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, classify squirrels based on their color, and play a game that measure how well adapted each color squirrel is to its environment. Together we can crack this nut! By engaging with SquirrelMapper you can contribute to an important scientific discovery about evolution in action in our own backyards.