Generally, in the animal kingdom, size means life. The bigger and badder an animal is, the longer it lives. There are exceptions, of course, but “survival of the fittest” is a phrase for a reason. A lion outlives a mouse, an elephant outlives darn near everything.
Within the dog community, however, things are different. Small breeds like the Chihuahua regularly live deep into the teens while a mighty mastiff or a Great Dane will rarely see a ninth birthday. But why do small breeds seem to last longer?
The question is also the answer. Small breeds literally “last” longer. In a 2013 research study by Cornelia Kraus, Samuel Pavard, and Daniel E. L. Promislow published in the American Naturalist, the scientists conclude that large dogs simply age faster than small dogs.
More wear and tear
Speaking to Pursuit, the University of Melbourne’s science journal, evolutionary biologist Mark Elgar said, “A larger dog, because of its size, may put more strain on its physiological processes, meaning they tend to wear out more quickly. Modern cars generally work well for eight or nine years, and then wear and tear sets in and they start falling apart. The speed with which they deteriorate varies between manufacturers. It’s the same with dogs.”
Basically, there’s more wear and tear on a large dog’s body. More weight on the joints. More strain in the heart to get the blood to the ends of those long limbs. And large dogs are larger, longer. A Great Dane, for instance, reaches its full height within a year to 18 months of age, while it can take another year for its body to reach full maturity. Basically, they’re big dogs quickly, without all the muscle they’ll eventually need to support that frame.
Adding another wrinkle to the shorter lifespans of our more massive friends is that large breeds seem to be more susceptible to life-altering health issues. This study found that “larger breeds died more commonly of musculoskeletal and gastrointestinal causes” than small dogs.
The Kraus study concludes that large dogs age at an accelerated pace, “as though their adult life unwinds in fast motion.” They may stay in “puppy” mode for a long time — picture that skinny, goofy Great Dane — but when they finally become “adults,” their lives fly by. The study even puts a number to how fast it can happen, showing that “an increase of 2 kg (4.4 lbs) in average body mass leads to a loss of about 1 month in life expectancy.” The bigger they are as adults, the shorter that time as adults might be.
Dogs are full of surprises
This isn’t to say that if you want a dog to be your companion for double-digit years you must stick to Pomeranians and dachshunds. Labrador retrievers and Australian shepherds regularly reach age 12 and beyond. And here’s the thing; dogs seem to live only to defy expectations. Painting an entire breed with a single brush is a great way to be proven wrong, and for every Yorkie who careens toward the age of 20, there’s a grey-faced old golden retriever nipping at their heels. Adopt the dog that fits your life and work to make their life as wonderful as they’ll make yours — however long that might be.
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