Why do quaking aspens grow in prominent clumps rather than randomly scattered across the landscape? Why and how does a rufous hummingbird drop its metabolism to one-hundredth of its normal rate? Why do bull elk grow those enormous antlers? Using his experience as a biologist and ecologist, George Constantz illuminates these remarkable slices of mountain life in plain but engaging language. Whether it sketches conflict or cooperation, surprise or familiarity, each story resolves when interpreted through the theory of evolution by natural selection. These provocative accounts of birds, insects, rodents, predators, trees, and flowers are sure to stir the reader's curiosity. Who wouldn't be intrigued by a rattlesnake's ability to hunt in total darkness by detecting the infrared radiation emitted by a mouse? Or how white-tailed ptarmigan thrive in their high, treeless alpine environments - even through the winter? The narratives, often brought home with a counterintuitive twist, invite readers to make new connections and broaden perspectives of a favorite outdoor place.