Why do cats purr? obviously they purr because they're happy but is there a point and do wild cats purr?

Cats purr to calm themselves and to calm their human. They purr because they are content or feel like they are threatened and want to send the message they aren't. All felines purr. I have been around lions; jaguars; mountain lions; tigers and every sort of house cat you can imagine. When the big cats are being given anesthesia they will purr to calm themselves, too. When threatened, they purr with the eyes partially open, when content the eyes close often. Watch and see. Nana