3 min read

Why Do Small Dogs Live Longer Than Big Dogs?

It's a little complicated.

The larger the animal, the longer the life: That's how things normally go with animal life spans, right?

Elephants, for example, can live into their 70s, while the life span of a mouse is only about two years.

But this general rule is totally and mysteriously broken when it comes to our canine companions.

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"The question of why smaller dogs tend to have longer life spans is a fascinating one," Dr. Louise Murray, vice president of the ASPCA Animal Hospital, told The Dodo. "Contrary to the general rule of thumb that mammals with higher metabolic rates tend to have shorter life spans, higher energy expenditure in dogs seems associated with longer life."

Small dogs (under 20 pounds) tend to live around three years longer than big dogs (over 90 pounds), one recent study found.

Another study released in 2013 noted that where smaller dogs live to be about 10 to 14 years old, bigger dogs live just 5 to 8.

But why?

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Murray said that there isn't a solid answer yet, however, to explain why smaller dogs live longer.

But some European researchers have a theory that this anomaly has to do with dogs being domesticated by artificial breeding (rather than leaving things to natural selection), a practice that started about 9,000 generations ago. Artificial selection can create a less harmonious relationship between size and the aging rate in dogs, causing large dogs to age quickly and die a few years before their smaller counterparts.

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These scientists looked at data from 74 breeds of dogs and found that "large dogs die young mainly because they age quickly."

Larger dogs are also prone to certain health disorders linked to aging quickly and artificial breeding. That's all the more reason to love dogs of all shapes and sizes — especially those who have more diverse genetics, the mutts.

If you're ready to give a loving and furry family member — big or small — a forever home, check out Adopt-a-Pet.