It's accepted knowledge the first anatomically modern humans hailed from Africa some 200 thousand years ago, but the exact location has long been up for debate.
Researchers led by Professor Vanessa Hayes of the Garvan Institute of Medical Research think they have the answer. Through their work, they concluded the earliest ancestors of anatomically modern humans were from a southern African "homeland" and were able to live and thrive there for 70 thousand years.
The early homeland held Africa's largest lake
This homeland was south of the Greater Zambezi River Basin region and includes all of northern Bostwana and stretches into Namibia to the west and Zimbabwe to the east. This region held Africa's largest lake system Lake Makgadikgadi. Prior to the emergence of modern humans, the lake began to drain because of shifts in tectonic plates that lay beneath it. The researchers' findings imply that ancient humans thrived because of the wetlands, providing a stable environment. The study was published in journal Nature.
"We observed significant genetic divergence in the modern humans' earliest maternal sub-lineages, that indicates our ancestors migrated out of the homeland between 130 and 110 thousand years ago," Hayes said in a press release announcing the study results. "The first migrants ventured northeast, followed by a second wave of migrants who travelled southwest. A third population remained in the homeland until today."
The slow tilt of Earth's axis drove migration
To determine what drove the migration co-corresponding author Professor Axel Timmermann, Director of the IBS Center for Climate Physics at Pusan National University analyzed climate computer model simulations and geological data from South Africa's climate history for the previous 250 thousand years. "Our simulations suggest that the slow wobble of Earth's axis changes summer solar radiation in the Southern Hemisphere, leading to periodic shifts in rainfall across southern Africa," said Professor Timmermann in the same press release highlighting the research. "These shifts in climate would have opened green, vegetated corridors, first 130 thousand years ago to the northeast, and then around 110 thousand years ago to the southwest, allowing our earliest ancestors to migrate away from the homeland for the first time."
New rare DNA from the LO lineage provides the answers
To come to the conclusion, Hayes and the team of researchers gathered blood samples to create a catalog of modern human's earliest mitogenomes from the LO lineage, which is the earliest known modern human population. Thanks to contributions from local communities and study participants in Namibia and South Africa the researchers found rare and new LO sub-branches. By merging the 198 new mitogenomes to the current database they were able to better trace the earliest modern humans.
"It has been clear for some time that anatomically modern humans appeared in Africa roughly 200 thousand years ago. What has been long debated is the exact location of this emergence and subsequent dispersal of our earliest ancestors," said Hayes in the press release. "Mitochondrial DNA acts like a time capsule of our ancestral mothers, accumulating changes slowly over generations. Comparing the complete DNA code, or mitogenome, from different individuals, provides information on how closely they are related."