Let me throw in a few thoughts that might just be helpfull.
Light sensitivity seems to be a pretty common feature of most all living critters. For example, many, many plants exhibit light conciousness, either opening or closing under certain light conditions, growing towards light sources or turning to present the largest surface area towards the sun.
None of these are a true eye or vision, but they do show some of the simple reactions possible towards the stimulus of light. In the simple animal category there are floating critters like jellyfish that rise or fall in the water column based on light. Again, no real vision but yet response to light.
So the basic parts seem to be pretty common. From that it is but a few steps to develop a true eye.
Here's a link to some info on how it
might have happened.
Aslan is not a Tame Lion
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