Where did you first hear the idea that seven dog years are equal to one year of human life?
No one knows who came up with it, but it first appeared in math textbooks in the 1960s, when students were asked to calculate the age of a dog using the 7:1 ratio. Apparently we were indoctrinated at a young age.
But those textbooks were barking up the wrong tree.
According to scientists, the myth that one calendar year is equal to seven dog years is just that – a myth. Since dogs age differently, depending on their breed and stage of life, the real calculation is far more complicated.
We all know that dogs are amazing: last week Care2 brought you the story of the pit bull who saved his owner from a burning house. Dogs can also use their super sniffers to track down invasive weeds, and comfort dogs have performed miracles working with the families of Newtown and Boston.
Dogs are also the most diverse mammal species on the planet. Once fully grown, they can vary in weight from six pounds to 200 pounds and have widely differing body shapes and hair types.
So it makes sense that there is a big variation among breeds in terms of life expectancy.
Here’s where the calculation gets more complex. Big dogs die younger than smaller breeds, meaning an adult chihuahua will age less every calendar year than a great dane, for example.
How does this work? The Telegraph explains:
But the equation is complicated further by the fact that smaller dogs also mature more quickly than larger ones, meaning that in the early stages of life they age faster, experts said.
This means that after two calendar years, a smaller dog is “older” than a larger one – but after five years it becomes “younger” in relation to its total lifespan.
Dr Kate Creevy, assistant professor of internal medicine at the University of Georgia told the BBC that once the varying rates of ageing at different stages of a dog’s life and its overall life expectancy are taken into account, the animals on average age about six, not seven years for every human year.
This is actually the opposite of what we see in most mammals: gorillas, whales and lions tend to live much longer than rats, mice, and voles. If that happened with dogs, great danes would live longer than chihuahuas, but actually it’s quite the opposite.
From the BBC:
“Small dogs reach skeletal and reproductive maturity sooner than larger breeds. Once they’ve achieved those measures of adulthood they carry on to live longer,” says Dr Kate Creevy, assistant professor of internal medicine at the University of Georgia.
What this means is that small dogs have a shortened juvenile period and an extended adulthood, while large dogs can take two years to achieve their fully mature size, but then may only live another four or five years.
You can click here to find a chart that will help you figure out your dog’s true age.
Across the spectrum, as Creevy points out, six is a more accurate number for the number of dog years that make up a human year.
But depending on whether your favorite pooch is a bulldog, a border terrier or a chihuahua, the actual growth period and life expectancy will vary greatly.
Next time someone talks about “dog years,” let them know it’s much more complicated than that!
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