Dogs seem to be breaking a rule found throughout the animal kingdom that bigger bodies mean longer lifespans. For example, elephants live to be 70 years old, and mice only live a fraction of that lifespan. However, dogs are the opposite, as small dogs live much longer than large dogs. According to some researchers, humans are partly responsible for this longevity.
Cause of the evolutionary delay of natural defenses against cancer
Around 27,000 to 40,000 years ago, domestic dogs as we know them started as wolves and were bred by humans to perform specific tasks, such as hunting, herding sheep and looking cute. . Thus, these traits are acquired by selectively crossing dogs with these traits with other dogs with the same traits, and then crossing the most favorable offspring from their litters with other dogs with the same traits. Over time, dogs have been divided into different breeds of different sizes and builds, from Chihuahuas and Dachshunds to Great Danes and Newfoundlands.
A study published in the journal American Naturalist revealed that selective breeding to make large, large-breed dogs made them more susceptible to cancer. Therefore, they are more likely to die prematurely. The researchers said higher cancer rates in large dogs could be the result of rapid reproduction and growth. This leads to an evolutionary delay in the natural defenses against cancer.
The disposable soma theory
The average lifespan of a dog is 11 years. But thanks to the care you give your best four-legged friend, it tends to increase. A surprising characteristic persists. In general, larger dog breeds have shorter lifespans than smaller ones. Research by the American Kennel Club confirms that small dogs live a few years longer than large breeds. For example, Chihuahuas live 15-17 years and Great Danes only 8-10 years.
As for biologists, they refer to a theory of aging known as life history optimization or disposable soma theory.
This theory is based on the concept that if you invest all your resources and energy in growth and reproduction, you cannot invest them in cell repair and the fight against cancer, said the co-author of the paper. article, Jack da Silva, a specialist in genetic evolution at the University of Adelaide, Australia. Researchers suggest that most of the current 400 breeds of dogs, which have emerged over the past 200 years, could be adapted to a longer lifespan. This especially concerns large dogs. This can be done naturally or by breeding selected dogs with lower cancer rates, but there is a price to pay, however: that of litters that are likely to be more limited in number.
