Why small dogs like Chihuahuas live LONGER than big breeds like Great Danes, according to science

Our furry friends come in all shapes and sizes, from the tiny handbag-sized Chihuahuas to the house-trained Great Danes.

Unfortunately, it is fairly common knowledge that the life expectancy of the larger breeds is often much shorter than that of the smaller ones.

Many different explanations have been put forward for this, but scientists at the University of Adelaide think they have finally found the real answer.

After analyzing the most common causes of death in 164 dog breeds of different sizes, they found that larger animals are more susceptible to cancer.

They say this is because the natural defenses against cancer in dogs have not been able to keep up with the selective breeding of giant dogs.

“When we analyzed these datasets, we found that larger dogs were more likely to die from cancer at a younger age compared to smaller dogs,” said study author Dr Jack da Silva.

‘Larger dogs don’t necessarily age faster than the smaller breeds, but the study did show that as the breed’s average body weight increased, so did the risk of cancer.

“We believe the relationship between a dog’s body size and their lifespan may be due to an evolutionary lag in the body’s defenses against cancer, which the rapid and recent selective breeding of larger dogs has failed to keep up with.”

A Yorkshire Terrier, which can grow up to 3.17 kg, can live up to 16 years.

But an English Mastiff, a gentle giant that can weigh as much as 250 lbs (113 kg), tends to only live between six and ten years.

For their study, published in The American naturalistthe researchers wanted to find out why there is such a huge and consistent difference in the lifespans of large and small dog breeds.

They analyzed published data on longevity and causes of death for different races from around the world.

Previous studies have attributed the shorter life expectancy of larger dogs to higher metabolic rates and their increased risk of certain health problems.

Some also said that their body size causes them to age faster than smaller dogs.

However, the team found that was not the case and instead revealed that the larger the dog, the more likely it is to die from cancer at a young age.

They say this is because over time humans selectively bred dogs to be as large as possible so they could guard livestock or hunt big game.

In addition, many of these breeds are now popular as pets because they look imposing, majestic and intimidating.

But as a result, dog breeds have evolved to extreme sizes much faster than natural evolution would allow.

This has meant that their bodies’ anti-cancer defenses haven’t had a chance to evolve in proportion to their size, so large breeds are more susceptible to the disease.

The conclusion is consistent with an aging theory known as “life history optimization” or the “disposable soma.”

“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,” said Dr. da Silva.

‘In all organisms the focus is on early reproduction, even if this is at the expense of maintaining and repairing the body and living longer.’

While this is sad news for large dog lovers, Dr. da Silva is optimistic that large breeds will eventually develop cancer defenses to match their smaller counterparts.

“This can happen naturally or through selective breeding, as people focus on breeding larger dogs that have less cancer and thus longer lifespans,” he said.

“Most of the 400 or so dog breeds we know today only came into existence in the past 200 years.

“Larger dogs haven’t had time to develop better cancer defense mechanisms to match their size.

“This can still happen, but it can be at the expense of reproduction.”

This is due to life history optimization theory, as the greater energy investment in cancer defenses means they have less available to produce large litters.

The researchers hope their findings could ultimately benefit both human health and dogs.

Dr. da Silva concluded: ‘Dogs provide a good model for studying aging in humans.

“Dogs, like humans in the industrialized world, live in an environment that protects them from accidental and infectious causes of death and are thus more likely to die from age-related diseases, such as cancer.”