All modern Indo-European languages are descended from a single tongue called Proto-Indo-European, or PIE, spoken by a people who lived from roughly 4500 to 2500 B.C., and left no written texts. The question became, what did PIE sound like?
A research team led by Mark Pagel at the University of Reading in England has identified 23 "ultraconserved words" that have remained largely unchanged for 15,000 years (Washington Post)