It’s like Survivor in reverse: we humans are the last of our genus, having outlasted hominin contemporaries like Neanderthals, Denisovans, Asian Homo erectus, and others, and we are still trying to figure out why. What allowed Homo sapiens to survive—was it complex communication, social collaboration, technological innovation, cognitive ability, or some other trait?
In the feature article of the August issue of Nature Human Behaviour, Stewart and co-author Patrick Roberts, of the Max Planck Institute for the Science of Human History, propose that Homo sapiens survived because of our unique ability to adapt to and thrive in diverse environmental settings. Homo sapiens, the authors argue, is not a generalist (a species that can adapt to various settings and use a variety of resources) or a specialist (a species with a limited diet that is adapted to a particular environment), but a “generalist specialist.”
Our species evolved between 200,000 and 300,000 years ago, in Africa. By 80,000 years ago, Homo sapiens was rapidly colonizing the globe. As generalist specialists, members of our species were able to employ highly specific adaptive mechanisms for coping with an extraordinary range of ecological configurations in challenging habitats like deserts, tropical ranforests, and mountains.
As far as we know, no other species in Homo had been able to accomplish this. The other species, which migrated out of Africa in waves starting around 2 million years ago, seemed to have moved to places where the environment closely matched the one they were familiar with: a combination of open grasslands and riverine forests.
Stewart explains: “One of the main reasons we began thinking about this is that, with so many behavioral traits that we used to think of as exclusive to Homo sapiens (such as complex language, symbolic use of material culture, etc.) now found in other taxa, especially Neanderthals, it is likely that most major cognitive advances had probably already occurred in the last common ancestor that we shared with them, an ancestor that lived around 300,000 to 600,000 years ago called Homo heidelbergensis. We think it is therefore important to re-examine what does make us truly unique: the colonization, use, and manipulation of the full range of global environments.”
“We suspect that at the root of this ecological savviness were selective pressures on cultural evolution —pressures likely exerted in Africa over a long (and climatically volatile) period of time before Homo sapiens left that continent. These pressures probably favored hyper-cooperative behaviors like long-distance exchange and ritual relationships—social mechanisms that tightly knitted people and groups across landscapes and through generations.”
Stewart and Roberts stress that more research is needed to support this hypothesis.