Fri 20 Aug, 2010 11:39 am
Why do cats purr?
Leslie A. Lyons, an assistant professor at the School of Veterinary Medicine at the University of California, Davis, explains.
Over the course of evolution, purring has probably offered some selective advantage to cats. Most felid species produce a "purr-like" vocalization. In domestic cats, purring is most noticeable when an animal is nursing her kittens or when humans provide social contact via petting, stroking or feeding.
Although we assume that a cat�s purr is an expression of pleasure or is a means of communication with its young, perhaps the reasons for purring can be deciphered from the more stressful moments in a cat�s life. Cats often purr while under duress, such as during a visit to the veterinarian or when recovering from injury. Thus, not all purring cats appear to be content or pleased with their current circumstances. This riddle has lead researchers to investigate how cats purr, which is also still under debate.
Scientists have demonstrated that cats produce the purr through intermittent signaling of the laryngeal and diaphragmatic muscles. Cats purr during both inhalation and exhalation with a consistent pattern and frequency between 25 and 150 Hertz. Various investigators have shown that sound frequencies in this range can improve bone density and promote healing.
This association between the frequencies of cats' purrs and improved healing of bones and muscles may provide help for some humans. Bone density loss and muscle atrophy is a serious concern for astronauts during extended periods at zero gravity. Their musculo-skeletal systems do not experience the normal stresses of physical activity, including routine standing or sitting, which requires strength for posture control.
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. The durability of the cat has facilitated the notion that cats have "nine lives" and a common veterinary legend holds that cats are able to reassemble their bones when placed in the same room with all their parts. Purring may provide a basis for this feline mythology. The domestication and breeding of fancy cats occurred relatively recently compared to other pets and domesticated species, thus cats do not display as many muscle and bone abnormalities as their more strongly selected carnivore relative, the domestic dog. Perhaps cats' purring helps alleviate the dysplasia or osteoporotic conditions that are more common in their canid cousins. Although it is tempting to state that cats purr because they are happy, it is more plausible that cat purring is a means of communication and a potential source of self-healing.
June 2009 Scientific American Magazine
The Evolution of House Cats
Genetic and archaeological findings hint that wildcats became house cats earlier--and in a different place--than previously thought
By Carlos A. Driscoll, Juliet Clutton-Brock, Andrew C. Kitchener and Stephen J. O'Brien
Unlike other domesticated creatures, the house cat contributes little to human survival. Researchers have therefore wondered how and why cats came to live among people.
Experts traditionally thought that the Egyptians were the first to domesticate the cat, some 3,600 years ago.
But recent genetic and archaeological discoveries indicate that cat domestication began in the Fertile Crescent, perhaps around 10,000 years ago, when agriculture was getting under way.
The findings suggest that cats started making themselves at home around people to take advantage of the mice and food scraps found in their settlements.
It is by turns aloof and affectionate, serene and savage, endearing and exasperating. Despite its mercurial nature, however, the house cat is the most popular pet in the world. A third of American households have feline members, and more than 600 million cats live among humans worldwide. Yet as familiar as these creatures are, a complete understanding of their origins has proved elusive. Whereas other once wild animals were domesticated for their milk, meat, wool or servile labor, cats contribute virtually nothing in the way of sustenance or work to human endeavor. How, then, did they become commonplace fixtures in our homes?
Scholars long believed that the ancient Egyptians were the first to keep cats as pets, starting around 3,600 years ago. But genetic and archaeological discoveries made over the past five years have revised this scenario—and have generated fresh insights into both the ancestry of the house cat and how its relationship with humans evolved.