Early Humans Did Not Evolve From A Single Population Or Time Period, Study Suggests

Famous prehistoric rock paintings of Tassili N'Ajjer, Algeria, dated back an estimated 10,000 years. Dmitry Pchugin/Shutterstock

Homo sapiens did not evolve from a single human ancestor or time period, according to research published in Trends in Ecology and Evolution. Rather, early human evolution was “multi-ethnic and multi-cultural” and spanned across the continent over millennia.

This new theory challenges a long-held and widely accepted belief that H. sapiens originated as a single population out of Africa 300,000 years ago.

An interdisciplinary group of researchers pulled experts from the fields of anthropology, archaeology, and population genomics to reconstruct Africa’s past climate and the populations that lived there. Their work showed that early H. sapiens were scattered across Africa and kept apart by environmental barriers changing over time. Just as the Sahara Desert was once a lush, green landscape teeming with lakes, rivers, and wildlife, climates across the continent shifted and changed over tens of thousands of years. This drove cycles of isolation between various groups of early hominids, followed by periods of contact allowing for shared cultural and perhaps genetic mixings.

It explains why human fossils have such variability over the last 300,000 years.

"In the fossil record, we see a mosaic-like, continental-wide trend toward the modern human form, and the fact that these features appear at different places at different times tells us that these populations were not well connected," Dr Eleanor Scerri said in a statement

DNA extracted from the fossils found in Africa from the last 10,000 years have been difficult for scientists to reconcile as one single population.

Evolutionary changes of braincase shape from an elongated to a globular shape. The latter evolves within the Homo sapiens lineage via an expansion of the cerebellum and bulging of the parietal. Left: micro-CT scan of Jebel Irhoud 1 (~300 ka, Africa); Right: Qafzeh 9 (~95 ka, the Levant). Philipp Gunz, Max Planck Institute for Evolutionary Anthropology

"We see indications of reduced connectivity very deep in the past, some very old genetic lineages, and levels of overall diversity that a single population would struggle to maintain,” said geneticist and co-author Professor Mark Thomas.

Similarly, researchers say stone tools used by early hominids didn’t modernize in one location or during one particular point in time.

“Stone tools and other artifacts – usually referred to as material culture – have remarkably clustered distributions in space and through time,” Scerri said. “While there is a continental-wide trend toward more sophisticated material culture, this ‘modernization’ clearly doesn’t originate in one region or occur at one time period.”

Middle Stone Age cultural artifacts from northern and southern Africa. Eleanor Scerri/Francesco d'Errico/Christopher Henshilwood

Altogether, the evidence suggests another line of edits to the story of human evolution. "This complex history of population subdivision should thus lead us to question current models of ancient population size changes, and perhaps re-interpret some of the old bottlenecks as changes in connectivity."

"The evolution of human populations in Africa was multi-regional. Our ancestry was multi-ethnic. And the evolution of our material culture was, well, multi-cultural," said Dr Scerri. "We need to look at all regions of Africa to understand human evolution."

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