Do all types of pigs have a curly tail?

Only domesticated pig species have curly tails and within each of those breeds, the tail may be straight or kinked, not necessarily curly. The origins of the curly tail appear to be a product of selective breeding for aesthetic purposes. Pigs have been domesticated for thousands of years and those possessing a kinked or slightly curled tail were targeted in order to increase the chances of the offspring having a curly (and hopefully more so than their parents) tail. Through time the trait became common and the degree of curliness even greater.