Dhaka, Oct. 14 -- Few animals show the link between size and lifespan as clearly as dogs. Within this one species, large breeds such as Great Danes typically die younger than small ones such as Chihuahuas. A new study indicates the reason may lie in how DNA changes with age in dogs.

Across mammals, bigger species like elephants usually live longer lives than smaller ones like mice, but within a species that pattern can reverse. Earlier comparisons across species linked certain biological mechanisms to exceptional longevity, but those are less suited to explaining differences among individuals within a species.

"We all know that big dogs usually don't live as long as small dogs, but we have not known whether their cells actually age fast...