Last Christmas, as I was patting my sister’s little female French bulldog, I found myself thinking how relaxing it felt – well, apart from the slightly itchy eyes. At some point, the dog tilted her head towards me, and we embarked on some sort of staring contest. As the mutual gaze prolonged, I started wondering: What could be going through her mind? Was she thinking about something? Why was she keeping her big but oh-so-cute bulgy eyes fixed on mine?
The interactions between humans and dogs are rather particular, with a level of social bonding and emotional engagement unusual for members of two different species. When compared with wolves, dogs’ closest relatives, and great apes, humans’ closest relatives, dogs appear much more skilled at recognizing and using social cues such as gesture or gaze direction to cooperatively interact with humans, even already as puppies.
But it’s not just that. Why is it that we feel genuinely attached to dogs? What are the biological mechanisms underlying the friendship and love we come to develop towards them?
Enters oxytocin, the one neuropeptide that seems to pop up in almost every narrative of bonding relationships.
Oxytocin is well known for its role in promoting bonding, between mother and infant for example, or between sexual partners in monogamous species. In an article recently published in Science, scientists wondered whether oxytocin may not also form the basis of a positive feedback loop promoting attachment and caring behavior between dogs and their owners, much as the one thought to happen between mother and infant.
It’s already known that patting a dog will increase the levels of oxytocin in both the dog and the human touching it. In a previous study, the authors of the Science’s article had observed that a social interaction in the form of a dog’s gazing at its owner also increased the levels of oxytocin in the dog owner. In the present study, the researchers found that mutual gazing between a dog and its owner not only increased oxytocin in the owner, but also in the dog. The change in oxytocin concentration was larger in owners whose dogs gazed at them the longest (about 110 seconds compared to about 40 seconds on average), and the oxytocin increase observed in the dogs, in return, correlated with that observed in their owners. When the scientists carried out the same experiment with wolves, they did not find evidence of such interactions, even though the wolves were tested with their owners who had hand-raised them since they were pups.
From an evolutionary perspective, the scientists suggest that dogs may have taken advantage of a system promoting parent-infant bonding and come to mimic social cues such as gazing to generate positive reward feelings in humans and direct parenting/caretaking behavior towards them. Dogs themselves may have come to experience similar feelings of reward, thus creating and propagating a feedback loop that reinforces bonding between them and their human handlers.
I don’t know if my sister’s dog or I experienced any oxytocin rush or feeling of bonding when we shared that moment of mutual gazing. I’m not her owner, so maybe she was just wondering what on earth this strange person was doing. But considering she finally rolled over to let me pat her belly, I’m guessing that she at least enjoyed the interaction as much as I did.
Besides the study on oxytocin and dog-human bonding, that particular issue of Science also contained a feature article looking into the story of dogs’ origins, or rather, into how scientists are trying to figure it out.
We now know that dogs have evolved from gray wolves. The current consensus among experts is that dogs’ domestication occurred in two waves. First, some wolves may have started feeding from carcasses discarded by early humans; these wolves that dared approach humans and thereby benefited from their food leftovers may have survived longer and produced more offspring; over many generations, this process may have favored animals that were increasingly comfortable getting close to humans. Second, humans themselves may have realized how useful these animals may be and started an active phase of domestication, breeding them to be better at helping humans in a range of activities such as hunting, herding, or pulling heavy loads across long distances.
However, despite a seemingly general agreement on how dogs were domesticated, the when and where of the emergence of the dog species remains unclear – and apparently, a source of heated argument among scientists working on the subject. Depending on the study, dates ranging from about 16,000 years ago to sometime between 19,000 and 30,000 years ago have been proposed for the beginning of the dog species.
Dogs are the first species ever domesticated by humans, before any other plant or animal species. Building on this fact to argue the importance of the topic and secure enough funding for researching it (apparently, despite the special relationship between humans and dogs – not to mention the absurd amounts of money some people lavish on their pet dogs, funding agencies have not really been bent on including dogs and the story of their origins in their list of projects to fund), two scientists from the UK have now managed to secure funding and build a large international collaboration to tackle the question of when and where dogs emerged.
The project intends to analyze a large number of samples from many different places in the world, combining ancient DNA analysis and a computer-based morphometric analysis of ancient bones. The latter technique, which is relatively new and has already been used on ancient human specimens, is based on recording the 3D shape of bones (e.g. skull, jaws, femurs) and taking thousands of measurements of shape details to then compare all the different specimens and get a more precise idea of how they differ (or not). From all these data, scientists hope to be able to reconstruct the story of how the dog species emerged.
Of course, analyzing huge amounts of data is no guarantee that a clearer picture will be reached – it might only make the whole thing more complicated. But even if that is so, this particular field of research will not be the worse not only for having collected an unprecedented, large and varied amount of data, but also for having managed to tame egos and unify previously brawling scientists to work cooperatively towards a common goal. Now we just have to wait for the first study stemming from this international effort to be published.
Oxytocin-gaze positive loop and the coevolution of human-dog bonds. Nagasawa M, Mitsui S, En S, Ohtani N, Ohta M, Sakuma Y, Onaka T, Mogi K, Kikusui T. Science. 2015 Apr 17;348(6232):333-6. doi: 10.1126/science.1261022 PMID: 25883356 Dawn of the dog. Grimm D. Science. 2015 Apr 17;348(6232):274-9. doi: 10.1126/science.348.6232.274.