Which Side of the Body a Dog Wags Matters

Dogs wag their tails because they're happy, right? Turns out, it might be because the tail-wagging makes people happy, reports the Washington Post. Or, as the researchers put it in their new study in Biology Letters, we humans have a "proclivity for rhythmic stimuli," and our forebears may have gravitated toward the trait when domesticating wolves eons ago. Generations upon generations later, dogs have become prolific waggers, while their wild cousins rarely wag at all. It's one of the insights gleaned by scientists who pored over more than 100 studies on why dogs wag, per Science.

"We may not be able to take a time machine back to the beginning of the dog-human relationship, but we can look at dog behavior today in tandem with human behavior to try and understand what that domestication process looked like," co-author Dr. Taylor Hersh of Max Planck Institute for Psycholinguistics in the Netherlands tells the Guardian. Another intriguing detail: Dogs tend to wag more to the right side of their bodies if they want to approach and to their left if they want to withdraw. "Perhaps the coolest thing is that dogs can perceive those asymmetries in other dogs," Hersh tells Science.

One big unknown is whether dogs are conscious of communicating different messages with their tails, notes Smithsonian. The next step would be to conduct more focused studies in which dogs' brains, heart rates, cortisol levels, etc., were monitored while they are wagging in different situations. "People think wagging tail equals happy dog," Emily Bray of the University of Arizona, who was not involved in the study, tells Science News. "But it's actually a lot more complicated than that." (More dogs stories.)