Planet of the Apes: Furry mammals evolved a tuned spin dry

Sep 04, 2012 by Faye Flam

When a wet dog shakes himself dry, he does something amazing. He hits just the right rhythm to maximize the drying effect with minimal effort. The seemingly casual jiggle imparts enough centrifugal force to expel 70 percent of the water in his coat in a fraction of a second.

This fact comes courtesy of experiments by David Hu, a professor of mechanical engineering and biology at Georgia Tech. He and his students found that the highly tuned drying ability is shared by 30 other furry mammals.

Hu thinks engineers can learn from some of the remarkable features that evolution has built into living things. He envisions harnessing this ability for devices that can dry or clean themselves, something like a Mars rover programmed to jiggle the dust off its solar panels.

He was initially inspired to study wet mammals by a toy poodle named Jerry, who was a gift to his current fiancee from her former boyfriend. Jerry ended up in Hu's lab, where high-speed cameras recorded and measured the rhythm by which he shook his coat dry.

Before Jerry, Hu had been interested in the way animals interact with water, but his focus had been on the insect world. Thanks to the surface tension of water, many insects can easily get stuck in a puddle or pond once they get wet. Predatory bugs called water striders - the subject of Hu's doctoral thesis - get around this with hairy feet that barely touch the water's surface.

The adaptation allows striders to make dinner out of less water-adapted insects.

Hu realized that surface tension also trapped water on mammals, and shaking was a common adaptation that helped them deal with it. The project expanded from Jerry to , , and a house cat.

In search of more mammals, Hu sent one of his graduate students to the Atlanta Zoo to spritz water on lions, tigers and bears, and record their drying techniques.

Fur, said Hu, is great for keeping animals insulated in cold air. It's not so good when it rains or when a furry animal falls into a frigid lake. Then, the fur can hold in cold water next to an animal's skin. A thoroughly wet 60-pound Labrador retriever, for example, holds about a pound of water.

Letting it dry by evaporation would sap energy equal to 20 percent of the dog's daily calories.

If an animal needs to get rid of the water to stay warm, then it's much more efficient to shake. Hu's study showed that most of the mammals that were observed did it. He watched shaking mice, rats, cats, goats, sheep, lions, tigers, bears, and giant pandas, to name a few. But the big surprise was that there was a predictable pattern across all these species - all imparted about the same amount of to expel water.

The force depends on the size of the animal and the frequency of the shake, Hu said, so to get the same force, little animals shake faster than big ones. Bigger dogs shake about three or four times a second; mice, about 30 times.

The water-expelling force also depends on how big the shakes are - their amplitude - said Hu, and most of the animals studied added oomph to each shake by having loose skin.

A dog, for example, shakes his spine through an angle of about 30 degrees, but his floppy skin swings through a full 90-degree angle. This, they measured by putting stickers on the dogs' backs and watching their motion.

Hu said he hasn't figured out a good way to get stickers on the backs of the lions and tigers - at least not yet.

Hu and his students Andrew Dickerson and Zachary Mills published their results in the Journal of the Royal Society Interface, which specializes in work that combines biology and engineering.

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. Fish said mammals probably co-opted the ability to shake, which originated far back in the evolutionary tree. Sharks, for example, do some fast twisting to help them tear up their prey.

"We can see the ability to twist all the way back to the first vertebrate."

Since evolution is basically a descent by modification, he said, mammals probably inherited the ability to shake from distant ancestors, and then modified it as a way to get dry.

And shaking with a definite rhythm isn't such a surprise, he said, since it happens all over the animal world. Dogs pant with a regular frequency, he said, tuned to help them get maximum cooling with minimum energy expenditure.

One mammal that doesn't seem too well-equipped to shake dry is the human being. Hu said he tried it once after a shower when he forgot to take a towel.

"It didn't work very well," he said. Humans don't have fur, so perhaps our ancestors lost the ability somewhere along the evolutionary line. There's also one type of hairless guinea pig that doesn't shake off water, he said. "They just sit there and shiver."

