Why Do Smaller Dogs Live Longer Than Big Dogs?
It's a weird paradox — though larger animals usually live longer than smaller animals on a species level (via National Institutes of Health), small dogs typically live longer than large dogs. In fact, this is true for lots of species, including humans. Studies have shown that short people tend to have a longer life expectancy than taller people, according to Healthline. While small dogs like Jack Russell terriers, miniature poodles, and the lhasa apso have an average lifespan of 14 years, bulldogs, great danes, and mastiffs have a lifespan of 8 or fewer years (via PetMD).
This might be because large dogs grow a lot in a short time, which may increase the activity of free radicals, the unstable atoms that react with and damage body cells, according to Mental Floss. A great dane, for instance, will be one hundred times their birth weight a year after their birth — the equivalent of a 1–year-old human weighing 750 pounds.
Victims of rapid growth
The quick growth means that large dogs age much more quickly than their ancestor, the gray wolf, which can live to be 15 or more in captivity, according to the National Wildlife Federation. A 2013 study in the American Naturalist (via Mental Floss) found that "large dogs age at an accelerated pace, suggesting that their adult life unwinds in fast motion." (It's enough to make you run and hug your rapidly aging pup).
This isn't the only reason that larger dogs tend to live compressed lives. According to the American Kennel Club, large dogs are also more prone to cancer because of their rapid growth, as well as certain health issues, like musculoskeletal and gastrointestinal disorders. It's a side effect, apparently, of rapid selective breeding.
If you have a large dog, don't despair. There are things you can do to lengthen your pet's lifespan, including annual professional dental cleanings by a veterinarian and keeping your dog at a healthy weight for their size.