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"