Bronze Age humans racked up travel miles

Humans’ Bronze Age ancestors were big travelers, but probably not so fond of dairy.  

A large-scale study of ancient genetics, published June 11 in Nature, provides evidence for migrations and lactose intolerance in Bronze Age cultures in Eurasia.

The Bronze Age, about 3,000 to 5,000 years ago, was a time of big cultural changes, says study coauthor Morten Allentoft, a geneticist at the Centre for GeoGenetics at the Natural History Museum of Denmark in Copenhagen. Archaeologists have argued about whether those changes came from the spread of ideas or the physical migration of ancient humans, Allentoft says.

Allentoft and his colleagues analyzed over 600 samples of Bronze Age human remains, mostly teeth, from Europe and Asia. Only 101 specimens provided usable DNA. The scientists extracted genetic material from the tooth’s hard outer layer, which preserves DNA better than the soft interior.

The study was unusually large in scale, says geneticist and coauthor Martin Sikora, also of the Denmark museum. That allowed the scientists to ask broad questions about the relationships between genes and cultures.

Allentoft says the most important finding is that the transition into the Bronze Age “certainly involved large-scale human migrations.” Geneticist Iosif Lazaridis of Harvard Medical School says that previous studies have indicated such migrations, though this work includes some new data. This study provides new evidence for eastward migration, says geneticist David Reich, also of Harvard Medical School. The findings suggest that the Yamnaya culture, a population of traveling herders that originated around 5,000 years ago in what is now southwestern Russia, is genetically indistinguishable from the slightly younger Afanasievo culture, which lived thousands of kilometers farther east.

One Eurasian Bronze Age culture showed genetic similarity to present-day Native Americans. This finding opens up new questions about human ancestry, says Sikora.

Only around 10 percent of Bronze Age Europeans had the ability to digest lactose, the study suggests. This percentage is surprisingly low, because these people had farming cultures with cattle, says Allentoft. Lactose tolerance is associated with a single change on the human lactase gene. The frequency of this genetic change must have increased dramatically after the Bronze Age, Allentoft says, because tolerance is widespread in Europe today. Previous research also has suggested this later onset of lactose tolerance, says Reich.

Allentoft says that large-scale studies like this one could help researchers understand other time periods, before and since the Bronze Age. The Bronze Age marks the last large genetic shift between ancestral and present-day humans, he says. “Looking at the Bronze Age could hold the key to our common identity, for Europeans and Asians of today.”