The choice to own a dog has a strong genetic element, according to new research.
A study of more than 35,000 pairs of twins from Sweden examined the extent to which people's genetic makeup corresponded to whether or not they owned a dog.
The investigators, who hail from Uppsala University and Karolinska Institutet, in Sweden, and the University of Liverpool, in the United Kingdom, found that genetic differences could explain more than 50% of the variation in dog ownership.
It also seems that the influence of genes on the choice to own a dog is stronger in women than in men.
In a recent Scientific Reports paper on the study, the researchers estimate that the contribution of genetic factors to dog ownership is "57% for females and 51% for males."
"We were surprised to see that a person's genetic makeup appears to be a significant influence in whether they own a dog," says lead study author Tove Fall, Ph.D., a professor of molecular epidemiology at Uppsala University.
"Perhaps some people have a higher innate propensity to care for a pet than others," she muses.
Humans and dogs go back a long way
In their study paper, the researchers explain that, while the origin of the domestic dog is still a topic of heated debate, there is no doubt that "pre-farming, hunter-gatherer societies" made much use of domesticated canines.
Humans likely began using dogs to help them with hunting and herding, as well as for protection. Today, pet dogs not only offer companionship, but they also assist in a range of settings, from prison rehabilitation to post-surgery care.
"Decades of archaeological research have helped us construct a better picture of where and when dogs entered into the human world," says study co-author Keith Dobney, Ph.D., a zooarchaeologist and professor at the University of Liverpool.
Now, by bringing together "modern and ancient genetic data," scientists can also "directly explore why and how," he adds.
He and his co-authors cite numerous studies that have explored the connection between dog ownership and human health.
These show, for example, that people who own dogs exercise more, experience less loneliness, "and have an improved perception of well-being." This is particularly the case with older people and those who live alone.
Untangling the contribution of genes
However, what is not clear from previous research is whether "health differences between dog owners and non-dog owners reflect effects of dog ownership itself or underlying preexisting differences in personality, health, and genetics," ask the authors.
The advantages of using a Swedish population to explore the genetics of this question are that Sweden has the largest twin cohort for this type of study in the world, and all dog ownership in Sweden has to be registered.
The team accessed Swedish Twin Registry data on all twins that were born during 1926–1996 and were alive in 2006.
Using national dog registers, they were able to obtain information on dog ownership and link this to the twin cohort with personal identity numbers.
These sources gave them a data set that "included 85,542 twins from 50,507 twin pairs with known zygosity," while "information on both twins [was] available in 35,035 pairs."
Knowing the zygosity of twin pairs can tell you if they are identical or nonidentical.
Scientists use twin studies to try and untangle the effects of environment and genes on biology and behavior. Identical twins have the same genetic makeup, whereas in nonidentical twins, on average, only around 50% of their genomes are the same.
Genes likely influence dog ownership
Using statistical tools, the researchers analyzed the data to estimate the extent to which genetics, shared environment, and non-shared environment may have contributed to dog ownership.
They found that twins who both owned dogs in adulthood were more likely to be identical than nonidentical, suggesting that genetics was indeed a strong factor in dog ownership.
"An effect of shared environmental factors," note the authors, "was only observed in early adulthood."
They suggest that the findings could also mean that genetic makeup may have played a role in influencing human beings' "ability to domesticate dogs and other animals."
In addition, they advise researchers to consider genetic variation as a factor when studying the impact of pet ownership on human health.
"The study has major implications for understanding the deep and enigmatic history of dog domestication."
Prof. Keith Dobney, Ph.D.