Above: Image © istockphoto.com/apeyron

If you are lucky enough to own a dog, chances are you see your dog as more than just a pet. People tend to feel very close to their dogs and treat them like members of the family. As your distant ancestors sought out furry companions and helpers, dogs evolved from wolves to produce the lovable pets of today. But a new research study points to an additional explanation for the strong bond between humans and dogs: oxytocin, the same “love hormone” that strengthens your bonds with human loved ones.

Did you know? New couples with higher concentrations of oxytocin in their blood are more likely to be together 6 months later compared to new couples with lower concentrations.Hormones like oxytocin are molecules used to communicate between cells located in different parts of your body. Depending on the type of hormone, it can cause different changes in the cell. For example, mothers’ bodies produce oxytocin when they see their infant children. The oxytocin then travels through the mother’s blood and encourages the production of milk in the mammary glands.

Japanese researchers interested in the relationship between dogs and people measured the concentration of oxytocin in both humans and canines before and after they interacted with one another. Dogs that gazed longer into their owners’ eyes, as well as humans who gazed into their dogs’ eyes, had increased concentrations of oxytocin in their urine. When the same experiment was repeated replacing dogs with wolves who had been raised by humans, no changes in oxytocin levels were detected.

Scientists attribute the fact that oxytocin was produced with dogs but not with wolves to genes and evolution. Dogs have evolved from wolves to take advantage of their bond with humans to ensure their needs are met. By living with humans, dogs get food, shelter, and a caring environment.

Did you know? Giving people oxytocin makes them more generous with their money.Meanwhile, countless generations of humans have benefited from living with dogs since they began to serve as trusted hunting companions or guardians of livestock such as sheep. DNA evidence suggests that humans first used wolves to help with hunting between 19,000 and 32,000 years ago. Contrary to dogs, wolves tend to be independent (not obedient), have large teeth, and can survive in the wild by themselves. When humans began selecting wolves to help them, they would have looked for characteristics such as friendliness, obedience, and hunting skill. When the selected wolves had their own pups, genes influencing these traits would have been passed down to the next generation and strengthened.

Over time, small changes accumulated, ultimately resulting in a distinct species. Over many generations, in the company of humans, wolves that lived with humans changed into the friendly animals you know as dogs. However, it now appears that the story is more than just a matter of “I’ll scratch your back if you scratch mine” (or “I’ll help you hunt and protect your livestock if you keep me fed and give me a warm bed”).

The new research into oxytocin reveals a hormonal component to the relationship between dogs and humans. At the same time, the fact that the “love hormone” is not a factor in the relationship between wolves and their owners helps explain why wolves do not make good pets. Thanks to the rewarding effects of oxytocin, both dogs and their owners have had an additional motivation to strengthen their bond. Ponder that the next time you stare into your dog’s eyes!

Learn more!

Oxytocin-gaze positive loop and the coevolution of human-dog bonds (2015)
M. Nagasawa et al., Science 348
Link to abstract. Registration or subscription required to view full text.

Scientific article on research into the release of oxytocin in humans and dogs when they are in each other’s presence.

Complete Mitochondrial Genomes of Ancient Canids Suggest a European Origin of Domestic Dogs (2013)
O. Thalmann et al., Science 342
Link to abstract. Registration or subscription required to view full text.

Scientific article on the genetic and geographic origins of dogs.

Kelly Resmer

Kelly is a chemistry undergraduate laboratory instructor in Halifax.  She loves working with students in the lab, watching chemistry happen! She has a PhD in chemistry and is very interested in studying and learning about bacteria, the good and the bad ones! 


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