CHAPTER TWELVE
Tiers of Time and Trials of
Extrapolationism, With an Epilog
on the Interaction of General
Theory and Contingent HistoryFailure of Extrapolationism in the Non-Isotropy
of Time and Geology
THE SPECTER OF CATASTROPHIC MASS EXTINCTION:
DARWIN TO CHICXULUBGreatness shines brightest in adversity. The logic of the Origin's 9th Chapter (1859,
pp. 279-311)—"On the Imperfection of the Geological Record"— shows Darwin's
reasoning at its very best and most systematic, all in the service of resolving his worst
problem. For, in this chapter, he must explain why the subject that should, at first
glance, have provided the strongest and most direct confirmation of evolution, seems
to mock, in its opposite message (at least if read in an empirically literal manner), the
gradual and incremental style of change touted throughout his book both as a
validation of natural selection, and as the primary empirical basis for confidence in
the factuality of evolution itself.
Darwin's logic proceeds in a systematic way within the norms of scientific
discourse, moving linearly and relentlessly through the chapter from the problem
with the easiest resolution (why do we not find living intermediary forms between
modern species) to the most difficult appearance of all (episodes of mass origination
and extinction in the fossil record). The opening issue, representing a misconception
and not a true threat, achieves an easy solution: evolution is a process of branching,
not of linear transformation, as the brilliant "tree of life" metaphor, closing the
operative chapter four on the mechanics of natural selection, had so well exemplified
(1859, pp. 129-130). Few, if any, living species are the unaltered forebears of another
modern form; rather, any two sister species have branched and diverged from an
ancient common ancestor. Therefore, we do not expect to encounter living
intermediates between extant species, for, although transitional forms surely existed,
they died long ago and should only be found in the fossil record.