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

278 BULLY FOR BRONTOSAURUS
The Spandrel's Thumb 279
But once the mystical version of Baupläne is shunned, what is left? Our
old friend: the claim that good reverse engineering takes the building process
into account. As Gould and Lewontin put it (p. 160), their view of matters
"does not deny that change, when it occurs, may be mediated by natural
selection, but it holds that constraints restrict possible paths and modes of
change so strongly that the constraints themselves become much the most
interesting aspect of evolution." Whether or not they are the most interesting
aspect, they are certainly important, as we have seen. Perhaps adaptationists
(like art historians) need to have this point repeatedly drawn to their attention.
When Dawkins, an arch-adaptationist if there ever was one, says, "There are
some shapes that certain kinds of embryology seem incapable of growing"
(Dawkins 1989b, p. 216), he is expressing a version of this point about the
constraint of the Bauplan, and it was something of a revelation to him, he
says. It was forcefully brought home to him by his own computer simulations
of evolution, not by the Gould and Lewontin paper, but we might let them
chime in: "We told you so!"
Gould and Lewontin also discuss other alternatives to adaptation, and
these, too, are themes we have already encountered in orthodox Darwinism:
random fixation of genes (the role of historical accident and its amplification),
developmental constraints due to the way genes get expressed, and
the problems of getting around in a fitness landscape with "multiple adaptive
peaks." These are all real phenomena; as usual, the debate among
evolutionists is not about whether they exist, but about how important they
are. Theories that incorporate them have indeed played a significant role
within the growing sophistication of the neo-Darwinian synthesis, but they
are reforms or complications, not revolutions.
So some evolutionists have accepted Gould and Lewontin's pluralism in an
irenic spirit, as a call not to abandon but, rather, to improve adaptation-ism.
As Maynard Smith (1991, p. 6) has put it, "The effect of the Gould-Lewontin
paper has been considerable, and on the whole welcome. I doubt if many
people have stopped trying to tell adaptive stories. Certainly I have not done
so myself." Gould and Lewontin's paper has had a welcome effect, then, but
one of its by-products has not been so welcome. The inflammatory rhetoric
suggesting that these somewhat neglected themes constituted a major
alternative to adaptationism opened the floodgates to a lot of wishful thinking
by Darwin-dreaders who would prefer that there not be an adap-tationist
explanation of one precious phenomenon or another. What would their dimly
imagined alternative be? Either the "internal necessity" that Gould and
Lewontin themselves dismiss as an appeal to mysticism, or utter cosmic
coincidence—an equally mystical nonstarter. Neither Gould nor Lewontin
explicitly endorsed either wild alternative to adaptation, but this was
overlooked by those who wanted to be dazzled by the authority of these
eminent Darwin-doubters.
Moreover, Gould, in spite of the appeal to pluralism in the co-authored
paper, has persisted in describing it as laying waste to adaptationism (e.g.,
1993a), and has held out for a "non-Darwinian" interpretation of its central
concept, spandrels. It may have occurred to you that I have overlooked an
obvious interpretation of spandrels: perhaps spandrels are just QWERTY
phenomena. QWERTY phenomena, you recall, are constraints, but constraints
with an adaptive history and hence an adaptationist explanation. 3
Gould himself briefly considered this alternative (1982a, p. 383): "If the
channels [that constrain current options] are set by past adaptations, then
selection remains preeminent, for all major structures are either expressions
of immediate selection, or channeled by a phylogenetic heritage of previous
selection." Nicely put, but he promptly rejected it, calling it Darwinian
(which it certainly is), and recommending an alternative "non-Darwinian
version" which he described as "not widely appreciated but potentially
fundamental." Spandrels, he then suggested (p. 383), aren't the frozen
constraints created by earlier adaptations; they are exaptations. What contrast
was he trying to draw?
I think he saw the difference between the exploitation of something
previously designed, and the exploitation of something originally undesigned,
and was claiming that it was an important difference. Perhaps. Here
is some indirect textual evidence for that reading. A recent article in the
Boston Globe quotes the linguist Samuel Jay Keyser of MIT:
"Language may well be a spandrel of the mind," Keyser says, and then waits
patiently while his questioner looks "spandrel" up in the dictionary— The first
builder who supported domes with arches created spandrels by accident
[emphasis added), and at first builders paid no attention to spandrels and
decorated only the arches, Keyser says. But after a couple of centuries, builders
began focussing on and decorating the spandrels. In the
3. In his own discussion of the original QWERTY phenomenon (1991a), Gould makes a
useful point ( 1991a, p. 71), but does not develop it further, so far as I know: because of
the curious historical sequence of events that led to the general adoption of the standard
QWERTY typewriter keyboard, "An array of competitions that would have tested
QWERTY were never held." That is, it is simply irrelevant to ask whether QWERTY is a
better design than alternatives X, Y, and Z, since those alternatives were never pitted
against QWERTY in the marketplace or the design workshop. They just never came up at
a time when, it seems, they could have made a difference. Adaptationists should be alert
to the fact that, even though whatever we see in nature has been "tested against all
comers" and not found wanting, only a Vanishingly small (and biased) subset of all the
imaginable competitions has ever been held. The inevitable parochiality of all actual
tournaments means that one must be cautious in characterizing the virtues of the winners.
An old Downeast joke makes the same point more succinctly: "Mornin', Edna."
'Mornin', Bessie. How's yer husband?" "Compared to what?"