Spin-Dry the Dog
Anyone with a dog has been amused or amazed at how well they shake water off after coming out of the pool or lake. The shakes start at the head and move like a spin-drying machine down to the tail. Did you know most mammals, except humans, have the same app pre-installed?
David Hu at Georgia Tech decided to take his students on a science safari and find out the evolution of the doggy shake, according to PhysOrg, “Planet of the Apes: Furry mammals evolved a tuned spin dry.” What they found was pretty remarkable: “The seemingly casual jiggle imparts enough centrifugal force to expel 70 percent of the water in his coat in a fraction of a second.” They put stickers on dogs to measure the action, and found about a 30-degree angle of shake.
The team watched 30 other mammals, from “mice, rats, cats, goats, sheep, lions, tigers, bears, and giant pandas” do a similar shake, despite being widely separated geographically. Smaller animals have to shake faster to get the same centrifugal drying effect, but the behavior is similar. It’s not just the shaking that does the job; the skin is also loose enough to impart the energy to the fur. Good thing; animals could face hypothermia if they can’t get the water away from their skin fast enough.
The original paper on the Royal Society website Aug. 17 (open access) had very little to say about evolution: just one mention in passing, that “Many animals evolved physical adaptations to minimize infiltration of water into their furs or feathers.” The PhysOrg article, by contrast, seemed obsessed with saying how this behavior evolved. It brought in Frank Fish as chief storyteller:
Shaking is a useful adaptation, but did it show up in some ancestral mammal millions of years ago, or did it evolve independently in different lines? That’s hard to say, said evolutionary biologist Frank Fish of West Chester University….
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