Humans conquered the planet 300 times faster than genetic evolution can explain
Just under 300,000 years from the moment Homo sapiens appeared in Africa, the species had encircled Earth, mastering desolate deserts and frozen wastelands and all the temperate climes in between. Throughout this staggering expansion, we seem to have relied surprisingly little on genetic adaptation to fuel our globe-conquering—all eight billion of us together remain less genetically diverse than individual populations of chimpanzees. So how did we do it?
Many scientists point to cultural evolution, the process by which knowledge, customs and technology spread over time. But according to Alex Mesoudi, who studies cultural evolution at the University of Exeter in England, “it’s always been just a vague claim.”
No longer. A recent paper in the Proceedings of the National Academy of Sciences USA by Arizona State University evolutionary anthropologist Charles Perreault calculates just how big a boost our capacity for culture might have given the great human takeover. Had we been a typical mammal, forced to adapt primarily through sluggish genetic evolution, Perreault concludes, we would’ve needed 88 million years to attain our current geographic footprint—and we would have split into some 2,200 distinct species in that time.
To arrive at those figures, Perreault compiled range maps for nearly 6,000 mammal species and charted how geographic spread relates to three proxies of evolutionary change for a group with a common ancestor, called a lineage: a lineage’s age, its number of species, and its spectrum of body sizes. Those relationships let Perreault gauge roughly how much “evolutionary work” mammals do to populate a given area.
By this yardstick, humans accomplished in a few hundred thousand years what otherwise would have required tens of millions. Cultural shortcuts meant that, unlike other mammal lineages, we didn’t have to wait an entire generation to adapt via natural selection. “We can just skip that,” Perreault says. A continuous stream of better tools, smarter ideas and more effective practices “really accelerates the pace of evolution.”
Collectively, Perreault found, humans occupy as much terrain as all other mammals combined, far more than any one species. (Gray wolves come closest, covering half as much land.) This makes us seem like the ultimate generalists, but he notes that in another sense we aren’t, really—it’s just that individual groups of people perfected the art of survival in vastly different places. The Kalahari hunter-gatherers of southern Africa might not last long in Greenland, and vice versa for the Inuit.
Mesoudi, who was not involved in the new study, agrees that cultural evolution was probably a key to human success while noting that the secret sauce could instead turn out to be social cooperation, language, individual intellect, or some combination of these factors. Still, he says, the paper is “a nice attempt to quantify something that we often write but don’t actually put any numbers on.”