Locke

In the book Locke talks about how the mind is capable of understanding an idea, but will be totally unaware of it until it is mentioned. He goes on to justify how it is not innate. he state that just because a person knows one thing that another does not, that does not mean that the idea is innate but the person is only familiarized with other ideas necessary for the understanding of a more general complex or maxim. however this is the question. If he is saying that more complex things are based on previous ideas then where did the first idea ever come from?