In Northern Spain, researchers have discovered clues to the identity of the victims of a mass murder committed 49,000 years ago. The bones of 12 men, women, and children may be the remains of an extended Neanderthal family that were killed and eaten by their fellow Neanderthals. Now, DNA analysis of the bones is providing rare clues into the family structure of these close cousins of modern humans. Researchers have long wondered why Neanderthals went extinct. Some think they lacked the genetic diversity to survive deadly viruses or other challenges. Others have proposed that their social groups were smaller and less sophisticated than those of modern humans.