It’s been more than five years since scientists sequenced the first ancient human genome, discovered in a 4,000-year-old tuft of hair. According to a report from Nature.com, ancient genomes since then have allowed scientists to fill in a number of gaps in early human history.

A recent boom in genetic analysis of DNA dating back to the Bronze Age has brought many new facts to light about the years between 3000 B.C. and 1000 B.C. Archaeologists have found a wealth of artifacts that have taught them about Bronze Age technologies and traditions, from the use of elaborate weapons and horse-drawn buggies to ancient burial traditions. We have a pretty good idea of what happened in the region between the Black and Caspian Seas during this time, but there is only so much information that can be garnered from artifacts.

Enter DNA testing, which has allowed scientists to figure out not only what people were doing in the Bronze Age, but also exactly who was doing it and where they came from. The mass genome approach has allowed scientists to paint an increasingly accurate image of the past, shedding light on ancient diets and diseases.

A team of palaeogenomicists led by Morten Allentoft and Eske Willerslev at the Natural History Museum of Denmark in Copenhagen have sequenced over 100 genomes of people who are believed to have lived throughout Eurasia during the Bronze Age. The sequences offered information that researchers could only previously dream about. The scientists found evidence of migration in the form of a massive genetic shift in northern and central Europeans. According to the evidence they observed, a mass migration from the Yamnaya culture had occurred somewhere around 2000 B.C. Scientists believe this migration was partially responsible for the spread of Indo-European languages throughout Western Europe.

Among the most interesting conclusions of the new DNA studies? Scientists have determined that the Yamnaya migration directly introduced the genes responsible for lactose tolerance – which may have something to do with Europe’s love affair with cheese, chocolate, and creamy butter.