Genome data sheds light on how Homo sapiens arose in Africa

Our species arose in Africa more than 300,000 years ago, with the oldest-known Homo sapiens fossils discovered at a site in Morocco called Jebel Irhoud

Our species arose in Africa more than 300,000 years ago, with the oldest-known Homo sapiens fossils discovered at a site in Morocco called Jebel Irhoud, located between Marrakech and the Atlantic coast.

But the scarcity of Homo sapiens fossils from early in our evolutionary history and the geographical spread of those remains in Africa in places like Ethiopia and South Africa have made it difficult to piece together how our species emerged and dispersed across the continent before trekking worldwide. A new study tapping into genome data from modern-day African populations is offering insight into how this may have unfolded.

The research indicated that multiple ancestral groups from across Africa contributed to the emergence of Homo sapiens in a patchwork manner, migrating from one region to another and mixing with one another over hundreds of thousands of years. It also found that everyone alive today can trace their ancestry to at least two distinct populations that were present in Africa dating back about a million years.

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The findings did not support a longstanding hypothesis that a single region in Africa gave rise to Homo sapiens or a scenario involving mixture with an unidentified closely related species in the human evolutionary lineage within Africa.

"All humans share relatively recent common ancestry, but the story in the deeper past is more complicated than our species evolving in just a single location or in isolation," said University of Wisconsin-Madison population geneticist Aaron Ragsdale, lead author of the study published this week in the journal Nature.

The ancestral groups were likely spread across a geographic landscape in a population structure that, Ragsdale said, "was 'weak,' meaning that there was ongoing or at least recurrent migration between groups, and this maintained genetic similarity across ancestral populations."