1320 THE STRUCTURE OF EVOLUTIONARY THEORY
and impersistent in timing, the capacity to "shut down" for periods of dormancy
between such favorable moments gains a second important adaptive value.
But these two reasons for dormancy—to survive seasonal periods of darkness at
high latitudes and to "wait out" silica-poor times between episodes of upwelling—
operate entirely in the microevolutionary world of ordinary Darwinian selection. In
this lucky case, these particular advantages did scale up to good fortune, given the
factor favored by many researchers for the primary agent of the K-T killing
scenario—extended darkness from a global dust cloud generated by the impacting
bolide and its excavated and elevated earthly products. Thus, in this hypothesis, the
relative prosperity of diatoms vs. the relative destruction of forams and other
planktonic groups arose by the fortuity of how key adaptations for background
conditions happened to "play" in an unpredictable and utterly different world of
catastrophic impact. These "different rules" happened to suit diatoms and spell
disaster for forams.
And if diatoms prevailed by such good fortune, let us not forget a key reason
behind the possibility of this most immediate interaction between me as writer and
you as reader. Dinosaurs and mammals had shared the earth for more than 130
million years, fully double the subsequent period of mammalian success that led to
the possibility of Homo sapiens among some 4000 other living species in our
mammalian clade. If the data of Sheehan et al. (1991) hold, and dinosaurs did persist
in respectable abundance right to the moment of impact, then we may reasonably
conjecture that, absent this ultimate random bolt from the blue, dinosaurs would still
dominate the habitats of large terrestrial vertebrates, and mammals would still be rat-
size creatures living in the ecological interstices of their world. In this most vitally
personal of all cases, we really should thank our lucky stars that, at least in one
cogent interpretation, certain marks of our ancestral incompetence—persistently
small size in a dinosaurian world, for example—suddenly turned into a crucial and
fortuitous advantage under the different rules of K-T impact, while the former source
of triumph for dinosaurs may have spelled their doom under these same newly
imposed rules. To be sure, this speculative scenario only references a particular event,
and its much later impact upon the possibility of origin for one odd species. Yes, of
course, we seek general theory as the goal of science, not the explanation of such odd
particulars. But this tale, above all, happens to be our particular, and the most
precious source of our possibility. Enough said.
THE PARADOX OF THE FIRST TIER: TOWARDS A GENERAL
THEORY OF TIERS OF TIMEAlthough I have tried to present a critical exegesis of both the sources and the logic
of Darwin's argument for general progress as a broad statistical and accumulating
consequence of biotic competition in a crowded world, I must also confess that
Darwin's rationale and development seem basically sound to