Are you saying that a blind person doesn't have a sense of truth? There are many things that are true that I personally have not seen, but we have evidence to confirm it's validity. For instance, I have never been to china, but the evidence that china exists is overwhelming, but I have not actually seen china with my own eyes.
Response: True. Not all things require sight as proof. For example, I know you exists and you know I exists despite the fact that we can't see each other. However, what color shirt do I have on?
So there are things that require sight in order for proof while some things don't. And a species evolving into another species requires just that, sight.