Repeated failures in human migration out of Africa remained a mystery until now. Humans ultimately managed to migrate out of Africa approximately 50,000 years ago, but before that, attempts had failed miserably. According to scientists, before the successful migration, humans began using a broad range of environments across Africa, from dense forests to harsh deserts. The adaptive edge resulting from this ecological flexibility enabled humans to survive in the more challenging exit routes into Eurasia.
Modern non-African humans have descended from a small group of people that migrated into Eurasia. However, fossil evidence shows that there were multiple failed attempts before this successful dispersal, which left no detectable traces in living humans.
A consortium of scientists led by Prof. Eleanor Scerri of the Max Planck Institute of Geoanthropology in Germany and Prof. Andrea Manica of the University of Cambridge found that humans were exploiting different habitat types in Africa in a way never seen before. This was before the migration into Eurasia.
“We assembled a dataset of archaeological sites and environmental information covering the last 120 thousand years in Africa. We used methods developed in ecology to understand changes in human environmental niches, the habitats humans can use and thrive in, during this time,” says Dr Emily Hallett of Loyola University Chicago, co-lead author of the study.
According to Dr Michela Leonardi of London’s Natural History Museum, the study’s other lead author, major human niche expansion from 70,000 years ago was driven by humans’ ability to exploit diverse habitat types, from dense forests to arid deserts.
According to Professor Manica, this is a key result. Previous dispersals occurred during periods of rainfall in the Saharo-Arabian desert belt, creating a favorable “green corridor” for people to migrate into Eurasia. However, 70,000-50,000 years ago, the easiest route out of Africa was far more challenging than it had been previously, yet humans found a way to migrate out of Africa successfully.
Technological innovations and immunities granted by admixture with Eurasian hominins have long been proposed as a reason for successful migration into Eurasia. However, previous admixture events do not appear to have saved older human dispersals out of Africa, and no technological innovations were apparent.
The researchers have shown that humans significantly expanded the range of habitats they exploited in Africa before their eventual expansion out of the continent. This increase in human niche may have arisen from the positive feedback of cultural exchange and greater contact. This broke down geographic barriers and allowed larger ranges of settlement.
According to Professor Scerri, unlike humans that previously attempted to migrate, humans migrating during 60,000-50,000 years ago were equipped with distinct ecological flexibility that allowed them to cope with climatically challenging habitats. This likely provided a key advantage in the adaptive success of human beings beyond their African homeland.
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