Lactose intolerance in Europeans started over 5,000 years ago, according to a new study of the condition. Examining DNA from bones of prehistoric people is allowing researchers do determine when genetic traits, like lactose intolerance and skin color, first developed.

Skulls of 13 people who lived in Europe were studied, including the DNA code hidden within their structures. The oldest of these human remains dated to 5,700 years ago, while the youngest was dated to around B.C.E. 800.

The petrous bone, located in the inner ear of humans, is hard and well-protected from damage, making it an ideal structure from which to extract DNA from ancient people.

"[T]he high percentage DNA yield from the petrous bones exceeded those from other bones by up to 183-fold. 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," Ron Pinhasi of the UCD Earth Institute in Dublin, Ireland, said.

This study was one of the few able to examine DNA from a geographically-small population over the course of thousands of years, in order to determine how genetic changes affected people.

Ancient Europeans appear to have started drinking milk before developing the genes needed to properly process the beverage in adult bodies.

The investigation also revealed that significant changes in technology were reflected in the genetic code of humans, as civilization progressed from the late stone age, through the Bronze Age, and into the Iron Age. As civilizations in the area developed farming, and the ability to smelt metals such as bronze and copper, additional people came to live in the society, interbreeding with the native population, altering the genetic code of the humans in the area.

Lactose intolerance is the inability of a body to digest sugars contained within dairy products. It is a common condition, and symptoms include bloating, gas, and abdominal cramps. People who suffer from the condition usually experience these effects between half an hour and two hours after consuming dairy products.

"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. 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," Pinhasi told the press.

Study of the history of lactose intolerence among ancient Europeans was detailed in the journal Nature Communications.