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There is “absolutely no doubt that animals love,” says Marc Bekoff, professor emeritus of ecology and evolutionary biology at the University of Colorado, Boulder, and author of . What makes him so sure? Years of observing wolves, coyotes and other animals in their natural habitats.

“A long-term close relationship, commitment to another person,” Bekoff says. “You travel with them, you defend territory and food, you have a family, you miss one another while you’re apart.”

That loving behavior he observed is supported by an experiment detailed in a recent article in The Atlantic, “.” In the experiment, Director of the Center for Neuroeconomics Studies at Claremont Graduate University collected blood samples from a dog and a goat after they played with one another. He then measured the animals’ levels of oxytocin, or “the neurochemical of love.”

The dog had a 48 percent increase in oxytocin, meaning it viewed the goat as a friend. The goat, however, was enraptured. “It had a 210 percent increase in oxytocin,” Zak explains. “At that level of increase, within the framework of oxytocin as the ‘love hormone,’ we essentially found that the goat might have been in love with the dog.”

And what of those animals that pair up for life, such as certain types of birds? Although penguins don't mate for life, they can sustain long-term relationships, says Dee Boersma, the cirector of the Magellanic Penguin Project at the University of Washington. One pair she observed was together for 16 years.

Boersma’s Ph.D. student Jeffrey Smith studies why female penguins, given the choice, will pick one male as her mate over another, but they have yet to pinpoint a reason. “We’re not sure if it’s a behavioral thing or if she sees a nest that she likes,” he says. Could this X factor be love? 

Boersma cites a story of seeming heartbreak among Galapagos penguins. When a male penguin disappeared, his mate remained in the nest waiting for him. Even when another male lured her away, she continued to return to the old nest.

“Was she pining away for her love?” Boersma asks. “She was distressed but was it love? With a bird brain is it the same as human love?” Perhaps not, but that doesn’t necessarily make it any less like love, just different.

“It’s not to say that dog love is the same as human love,” says Bekoff, “but your love might not be the same as mine.”