Genome data shed light on how Homo sapiens evolved in Africa

WASHINGTON (Reuters) – Our species originated in Africa more than 300,000 years ago, with the oldest fossils of Homo sapiens discovered at a site in Morocco called Jebel Irhoud, located between Marrakech and the Atlantic coast.

But the paucity of Homo sapiens fossils from early in our evolutionary history and the geographic spread of those remains in Africa in places like Ethiopia and South Africa made it difficult to piece together how our species emerged and spread across the continent before traveling around the world. A new study making use of genome data from modern African populations provides insight into how this happened.

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

The results did not support a long-standing hypothesis that a single region in Africa gave rise to Homo sapiens or a scenario involving admixture with unspecified closely related species in the human evolutionary lineage within Africa.

“All humans share a relatively recent common ancestry, but the story in the deeper past is more complex than our species evolving in just one place or in isolation,” said University of Wisconsin-Madison population geneticist Aaron Ragsdal, lead author of the published study. This week in the magazine nature.

The ancestral groups were likely spread across a geographic landscape in a population structure that was “weak,” Ragsdahl says, meaning there was continuous or at least frequent migration between groups, and this preserved genetic similarity across the ancestral groups.

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Because of the scarcity of fossil remains and archaeological evidence, researchers have turned to genome data from living people to find clues about the past. They examined genome data from 290 people, mostly from four geographically and genetically diverse African peoples, to track similarities and differences between populations and identify genetic relatedness over hundreds of thousands of years.

These include: 85 individuals of a West African group called the Mende from Sierra Leone; 44 individuals from the Nama Khoe-San group from South Africa; 46 members of the Amhara and Oromo groups of Ethiopia; and 23 members of the Gumuz group, also from Ethiopia. Genome data was also examined from 91 Europeans to account for the influence of the postcolonial era and from Neanderthals, the extinct human species that was concentrated in Europe until about 40,000 years ago.

The researchers said the fossil record is scant for the time period that would be most informative about the emergence and spread of Homo sapiens, and there is no ancient DNA from skeletal or dental remains from these time periods.

“While we find evidence of human remains and modern anatomical artifacts in various parts of Africa, they are so scattered in space and time that it is difficult to understand their relationships to each other, and to us,” said the study’s geneticist and study co-author. The author is Simon Gravelle of McGill University in Montreal. “Were they related to each other? Are they related to our ancestors, or are they local populations that have gone extinct?”

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“It inherited genetic data from an ongoing chain of transmissions that dates back long before modern humans appeared. The interconnectedness of modern humans holds a lot of information about this chain of events,” Gravel added. “By building models of how these transfers occur, we can test the detailed models that connect past populations with the current population.”

(Reporting by Will Dunham; Editing by Rosalba O’Brien)

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