- The traditional origin story for modern humans says that early groups migrated out of Africa 60,000 years ago.
- Most non-Africans can trace their origin to those migrations, but new evidence suggests that humans actually migrated out of Africa as far back as 120,000 years ago.
- Those early groups may have brought tools and culture with them, and they interbred with other hominin species that existed at the time.
Tens of thousands of years ago, the first Homo sapiens — modern humans — started to cross mountains, deserts, and even oceans to leave Africa, where our species first evolved, and populate Asia and Australia.
The traditional understanding has been that this "Out of Africa" movement, as it's often referred to, happened approximately 60,000 years ago. Researchers still agree that most present day non-Africans trace the majority of their lineage to the large migration that occurred then.
But several recent discoveries have found evidence that humans started migrating into Asia as far back as 120,000 years ago. These early migrants interbred with other hominin species that existed at the time, including Neanderthals and Denisovans. Genetic traces of those early migrant groups can still be found today.
This new information has challenged the previous understanding of human migration to the point that it needs to be revised, according to a new review of research published in the journal Science.
"The initial dispersals out of Africa prior to 60,000 years ago were likely by small groups of foragers, and at least some of these early dispersals left low-level genetic traces in modern human populations," Michael Petraglia, an archaeologist at the Max Planck Institute for the Science of Human History and an author of the study, said in a press release. "A later, major 'Out of Africa' event most likely occurred around 60,000 years ago or thereafter."
Rethinking the human origin story
The recent studies evaluated in this new review all suggest that the story of how humans spread throughout the world is more complex than researchers had thought.
The first fossils of what we'd consider "modern humans" based on physical characteristics date back close to 200,000 years. In the Horn of Africa, archaeologists have found remains of Homo sapiens at least 195,000 years old.
According to the older model, behaviors like the use of tools were thought to have been brought from Africa 60,000 years ago and spread north and east.
But some of these recent discoveries show that "modern" behaviors like blade use, deep-sea fishing, and cave art existed around the world before that major migration, and in some cases were associated with populations from other hominin species. Earlier dispersals of Homo sapiens and interbreeding with other populations may have helped spread some of these behaviors.
That also helps explain why today, non-Africans have between 1-4% Neanderthal heritage and why modern residents of Melanesia have approximately 5% Denisovan heritage. These early hominin groups mixed together and spread genetic material and culture amongst each other.
"Indeed, what we are seeing in the behavioral record is that the spread of so-called modern human behaviors did not occur in a simple time-transgressive process from west to east," Christopher Bae of the University of Hawaii at Manoa, lead author of the study, said in the press release.
