Much of the planet became uninhabitable during the last Ice Age, and earlier members of our species survived by clustering into so-called refugia. According to new findings published in Scientific Reports this week, humans moved into what’s now southern Arabia by the time ice sheets reached their maximum, and when conditions got better, they went on to the Horn of Africa and towards the Indian Ocean.  

Exactly when humans settled in Arabia and the area’s role in our dispersal out of Africa remains controversial. While researchers have previously argued for the southern-route dispersal out of Africa via Arabia, they had little genetic data to support them. 

Now, a large international team led by the University of Huddersfield’s Martin Richards and Anna Olivieri of Università di Pavia has turned to a rare mitochondrial lineage called R0a. This lineage is most frequently found in Arabia and the Horn of Africa, though it’s distributed widely from Europe to India. The researchers examined 205 whole mitogenomes from R0a, as well as 733 sequences from R0a and R0b (a sister lineage). Because R0a has never been recovered from prehistoric remains, the team had to rely entirely on modern-day diversity for information about its history. 

They found that R0a has a much deeper presence in Arabia than researchers previously thought. That suggests there was at least one glacial refugium in Arabia – likely on the Red Sea plains – during the Pleistocene, which spanned the last Ice Age. 

When the ice sheets receded, people living in southern Arabian dispersed outwards. They went on to populate the rest of Arabia and the Horn of Africa on the eastern part of the continent around 11,000 years ago. The team also found evidence of gene flow from Arabia into what’s now Iran, Pakistan, and India around 3,000 years ago.