I’ve always wondered how eyes evolved.
You need an optic nerve to transmit the info to the brain, but why would we evolve eyes without that, or an optic nerve without eyes. What purpose would it serve?
Maybe a random mutation led to eyes that were useless till then a nerve evolved like a million years later?
Or they both happened at the same time over a million years or so?
In: Biology
You have the nerve for lot of other usages than to see that go to the brain.
Then the question is what is an eye and what is an optic vs other nerves? Single-celled organisms can detect light but it is not an eye. Multicellular life has never sent a lot of different signals like for touch and nerve like that can be adapted to transmit information of a cell detect light.
Look at [https://en.wikipedia.org/wiki/Evolution_of_the_eye#/media/File:Diagram_of_eye_evolution.svg](https://en.wikipedia.org/wiki/Evolution_of_the_eye#/media/File:Diagram_of_eye_evolution.svg) that is how eyes evolved in vertebrates. There are nerve-to-light cells with nerve connections that are not eye but at the same time, we do not call it an optic nerve. It is clear the nerve connection is there before the eye because the eye is an advanced form of light light-sensitive body part.
If you require it to be an optic nerve the answer might be the same time if we define an optic nerve as the nerve connection to the eye. It is alos quite a meaningless answer because it is only one about of a word change
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