For most of human history in Europe, life moved slowly. After modern humans arrived there around 50,000 years ago, they lived for thousands of years in small groups, hunting animals and gathering plants.
Then everything began to change. Around 10,000 years ago, farming spread across Europe and people started settling down.
About 5,000 years after that, herders from the Eurasian steppes moved into Europe bringing cattle, wheels, and metal tools and weapons. This event brought the Stone Age to a close and opened the way for the Bronze Age.
From there, the pace of change only picked up. Cities emerged, empires spread, and over many centuries human societies became more crowded, more complex, and more connected.
A new study suggests that all of this upheaval may have changed not just how people lived, but how they evolved.
The researchers analyzed nearly 16,000 ancient human genomes and found signs that natural selection may have been acting on European populations much more strongly over the last 10,000 years than many scientists once assumed.
Ancient DNA changes things
For a long time, studies based mostly on the DNA of people alive today suggested that human genomes had been relatively stable over the past tens of thousands of years.
Modern populations such as western Europeans, East Asians, and Africans are genetically similar enough that the broad impression was one of slow change. But ancient DNA tells a more detailed story.
In the new study, instead of comparing only living people, researchers compared the DNA of ancient people from Europe and the Middle East with one another and with about 6,000 modern individuals.
That gave them a much better way to see how genetic variants rose or fell over time.
The study drew on thousands of previously published genomes, but what made it especially powerful was the addition of nearly 10,000 previously unpublished ancient genomes, most collected by a team led by Harvard University geneticist David Reich.
That enormous dataset gave the researchers something earlier studies lacked: enough ancient DNA to look for broad, population-level trends over time.
“This is the most important work I have been involved in for a decade. It is finally realizing the promise of ancient DNA to reveal as much about biology as history,” Reich said.
Selection after farming
The team found that after farming took hold around 10,000 years ago, 479 genetic variants became either more common or less common in Europe, a pattern that points to natural selection.
Once people began changing the world around them more dramatically, through farming, settlement, animal domestication, and later denser societies, their own biology seems to have started shifting more quickly too.
“The genome is under massive selection pressure over the last 10,000 years,” said Harvard University geneticist Ali Akbari, a co-author on the study. “Everything has changed about the way we live, and that’s reflected in our genome and how it’s trying to catch up.”
Variants linked to tuberculosis resistance became more common beginning about 6,000 years ago, then declined again over the last 3,000 years. Variants associated with higher body fat became less common.
Genes linked to red hair rose in frequency around 4,000 years ago. Variants associated with male pattern baldness became less common over the past 7,000 years.
“The genome is alive with signal,” Reich said, describing a “a period of unusually intense … and also fluctuating natural selection.”
The Bronze Age effect
One of the clearest patterns showed up around the Bronze Age, roughly 5,000 years ago.
That was a time when Europe’s population density began rising much more sharply. People were living closer together, and they were also living more closely with domesticated animals.
That kind of environment creates new disease pressures. The study found that many mutations tied to immune function, disease resistance, and autoimmune conditions rose quickly in frequency during that period.
“The Bronze Age probably saw massive change in pathogenic exposure, leading to selection touching genes related to immunity and host-pathogen interactions,” said Lluis Quintana-Murci, a population geneticist at the Pasteur Institute.
As humans changed how they lived, crowding into denser settlements and sharing space with animals, they also changed the disease landscape around them. Their genomes may have been responding in real time.
Interpreting the results
Not every result is easy to interpret.
The team also found that certain clusters of genes associated with traits like walking pace, and even genes correlated in modern data with things like income and years of schooling, became more common over the past 5,000 years.
That does not mean prehistoric people were somehow evolving for modern social outcomes. It means the genetic variants associated with those traits in present-day datasets may reflect some other underlying characteristic that mattered in the past.
Still, it is not yet clear what that characteristic would have been.
“This study represents almost a decade of intense work, but it’s really just scratching the surface,” says Harvard evolutionary biologist Annabel Perry, another co-author.
“They didn’t have college in the Neolithic, so what is the trait that’s really changing? This is an invitation for researchers to do the digging to find those associations.”
Study limitations and future research
The study is exciting, but not everyone is convinced the interpretation is settled.
One challenge is that shifts in gene frequencies can happen not only because of natural selection, but also because populations move, mix, and replace one another.
Europe’s history over the last 10,000 years included a lot of migration, and separating the effects of selection from the effects of ancestry is not always simple.
The team tried to account for that using methods borrowed from medical genetics, but some researchers think the issue remains open.
“The study is best viewed as offering amazing data and provocative hypotheses that will require much further scrutiny, rather than a settled account of adaptation in Eurasia,” concluded Arbel Harpak, a population geneticist at the University of Texas at Austin.
The study is published in the journal Nature.
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