Explore further: Nature collides with James Bond: Newly discovered ant species hides in plain sight

More information: rsif.royalsocietypublishing.or… 08/16/rsif.2012.0429

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User comments : 17

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rod_russell_9
1 / 5 (9) Sep 04, 2012
I don't follow the evolution aspect of dogs shaking to dry off. It seems gratuitous since the article does not explain how only evolution could possibly explain this behavior.
Deathclock
1.6 / 5 (7) Sep 04, 2012
I don't follow the evolution aspect of dogs shaking to dry off. It seems gratuitous since the article does not explain how only evolution could possibly explain this behavior.


Cold and wet, shake off the water or die... clear path for natural selection to select individuals who shake when wet...

No one said it's the ONLY possible explanation, only that it is a plausible explanation.
antialias_physorg
5 / 5 (2) Sep 04, 2012
No one said it's the ONLY possible explanation, only that it is a plausible explanation.

Putting the label 'evolution' on this seems hasty/implausible (and I'd even argue: wrong).

This looks much more like simple learned behavior. Like learning to walk. Or learning to speak. You try until you find the method that works best.
And with something as frequent as the need to dry yourself off that learning comes very early in life.
El_Nose
1 / 5 (3) Sep 04, 2012
I don;t think this is instintual or even genetic... it seems to me because some mammals need not ever get wet ... rich person's dog, and they still know to do this, and have the same frequency. It seems to me this is just behavior... much like a baby knowing how to suck from birth .. we say insticnt, but given the animals limitations this is the only course possible. It's the only thing it can do... the fact that the guinea pig with no fur just sits there and shivers I think reflects the cognitive thinking of the pig. glue on fur and see if it behave differently. that would be a test.
foolspoo
2.6 / 5 (5) Sep 04, 2012
I don;t think this is instintual or even genetic... it seems to me because some mammals need not ever get wet ... rich person's dog, and they still know to do this, and have the same frequency. It seems to me this is just behavior... much like a baby knowing how to suck from birth


are you aware that you are arguing with yourself.. you deny the fact that an animal has an instinct and go on to explain (poorly) what an instinct is.
Deathclock
1.6 / 5 (7) Sep 04, 2012
No one said it's the ONLY possible explanation, only that it is a plausible explanation.

Putting the label 'evolution' on this seems hasty/implausible (and I'd even argue: wrong).

This looks much more like simple learned behavior. Like learning to walk. Or learning to speak. You try until you find the method that works best.
And with something as frequent as the need to dry yourself off that learning comes very early in life.


If the behavior is present at or very shortly after birth then it is not learned... babies don't learn to cry when hungry, chimps don't learn to grab on to their mothers fur by first falling 50ft out of the tree...

Also, as el nose stated (accidentally against the point he was trying to make...) even dogs who live to adulthood isolated from other dogs and who never get wet will shake off the first time they get wet... that's not possibly learned behavior.
Deathclock
1 / 5 (3) Sep 04, 2012
I don;t think this is instintual or even genetic... it seems to me because some mammals need not ever get wet, rich person's dog, and they still know to do this, and have the same frequency. The fact that the guinea pig with no fur just sits there and shivers I think reflects the cognitive thinking of the pig.


okay, wow... first, you argue that this is NOT instinct or pre-programmed behavior by stating that a rich persons dog who never gets wet will still know how to shake off water the first time they do... which is of course evidence to the OPPOSITE of your claim... then you go on to assert that shivering is a conscious and intentional behavior when it absolutely is not, it is a reflex.

You couldn't have been more wrong if you were trying to be intentionally and comically wrong.
antialias_physorg
5 / 5 (1) Sep 04, 2012
It seems to me because some mammals need not ever get wet ... rich person's dog, and they still know to do this

Even rich people's dogs get bathed.
Deathclock
1 / 5 (3) Sep 04, 2012
It seems to me because some mammals need not ever get wet ... rich person's dog, and they still know to do this

Even rich people's dogs get bathed.


Maybe... I have an indoor dog and I haven't bathed her in years... She doesn't smell, she isn't dirty, and she is healthy. Dogs are pretty self sufficient like that, they don't sweat and they clean themselves with their tongues (and as long as they have good oral hygiene this is more than adequate). She is a short hair breed though, might be different with long hair dogs, I've never had one.

