For the human majority, dogs hold a special place in comparison with our relationships to other animal species. Scientific evidence suggests that dogs were the earliest animal domesticated by man. The paleontological evidence suggests that this occurred 14,000 to 17,000 years ago, and the genetic evidence suggests that domestication might have started thousands of years before that.
Because of their relationship with humans, dogs are the most widely distributed animal across the globe, inhabiting virtually every area of the world where people can be found. They are the most commonly kept companion animals, and the love people have for dogs in general is evidenced by the thousands of books and stories written about them and the myriad websites devoted to canines. But the question of interest is “why?” What is so special about our relationship with dogs?
Why Should We Like Dogs?
Psychologists presume that attitudes toward dogs and dog ownership, whether positive or negative, are influenced by culture, social factors, and history. For example, certain religions or societies may cherish or detest interactions with dogs; this can shape an individual’s personal experience and attitudes. This idea has been supported by research, which indicated that exposure to dogs during childhood is associated with more positive attitudes towards dogs and an increased likelihood of dog ownership in adulthood. But more may be going on.
When a human (especially a child) encounters a nonhostile dog for the first time, they tend to approach and try to interact with the animal. Contrast this to first encounters with snakes or spiders. These creatures are typically met with revulsion or fear, and people try to stay away from them even if they have never seen such animals before. Could such responses be genetic?
The Personality Factor
Currently, ample research suggests that an individual’s personality determines whether a person is apt to become a dog owner, cat owner, or a non-pet owning individual. For example, studies at the University of Texas at Austin and the University of Florida showed that people who were more extroverted, sociable, and low in neuroticism were most likely to be dog owners; cat owners tended to be more solitary, sober, and a bit more neurotic. This is consistent with the results of a study I conducted involving more than 6000 people, which showed that a person’s personality predicted whether or not they liked dogs and also which breeds they would tend to prefer.
Such findings are significant because there is a lot of evidence suggesting that genetic factors determine much of our personality; for example, estimates of the heritable contributions to extraversion are about 53 percent, to neuroticism around 41 percent, and to agreeableness around 42 percent. Given the evidence that shows genetic influences on personality characteristics, and personality is associated with feelings toward dogs, it is a natural next step to wonder if there might be a genetic factor in determining whether a person will be attracted to dogs and want to own one.
A Large Twin Study
Reasoning along these lines, Swedish researchers headed by Tove Fall at Uppsala University took advantage of some remarkable databanks available in Sweden to test this hypothesis. Specifically, her team had access to the Swedish Twin Registry, which was founded in the late 1950s and contains information on all twins born in Sweden. Secondly, national information on dog ownership has been available since 2001, when two dog registries were established and a legal requirement that all dogs in Sweden must be registered was enacted.
Is this particular factor influenced by genetics? The clearest way to answer this question is to use twins. There are two types of twins, identical and fraternal. Identical twins arise when a single egg is fertilized by a single sperm cell to form what is technically called a zygote. As that zygote develops, usually within the first or second cell division, it splits to form two separate individuals. The magic of this is that these two individuals, since they come from the same sperm and ovum, have an identical genetic makeup. Thus, the resulting individuals will be of the same sex, look the same, and share every genetically determined characteristic.
Fraternal twins come about when two egg cells are fertilized by two different sperm cells and develop in the same womb. In this case, the twins share the same amount of genetic material that any pair of brothers or sisters might. They might not look the same or be the same sex.
Both kinds of twins have very similar personal histories since they grow up in the same family and share the same environment, culture, and parenting influences. If we compare the similarities in the behaviors of the two types of twins, and we find greater similarities between the identical twins (with their matching genetic makeup), than between the fraternal twins (who only share about half of their genes), this would confirm that we are looking at something that has a genetic component.
The researchers looked at 35,035 pairs of twins, established whether they were identical or fraternal, and then determined whether each twin had become a dog owner. If there is a genetic factor, the concordance rate should be higher for identical twins. Concordance would be shown when both twins owned dogs or both did not own dogs, while a lack of concordance would be present when one twin owned a dog and the other did not. The researchers concluded that identical twins had higher concordance than the concordance in fraternal twins, which is consistent with the presence of genetic effects.
How Much of Our Feelings for Dogs Is Genetic?
Following a lot of statistical analysis involving structural equations, these researchers came up with the estimate that the size of the genetic component influencing whether we are inclined to own a dog is 57 percent for females and 51 percent for males. Approximately half of the psychological pressure that we feel to own, or to not own, a dog is influenced by our DNA, with the other half influenced by environmental factors such as our personal histories or culture.
The conclusion: A significant portion of our affection for dogs may be due to our genetic heritage. This has likely come about through a process known as co-evolution, where two species shape each other’s evolutionary history due to social interaction over an extended period. Based on an analysis by researchers at Washington State University, this process began thousands of years ago when dogs and humans first began to live together, hunt together, and mutually defend each other. These researchers believe that over time, the resultant bond evolved into part of our genetic makeup.
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