Large dog breeds die younger. Biologists think they finally know why.

A first-of-its-kind genetic analysis of dog breeds presents the clearest insights into why larger dogs rarely outlive their smaller relatives. According to a team of biologists writing in the journal Science, the longstanding size–age correlation is likely due to “jumping genes” that inevitably begin sowing chaos inside canine DNA as dogs get older.Most dog owners are aware of an unfortunate rule of thumb—the bigger the pooch, the shorter the lifespan. While this trend is