When your dog gazes into your eyes and you feel that unmistakable warmth in your chest, something remarkable is happening at the molecular level. That emotional connection you share with your canine companion isn’t just sentiment—it’s biology. And it’s the same biological machinery that bonds human parents to their children.

Over the past two decades, scientists have uncovered a fascinating truth: dogs and humans have co-opted the mammalian attachment system, originally designed to bond mothers and infants, to create one of the most unique cross-species relationships in nature. The result is a bond so powerful that it shows up in our hormones, our brain activity, and even our genetic expression.