7th April 2011 Blind Cavefish

Three separate populations of cave fish have evolved to be

• blind,
• pale,
• sleep 2-4 hours. 

 When interbred, these separate populations produced young that could see, showing that the genes causing the degenerate blindness were different in the different populations.

http://blogs.discovermagazine.com/notrocketscience/2011/04/07/sleepless-in-mexico-–-three-cavefish-groups-independently-evolved-to-lose-sleep/