@doonxib @judgedread He gives you a clear and logical explanation of how evolutionary pressure could effect such a change. You can call it "hypothetical" and "speculative" since we have no fossilized eyes, but give that lack of material evidence, we have little choice but to pick the most likely explanation. And that explanation is natural selection, which has proven its merit over and over and over again, both in the field and in the laboratory.

You apparently do not accept that such a thing as a light-sensitive cell could be created by mutation, so that precludes you from believing in evolution, but IF you were to assume that such a thing might happen, his explanation is perfectly rational and in accordance with what we observe in nature today: eyes of different designs and in different stages of development.