Your wiggle-butt pup wags his or her tail to show they’re happy, right? They’re signaling an incoming treat, scritches, or other joyful events. That’s what most pet parents assume. It turns out there can be much more to the story a tail tells! Researchers from Oregon State, Turin, and Sapienza universities recently published an exhaustive review in Biology Letters that gathers research from more than 100 studies of tail-wagging in dogs. The cumulative findings led the authors to call for a more systematic analysis of this prevalent behavior. They propose gathering videos of dogs exposed to different stimuli with tracking of physiological measurements such as heart rate, heart rate variability, cortisol, oxytocin, serotonin, and testosterone to truly decode the mysteries and meaning of tail wags.
“As it turns out, tail talk is complex: It can signal aggression, fear, appeasement, love, arousal and anticipation depending on direction, carriage, and tempo. In senior companion animals, low tail carriage can also signal pain or discomfort, arthritis, injury, or a sign of a medical issue such as a urinary tract infection,” said Dr. Laurie Brush, founder of Heaven at Home Pet Hospice.
The Way of The Wag – Left & Right
Dogs show biases in direction of wag depending on the stimuli. Right side wagging shows left hemisphere activation in positive associations, such as seeing their person.
Left side wagging indicates right hemisphere activation, which controls fear or depression. Dogs shown videos of left-wagging tails exhibited physiological signs of stress. Researchers believe the cerebellum is involved because increases in electrical stimulation in that area correspond to an increase in tail wagging.
Which leads to another interesting finding. Aggressive dogs actually wag their tails more and have lower serotonin levels than non-aggressive dogs.
So how did this complex system of communication between dogs – and to humans – evolve?
Keep the Beat to Eat
One popular theory called the “Domesticated rhythmic wagging hypothesis” suggests that tail-wagging evolved as dogs differentiated themselves from other canids by catering to the human ability to perceive and produce rhythmic sequences. In human brains, rhythmic stimuli triggers pleasurable responses and engages brain networks that are part of the reward system. Humans are believed to have domesticated dogs sometime between 165,000 – 50,000 years ago. But one wonders, who domesticated who?
Canny canines interested in befriending an abundant food source clearly understood that natural selection made happy tail talk a survival tactic. So, what’s your modern-day dog’s tail telling you?