The Cost of Reproductive Investment on Canine Life Span

By: Jentry Allen, Isabella Caldarone, Jacqueline Foley, and Nicole Godbout (Stonehill College, BIO323: Evolution, Spring 2023)

Dogs are said to be a man’s best friend as they are wonderful companions and can be trusted like no other pet; they are loyal to a fault. We find comfort in our dogs, maybe even purpose. Some people are willing to put their lives in the hands of dogs, allowing them to be their eyes, tell them if a food contains an allergy that may cost them their life, and inform a person if they are on the brink of an epileptic attack so that they may find a safe space and be prepared. An article from The American Naturalist titled, “High Investment in Reproduction is Associated with Reduced Life Span in Dogs”, discusses research on this ever-reliable friend and pet that shows a pattern in their life span in relation to offspring production. It was found that higher reproductive investment, or the work and energy that goes into reproduction, causes a decrease in canine life span. Additionally, it was discovered that this effect on life span was greater for larger dog breeds. With breeders today who want to breed more and larger puppies, we questioned the possible evolutionary effects of artificial selection, or the act of humans breeding animals to achieve a certain characteristic. If a breeder selects for a larger litter with larger puppies, the reproductive investment will be higher, and in theory, the life span of the mother will be decreased. Hear more about our discussion on this topic on the Everyday Evolution podcast!

A short podcast summarizing the article
Artificial selection, in addition to other forms of selection, has led to hundreds of dog breeds. Artificial selection is the process in which humans breed animals or plants to obtain a desired trait and is often performed by breeders. Image source.

The Research
A 2022 study published in The American Naturalist by Drs. Iker Bargas-Galarraga, Carles Vilà, and Alejandro Gonzalez-Voyer, investigated the impact of reproduction on the life span of dogs. They researched factors that contribute to a dog’s life span and collected data from previous research that included 253 dogs, representing 92 breeds in total. The researchers looked specifically at the life span of the dog, the weight of both adults and newborns, litter size, and growth, then used various forms of statistical analysis to see how those factors affected life span. The weight of the adults were the mean weight of the males and females combined for that specific breed. Additionally, growth was determined by subtracting average newborn weight from average adult weight.

The Results
In the paper, it is stated that the “…results also show that reproductive investment negatively impacts life span, and more strongly so in large breeds, an effect that is not merely a correlated response of adult size.” Although the quote uses a lot of scientific language, it is saying that the more energy a dog puts into reproducing, the shorter the dog’s life will be. The more puppies the mothers have and the larger those puppies are, the more her life span is affected.

Diagram of lifespan versus offspring production. The more children an organism obtains from one pregnancy, the shorter it will live on average. Image from

The Consequences
Breeders purposely pick dogs that have large litters of sizeable puppies so that they produce as many as they can sell, and the larger dogs are considered to be “healthier” to potential buyers. Breeding a dog repeatedly has been proven to shorten its life span as a dog that is constantly having litters of puppies will never outlive a normal dog of the same breed. There is nothing wrong with selling puppies, but the health and quality of life for the mom is also something to take into consideration. Additionally, through evolution, the children of the overbred mothers could end up with shorter life spans themselves. Adopting a dog from a shelter is always something to consider over buying from a breeder as the shelter is trying to give the animal another chance at life. A breeder, on the other hand, is making money while shortening the life of another animal. It should be mentioned that not all breeders are doing this, and some truly care for their dogs above all else.

The Interview
When asked about his opinion on artificial selection and breeding, Dr. Bargas-Galarraga said the following:
“It is also likely that, historically, humans have not always selected and bred dogs ethically. This may partly explain the enormous diversity of dogs today: some breeds live less than others, and some breeds suffer from or get sick from very specific things compared to others. I am not a veterinarian, but I understand that there are currently efforts to improve these circumstances through constant communication between owners, breeders, kennel associations, and veterinarians.”

When asked about what applications to the outside world his research has, Dr. Bargas-Galarraga answered:
“To imagine applications with this information is not a straightforward process. Rather, our work provides reasons to further investigate the costs of reproductive investment and the potential effect this has on lifespan in other animals, including humans. For example, in order to reproduce, the body triggers a physiological cascade of signals, some of which could be related to individual aging. My PhD project focuses on this.”

Article: Bargas-Galarraga, I., C. Vilà, & A. Gonzalez-Voyer. 2023. High investment in reproduction is associated with reduced life span in dogs. The American Naturalist 201: 163–174.

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