Why Don’t Dogs and Cats Live as Long as Humans?

When you’re a vet, it’s not uncommon for an owner with a sick or dying pet to look at you, usually with tears in their eyes, and tell you they wished their dog or cat could live as long as they did. Why is it that the lifespans of dogs and cats are so much shorter than those of humans? Why can’t they stay with us longer?

To answer this, consider that everything about a dog or cat’s life, from their growth to their ability to learn, is accelerated.

Tooth development is a great example of this. Puppies and kittens are born with no teeth, begin to acquire their baby teeth in as little as 3 weeks, and have all their baby teeth by 45 days. Puppies and kittens generally have all of their adult teeth by the time they are 6 months old. Compare that to the development of humans, in which it can take 4 to 7 months for the immature (baby) teeth to start coming in.

Another way that growth is accelerated is in reproduction. Dogs and cats can be reproductively active as young as 6 months. When a dog or cat gets pregnant, they deliver their young in 60 to 65 days, often producing a litter ranging from a few to over a dozen offspring.

All of this expedited growth means that the bodies of dogs and cats do an immense amount of work that can hasten the aging process. Consider, too, that the processes involved in day-to-day life also require a lot of resources. Humans have a normal body temperature of approximately 98.6 degrees Fahrenheit (F), but dogs and cats maintain normal body temperatures in the 100.5 to 102.5 degrees F range. Those extra few degrees mean your dog or cat’s body is working extra hard every day, even when they are fully grown. In addition, the metabolism of dogs and cats is much higher than that of humans, who burn calories at about half the rate of the most common animal companions.

With all this acceleration, the senior years start early. For cats, it may be as early as age 8; for dogs, the senior age frequently starts at 4 or 5 years for large or giant breed dogs or 8 or more years for small breed dogs. The lifespan of some large breed dogs can be as little as 7 years, such as the case with Great Danes.

This still doesn’t totally answer the question of why the lifespans of dogs and cats are so much shorter, though, so we spent hours of research and called a number of professors and professionals. As it turns out, when all was said and done we learned that no one really knows why this happens.

Scientists suggest that a combination of genetics, inbreeding, metabolism, and evolution are all components of why a dog or cat’s life span is so much shorter than a human’s.

A study published in the Proceedings of the National Academy of Sciences by
Professor Herman Pontzer of Hunter College, New York, helped to give us some insight. Pontzer and his associates worked with 17 primate species to determine how the body used energy and to characterize their overall metabolic rates. The results of their study showed that the lower metabolic rate of primates, and thus humans, was associated with a prolonged lifespan (compared to those of dogs and cats).

Current research does not have a definitive answer to the question of why dogs and cats don’t live as long as humans. However, it has enabled us to enrich the lives of our pets so they can enjoy every moment to the fullest. We may never be able to give our animal companions the same length of life that we have, but we are better equipped than ever to make every minute special for them.