“But for most trees, height is all about getting more sun. A forest is an intensely competitive place, and sunlight is a scarce but critical resource. And even when you’re a redwood, the tallest of all tree species, you still have to worry about getting enough sun because you’re in a forest of other redwoods. Often a species’ most important competitor is itself. Thus the redwood is locked in an evolutionary arms race—or in this case, a “height race”—with itself. It grows tall because other redwoods are tall, and if it doesn’t throw most of its effort into growing upward as fast as possible, it will literally wither and die in the shadows of its rivals.”