remains, thought to be from at least five individuals, were found at the Jebel Irhoud archaeological cave site, located near Sidi Moktar, about 100 kilometres west of Marrakesh.

The site was already known as the source of some of the earliest modern human remains ever uncovered, but the latest discovery pushes back the emergence of Homo sapiens by a full 100,000 years.

Hominid fossils unearthed at Jebel Irhoud in 1991 were dated to about 160,000 years ago and were initially thought to be Neanderthals. Further analysis in 2007, however, revealed them to be anatomically modern humans, making them some of the earliest ever discovered.

Until now, the oldest dated modern human remnant was the Omo 1 cranium found in southwest Ethiopia, dating to 200,000 years ago.

A 2013 genomic study led by Teresa Rito of the University of Porto in Portugal suggested that “mitochondrial Eve” – the last common ancestor of the Khoe and San populations of southern Africa and the east African lineage that seeded the rest of modern humans around the globe – had lived around 180,000 years ago.

The Jebel Irhoud discoveries now throw that conclusion into significant doubt. They also recast one of the most perplexing questions about the emergence of modern humans: did Homo sapiens emerge from ancestral stock comparatively rapidly, or was it a much more gradual process?

The matter remains significantly unresolved because of the severely fragmented nature of the fossil record. However, Hublin and colleagues report the latest Jebel Irhoud specimens have face, jaw and teeth structures that align “with early or recent anatomically modern humans”, while skull shapes are more closely aligned with more archaic hominids.

This, the researchers suggest, conflicts with the idea that modern humans emerged in a single geographic location, instead suggesting that “the evolutionary processes behind the emergence of H. sapiens involved the whole African continent”.

Some of the Middle Stone Age stone tools from Jebel Irhoud.

In a second, related paper in Nature, scientists led by Daniel Richter, also from the Max Planck Institute for Evolutionary Anthropology, confirm the Hublin team’s age estimates by dating flint artefacts found at the same excavation.

Using thermoluminescence techniques, the team dated the flint tools to about 315,000 years ago. Separate dating of a tooth from one of the hominid jawbones, using electron spin resonance, returned a broadly compatible date of 286,000 years (give or take 34,000 years).

Richter’s team suggest that the emergence of modern humans may be tied to climate changes around or before 330,000 years ago which “greened” much of what is now the Sahara desert and allowed biological continuity between north and sub-Saharan Africa.

Echoing the first paper’s conclusions, the second also raises the possibility that Homo sapiens arose over a wide geographic area, suggesting a “complex pan-African process”.

“We caution against favouring one region over another in constructing models to account for these changes in human behaviour and biology,” the researchers conclude.