I was doing some research on frequency dependent selection and I found a really amusing and interesting article relating frequency dependent selection to the persistence of left handedness in humans! After many articles about butterflies this was a find!
Reminded me of you all and thought you might want to read it to:
TL;DR: Basically the left handedness trait has been consistent at 10& since neolithic times. Scientists now think that this is an example of negative frequency dependent selection. The rare lefties have a slight fitness advantage in combat but only while they're percentage remains low. Neat!