Contrary to what we assume about the migration of modern humans from Africa, at least some movements may have resulted from deprivation and not from “green corridors.” New analysis of volcanic glass found in Ethiopia shows that humans lived in drought conditions in the Horn of Africa 74,000 years ago, forcing them to adapt and possibly travel to maximize available resources. Sticking to seasonal rivers and bodies of water where food is more abundant may have created what the team of scientists call “blue highways” that facilitated dispersal from Africa to the wider world.

“As people lost food at a waterhole in and around a particular dry season, they probably had to move to new watering holes,” says anthropologist John Kappelman of the University of Texas at Austin, who led the study.

“Seasonal rivers thus functioned as ‘pumps’ pumping populations from one waterhole to another along channels, potentially causing their eventual dispersal out of Africa.”

Humans and their ancestors are known to have migrated from Africa many times in prehistoric times, and changing climatic conditions seem to be a very good reason for this. But figuring out when and why people left Africa en masse can be quite difficult. The “green corridor” theory suggests that as food resources expand and become more abundant, people expand with them. Kappelman and his colleagues sought to investigate the alternative driving force behind the last and largest migration, which occurred less than 100,000 years ago.

Their research focused on the Shinfa Metema 1 archaeological site in what is now northwestern Ethiopia and explored how people lived there. There they found stone tools, bones of animals eaten by humans, remains of a cooking stove, and microscopic fragments of volcanic glass known as cryptotephra, which matched the chemical composition of the Toba eruption.

“One of the revolutionary results of this work is that with new cryptotephra techniques developed for our previous work in South Africa and now applied here in Ethiopia, we can link regions across Africa, and possibly the world, within a few weeks of resolution.”

Cryptephras are smaller than the width of a human hair, but they can tell a lot about human history. For example, cryptotephra can help reveal the extent of an explosion. Previous studies have shown ash from eruptions in other parts of Africa. But they also help scientists date archaeological artifacts.

In the Shinfa-Metema 1 case, investigators assembled a collection of different types of evidence. Bones and teeth, along with traces of hunting and butchering, show what kind of food the inhabitants of the area ate. They hunted and ate mammals such as monkeys and antelope; When these resources became scarce, they relied more on fish.

Interestingly, some of the stone artifacts found at the site correspond to arrowheads. Researchers say this is the oldest evidence of archery found to date. The researchers also conducted oxygen isotope analysis of mammal teeth and ostrich egg shell fragments found in the area. The rates they obtained corresponded to a period of high drought.

Although the inhabitants of Shinfa Metem 1 were probably not among those who emigrated, they showed a high level of adaptability in difficult times, indicating that people were willing to go with the flow, so to speak. When times got tough, they found new ways to live; even if those paths mean finding greener pastures.

“This study supports the Pinnacle Point results in South Africa,” says Marean. “The Toba eruption may have changed the environment in Africa, but people adapted and survived.”