Darwin's Dangerous Idea - Evolution and the Meaning of Life

270 BULLY FOR BRONTOSAURUS The Spandrel's Thumb 271
should expand our reverse-engineering perspective back onto the processes
of R and D, and embryological development, instead of focusing "exclusively
on immediate adaptation to local conditions." That, after all, is one of
the main lessons of the last two chapters, and Gould and Lewontin could
share the credit for drawing it to the attention of evolutionists. But almost
everything else that Gould and Lewontin have said militates against this
interpretation; they mean to oppose adaptationism, not enlarge it. They call
for a "pluralism" in evolutionary biology of which adaptationism is to be just
one element, its influence diminished by the other elements, if not utterly
suppressed.
The spandrels of San Marco, we are told, "are necessary architectural byproducts
of mounting a dome on rounded arches." In what sense necessary?
The standard assumption among biologists I have asked is that this is
somehow a geometric necessity, and hence has nothing whatever to do with
adaptationist cost-benefit calculations, since there is simply no choice to be
made! As Gould and Lewontin (p. 161) put it, "Spandrels must exist once a
blueprint specifies that a dome shall rest on rounded arches." But is that true?
It might appear at first as if there were no alternatives to smooth, tapering
triangular surfaces in between the dome and the four rounded arches, but
there are in fact indefinitely many ways that those spaces could be filled with
masonry, all of them about equal in structural soundness and ease of
building. Here is the San Marco scheme (on the left) and two variations. The
variations are both, in a word, ugly (I deliberately made them so), but that
does not make them impossible.
Here there is a terminological confusion that seriously impedes discus-
FIGURE 10.2. The ceiling of King's
College Chapel.
"constraint"—as if the discovery of such constraints weren't an integral part
of (good) adaptationist reasoning, as I have argued in the last two chapters.
Now, perhaps we should stop right here and consider the possibility that
Gould and Lewontin have been massively misunderstood, thanks to the
misfiring rhetoric of this opening passage, rhetoric which they even correct
somewhat, in the last sentence quoted above. Perhaps what Gould and
Lewontin showed, in 1979, is that we must all be better adaptationists; we
FlGURE 10.3