Dogs provide a much better model for studying human aging. They are unique in sharing our environment. Pet dogs live in our homes with us, breathe the same air we do, and often share our exercise routines, to some degree. “They’re eating our food, they’re walking on our lawns with pesticides, they’re drinking whatever is in our water,” says Elaine Ostrander, who leads a team studying human and dog genetics at the National Human Genome Research Institute of the National Institutes of Health in Bethesda, Maryland.
They also develop many of the same age-related diseases that we do. Technically, most pet dogs die as a result of euthanasia. But in most of these cases, the animals have cancer, says Kaeberlein. Dogs can also develop heart disease in later life, just like humans. There are some differences—dog brains aren’t the same as human ones, although the animals do seem to develop a form of dementia. And dogs don’t tend to develop vascular diseases as humans do.
But there are plenty of similarities. Both dogs and people experience aging of the immune system and an increased risk of kidney disease as they get older, says Kaeberlein. “It seems like, at the level of individual age-related diseases, it’s very, very similar,” he says.
One main difference is that aging is a much quicker process in dogs—it happens around seven times faster than in humans, though small dogs generally live longer than larger ones. (It’s not quite the case that one year of dog life is equivalent to seven human years, however. Dogs seem to age more rapidly than humans do in their first years of life, and the pace slows as they get older.)
While this can be devastating for devoted owners, it is useful for researchers, who are able to study the effects of potential anti-aging drugs over the entire lifespan—something that is much more difficult to achieve in people.
Another unique feature of dogs is their incredible diversity. Only in dogs do we see such extreme differences in size and appearance within a single species. A Great Dane is around 20 times heavier than a Chihuahua, for example. A Pomeranian looks nothing like a Staffordshire bull terrier.
This variation makes the animals particularly fascinating to geneticists like Ostrander. “Dogs were only domesticated around 30,000 years ago, and most breeds have only been around since the Victorian times,” she says. It was around the mid-1800s that modern dog breeding took off, and owners bred dogs for aspects of their appearance, such as a curly coat or a flat face. Breeders essentially selected dogs with genes for these features.
Because many such modifications only occurred in the last hundred or so years, genetic differences between today’s dog breeds are likely to have a significant impact on these traits—and on the risks of certain diseases that vary between breeds.