A study of the genetic history of bones dug up in central Europe shows that humans generally remained lactose intolerant until 3,000 years ago

Researchers suggest that ancient Europeans weren't relying on dairy enough to develop the trait. "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," says researcher Ron Pinhasi. Instead, they might have been making cheese and yogurt, the processes of which break down lactose. The study focused on the remains of 13 individuals found in the Great Hungarian Plain who lived between 5700 BC and 800 BC. Researchers unraveled their genetic secrets by examining the petrous bone, which happens to be the hardest bone in the body and is found inside the skull where it protects the inner ear. As Pinhasi explains, "The 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." Teeth, fingers, and rib bones yield no more than 20%.