Why Do Dogs Wag Their Tails?

Dogs wag their tails primarily as a social signal to other dogs and to humans. A broad, relaxed wag usually indicates friendliness or excitement, while a stiff, high wag can signal alertness or dominance. Research published in Current Biology found that dogs wag more to the right when experiencing positive emotions (seeing their owner) and more to the left when feeling anxious or encountering an unfamiliar dog. The tail is controlled by muscles connected to the spine and is rich in nerve endings. Puppies do not wag their tails until about 30-50 days old, roughly when they begin social interactions with littermates.