For the first time, scientists have shed light on why larger dog breeds tend to have shorter lifespans than their smaller counterparts. Researchers at the University of Adelaide have discovered that selective breeding for size has made large breeds more susceptible to cancer.
The groundbreaking study, published in the journal The American Naturalist, is the result of a year-long comparative analysis using published data on 164 dog breeds from around the world, including chihuahuas and Great Danes.
Dr. Jack da Silva from the University of Adelaide’s School of Biological Sciences and his team examined the causes of differences in lifespan and death among these various breeds.
“When we analyzed these data sets, we discovered that larger dogs were more likely to die from cancer at a younger age when compared with smaller dogs,” said Dr. da Silva.
The study showed that although larger dogs did not necessarily age faster than smaller breeds, their rates of cancer increased as their average body weight did. The researchers believe that the relationship between a dog’s body size and its lifespan could be attributed to an evolutionary lag in the body’s cancer defenses.
According to Dr. da Silva, these defenses have been unable to keep up with the rapid and recent selective breeding of bigger dogs. The shorter lifespans of larger breeds were found to be consistent with a theory of aging known as life history optimization or the “disposable soma.”
Dr. da Silva explained that this theory is based on the idea that if an organism invests most of its resources and energy into growth and reproduction, it cannot also invest in cell repair and cancer defenses. Consequently, the focus is on reproducing early, even if it comes at the expense of maintaining and repairing the body and living longer.
The findings of the study have implications beyond the canine world, as dogs serve as a good model for studying aging in humans. Dr. da Silva noted that dogs, like humans in industrialized societies, live in environments that tend to protect them from accidental and infectious causes of death, making them more likely to die from age-related diseases like cancer.
While the results may be concerning for owners of large dogs, the researchers predict that bigger breeds will eventually evolve to develop better cancer-fighting genes.
Dr. da Silva said that most of the 400 or so dog breeds we know today have only been established in the past 200 years, so larger dogs have not had time to evolve better cancer defense mechanisms to match their size. He believes that this evolution could still occur, but it may come at a cost to reproduction.
Dr. da Silva predicts that larger dog breeds will adapt and extend their lifespan, but based on the theory of aging, they are more likely to have smaller litter sizes in the future. “This may occur naturally or through selective breeding, as people focus on breeding larger dogs that have lower cancer rates and thus greater longevity.”
Dr. da Silva is now investigating the connection between litter size, cancer rates, and lifespan in dogs and other mammals to further understand the implications of selective breeding and body size on life expectancy.
The average lifespan of dogs varies depending on factors such as breed, size, and overall health. Typically, smaller dog breeds tend to live longer than larger breeds.
For small breeds, the average lifespan ranges from 12 to 16 years. Some common small dog breeds and their average lifespans are:
For large breeds, the average lifespan ranges from 8 to 12 years. Some common large dog breeds and their average lifespans are:
Please note that these are just average lifespans and individual dogs may live longer or shorter lives depending on various factors such as genetics, diet, exercise, and veterinary care.