Haeckel described the revolutionary power of Darwinian thought with a characteristic nourish:
Dogma and authority, mutually dedicated to the suppression of all free thought and unfettered knowledge of nature, have erected a barrier of prejudice two or three times stronger than the Great Wall of China about the fortress of organic morphology—a citadel into which all kinds of distorted superstition have withdrawn as their last outpost. Nevertheless, we go into the battle without fear and sure of victory. (1866, l:xv)
We may smile at the exaggeration or wince at a vigor rarely encountered in scientific treatises; still, we cannot deny that evolutionary theory was the most upsetting idea that later nineteenth-century science introduced to a world steadily retreating from traditional notions of static order. The influence of evolution in fields far removed from biology has been documented almost to exhaustion (at least to mine), but the impact of Haeckel's favorite weapon has not been widely noted by historians. Nonetheless, the theory of recapitulation played a fundamental role in a host of diverse disciplines; I suspect that its influence as an import from evolutionary theory into other fields was exceeded only by natural selection itself during the nineteenth century.
The historical chapters of this book deal almost exclusively with theories and debates about the mechanisms of relationships between ontogeny and phylogeny. I would need another volume even to begin an adequate treatment of how biologists used recapitulation in their