Is “one-of-a-kind diversity” a contradiction in terms? Not when it comes to dogs. Canis familiaris is the only species on the planet with such incredible variety: the towering Great Dane and the tiny Chihuahua, the sleek Dachshund and the muscular Rottweiler, the elegant Afghan Hound and the playful Yorkshire Terrier. Today, there are around 400 recognized breeds—and countless mixes—within this one species.

So, how did dogs become so diverse? The answer lies in their unique bond with us.