Why Are Dogs [Wo]man’s Best Friend? New Research Has the Answer

Scientists have struggled for decades to explain why dogs are so successful at living with people. They measured snout lengths and tooth sizes; they tested dogs’ intelligence; and they came up with elaborate theories. But for the longest time, these experts resisted the most obvious answer — I know because I was one of them.

It turns out that the secret to dogs’ success around people is not in their smarts; it’s in their hearts. It lies in their ebullient, unlimited, extravagant — almost abnormal — desire to form strong emotional connections with members of other species. The bond a dog has with a human is actually rather simple.

Dogs enthusiastically bond with individuals from any species that they meet during their first three months of life. Usually, this is us — but it doesn’t have to be. I have visited with goat ranchers in Arizona who have Anatolian livestock-guarding dogs, a breed originally from Turkey. These gentle giants protect the goats simply because they were put into the goat barn when they were pups. They grew up seeking out goats for the kinds of emotional connections that we are used to seeing our dogs look for with us.

Denying the Role of Affection

Ancient Greeks wrote about how dogs love people, but we scientists were slow on the uptake. We looked for special forms of intelligence that might explain how canines became the most widespread larger mammal on the surface of this planet. There certainly are some smart pups out there. Take Chaser, for example, the dog the BBC called “the world’s smartest.” Chaser knew the names of over 1,200 toys. She’d bring you any one of them if you asked for it. I saw it for myself when I met her. I asked for about 50 toys by name and she happily obliged, never once making a mistake.

Most dogs aren’t as smart as Chaser, though. The kinds of clever things they do in our daily lives — things like following our gestures to find stuff and realizing that we can’t see them when we turn our backs — can be done by other animals too, if they are raised by people and live their lives dependent on human beings for everything they need. Maybe scientists went after intelligence in dogs because at least we knew how to measure it. Affection — love — just seemed too squishy to turn into the cold hard numbers of science. Recently, however, my collaborators and I have found some ways to measure dogs’ capacity for love. Pet owners won’t be surprised to hear that we find this ability shines through every pore of their furry bodies.

Testing the “Love Theory”

In one super-simple test, we just asked people to sit down in a chair. Then, we let their dog into the room with them. We measured how much time the dog spent in close proximity to their person. We did this with dogs and we also did it with hand-reared wolves. All dogs are descended from wolves. If we want to understand what makes dogs truly special, we need to compare them to their wild ancestors.

We tested wolves at Wolf Park in Indiana, where the animals have been hand-reared since 1974. The park’s wolves are some of the most beautifully human-focused animals you could ever hope to meet. The person who sat down in the enclosure for our study had helped hand-rear the wolf we were testing. Therefore, we knew that this human and wolf had an extraordinarily strong bond. The wolf spent about a quarter of the two-minute test close by its human. Then we repeated the test with people and their dogs. The wolves may have been pretty interested in their people, but the dogs were totally off the charts. Most of the dogs spent every last second of the two-minute test period right up close to their person. That’s nearly four times longer as the wolves spent with their special human.

In the Genes

Armed, then, with this delightfully simple way of measuring the intensity of affection that dogs have toward people, we sent DNA samples (just a painless mouth swab) off to a geneticist to see if we could find the genes that might be responsible for the amazing change in loving behavior between dogs and wolves. It’s not easy finding genes for qualities like friendliness because the loving nature of an animal isn’t a direct consequence of its genetic endowment, but also depends on every single life experience that individual has had right up to the moment you carry out the test. To my amazement, we were able to discover the three genes that make the loving natures of dogs possible. I was doubly astonished to learn that there is an exceedingly rare syndrome in our own species that also involves changes to those same
genes. Williams-Beuren syndrome involves 28 genes and has many impacts. They range from a strange facial structure to heart defects, but its key symptom is an exceptional level of friendliness. Since we published our discovery, I have had many family members of people with Williams-Beuren syndrome reach out to me to share that they always felt there was something about their relatives that resembled the loving nature of dogs.

The Love Hormone

Additional research into dogs’ affection for the human species now circles the globe. Oxytocin gets called the “love hormone” because it has been found to increase when two people who are in an intense loving relationship — like mothers and their infants — look into each other’s eyes. At Azabu University in Japan, a research team led by Takefumi Kikusui, PhD, found the same oxytocin spikes in both dogs and their people when they looked at each other’s eyes. Researchers in Sweden, Hungary, and elsewhere have adapted a test that was originally developed to assess the relationship between caregivers and young children.

In this assessment, designed to mimic the comings and goings of real life, a young child is brought into an unfamiliar room and then left alone briefly with a stranger. Researchers observe how a toddler is mildly distressed to be separated from the mother, but then happy to be reunited. The same test, when applied to dogs and their people, produces remarkably similar results. This indicates that the bond between a pup and a person is very much like a child’s to his or her mom.

Dogs and Their Humans

Two scientists in Australia strapped heart-rate monitors onto the chests of people and their dogs and then asked them to snuggle while monitoring their heartbeats. The researchers found that when people and their dogs relax together their heartbeats come into synchrony — literally, “two hearts beating as one.”

At Emory University in Atlanta, Gregory Berns, PhD, and his team have trained dogs, using solely positive training techniques, to lie perfectly still in magnetic resonance imaging (MRI) scanners. MRI scanners produce beautifully clear pictures of brain activity. Before Berns’ work, they had only been used on people, because only humans could understand the importance of remaining perfectly still in the noisy and claustrophobia-inducing machine. Berns’ team observed the dogs’ brain activity as they were reminded of their special people — or the possibility of a piece of sausage. Of course, the reward centers of the dogs’ brains lit up at the prospect of sausage, but for most dogs, the reward centers were even more intensely active at the prospect of being reunited with their human.

True Connection

Sometimes I’m embarrassed to admit that it took me so long to realize that the uninhibited loving relationship I had with Benji, the dog of my childhood, actually captured the essence of the dog-human bond and explains dogs’ amazing success in the human world. We scientists wanted the answer to be more complicated.

Some people might want to say that science that only affirms what people already know is a waste of time — but I really don’t believe that, for a couple of reasons. First, many people think that dogs only love us for what we give them. “Cupboard love” is what we called it when I was growing up in England. But we can say now that this isn’t true. Most dogs love their people sincerely — not just as a means to get more treats. Second, we should use this knowledge to give our dogs what they need for happy lives with us. We love dogs because of their wonderful outgoing natures. We need to recognize that our pets’ very real social needs demand something back from us.

Giving Our Dogs What They Need

It is cruel to leave a dog alone all day while we are out at work and play. These exquisitely social beings cry out for company. Separation anxiety is the most common psychological problem in dogs. Often it is not an abnormal response to normal circumstances, but an understandable response to really unreasonable situations. Dogs are not like our smart devices that can be left alone for hours or days. Our dogs require company for their psychological health. So I am happy that we scientists got there in the end, and now we are doing everything we can to improve dogs’ lives with people by making the science of dog love and its implications more widely known.

Clive D.L. Wynne, a comparative psychologist at Arizona State University, is the author of Dog Is Love: Why and How Your Dog Loves You.

A version of this article appeared in our partner magazine Inside Your Dog’s Mind in 2021.