Life has evolved over millions of years. Yet evolution can produce dramatic change quickly! The coat color of gray squirrels, which occur over much of eastern North America and are introduced around the globe, is a good example. Today most are indeed gray but two centuries ago most were apparently black. How could evolution change this species so profoundly and so quickly? Help us explore this question at SquirrelMapper where you can: contribute observations of squirrels from your own neighborhood, test hypotheses about why squirrel color varies geographically, directly measure natural selection on squirrel coloration by participating in our "squirrel hunt" exercise, view the geographical pattern of morphs across the gray squirrel's range. Together we can crack this nut!