Carl Zimmer, When Humans Learned to Live Everywhere, NYTimes, June 19, 2025.
Geography is one of the things that sets apart modern humans.
Our closest living relatives — chimpanzees and bonobos — are confined to a belt of Central African forests. But humans have spread across every continent, even remote islands. Our species can thrive not only in forests, but in grasslands, swamps, deserts and just about every other ecosystem dry land has to offer.
In a study published on Wednesday, scientists pinpoint the origin of our extraordinary adaptability: Africa, about 70,000 years ago.
This simple observation is extremely important. Why are we the only higher primate that has been able to survive outside the tropics?
Traditionally, experts have envisioned our species evolving on the savanna, adapted to life in the open woodlands and grasslands of East Africa. But Dr. Scerri and other researchers have found that early humans were more versatile than that.
In February, for example, Dr. Scerri and her colleagues reported that humans lived in a West African rainforest 150,000 years ago. Findings like that prompted the team to figure out just how wide-ranging early humans were. [...]
Dr. Manica, Dr. Scerri and their colleagues analyzed hundreds of archaeological sites across Africa to reconstruct the human niche over the past 120,000 years.
The oldest sites revealed that early humans were fairly versatile, living in a range of habitats. But they did not push too far into extreme environments. As a result, populations remained largely isolated from one another, cut off by deserts, towering mountains or impassible marshlands.
The human niche didn’t change for tens of thousands of years. But then a sudden shift occurred 70,000 years ago. Humans pushed into more challenging deserts and forests, filling the gaps on the ecological map of Africa.
Climate change forced early humans to generalize:
Dr. Leonardi and her colleagues believe that a change in the climate prompted humans to expand their habitats. “We can see a pressure for this,” Dr. Scerri said.
Before 70,000 years ago, much of Africa was lush and wet. Even the Sahara was green. But then the planet entered an ice age. Ice sheets built up around the North and South Poles and the global climate cooled. In Africa, many regions lost much of their rainfall.
The comfortable habitats that humans had long enjoyed shrank and became fragmented. Dr. Scerri and her colleagues speculate that this change forced humans to move into environments that they had not bothered with before.
“It probably was not just one magical adaptation,” Dr. Manica said.
Instead, humans 70,000 years ago learned different skills to survive in different places. “They’re becoming the ultimate generalist,” he said.
Dr. Manica speculated that the human niche kept expanding in a cultural feedback loop. As humans continued to push into extreme environments, the barriers that had divided them fell away. Now African populations came into more contact with one another. [...]
This dramatic expansion of the human niche might explain why our species was so successful in migrating out of Africa about 50,000 years ago. Humans were now ready to learn about any place that they reached.
There's more at the link.
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