Briefly what we did......Forty-seven felids were recorded including cheetahs, ocelots, pumas, domestic cats, and servals. A Sony TCD-D8 Digital Audio Recorder (DAT) and Statham Radio microphones recorded the purrs. Cat's Purr bio-mechanical healing mechanism
FFTs and spectrographs were performed using National Instrument's Polynesia. An accelerometer was also used to measure domestic cat purrs. Then we analyzed hours and hours and hours of purrs! This is what we concluded...
All smaller felids, including the domestic cat, caracal, serval, puma, ocelot, and even some large cats such as lions and cheetah purr. Since the 1970's no one has pursued research into the 3000 year old question, "Why do cats purr?" Perhaps it is because, one, we didn't have the knowledge we have now, and two, it was simply easier to assume that cats purr when they are content, which cannot be argued-they do purr when they are content. However they also purr when frightened, severly injured, giving birth and even while dying. Because of this, the contentment hypothesis clearly cannot be the only reason cats purr:.
(1) A vocalization is used to display a particular emotion or physiological state. This enables an individual in society or pack to be able to express themselves. As any cat owner knows well, there are different "meows" for different emotions. A cat owner knows the difference between their cat's "fearful hiss", "food meow", and "let me oooouuutttt!!!" This cannot be applied to the purr however. Cats purr even when they give birth and when severely injured in a barren cage at the veterinarian's. There are cases of cats purring when they are in grave physiological or psychological stress, as well as when they sit on your lap. Therefore, purring really cannot be considered a vocalization, as the purr is produced under differing emotions or physiological states. As an example, a cat hissing when he/she was happy and when he/she was scared, would confuse the rest of the cat's companions and probably would lead to him/her being ostracized.
(2) Natural selection insures that a particular trait be advantageous to an animal. Admittedly, there is some benefit obtained from purring to ones' self or to kittens, (a sort of kitty lullaby if you wish). Yet, there does not appear to be a strong 'survival' advantage to this behavior, unless, of course, you wish to constantly display submission. For the purr to exist in different cat species over time, geographical isolation etc. there would likely have to be something very important (survival mechanism) about the purr. There is also would have to be a very good reason for energy expenditure (in this case creation of the purr), when one is physically stressed or ill. The vibration of the cat's diaphragm, which with the larynx, creates the purr, requires energy. If an animal is injured they would not use this energy unless it was beneficial to their survival. When was the last time you heard someone singing, or humming to themselves (before pain drugs, and they weren't on any when they came in) when they were in the emergency room with a broken leg? The purr has to be somehow involved with survival.
Old wives' tales usually have a grain of truth behind them, and most people have heard of a cat's "nine lives." There is also an old veterinary adage still repeated in veterinary schools which states, "If you put a cat and a bunch of broken bones in the same room, the bones will heal." Any veterinary orthopedic surgeon will tell you how relatively easy it is to mend broken cat bones compared with dog bones which take much more effort to fix, and take longer to heal. There is excellent documentation of the cats' quick recovery from such things as high-rise syndrome. First mentioned by Dr. Gordon Robinson in 1976, high-rise syndrome was later studied by Whitney, W., and Mehlhaff, C., (1987) the Journal of the American Veterinary Medical Association. They documented 132 cases of cats plummeting many stories from high rise apartments, (average 5.5 stories) some suffering severe injuries. Interestingly, 90% of these cats survived. The record for survival from heights is 45 stories, however most cats suffer from falls of 7 stories or more and manage to live.
It's not antigravity but it sure proves the Cymatic point of the previous post.