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.

That’s when modern humans learned to thrive in more extreme habitats. We’ve been expanding our range ever since. The finding could help resolve a paradox that has puzzled researchers for years.

Our species arose in Africa about a million years ago and then departed the continent a number of times over the past few hundred thousand years. But those migrants eventually disappeared, with no descendants.

Finally, about 50,000 years ago, one last wave spread out of Africa. All non-Africans can trace their ancestry to this last migration. The new study might explain why the final expansion was so successful.

In the new study, Eleanor Scerri, an archaeologist at the Max Planck Institute of Geoanthropology in Jena, Germany, and her colleagues sought to understand what sort of habitats early humans lived in across Africa.