For National Puppy Day, we created an adorable photo gallery that shows puppies playing with each other, posing for the camera, and interacting with people around them. But what is it that makes them seem so cute as they melt our hearts?

The leading theory, known as the "baby schema" effect, says a release of the chemicals dopamine and oxytocin is triggered in the brain when humans look at puppies. The same chemicals are released when we look at babies, and similar chemicals are released when we fall in love.

This chemical release is triggered by visual cues in baby mammals, including a large head relative to body size, big eyes, rounded body shape, and soft body surfaces. Since human