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upstart writes in with an IRC submission for Bytram:

Why do small dogs live longer than big dogs?:

Professor Elgar says the answer to the puzzle of canine lifespans can be found in data that charts "the schedule" of a species' rate of ageing.

This reflects the relationship between the age of an individual and how susceptible it is to dying. So while larger species typically live longer than smaller species, within a species smaller individuals could outlive larger individuals.

And this is particularly important when it come to dogs. A millennia of domestication and breeding means that dog breeds can vary in body size by up to 50 times.

Professor Elgar says that the research comparing size and age-related mortality in dogs shows that larger dogs die younger because they age significantly faster than smaller dogs.

A large study of 74 dog breeds in North America concluded "the driving force behind the trade-off between size and lifespan is apparently a strong positive relationship between size and ageing rate.

"We conclude that large dogs die young mainly because they age quickly."

Professor Elgar says that 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."

Dog morbidity rate is also impacted—as it is for humans—by lifestyle.

Just as young men aged 18 to 25 are more likely to die by misadventure, a working dog like a kelpie or sheepdog is more likely to die in an accident than a schnoodle whose only occupation is to look cute in its favourite chair.

Professor Elgar says the rule of thumb is that "the average lifespan for quite large dogs is about seven years, and 14 years for smaller dogs."

Original Submission