Twenty-one years passed between Charles Darwin'sepiphany that "natural selection"formed the basis ofevolution and thescientist's publication of On the Origin ofSpecies. Why did Darwin delay, and what happenedduringthe course of those two decades? The humandrama and scientific basis of theseyears constitute afascinating, tangled tale thatelucidates the character of a cautious naturalist who initiated anintellectualrevolution.