Dogs are the most diverse mammal species on the planet (http://buff.ly/1pxxt0k). They can vary in weight from 6 lb (3kg) to 200 lb (90kg) when fully grown and have widely differing body shapes and hair types.
BBC: Have you ever wondered why it's so relaxing to hang out with a dog?
Dogs could be called wonder drugs
People who have dogs as pets are much less likely to have a heart attack. If they do have a heart attack, they are 2-3 times more likely to survive it.
Over more than 100,000 years dogs have evolved to recognize human emotions. It has been a collaborative process all along. Humans are able to recognize 6 types of dog barks expressing emotions and "intentions" such as fear, excitement, aggression and so on. Dogs are the only animals that specifically look at the right side of the human face where emotions are expressed.
Dogs follow directions while chimpanzees, the apes evolutionary closest to humans, do not. The smartest dog can learn 300 different words which is the vocabulary size of a 2-year-old child.
The "400 mnemonic":
400 million dogs worldwide
400 breeds of dogs have been developed by humans
According to a Cleveland Clinic psychologist, "dogs could be called wonder drugs":
Doctor's Dog Will See You Now - Therapists Use 'Canine Assistants' to Comfort and Cheer Patients http://buff.ly/1cTwfDW
Dogs Decoded transcript and more. NOVA.