Myth Bust: One Dog Year Does Not Equal Seven Human Years

This just in: One dog year will no longer equal seven human years.

Well, not just in. Animal scientists have known that this ratio is not correct for a long time, but the myth persists.

Dog years were not always presumed to equal 7. An inscription at Westminster Abbey from the 13th century puts the ratio at 9 to 1, noting that dogs live nine years and men 81. An18th-century French naturalist, Georges Buffon, calculated that dogs can live to 10 or 12, and man to 90 or 100. 

So, where did the whole myth about a dog year being equal to 7 human years get started? No one knows for sure. But a pretty good guess is that it has its origins in business. "My guess is it was a marketing ploy," says William Fortney, a veterinarian at Kansas State University, told the Wall Street Journal. "[It's] a way to educate the public on how fast a dog ages compared to a human, predominantly from a health standpoint. It was a way to encourage owners to bring in their pets at least once a year."

But as Business Insider recently pointed out, the math does not even make sense when you think about it. "If humans aged seven times slower than dogs, then many of us would be able to reproduce at age 7 and live to be 150," number cruncher Jessica Orwig writes. "Obviously that's not the case."

Dogs tend to reach sexual maturity after one year of life, so that year alone is more like 12-15 human years. So, first of all, dogs age faster in the first year of life. By age 2, dogs are fully mature, and old enough to vote, not a right you'd want to extend to human toddlers. Add to that complexity that smaller breeds mature even faster than larger dogs, and that for dogs, unlike the rest of the animal kingdom, size is inversely related to life span. Dog lifespans average anywhere between 8 and 16 human years, with smaller breeds outliving large ones.

But don't despair, you can still calculate your dog's age, and place the appropriate number of candles on your pup's birthday meatloaf. It's just no longer a case of simple multiplication, since dogs age faster in early years, and slower in later years, (wouldn't it be nice if human aging slowed down in later years, or halted!) To get a more accurate sense of your dog's age, you'll need to know your dog's weight, because that determines whether the dog is small (20 pounds or less), medium (21-50 pounds) or large (more than 50 pounds.) Tip: To weigh your dog, first weigh yourself, then pick up your dog, and get on the scale. Then subtract your weight.

Click here for a handy-dandy chart that will help you figure your dog's approximate age.


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