Do you ever wonder what makes some dogs so into us? Why at any moment Pluto might propel himself into Mickey's arms, giving Mickey a full-on scrub-down with his tongue? Why some dogs want to meet everybody and anybody, whereas others would prefer you stay right where you are?

A recently published study in PLOS ONE led by Anna Kis, Melinda Bence and other researchers at the Family Dog Project at Eötvös Loránd University in Budapest used a novel method to explore the role that oxytocin plays in dogs' sociability toward humans.

Maybe you have heard oxytocin described as the “love hormone” because of its involvement in social interactions, stress relief and feelings of connectedness with other people. Spend time petting your dog, scratching Pluto's body and ears, and you are both apt to see increases in the oxytocin levels in your blood, indicating a positive experience for you both. Yet oxytocin is also not simple. Science writer Ed Yong points out in a 2012 Slate article: “The ‘love hormone’ fosters trust and generosity in some situations but envy and bias in others, and it can produce opposite effects in different people.” Part of the story could be that variations in the gene that codes for the oxytocin receptor—the molecule that oxytocin binds to on nerve cells in the brain—mediate differences in social behavior.

To investigate whether Pluto's exuberance for Mickey and “people” in general is somehow associated with Pluto's genes, Kis and her colleagues took the following approach:

Step 1. Get to know the dog oxytocin receptor (OXTR) gene. For this study, the researchers selected dogs from two breeds, German Shepherds and Border Collies, and extracted DNA by swabbing the insides of their cheeks. This process ultimately identified three variations of the OXTR gene that themselves each come in two forms, with the forms seemingly having different effects on behavior. The three variations, or “polymorphisms,” have the incredibly easy names of −212AG, 19131AG and rs8679684.

Step 2. Get a sense of how the dogs interact with people. More than 200 German Shepherds and Border Collies living as companion dogs participated in a series of specific interactions with people. The tests investigated how dogs greeted both a known and an unknown person, how dogs responded to a stranger approaching in a threatening manner, and how dogs responded when their owner hid behind a large tree.

Step 3. Bring dog genes and behavior together. The researchers examined whether there was a relation between the OXTR polymorphisms and the way the dogs interacted with people during the social tests. They were particularly interested in how readily dogs approached people, as well as the canines' level of friendliness.

Describing the results, Kis says “the way dogs behave toward humans, at least among German Shepherds and Border Collies, is influenced by the oxytocin receptor gene.” For example, when it came to the –212AG gene, both German Shepherds and Border Collies carrying the form, or allele, known as G showed less interest in being around people, than did those with the allele called A, suggesting the effect was the same in both breeds.

Yet analysis of the genes 19131AG and rs8679684 revealed opposite trends in the two breeds. For example, in the 19131AG polymorphism, the investigators report, “the presence of the A allele, as opposed to the G allele, was associated with higher friendliness scores in German Shepherds and lower friendliness scores in Border Collies.” This opposite effect suggests that “other genetic and cellular mechanisms (unexplored in the present study) might play a role in the regulation of this behavior besides our candidate gene.”

Overall, then, the study indicates that dog sociability toward people is related to the varieties in the OXTR gene they possess but that oxytocin is “part of a bigger system” contributing to dogs' feelings toward humans.

Next up for this line of research: replication and the exploration of possible molecular interactions that account for the effects that particular oxytocin receptor variants have on dogs' behavior toward people.