Dog Duration

There's a persistent urban legend—or, old wives' tale, as some folks might put it—that for every year a human lives, a dog experiences seven years. People can live, on average, for 70-90 years, unless they experience circumstances of deprivation or disease. In contrast, a dog lives about 15 years, depending on breed and health. Big dogs die earlier than little dogs.

So this form of urban legend has it that a dog's equivalent human-like age is about seven times that of a human. Thus, a three-year-old dog is comparable to a 21-year-old human, and a 10-year-old dog is equivalent to a 70-year-old human.

That urban myth persists, along with similar stories, such as daddy longlegs spiders being poisonous, or alligators thriving in the New York City sewer system (having been brought north as small pets from Florida and then released in toilets, when they grew too large). Similarly, the belief in Scotland's Loch Ness Monster persists, despite no real evidence for its existence. Another myth: it was once claimed that microwave ovens will harm you—even sterilize you.

The urban legend of a dog's equivalent human age being seven times its actual age was recently refuted by a research group that examined over 100 Labrador retrievers, who were from four weeks to 16 years old. The research examined the dogs' DNA methylation—a mechanism that influences one’s genes by turning them off and on. It is a kind of “epigenetic clock,” which describes the aging process of a creature.

As a result of this study, dogs actually age much faster than the seven-times-human formula when they are young. For example, when a dog is 5 years old, its equivalent human age is not 35 (7 X 5), but more like 53. They seem to be in a hurry to get old.

But as a dog moves into middle age, its rate, relative to humans, slows down. So, for example, at a dog’s age of 15 its human-age equivalent is not the old concept of being like 105 (7 X 15), but more like a human who is not quite 75 yet.

Thus scientific research debunks one more urban legend. But be careful when you sit on a toilet in New York City... one of those alligators might be waiting. Also, look out for those poisonous daddy longlegs spiders, and never go for a swim in Loch Ness… the monster awaits.