Need help with biology facts for story

[Michelle A Cox]

Hi

I am writing a story and am stuck on the bilogy part.  The gist is that  
this group of people have been living underground for a great many years.   
They fear the sun, so they only come out at night.

What I would like to know is what physical changes the body would go  
through after so many years without the sun.  Would they lose all the  
melanin in their bodies?  Would their eyes get bigger since firelight and  
moonlight is all they would have?  Things like that.

Also, I would like to know what would happen when they got out in the sun  
again.  If they did lose all the melanin, would it come back when exposed  
to sunlight?  Would it even be possible for them to ever live in the sun  
again?

Also, is there anything that could have caused them to not be able to  
stand the sun to begin with?  This would have to be something that would  
"evolve out" after a while so that this current generation could go back  
in the sun.  This doesn't have to be a real cause; a plausable  
hypothetical one would be ok, too.

Thanks,

Michelle

(Please e-mail me at cox_ma at cslab.uwlax.edu)