Humans adapted to diverse habitats before trekking out of Africa
By Will Dunham
(Reuters) -Small bands of Homo sapiens made a few failed forays leaving our home continent before the species finally managed to launch a major dispersal out of Africa roughly 50,000 years ago, going first into Europe and Asia and eventually the rest of the world.
So why was this migration successful after the prior ones were not? New research is offering insight. It documents how human hunter-gatherers in Africa began about 70,000 years ago to embrace a greater diversity of habitats such as thick forests and arid deserts, acquiring an adaptability useful for tackling the wide range of conditions awaiting beyond the continent.
"Why the dispersal 50,000 years ago was successful is a big question in human origins research. Our results suggest that one part of the reason is that humans had developed the ecological flexibility to survive in challenging habitats," said Loyola University Chicago archeologist Emily Hallett, co-leader of the study published in the journal Nature.
Looking at an array of archeological sites in Africa, the study detailed how human populations expanded their range into the forests of Central and West Africa and the deserts of North Africa in the roughly 20,000 years preceding this dispersal.
Some examples of archeological sites dating to this time that illustrate the expansion of human niches to harsh deserts include locales in Libya and Namibia, and examples of expansion to forested habitats include locales in Malawi and South Africa.
Homo sapiens arose roughly 300,000 years ago, inhabiting grasslands, savannahs and various other African ecosystems.
"Starting from about 70,000 years ago, we see that they suddenly start to intensify this exploitation of diverse habitats and also expand into new types of habitat in a way we don't see before. They exploit more types of woodland, more types of closed canopy forests, more types of deserts, highlands and grasslands," said archeologist and study co-leader Eleanor Scerri of the Max Planck Institute of Geoanthropology in Germany.
"An Ice Age was coming, which means drier conditions in parts of Africa. It seems possible that humans responded to this squeeze by learning how to adapt to new niches," Scerri added.
The increased ecological flexibility of the species appears to have reflected cultural and social advances such as passing knowledge from one generation to the next and engaging in cooperative behavior, the researchers said.
"This must have entailed profound changes in their interaction with the natural environment, as it allowed them to occupy not only new environments in Africa, but entirely new conditions in Eurasia as well," said evolutionary biologist and study co-leader Michela Leonardi of the Natural History Museum in London.
"Another way to phrase this is that the ability to live in a variety of environments in Africa is not directly the adaptation that allowed a successful out of Africa, but rather a sign that humans by that point were the ultimate generalist, able to tackle environments that went from deep forest to dry deserts," said University of Cambridge evolutionary ecologist and study co-leader Andrea Manica.
"This flexibility is the key trait that allowed them, later on, to conquer novel challenges, all the way to the coldest tundras in Siberia."
Trekking out of Africa, Homo sapiens encountered not only new environments and unfamiliar animals and plants, but also other human species, including the Neanderthals and Denisovans. The ecological flexibility learned in Africa may have provided an edge when Homo sapiens encountered these other humans, both of whom disappeared relatively soon thereafter, the researchers said.
Genetic evidence indicates that today's people outside of Africa can trace their ancestry to the population of humans, numbering perhaps only in the thousands, who engaged in that pioneering migration out of Africa approximately 50,000 years ago.
"I think that adaptability and innovation are hallmarks of our species, and that they allowed us to succeed in every environment we encountered," Hallett said. "At the same time, we are almost too good at adapting to different places, to the detriment of most other species on Earth."
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