One of these rapid examples of evolution was hidden away in the drawers of Chicago’s Field Museum. “Museum collections allow you to time travel,” Stephanie Smith, a study co-author and mammalogist at the Field Museum, said in a statement. They found small–but significant–changes in the rodents’ skulls over the past 100 years. The bony bumps in the voles’ skulls that hold the inner ear became smaller over time. Changes in climate didn’t explain the alterations in the rodents’ skulls, but the degree of urbanization did.