I adopted my cat from the shelter and he also probably had a tough life before being rescued (he's just a regular domestic short haired orange tabby). When I first got him he didn't purr ... but one day I noticed that he was breathing like cats do when the purr (short & fast) but there wasn't any purring sound. He continued to do that and if I put my ear close to his side I can hear a tiny purr sound. After a year he's got a little louder but not much and most people can't tell he's purring. He startles very easily (even when sleeping) and I think that he must have learned that before when he was younger. I guess both our cats must have had it tough as kittens and didn't learn how to purr like most cats do. But some seem to be able to learn as they get older ... I guess the most important thing is they now have good and safe homes to live as happy cats!