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

302 BULLY FOR BRONTOSAURUS Tinker to Evers to Chance 303
The cone of increasing diversity. The false but still conventional iconography of
the cone of increasing diversity, and the revised model of diversification and decimation,
suggested by the proper reconstruction of the Burgess Shale. [Gould 1989a,
p. 46.]
FIGURE 10.12
it must be, on every branch of the Tree of Life. Species go extinct all the
time, and perhaps 99 percent of all the species that have ever existed are now
extinct, so we must have plenty of decimation to balance off the
diversification. The Burgess Shale's flourishing and demise may have been
less gradual than that of other fauna, before or since, but that does not
demonstrate anything radical about the shape of the Tree of Life.
Some say this misses Gould's point: "What is special about the spectacular
diversity of the Burgess Shale fauna is that these weren't just new species, but
whole new phyla! These were radically novel designs!" I trust this was never
Gould's point, because if it was, it was an embarrassing fallacy of
retrospective coronation; as we have already seen, all new phyla—indeed,
new kingdoms!—have to start out as mere new subvarieties and then become
new species. The fact that from today's vantage point they appear to be early
members of new phyla does not in itself make them special at all. They might
be special, however, not because they were "going to be" the founders of new
phyla, but because they were morphologically diverse in striking ways. The
way for Gould to test this hypothesis would be, as Daw-kins (1990) has said,
to "take his ruler to the animals themselves, unprejudiced by modern
preconceptions about 'fundamental body plans' and classification. The true
index of how unalike two animals are is how unalike they actually are!" Such
studies as have been done to date suggest, however, that in fact the Burgess
Shale fauna, for all their peculiarity, exhibit no inexplicable or revolutionary
morphological diversity after all (e.g., Con-way Morris 1992, Gee 1992,
McShea 1993).
The Burgess Shale fauna were, let us suppose (it is not really known),
wiped out in one of the periodic mass extinctions that have visited the Earth.
The dinosaurs, as we all know, succumbed to a later one, the Cretaceous
Extinction (otherwise known as the extinction at the K-T boundary),
probably triggered about sixty-five million years ago by the impact of a huge
asteroid. Mass extinction strikes Gould as very important, and as a challenge
to neo-Darwinism: "If punctuated equilibrium upset traditional expectations
(and did it ever!), mass extinction is far worse" (Gould 1985, p. 242 ). Why?
According to Gould, orthodoxy requires "extrapolationism," the doctrine that
all evolutionary change is gradual and predictable: "But if mass extinctions
are true breaks in continuity, if the slow building of adaptation in normal
times does not extend into predicted success across mass extinction
boundaries, then extrapolationism fails and adaptationism succumbs" (Gould
1992a, p. 53). This is just false, as I have pointed out:
I cannot see why any adaptationist would be so foolish as to endorse
anything like "extrapolationism" in a form so "pure" as to deny the possibility
or even likelihood that mass extinction would play a major role in
pruning the tree of life, as Gould puts it. It has always been obvious that the
most perfect dinosaur will succumb if a comet strikes its homeland with a
force hundreds of times greater than all the hydrogen bombs ever made.
[Dennett 1993b, p. 43.]
Gould responded (1993e) by quoting a passage from Darwin himself, clearly
expressing extrapolationist views. So is adaptationism (today ) committed to
this hopeless implication? Here is one instance when Charles Darwin himself
has to count as a straw man, now that neo-Darwinism has moved on. It is
true that Darwin tended to insist, shortsightedly, on the gradual nature of all
extinctions, but it has long been recognized by neo-Darwinians that this was
due to his eagerness to distinguish his view from