There's a very scientific explanation as to why we consider dogs "man's best friend."

A new study in Japan shows that oxytocin - a hormone that helps reinforce bonds between parents and their babies, also increases in humans and their dogs when they interact, reported Reuters

After a series of experiments, the researchers concluded that this chemical bond between pups and their humans began thousands of years ago when canines first became domesticated. 

In one of these experiments, dogs were put in the same room as their respective owners while the researchers tracked their interaction and measured oxytocin levels through urine samples, reported Reuters. 

"I personally believe that there is a tight bond between the owner and dogs," Takefumi Kikusui, a veterinary medicine professor at Japan's Azabu University, whose research was published in the journal Science, told Reuters. "I have three standard poodles. I strongly feel the tight bonding with these dogs. Actually, I participated in the experiment, and my oxytocin boosted up after the eye gaze, like 300 percent."

Interestingly, the researchers also tried the experiment with wolves (a close relative of the dog) and the human who raised them but there was no oxytocin reaction.