In the most massive study of genetic variation yet, researchers estimated the age of more than one million variants, or changes to our DNA code, found across human populations. The vast majority proved to be quite young. The chronologies tell a story of evolutionary dynamics in recent human history, a period characterized by both narrow reproductive bottlenecks and sudden, enormous population growth. 

The evolutionary dynamics of these features resulted in a flood of new genetic variation, accumulating so fast that natural selection hasn’t caught up yet. As a species, we are freshly bursting with the raw material of evolution.

“Most of the mutations that we found arose in the last 200 generations or so. There hasn’t been much time for random change or deterministic change through natural selection,” said geneticist Joshua Akey of the University of Washington, co-author of the Nov. 28 Nature study. “We have a repository of all this new variation for humanity to use as a substrate. In a way, we’re more evolvable now than at any time in our history.”

Akey specializes in what’s known as rare variation, or changes in DNA that are found in perhaps one in 100 people, or even fewer. For practical reasons, rare variants have only been studied in earnest for the last several years. Before then, it was simply too expensive. Genomics focused mostly on what are known as common variants.