What is Purring?

By RACHEL IBERS

Published: Monday, September 9, 2013

Even if you’re a dog person, you have to admit there’s something about having a warm, snuggly kitten on your lap that makes you smile. Maybe it is because kittens are so soft, or maybe it is simply because they are cute. But you know what I think? I think the way they purr is what makes kittens one of the best baby animals out there. 

But what exactly is purring? Is it really just the feline equivalent of smiling, or is it something more?

Purring is unique among cat sounds because it is continuous. This means a cat can purr both while it’s inhaling and exhaling. You and I can only talk or hum while we are exhaling, and similarly, cats can only meow, hiss or (in the case of big cats) roar while they’re exhaling. Purring, however, is continuous throughout a cat’s breathing cycle.

Purring is a result of the vibration of muscles in a cat’s voice box (vocal cords). Scientists don’t really know much more than that right now—a lot of how and why cats purr is still a mystery even to the experts.

While purring is unique to cats, not all cats can purr. There are two subfamilies of cats within the family Felidae (which contains all cats, big and small). One is called Pantherinae and includes big cats such as  tigers, leopards, jaguars and lions. None of these big cats can purr. The other subfamily, Felinae, contains domestic cats as well as small wild cats (like caracals, ocelots and servals), cheetahs and cougars. Many of these cats in Felinae can purr.

This distinction between cats that can and cannot purr indicates purring is a more recent evolutionary trait. It only occurs in domestic cats and their closest relatives. Lions can make a purr-like noise, but it is not truly caused by the vibration of the vocal cords and is not a real purr.

Like every odd animal attribute out there, purring is a result of evolution. Purring appeared in an early cat, and it was beneficial in some way. The trait of purring made a cat better than a cat who could not purr, and over time this helpful skill of purring became mainstream. But what made purring so great?

There are several theories about the purpose of purring. Like I said before, even scientists aren’t sure why or how cats purr. Purring probably is not simply a reflexive happy action (like smiling or a dog wagging its tail) because cats also purr when they are taking care of their kittens or when they are nervous or injured.

One theory about purring is it is a way to communicate with their young. Kittens are born deaf and blind and learn to purr within a few days. Some experts think purring is a way for the kittens to check in and let mama cat know they are okay, and for mama cat to help the kittens find her for warmth and milk. If this is true, the purring continues into adult life as a way to communicate with other cats and (in the case of domestic cats) to communicate with humans.

Purring  may also contribute to the cat’s health. Cats purr at a frequency between 25 and 150 Hertz. This frequency of vibration has been shown to help increase bone density and strength as reported in medical research article “Why Do Cats Purr?” by Scientific American. Cats are known for being durable (they supposedly have nine lives because they’re difficult to kill). They can fall from great heights, go for long periods without food or water and are commonly found alive after natural disasters like earthquakes and hurricanes. These purring vibrations may help to heal fractured bone and torn muscle and to keep cats healthy and strong.

Cats can, for example, spend long periods of time resting or hiding and conserving their energy. The purring may be a way to keep their muscles active and strong, without much activity or wasted energy. This kind of theory has huge implications for humans. Research is already being done with vibration and sound therapy to help heal and strengthen bones. Additionally, astronauts, who spend a lot of time in low-gravity environments, can quickly lose bone density and muscle strength. Scientists are looking at ways to create a kind of human purr that would help keep their muscles strong while they’re in space.

So the next time your kitty deigns to purr for you, consider it’s not just a version of the doggy tail wag—it could mean a variety of things and is probably good for both of you!

source