ELI5: How did single cell organisms evolve into having things like eyes which seems like one of the senses that would evolve out of nowhere?

ELI5 (Explain it Like I'm 5): How did single cell organisms evolve into having things like eyes which seems like one of the senses that would evolve out of nowhere?
REDDIT TOP NEWS | AUGUST 15, 2013
http://pulse.me/s/pdpnS
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Also see the book, The Greatest Show on Earth: The Evidence for Evolution by Richard Dawkins -- Available at fine bookstores and libraries everywhere, including BookRenter and Amazon.