So, the useless mutation - that supposedly later led to a useful adaption after many more non-useful mutations - would not be passed on.
Sometimes they're useful, sometimes they aren't.
Sometimes they're passed on, sometimes they aren't.
Light sensitive cells cannot be the first step.
Why not?
What are the steps that led to light sensitive cells?
Feel free to google your little heart out.
You tell me: how many random mutations, none of which added survival and reproduction advantage have to accumulate before there is a useful trait?
I don't know. Do you?
If you're really asking me, I would say thousands at a bare minimum.
OK.
a thousand random mutations can occur, but why would they be passed on if they were not useful?
Unless they're harmful, why wouldn't they be passed on?