Why do cats purr?

Cat Facts, Cat Health posted on September 02 2016 by

Everyone knows that cats purr when they’re happy, but did you know they also do it when they’re sick or frightened, when they’re giving birth, and even when they’re dying? And not just practicing feline masochists—it’s regular, normal cats, too. Even your cat.

Not Just Because They’re Happy

Our sense that a purring cat is a contented cat actually results from a lapse in logic. We’re just used to hearing and feeling our cats purr as they curl up in our laps, lounge about on our beds, or secretly rub their saliva all over the sofa as we scratch them under the chin—moments when they are obviously happy. But how often do we find our cats under serious duress or feeling totally crummy? How often do we coach kitties as they push out litters of new cats?

Scientists have long known that cats purr under many different circumstances. In fact, enough cats purr nervously during stethoscope exams that one study advises veterinarians to shut down this noisy interference by blasting a spray can or by running tap water to get the cat to stop.

That said, researchers still haven’t figured out all the reasons for purring, although most hypotheses rely on the idea that its main function is communication. Cats learn to purr a few days after birth, at which point it likely has a twofold purpose: Kittens purr to tell their mother where they are (quietly, so as not to alert predators); and the mother purrs to bond the kittens to her and to lull them to sleep. Although they can’t hear for the first two weeks, they still feel the vibrations.

Once cats are on their own and depend on someone other than Momcat for food—you know, someone like you—they may purr to remind you to feed them, although scientists have determined that the “feed me” purr is not a pure purr, but rather includes meows and other high-pitched vocalizations intended to compel you to break out the can opener, in the same way that a (human) baby’s shriek demands immediate attention.hand petting cat purring orange cat cropped

This similarity between the cry of an infant and the “feed me” purr of a domestic cat is no coincidence. Nor is it some kind of adaptation that cats have developed over centuries of contact with people. Evidence suggests that it’s actually a manipulative tactic that your cat figured out in his own short lifetime, based on your responses, or lack thereof, to the whole range of sounds he makes. Feral cats do not make these sounds, nor, for that matter, do other purring felines like cheetahs, bobcats, and pumas.

With this knowledge in hand, you have no doubt arrived at a crossroads. Should you feed Kitty more often, or entrench yourself even further lest you surrender your last shred of self-respect to a ten-pound Machiavelli?

The Healing Power of the Purr

Other situations when cats purr seem, paradoxically, not to hinge on communication with humans or other cats, but with themselves. When cats are injured or very sick, and even at the very end of their lives, they often purr. Scientists theorize that in these moments, cats purr to comfort themselves through pain and fear, in much the same way that people tell themselves “I’m okay, I’m okay, I’m okay” when ill or agitated. If Freud analyzed cats, he’d probably say that purring returns a sick cat to the cocoon of kittenhood, when his mother and littermates surrounded him with their rumbling.

Particularly fascinating is a newish line of research that suggests purring may be essential to cats’ survival—not only because purring helps them to cope with illness and stress, but also because the vibrations may help cats’ injured bodies to heal.

Unlike dogs, who over centuries of inbreeding now have osteoporosis, dysplasia, and other bone disorders, cats can often survive broken or injured bones without treatment. An old veterinary joke has it that you can stick a cat in a room with all his parts and he will put himself back together. This myth may have some grounding in truth. According to Leslie A. Lyons, now a professor of veterinary medicine at the University of Missouri, “Because cats have adapted to conserve energy via long periods of rest and sleep, it is possible that purring is a low-energy mechanism that stimulates muscles and bones without a lot of energy.”
Design. Engineering. Function.

There are ramifications for human medicine, too. If cats can vibrate themselves back to health, how might our bodies respond to those same vibrations? If sedentary kitties can keep their bones healthy by purring, what are the possibilities for osteoporosis patients, or for folks who haven’t exercised since flunking the Presidential Physical Fitness Test in sixth grade? And what about astronauts, who move only minimally during long missions, and who know that bone loss and other health risks are part of the game?

Treatments have been developed in recent years that subject hopeful osteoporosis patients to so-called “whole-body vibrations,” and products have flooded online markets, at all price ranges, to take advantage of popular interest. After all, if you can stand on a vibrating platform for 20 minutes a few times a week, do you really need to walk, run, or brush up on your rhythmic gymnastics?

At the same time, researchers have studied whether whole-body vibrations actually do anything to stop, or even reverse, bone loss, as they seem to do in cats. Results were promising in initial studies on chickens and rabbits, but so far findings in humans are disappointing. Studies at Cornell and Harvard Universities found no evidence that vibrations slow, stop, or reverse bone loss in postmenopausal women, who are most likely to suffer from it. The studies instead recommended those old standbys: calcium, vitamin D3, and weight-bearing exercise. (Take that, Internet hucksters!)

Some evidence, however, suggests that vibration therapy may offer mild bone strengthening in young patients (who are unlikely to suffer bone loss in the first place). Interest in developing vibration therapies for astronauts seems to have already peaked, perhaps due to the unpromising findings of the most rigorous studies.

But what of the kitties? At least cats seem to benefit from their own survival mechanism, which is not only good news for cat people but also, in its own way, pretty catlike. (With the rare exception of house-fire heroines, when have cats been known for their altruism?) And even if your own purring kitty, or a reasonable facsimile of him, can’t save your bones, the mental benefits can’t be beat.


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