Willie, I just read through Aceresearcher's question asking GARs to
list their favourite answers and I saw with a mixture of pleasure and
dismay that you'd listed a question of mine. I was really, really
delighted to think you'd remembered this question. From my point of
view, it meant so much to finally get this piece of music from the
other side of the world within the day and it was duly warbled by moi,
recorded for posterity and given to a friend who, thankfully,
absolutely *adored* it (there's a significant 'provenance' associated
with the song for her family). I was dismayed to see, however, that
you put in a fair amount of effort for comparatively small recompense.
So, in order to go some way towards rewarding you for the work you put
in all those months ago, here's a no-brainer, one link, quickie that
will, naturally, result in a superb answer, worthy of a quintustellar
(??) rating. Why do cats purr?

Thank you kindly , I wasn't complaining (honest)...I'm just happy to
bring joy to other folks :)

As to why cats purr.....

The search term used (see below) yields a variety of links, raging
from the extremely interesting to the completely useless.

Here's the scientific view from the Scientific American: Ask the
Expert: Biology site (
http://www.sciam.com/askexpert_question.cfm?articleID=0005CB0D-82FC-1E31-82FC809EC5880000
):
 
Leslie A. Lyons, an assistant professor at the School of Veterinary
Medicine at the University of California, Davis, explains.

"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.

"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.

                                   ..o0o..

Personally, I think they do it because they can!

willie-ga

Google search terms used:
"why do cats purr"

Yeah, if I could purr, I would. I know you weren't complaining,
Willie. Your effort brought a lot of enjoyment to several people, more
than you'll ever know, and it's my pleasure to revisit it and give
you, hopefully, a fairer return on your effort. Best wishes.

Hey, Pinkfreud, I used to have a dear old cat called 'Wombat' who used
to sing a duet with my dog -- and I swear that they were singing
lyrics. Wombie would do the "Yow, yow, yo-o-o-o-ow" part and Zac would
do the "Woo, woo wo-o-o-o-o-oos". They'd even do little solos and then
back together for the chorus.

My theory is that the purr is essentially a cat humming because he
can't remember the lyrics. :-D