Many dogs are taken from their parents/siblings shortly after birth, mine was... We picked her up at only a few days old. Since then she has had very limited contact with other dogs... only in passing while walking outside. If she learned how to shake to dry off it wasn't from other dogs and it certainly wasn't from me.
antialias_physorg
5 / 5 (1) Sep 04, 2012
Some things you really don't need anyone else to learn it from.
Example: Rubbing your hands to get them clean of rough dirt. Genetic? I would argue: no. It just works. You do it once and you figure "Hey: that works - I'll keep doing that"...for an extreme example one might go for: how do we know how to masturbate? We don't need to learn that. We do something and figure: "Cool". So we keep doing it.

Similar with shaking to get dry. You try three different ways in the space of a few seconds and you've got the one that works. Invocing genetics or evolution or taught behavior for that is overkill.
Trial and error is more than enough, if your search space is small (and in the case of shaking to get dry it's very small)
rubberman
1 / 5 (2) Sep 04, 2012
This one may have been a waste of money guys. The only way a quadriped CAN shake itself is to create the centrifugal motion via a combination of head rotation around the spine coupled with weight transfer from left side to right. The rythym of the shake is dictated by limb length although the intensity can vary with the degree of wetness. Not instinct so much as choice, stay wet or shed the water.
But if anyone has any video of animals trying to "buck" the water off or using a towel I'd love a peek! (some animals find that ground rolling also works, depending on how loose the soil is).
Deathclock
1 / 5 (3) Sep 04, 2012
Well, we know that evolution can dictate behavior... so why not this?

Is there a good reason that you don't think this behavior was selected for when we know things like altruistic behaviors are?
Deathclock
1.7 / 5 (6) Sep 04, 2012
I don't believe in Tabula Rasa... We are "pre-programmed" with behaviors that we call "instincts". Most of what infants do is instinctual rather than learned, and I am willing to bet that if you took a dog from the day it was born and isolated it from all other dogs and prevented it from getting wet until adulthood it would shake to dry off the very first time it got wet without "trying" anything else first.
Shabs42
not rated yet Sep 05, 2012
Another interesting experiment could be to take mice or other mammals, shave their fur off and see if they still shake out of habit. Try it with those that have been wet before, some that have seen other animals shake but not been wet themselves, and some that have never been around another wet animal in their lives.
antialias_physorg
not rated yet Sep 05, 2012
Well, we know that evolution can dictate behavior... so why not this? Is there a good reason that you don't think this behavior was selected for when we know things like altruistic behaviors are?

Altruistic behavior is not genetically selected for. People who behave in a altrusitic manner are selected for. The first is a genetic selection the latter is a memetic selection.
You can make the children of a saint into just as much a killer machine given the appropriate surroundings as you can make the children of mass murderers into social indiviudals. The Stasi (and the KGB) demonstrated that amply by taking away the children of dissidents and raising them in state run organisations while the parents were in prison.

The main reason why I think most behavior is not genetic is: The amount of information on DNA is very little. 2GB of information isn't enough to code for a complicated body blueprint AND behavior (especially since a lot of that info is similar to bacteria)
Deathclock
1 / 5 (3) Sep 05, 2012
Well, we know that evolution can dictate behavior... so why not this? Is there a good reason that you don't think this behavior was selected for when we know things like altruistic behaviors are
Altruistic behavior is not genetically selected for. People who behave in a altrusitic manner are selected for. The first is a genetic selection the latter is a memetic selection.


Selection only works through genetics... Altruistic behavior is driven by empathy, and empathy is what was selected for through genetics. Empathy you have no control over, either you feel it or you do not, your behavior you do have control over (disregarding the free will argument).
Deathclock
1 / 5 (3) Sep 05, 2012
You can make the children of a saint into just as much a killer machine given the appropriate surroundings as you can make the children of mass murderers into social indiviudals.


Of course you can. But the discussion of evolved traits necessarily precludes the effects of experiences after birth. A trait is something you are born with, and the trait that you are born with that leads to altruistic behavior is the capability to feel empathy towards others... there is evidence that some people are not born with that trait and never possess it.

The main reason why I think most behavior is not genetic is: The amount of information on DNA is very little.


Genetics causes the initial configuration of your brain, this leads to emotions such as fear and empathy, these emotions drive behaviors. The capability for the emotion is selected for, the behaviors follow.

Don't tell me that you think fear is a choice... it is a pre-programmed emotion that was selected for.