When people come to realize that homosexuality is not "unnatural", then it is the moral teaching that should change. Thomas Aquinas, in the Summa I, q 1, art 1, says "there is no reason why those things which may be learned from philosophical science, so far as they can be known by natural reason, may not also be taught us". This is taken to mean that as "philosophical science" -- that is, our knowledge of nature -- increases, this knowledge should be included in doctrine.