Why early human migrations out of Africa failed to take hold

Today, nearly all non-Africans descend from a group of people who left Africa around 50,000 years ago. But other human groups attempted this migration out of Africa long before.

Fossil records show that earlier waves moved into Eurasia, yet they vanished without leaving a genetic legacy. Why did only one expansion succeed?

A new study led by Professor Eleanor Scerri of the Max Planck Institute of Geoanthropology and Professor Andrea Manica of the University of Cambridge, offers a detailed explanation.

The research combines archaeology with climate models, and it introduces a fresh parameter: ecological adaptability.

Habitats used by humans in Africa

Before the successful exit, humans in Africa began using new types of environments. According to study co-author Dr. Emily Hallett, the team assembled a dataset of archaeological sites and environmental information covering the last 120,000 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,” said Dr. Hallett.

The researchers used a continent-wide database of 479 dated archaeological layers and bioclimatic reconstructions.

The analysis tracked five environmental variables: leaf area index, temperature and rainfall during the wettest and warmest quarters, and annual temperature range.

Expansion of the human niche

The research team created a time-series model to analyze ecological changes. These generalized additive models (GAMs) showed a clear result: around 70,000 years ago, humans began expanding into new habitats.

This expansion wasn’t just driven by climate change. The study showed that even when forest and desert areas remained constant, humans began settling in them more frequently.

“Our results showed that the human niche began to expand significantly from 70,000 years ago, and that this expansion was driven by humans increasing their use of diverse habitat types, from forests to arid deserts,” noted Dr. Michela Leonardi.

Humans adapted to Africa’s changing climate

“Previous dispersals seem to have happened during particularly favourable windows of increased rainfall in the Saharo-Arabian desert belt,” explained Professor Manica.

“However, around 70,000-50,000 years ago, the easiest route out of Africa would have been more challenging than during previous periods, and yet this expansion was sizeable and ultimately successful.”

The shift to more stable desert use marked a turning point. Even during arid periods, humans continued to occupy deserts and forests. This reflects a growing resilience to climate variation, not just opportunistic movement.

Cultural shifts supported human expansion

Between 70,000 and 50,000 years ago, several behavioral changes occurred human populations. These included wider diets, water storage, landscape burning, and increased long-distance social ties.

The archaeological record shows signs of territoriality and group identity emerging during this period.

Around 29,000 years ago, a second major niche expansion occurred. By then, humans occupied nearly all ecosystems across Africa. This wide habitat usage became the baseline for the start of their global spread.

From Africa to the world

Earlier hypotheses credited tools or symbolic behavior for the successful human migration out of Africa. But many of these traits existed at much earlier times. The experts concluded that success rested instead on a gradual build-up of ecological flexibility.

“Unlike previous humans dispersing out of Africa, those human groups moving into Eurasia after ~60-50 thousand years ago were equipped with a distinctive ecological flexibility as a result of coping with climatically challenging habitats,” said Professor Scerri.

“This likely provided a key mechanism for the adaptive success of our species beyond their African homeland.”

Africa shaped modern human success

This was not a sudden revolution. It was a long African process shaped by regional adaptations. The forests in West and Central Africa, the deserts of the Sahel, and the savannas all played roles.

The researchers avoided attributing the shift to a single cultural driver, pointing instead to overlapping local innovations.

Climate instability may have helped, not hindered. Dry and wet spells forced humans to adapt constantly. Over time, these pressures helped shape a species that could survive nearly anywhere.

The study reframes the question of human expansion by showing it began with changes in Africa.

Successful human migration out of Africa wasn’t just about tools or genes. It was about being able to survive in more places than ever before. That transformation started inside Africa, and it paved the way for global colonization.

Supported by the Max Planck Society, the European Research Council, and the Leverhulme Trust, this work builds a strong case that ecological readiness, not technology, explains the success of our species.

The study is published in the journal Nature.

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