Adventures in the genetic time machine

This narrative has made him a favorite on television programs like Nova and secured lavish funding from Danish corporations. His first autobiography was titled From Fur Hunter to Professor. A more recent one is called simply It’s a Fucking Adventure.

Peering into the past

The scramble for old bones has produced a parade of headlines about the peopling of the planet, and especially of western Eurasia—from Iceland to Tehran, roughly. That’s where most ancient DNA samples originate, thanks to colder weather, centuries of archaeology, and active research programs. At the National Museum in Copenhagen, some skeletons on display to the public have missing teeth—teeth that ended up in the Globe Institute’s ancient-DNA lab as part of a project to analyze 5,000 sets of remains from Eurasia, touted as the largest single trove of old genomes yet.

What ancient DNA uncovered in Europe is a broad-brush story of three population waves of modern humans. First to come out of Africa were hunter-­gatherers who dispersed around the continent, followed by farmers who spread out of Anatolia starting 11,000 years ago. That wave saw the establishment of agriculture and ceramics and brought new stone tools. Last came a sweeping incursion of people (and genes) from the plains of modern Ukraine and Russia—animal herders known as the Yamnaya, who surged into Western Europe spreading the roots of the Indo-European languages now spoken from Dublin to Bombay.

Mixed history

The DNA in ancient human skeletons reveals prehistoric migrations.

The genetic background of Europeans was shaped by three major migrations starting about 45,000 years ago. First came hunter-gatherers. Next came farmers from Anatolia, bringing crops and new ways of living. Lastly, mobile herders called the Yamnaya spread from the steppes of modern Russia and Ukraine. The DNA in ancient skeletons holds a record of these dramatic population changes.

Archaeologists had already pieced together an outline of this history through material culture, examining shifts in pottery styles and burial methods, the switch from stone axes to metal ones. Some attributed those changes to cultural transmission of knowledge rather than population movements, a view encapsulated in the phrase “pots, not people.” However, ancient DNA showed that much of the change was, in fact, the result of large-scale migration, not all of which looks peaceful. Indeed, in Denmark, the hunter-gatherer DNA signature all but vanishes within just two generations after the arrival of farmers during the late Stone Age. To Willerslev, the rapid population replacement “looks like some kind of genocide, to be honest.” It’s a guess, of course, but how else to explain the “limited genetic contribution” to subsequent generations of the blue-eyed, dark-haired locals who’d fished and hunted around Denmark’s islands for nearly 5,000 years? Certainly, the bodies in Copenhagen’s museums suggest violence—some have head injuries, and one still has arrows in it.

In other cases, it’s obvious that populations met and mixed; the average ethnic European today shares some genetic contribution from all three founding groups—hunter, farmer, and herder—and a little bit from Neanderthals, too.“We had the idea that people stay put, and if things change, it’s because people learned to do something new, through movements of ideas,” says Willerslev. “Ancient DNA showed that is not the case—that the transitions from hunter-­gatherers to farming, from bronze to iron, from iron to Viking, actually due to people coming and going, mixing up and bringing new knowledge.” It means the world that we observe today, with Poles in Poland and Greeks in Greece, “is very, very young.”

With an increasing number of old bodies giving up their DNA secrets, researchers have started to search for evidence of genetic adaptation that has occurred in humans since the last ice age (which ended about 12,000 years ago), a period that the Copenhagen group noted, in a January 2024 report, “involved some of the most dramatic changes in diet, health, and social organization experienced during recent human evolution.”

Every human gene typically comes in a few different possible versions, and by studying old bodies, it’s possible to see which of these versions became more common or less so with time—potentially an indicator that they’re “under selection,” meaning they influenced the odds that a person stayed alive to reproduce. These pressures are often closely tied to the environment. One clear signal that pops out of ancient European genes is a trend toward lighter skin—which makes it easier to produce vitamin D in the face of diminished sunlight and a diet based on grains.

New technology and changing lifestyles—like agriculture and living in proximity to herd animals (and their diseases)—were also potent forces. Last fall, when Harvard University scientists scanned DNA from skeletons, they said they’d detected “rampant” evidence of evolutionary action. The shifts appeared especially in immune system genes and in a definite trend toward less body fat, the genetic markers of which they found had decreased significantly “over ten millennia.” That finding, they said, was consistent with the “thrifty gene” hypothesis, a feast-or-famine theory developed in the 1960s, which states that before the development of farming, people needed to store up more food energy, but doing so became less of an advantage as food became more abundant.