Well, the superiority of Tit-for-Tat to most other Iterated PD strategies was discovered by evolutionary sims, and evidence has been found of its being used in nature. For instance, the behavior of WWI soldiers who stopped killing each other in the trenches by mutually choosing to only fire their artillery when fired upon first, and several instances in animals. I'm too lazy to look up the latter, but I'm pretty confident they're in The Selfish Gene. I think lessdazed is asking if there are any other important game theory findings that don't have that kind of real world support.