560 THE STRUCTURE OF EVOLUTIONARY THEORY
Mayr, however, did offer the following conjecture—wrong in many details (as we
now know), yet firm in its confident adaptationist scenario—for the evolution of
lungs. (Devonian fishes already possessed lungs, for the trait is symplesiomorphic
in tetrapods and their aquatic ancestors, with the swim bladder of later fishes as its
derived homolog. But note Mayr's confidence in his erroneous conjecture for the
easy construction of such a novelty—from scratch, gradually, and in pure adaptive
continuity with unchanging function):
I think the development of lungs is now pretty well understood. Certain
fishes during the Devonian period lived in stagnant, fresh water swamps,
where oxygen was so scant that respiration through the skin and the gills no
longer provided the necessary oxygen. Apparently they came to the surface
and gulped air, from which the membranes of the digestive tract took up
oxygen. When that stage was reached, there was a tremendous selection
pressure for developing diverticles and enlarging this respiratory surface of
the digestive tract. As soon as the necessary gene combination providing
such diverticles appeared, selection pressure could push this tendency
further and further, and this led quite naturally to the development of lungs
(in Tax, 1960, volume 3, p. 136).As documented in Chapter 6, the putative domination of biotic over abiotic
competition provided Darwin with a rationale for defending general progress in the
history of life. The synthesists upheld this orthodoxy as well, thereby imparting
broad predictability to the stately unfolding of life. Huxley offered a clear
assessment of relative frequencies in the founding document (1942, p. 495):
"Sometimes the inorganic environment changes markedly, as when there is a
climatic revolution, such as occurred at the end of the Cretaceous; but in general it
is the organic environment which shows the more rapid and important alterations."
In his concluding address to the entire Chicago symposium, Huxley then
remarked, with the expanded scope and surer resolve of nearly two decades in
hardening: "Improved organization gives biological advantage. Accordingly, the
new type becomes a successful or dominant group. It spreads and multiplies and
differentiates into a multiplicity of branches. This new biological success is usually
achieved at the biological expense of the older dominant group from which it
sprang or whose place it had usurped. Thus, the rise of the placental mammals was
correlated with the decline of the terrestrial reptiles, and the birds replaced the
pterosaurs as dominant in the air" (1960, p. 250).
In citing the canonical example of dinosaurs and mammals, Huxley exposes
the heart of the extrapolationist error—the assumption that large-scale pattern can
be inferred by extending, through immense time, the small effects of observable
processes (in this case the supposed general and overall "superiority" of mammals
over reptiles in most cases of immediate competition). In explaining trends, the
greatest threat to this orthodoxy lies in occasional but profound environmental
catastrophe that disrupts and resets the pattern accumulating