Every day millions of people ask Google lifes most difficult questions. Zoologist and author Jules Howard answers this one
As luck would have it, this is rather a prescient question for me right now. At home, we are attempting to coax a neurotic four-year-old out of a dog-bite avoidance technique that works as follows. Upon seeing from a distance any four-legged animal that may or may not be a dog, the four-year-old elucidates an escape response that involves her climbing the torso of the nearest adult and wailing an ear-piercing song of terror that is deeply embarrassing to her zoologist father. Her new-found fear of dogs is understandable, however. Our pet cat (he of milky-eyed bastard fame) is now no more after being killed by two huskies that had escaped in the night from their owners. While explaining this news to the four-year-old, the two specific words DOGS and KILLED seem to have become clogged-up somewhere in the digestive system of her cognition, hence the sudden phobia which we are working hard as a family to resolve.
Tail wagging, I tell her (as she climbs me like a tree upon seeing a hamster-sized bichon frise puppy approaching at our local park) is a good indicator of the friendliness of a dog. Dogs with wagging tails are the friendly ones, I say. Dont be scared of the wagging ones, I tell her. But well, you and I know that this dog management advice is a bit of a fudge. Like a picture, a wag paints a million words. But not all of them are love stories.
To get a feel for why dogs wag their tails, it helps to remember that dogs are mammals well adapted for sociality. This is because in wolves (from which dogs evolved) a genuine threat to life is living alone. In very few cases does it help for a wolf to be ostracised from the group. This is because lone wolves are treated with deep unease by other wolf packs, who are eager to defend their territories. For instance, territorial fights may be behind up to 65% of wolf deaths in some populations in parts of the US. To stay alive, individuals must fit in. And to fit in, social animals must signal their contentment their intention not to rock the boat.
A dogs tail is, quite literally, a happy flag. The more the flag waves, the more everyone knows a dog is happy and content and definitely in no way seeking to overthrow the alpha breeding pair and start a bloody turf war leading to local societal collapse and the canine equivalent of a season of Game of Thrones.