People sometimes try to score debating points by saying, Evolution is only a theory. That is correct, but it's important to understand what that means. It is also only a theory that the world goes round the Sun - it's just a theory for which there is an immense amount of evidence. There are many scientific theories that are in doubt. Even within evolution, there is some room for controversy. But that we are cousins of apes and jackals and starfish, let's say, that is a fact in the ordinary sense of the word.