Decline, Fall, and

A Clever Argument

Ernst Haeckel, consummate as ever in debate, had structured his argument ingeniously. His biogenetic law was an exhaustive taxonomy of all possible results, for its umbrella extended to include the treacherous interpolations of cenogenesis along with the phyletic markers of palingenesis. It could engender no refutation because it included all phenomena. Haeckel's sycophants could ignore this tautological necessity, and rejoice with Schmidt that "the biogenetic law has no exceptions" (1909, p. 125).

Yet a fair moderator of this debate would have admitted a crucial question about relative frequency: the utility of Haeckel's law depended upon the dominance of palingenesis over cenogenesis. But if exceptions are more frequent then the supposed rule, then the theory must fall. It is a common assumption, repeated in almost every textbook, that Haeckel's theory of recapitulation collapsed under the ever-increasing weight of slowly accumulated exceptions—particularly of larval adaptations and paedomorphosis.1 My aim in this chapter is to argue that nothing could be further from the truth.

Natural history does not refute its theories by cataloguing empirical exceptions to them (while working within a paradigm that engendered the theory in the first place). With millions of potential examples in a discipline second to none for its superabundance of empirical information, how can a catalogue of counter cases ever refute a theory—especially when the theory itself allows a " reasonable"