Most people believe cats purr when they are content or happy, end of story. While cats do purr when they are content, researchers attempting to uncover the answer to this 3,000-year-old mystery are finding the answer more complicated – and fascinating - than an expression of happiness.
All domestic cats purr, as do many wild cats, and purring occurs in a variety of situations. When cats purr in the presence of other unknown cats or kittens, the behavior may serve as a friendly greeting or to convey submissiveness. While it’s true that cats purr contentedly while on their pet parent’s lap, they also purr when they give birth, when they are frightened or even injured. Because kitties clearly cannot be content in all these situations, contentment or friendliness cannot be the only reason they purr.
So why else would they purr?
Natural selection tells us that a particular behavior or trait will persist through multiple generations only if it aids survival. For purring to exist in both domestic and wild cats, there must be something vital about the behavior. Purring is created by the vibration of the cat’s larynx and diaphragm, and therefore requires an expenditure of energy. If a kitty is sick, surely they wouldn’t burn calories unless it resulted in some sort of benefit, right?
We're all familiar with the expression “cats have nine lives”. Similarly, veterinarians have an old saying that if you put a cat who has broken bones in a room with other cats, the breaks will heal. In fact, cats are amazing self-healers: they have fewer post-operative complications than dogs, have a lower incidence of bone and joint disease than dogs, and 90% of cats survive high-rise falls! What could account for this remarkable set of facts, and is it related to purring?
In fact, there’s striking evidence that purring has healing properties. Researchers have found that vibrations in the frequency range between 25-50 hertz promote bone strength, stimulate healing of fractures, provide pain relief and help heal tendons and muscles. Bioacoustic researchers studied the purring of dozens of both domestic and wild cats, paying particular attention to frequency, pitch, loudness, and duration of purring in relation to the cat’s behavior. Guess what they found? The purring is in the range of 25-50 Hz, the exact range associated with healing properties such as increased bone density!
Maybe this has something to do with a cat’s uncanny ability to heal. And just maybe purring is part of the reason why, when we fall ill, having a cat sit on our laps can actually make us feel better! Whether it is simply the comfort of having a friend nearby, or the vibrational frequencies of your kitty’s rumble, the joy of a cat purring on your lap is priceless.
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