Have you ever wondered why you seem to know a lot more elderly Chihuahuas than aged Rottweilers? It's just a fact of life that small dogs, if they escape disease or misadventure, live longer lives than larger ones. This trend has puzzled veterinary researchers for as long as we've been fussing over our faithful four-legged friends, and it's a mystery that hasn't been definitively solved.

Conventional wisdom in the animal world dictates that between species, larger animals live longer than smaller ones — an elephant can live into its 70s while a mouse might have only a year or two to do its earthly business. However, the opposite seems to be true within single-species subsets, and our dogs, although they come in lots of different shapes and sizes, are all the same species. The average l

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