Question: Does the eyeballs grow before the eyelids or is it the other way around?

Ian Stephenson answered on 25 Jun 2014:

evolutinary wise, one way eyes evolve (its believed they evolved several times independently) is that an area of skin becomes slightly more sensitive to light purely by chance. This allows a simple creature to detect an approaching predator and take action, so it turns out to be slightly useful, conveys an advantage to the animal which has it, and that animal survives better, and has more offspring – so the change becomes more common (offspring are kind of like their parents).

The area may become more sensitive, because it really helps you not get eaten! but then one day a creature is born with a natural dimple in its skin around that sensitive patch. Not necessary very deep, but it means the sensitive patch is shaded from the sides a tiny bit, and is a little directional. this works even better as the creature can now get some kind of idea where the predator is coming from, so over generations the dimple turns into a deeper pit, and the patch gets more sensitive.

However now we’ve got this great tool for surviving – we can see things attacking us and LOOK for food (feed, fight, and flight) we need to protect it, and keep it clean which means eyelids evolve.

This might seem a bit crazy – after all being able to see REALLY BADLY isn’t much of an advantage. But imagine everyone was blind, but one person got a tingling on their skin when they were close to someone else… BIG ADVANTAGE. Even if it only works 1% of the time, getting eaten a tiny bit less than other similar creatures turns into a VERY BIG advantage over thousands of years, with thousands of your offspring, each potentially getting eaten thousands of times. If it saves 1% per day, within a few years only you’d be left.