By 14,000 years ago, humans had marched across modern-day Asia, into North America and to the southernmost part of South America. The key? Food.
That, and the adaptability of our ancestors to the changing environmental conditions of the planet as they marched out of Africa over 70,000 years ago, was essential to populating every landmass on Earth.
“The first human migrants favoured routes that provided essential resources and facilitated travel, as well as regions with a mix of forests and open areas for shelter and food, while allowing them to expand into new territories,” says Frédérik Saltré, an ecologist and biogeographer at Flinders University.
He’s the lead author of new research that explored the environmental factors enabling human movement across the planet within just over 50,000 years.
After arriving in the Fertile Crescent – a region today expanding from Kuwait, Iran and Iraq west through Syria, Lebanon, Jordan, Israel and Palestine – humans radiated through the Caucasus , Asia and Western Europe as late as 44,000 years ago.
Resource availability aided movement across the planet – where conditions were good, and food sources plentiful, early hunter-gatherer communities were able to keep moving.
As they reached harsher climates, humans clung to routes that provided food and shelter along rivers, allowing them to reach the northern grasslands of Asia, where they could cross a land bridge from what is now Siberia into Alaska.
Rising sea levels flooded this landbridge to cut off the Americas from Asia, but through the icy landscape of North America, they walked south along the Pacific coast before rising temperatures enabled them to migrate inland and towards present-day Central and South America.
These routes, which were modelled by an international collaboration led by researchers affiliated with the ARC Centre of Excellence for Australian Biodiversity and Heritage by combining radiocarbon-dated genetic data from nearly 25,000 archaeological samples with detailed ecological data.
The migration ‘rate’ (or how quickly humans moved) into North America is notably quick – tens of kilometres a year rather than comparatively slow for other extreme points like those for Sahul (the supercontinent that preceded Australia) and western Europe.
This, they say, is due to the rapid movement of hunter-gatherers compared to Europe’s neolithic agriculturalists though acknowledge some data limitations may play a role in higher movement rates across Asia.
Though recent studies put the speed at which Sahul was populated, it’s still much slower than the rapid Asian and American migrations.
Ultimately, the viability of quick movement, and the pathways used to achieve it, was driven by resource availability and could, Saltré says, provide a counterpoint to what is being described as a major extinction crisis underway in the present.
“[The research] underscores how climate and ecology shaped human prehistory, highlighting biodiversity’s role in human survival and mobility, demonstrating that rich ecosystems enabled humans to thrive in new environments for thousands of years,” he says.
“The biodiversity crisis that we are experiencing now compromises our ability to thrive. Despite the advanced technology we have today, I genuinely wonder if we will last long without maintaining the bulk of current biodiversity.”
The study was published in the journal Nature Communications.
