Scientists explain which dog breeds live less than others

Scientists from the University of Adelaide have explained for the first time why large dogs live less than smaller breeds.

Their study, published in The American Naturalist, showed that selective breeding for size made large breeds more susceptible to cancer.

The researchers analyzed data on the life span and death of 164 dog breeds, ranging in size from Chihuahuas to Great Danes. They found that larger dogs are more likely to die of cancer at a younger age than small dogs.

"We think the link between a dog's body size and its life expectancy may be due to an evolutionary lag in the body's defenses against cancer," said Dr. Jack da Silva, a researcher at the University of Adelaide's School of Biological Sciences.

"This theory is based on the idea that if you invest most of your resources and energy in growth and reproduction, you can't also invest them in cell repair and cancer defense. In all organisms, the focus is on early reproduction, even if it comes at the expense of maintaining and repairing the body and living longer," he added.

The results of the study are in line with the theory of aging known as life cycle optimization or "disposable soma". This theory states that organisms that invest more resources in growth and reproduction age faster and have a shorter lifespan.

The results of the study can be useful when considering human aging. Dogs are a good model for studying human aging because they live in an environment that protects them from accidental and infectious causes of death, and thus they are more likely to die from age-related diseases such as cancer.

While the study's findings may be a concern for large dog owners, the researchers predict that larger breeds will eventually develop better cancer-fighting genes.

"Most of the 400 or so dog breeds we know today were created only in the last 200 years. Larger dogs have not had time to develop better cancer defense mechanisms to match their size. It could still happen, but it could be detrimental to reproduction," said Dr. da Silva.

The scientist predicts that larger breeds will adapt and extend their lives, but based on the theory of aging, they are likely to have smaller litter sizes in the future.

"This may happen naturally or through selective breeding as people focus on breeding larger dogs that have lower cancer rates and therefore longer life span," he said.

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