The world's oldest genome shows when our ancestors had sex with Neanderthals. Analysis of a 45,000 year-old femur shows that modern humans and Neanderthals mated 52,000 to 58,000 years ago — a much smaller window than previously estimated (a 49,000 year span). It's the oldest-known human genome ever sequenced, revealing a mysterious population that once spanned northern Asia.

Image: Bence Viola, MPI EVA.