Why did Homo sapiens emerge in Africa?

Every person on Earth today can trace their ancestry to Africa, where modern humans (Homo sapiens) emerged at least 300,000 years ago. But our ancestor Homo erectus lived in Africa, Europe and Asia, and so did its likely descendant Homo heidelbergensis. H. heidelbergensis gave rise to at least three hominins in different places: Neanderthals (in Eurasia), Denisovans (in Asia) and modern humans (in Africa). 

So why did H. heidelbergensis give rise to H. sapiens in Africa? 

"That's the thousand dollar question," Brenna Henn, a population geneticist at the University of California, Davis, told Live Science. To try to answer it, she said, we must first examine the process through which H. sapiens first evolved. A 1987 paper published in the journal Nature traced all modern human mitochondrial DNA back to one population in Africa which lived between 200,000 and 150,000 years ago. 

Related: When did Homo sapiens first appear?

However, Henn and other scientists challenge the idea that only one population gave rise to modern humans. When modern humans began to emerge, our Homo sapiens ancestors were spread out in dozens of specialized populations across Africa. Africa is a massive continent with a highly diverse set of ecosystems, so these populations had to adapt to suit their specific areas. 

In a 2023 study published in the journal Nature, Henn and her colleagues found that it was likely that at least two of these stem populations were the originators of H. sapiens. They proposed that, despite living separately for thousands of years, individuals from these populations still mingled at some point, creating a loose stem population that eventually became our species.

Henn speculated that the ecological diversity of the African continent and the subsequent intermingling of multiple populations may be what allowed modern humans to evolve. "Because you had all of that either genetic or behavioral diversity, that's really what facilitated a complex package that allowed Homo sapiens to be what they are," she told Live Science.