Woof Woof!

Why Do Dogs Wag Their Tails? A New Theory Speaks Volumes

Scientists have two hypotheses why dogs evolved to wag their tails, and one is absolutely adorable.

Vertical full length view of caucasian woman relax at home with American Stanford dog on woodblock f...
Vera Vita/Moment/Getty Images

Whether a dog is thumping its tail along to a beat or giving a full wiggle butt, people love when pups wag their tails. We often take it as a sign that an unfamiliar dog is friendly or that our family pet is happy. But in a new paper, scientists argue that the reason dogs evolved to wag their tails might be even more heartwarming than that: They may have started wagging their tails just because people liked it.

First, it’s important to know that dogs are different from their close relatives in that they wag their tails much more frequently. Even when dog and wolf pups are raised the same way, the species have different tail-wagging behaviors as early as three weeks of age. Although individual dogs wag their tails different amounts, and wagging can vary by breed and sex, dogs wag their tails more often and in more contexts than any other canid, which includes species like coyotes and foxes.

And dogs wag their tails to communicate a lot of different messages. When carrying their tail low, wagging can be a sign of submission, appeasement, or that they’re not being aggressive. Dogs may wag their tail as a requesting signal — like to ask for more food from humans. Of course, dogs also wag when they’re fired up or happy. Interestingly, dogs wag more to the right when they have positive emotions and more to the left when they’re withdrawing from a situation.

But why did dogs evolve to wag so much?

For a new opinion letter published in the journal Biology Letters, researchers had two hypotheses. Both have to do with dogs’ domestication about 35,000 years ago — because their evolutionary history is deeply tied to ours.

The first hypothesis is that dogs evolved to wag their tails so frequently because ancient humans liked it. Either consciously or unconsciously, people may have preferred dogs who wagged more often — and perhaps more rhythmically. Humans have a keen sense of rhythm, and our brains prefer rhythmic stimuli, which are evenly spaced in time. This could have led humans to select for dogs who wagged more often and more rhythmically and could explain why present-day doggos wag their tails so often when interacting with people.

The other hypothesis is that as dogs became domesticated, and humans selected for traits like friendliness, genetically linked but unexpected traits became more common. In one famous example of this phenomenon, scientists bred the most docile silver foxes in a speed-run at domestication, and the foxes evolved floppier ears and wagged their tails more frequently than their wild ancestors. This could be due to a genetic link between tail anatomy or brain function related to a wagging tail and friendliness — and could be exactly what happened to dogs tens of thousands of years ago.

But no matter how or why tail-wagging evolved in dogs, two things are certain: Tail-wagging doggies are cute as heck, and they’re all good boys (and girls).