Research has shown what many of us have suspected for a long time: dogs can love their human companions. And if dogs are capable of feeling love for humans, that naturally leads to another question: are they also capable of loving other dogs? When we consider adding another dog to our family, can we pick the cutest puppy at the pound, or should we instead search for an appropriate mate for our current pet?

Though it’s impossible to know exactly what our pets are feeling, Marc Bekoff, professor emeritus of Ecology and Evolutionary Biology at the University of Colorado, Boulder, says that dogs can, in fact, fall in love with other dogs and remain faithful lifetime mates. He says that, “If you define love as a long-term commitment – meaning they seek one another out when they’re apart, they’re happy when they’re reunited, they protect one another, they feed one another, they raise children together – then of course non-human animals love each other.” He tells a story of a friend’s dog who fell in love, raised eight litters of puppies with her mate, and was carefully cared for by the mate during a prolonged illness that necessitated a leg amputation.

Dr. Stanley Coren, author of How to Speak Dog, says he believes it is “more of a family love than romantic love,” something that resembles what parents and children feel for one another. This is because many researchers believe that a dog’s emotional range isn’t as developed as a human’s.

The American Psychological Association likens canine intelligence to the mental development of a two-year-old toddler. They’re capable of strong emotions, complex problem-solving, understanding more than 150 words, and manipulating others to get what they want. Emotional development, range and intelligence varies dog-to-dog, but some believe that since humans don’t develop romantic inclinations until they’re much older, dogs wouldn’t be capable of romantic leanings, either. But no one has definitively answered the question just yet. And whether or not puppy love is sexual or familial, the fact remains that the relationships and emotions are every bit as real and heartwarming.

The evidence for this isn’t purely anecdotal, either. Science supports the idea of puppy love, as well. When experiencing strong emotions, dogs show neurochemical changes similar to humans. A study published by the Proceedings of the National Academy of Sciences states that oxytocin, also known as the love hormone, increases after dogs spend time with their chosen dog partners. Elevated oxytocin levels represent the very same chemical reaction scientists use to explain human love. Oxytocin can be indicative of both romantic and familial love. In addition to being tied to mating, female dogs release it when they return to their puppies and puppies experience it when the mom comes back.

Scent also plays a role in canine mating. Coren writes about the Jacobson organ, a scent detection system distinctive to dogs. The system allows dogs to extract essential information from another dog’s pheromones, including gender, age, health, mood, and stage of menstrual cycle. This information forms the basis of what humans think of as the chemistry or initial attraction between them.

Bekoff argues that dog-to-dog relationships can be more “honest” and unfiltered than human love affairs and that, while it’s certainly not always the case, most dogs are monogamous.

Dogs are capable of feeling the anguish of love, too, and hurt one another in many of the same ways humans spurn their partners. Certain dogs that aren’t interested in monogamy, for example, bounce from partner-to-partner. There’s even a term for dogs who attempt to seduce a mate that’s already committed to someone else: they’re called sneak copulators. Dogs that have been rejected by a mate will react in similar ways to humans feeling the same emotions: grief, sadness, jealousy, anger.

Nicholas Dodman, who runs the Animal Behavior Clinic at the Cummings School of Veterinary Medicine at Tufts University, treats many dogs for depression caused by the death of a dog they loved. Dodman describes dogs that became hysterical or completely shut down following a death and says that “you cannot have depression without a strong bond.”

Another recent study conducted in Japan, centering on both cats and dogs, found that more than half of the pet owner participants could often or sometimes attribute the following emotions to their pets: joy, surprise, anger, fear, sadness, disgust, compassion and jealousy.  

Though we can’t be sure of the exact nature of canine love, and how closely it aligns with what two humans feel for one another, it’s clear that the bond between two companion dogs can be intense and deeply felt. So it might be worth involving your dog in any decisions relating to future pets. You might be lucky enough to observe one of these loving relationships and decide for yourself.