A study published Thursday in the journal Nature Communications reveals that Europeans became lactose intolerant over 5,000 years ago, a discovery made through the analysis of DNA from the bones of the prehistoric people.

Tech Times reports that researchers of the study examined the skulls of 13 people who lived in ancient Europe, including each individual’s DNA code extracted from the petrous bone. The human remains in the study range back from 5,700 years ago to around B.C.E. 800.

“[T]he high percentage DNA yield from the petrous bones exceeded those from other bones by up to 183-fold,” said co-author Ron Pinhasi, from the University College Dublin Earth Institute and School of Archaeology, in a recent statement. “This gave us anywhere between 12% and almost 90% human DNA in our samples compared to somewhere between 0% and 20% obtained from teeth, fingers and rib bones.”

According to the statement, the high percentage DNA yields made it possible for the team to analyze skeletons from the same region to compare and contrast genetic markers such as lactose intolerance.

“Our findings show progression towards lighter skin pigmentation as hunter and gatherers and non-local farmers intermarried, but surprisingly no presence of increased lactose persistence or tolerance to lactose,” said Pinhasi. “This means that these ancient Europeans would have had domesticated animals like cows, goats and sheep, but they would not yet have genetically developed a tolerance for drinking large quantities of milk from mammals.”

Results from the study also suggest significant technological changes reflected in the genetic code, as civilization transitioned from the late stone age through the Bronze Age and Iron Age.

“[O]ur results also imply that the great changes in prehistoric technology including the adoption of farming, followed by the first use of the hard metals, bronze and then iron, were each associated with the substantial influx of new people,” said co-author Dan Bradley from the Smurfit Institute of Genetics, Trinity College Dublin. “We can no longer believe these fundamental innovations were simply absorbed by existing populations in a sort of cultural osmosis.”