An analysis of ancient teeth is giving scientists a rare peek into interactions between human relatives hundreds of thousands of years ago. A new study reveals genetic clues about a human ancestor called Homo erectus. Researchers found two new mutations in ancient proteins from 400,000-year-old teeth. One hints at ancient mixing and mingling between Homo erectus, an extinct group of human cousins called the Denisovans and modern humans. Finding more fossils can help firm up the human evolutionary story. The study was published Wednesday in the journal Nature.