In many mammal species, larger size corresponds to longer lives. That's not the case with dogs, however. Credit: Brand X Pictures via Getty Images

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 isn’t always the case, breeds like the Great Dane generally don’t stick around as long as smaller relatives like golden retrievers or even pugs. Larger dogs are also much more prone to age-related health issues and diseases.…