Blue Eyed Baby
Blue eyes seem to be a rare example of a genetic trait that originated relatively recently (6000-10000 years ago) and spread aggressively. All blue-eyed individuals now alive appear to be descended from a single individual. The trait has spread very widely through Europe and the Middle East, and has nearly completely displaced brown eyes in several parts of the world (99% in Estonia) even though blue eyes represent only 2% of the World population.
Since blue eyes are usually recessive, the large number of blue-eyed individuals in some populations suggests a significant selective advantage. This is somewhat surprising in that blue eyes are very rare among mammals in general.
I have heard anecdotal claims that blue-eyed individuals see better in the dark.