Darwin's Dangerous Idea (56 page)

speciation.
How could this make a difference? Look at figure 10.10.

Couldn't there be special processes of what we might call
hopeful
spe-In both cases, the lineage at K got where it got by exactly the same ciation—or
incipient
speciation? Consider a case in which speciation does sequence of punctuations and equilibria, but the case illustrated on the left occur. Parent-species A splits into daughter-species B and C.

shows a
single species
undergoing rapid periods of change followed by long Now wind back the tape just far enough in time to drop a bomb (an periods of stasis. Such change without speciation is known as
anagenesis.

asteroid, a tidal wave, a drought, poison ) on the earliest members of the B

The case illustrated on the right is an instance of
cladogenesis,
change via species, as in the middle diagram. Doing this turns what had been a case of speciation. Gould claims that the rightward trend in the two cases would have speciation into something indistinguishable from a case of anagenesis (on the a different explanation. But how could this be true? Recall what we right). The fact that the bomb prevents those whose offspring it kills 6. George Williams (1992, p. 130) disputes the importance of habitat tracking in stasis, noting that parasites, "seasonal amplitude of insolation" (amount of sunshine), and many other environmental factors would always be different after a geographical move, so that populations would never be able to stay in exactly the same selective environment, and hence would be subjected to selection pressure in spite of moving. But it seems to me that much if not all of the adjustment to these selection pressures could be invisible to paleontology, which can only see in the fossil record the preserved changes in hard-part design. Habitat tracking could be responsible for much of the
paleontologically observable
stasis (and what other stasis do we know about?), even if Williams is right that this body-plan stasis would have to mask concurrent nonstasis at most if not all other design levels in response to the many environmental changes that would have to accompany any long-range habitat-tracking moves. And unless many species
moved in unison
in their habitat tracking, there couldn't be habitat tracking at all, since other species are such crucial elements in any species' selective environment.

296 BULLY FOR BRONTOSAURUS

Punctuated Equilibrium: A Hopeful Monster
297

from ever being grandparents could hardly make a difference to how their you take to be its offspring that you can be quite sure that there is a direct path contemporaries got sorted out by selective pressure. That would require some from the earlier form to the later form. As an epistemological point, this sort of backward-in-time causation.

completely undercuts the claim that Gould has wanted to make: that most Is this really true? You may think that this would be true if the event that swift evolutionary change has been accomplished by speciation. For if, as kicked off the speciation was a geographic split, guaranteeing the complete Eldredge says, the fossil record
usually
shows abrupt shifts
without
any causal isolation of the two groups (allopatric speciation), but what if the

"ancestral survival after punctuated branching," and if there is no telling speciation got under way within a population that formed two reproduc-tively which of these are cases of punctuated anagenetic change (as opposed to incommunicative subgroups that competed directly against each other (in a immigration phenomena), then there is no way of telling from the fossil form of sympatric speciation)? Darwin proposed, as we noted (see page 43), record whether speciation is a very frequent or very rare accompaniment of that competition between closely related forms would be a driving force in rapid morphological change.7

speciation, so the presence—the nonabsence—of
what can be retrospectively
There might still be another way of making sense of Gould's insistence that it is
identified as
the first generations of a "rival" species might be very important speciation, not mere adaptation, that makes the big difference in evolution.

indeed for speciation, but the fact that these rivals are "going to be" the What if it turned out that some lineages go in for a lot of punctuation (and, in founders of a new species could not play a role in the intensity or other the process, produce lots of daughter species) and other lineages do not, and features of the competition and hence in the speed or direction of the those that do not do so tend to die out? Neo-Darwinians usually assume that horizontal motion in Design Space.

adaptations occur by the gradual transformation of the organisms in particular We may well suppose that relatively rapid morphological change (sideways lineages, but "if lineages do not change by transformation, then long term trends movement) is a normally necessary precondition for speciation. Rapidity of in lineages can hardly be the result of their slow transformation" (Sterelny 1992, change is crucially affected by the size of the gene pool; large gene pools are p. 48). This has long been considered an interesting possibility (in their original conservative and tend to absorb innovation attempts without a trace. One way article, Eldredge and Gould discuss it very briefly, and credit Sewall Wright of making a large gene pool small is dividing it in two, and this may in fact be 1967 as one of its sources). Gould's version of the idea (e.g., 1982a) is that the most common sort of downsizing, but thereafter it makes no difference whole species don't get revised by the piecemeal redesign of their individual whether or not nature discards one of the halves (as in the middle graph in members; species are rather brittle, unchanging things; the shifts in Design figure 10.11). It is the bottleneck of a diminished gene pool that permits the Space happen (largely? often? always?) because of species
extinction
and rapid motion, not the presence of two or more different bottlenecks. If there is species
birth.
This idea is what Gould and Eldredge (1993, p. 224) call "higher speciation, then
two whole species
pass through their respective bottlenecks; if level sorting." It is sometimes known as species selection, or
clade
selection. It there is no speciation, then
one whole species
is pressed through a single is hard to get clear about, but we have the equipment already at hand to clarify bottleneck. So cladogenesis
cannot
involve a process during a punctuation its central point. Remember bait-and-switch? Gould is in effect proposing a new period different from the process that occurs in anagenesis, because the application of this fundamental Darwinian idea: don't think that evolution
makes
difference between cladogenesis and anagenesis is definable only in terms of
adjustments
in existing lineages; evolution
throws away
whole lineages, and lets postpunctuation
sequelae.
Gould sometimes speaks as if speciation does make other, different, lineages prosper. It looks as if there are adjustments to lineages a difference. For instance, Gould and Eldredge (1993, p. 225) speak of "the over time, but what is really going on is bait-and-switch at the species level. The crucial requirement of ancestral survival after punctuated branching" (as
right level
at which to look for evolutionary trends, he could then claim, is not shown on the left in figure 10.11), but according to Eldredge (personal the level of the gene, or the organism, but the whole species or clade. Instead of communication) this is only a crucial
epistemological
requirement for the looking at the loss of particular genes from gene pools, or the differential death theorist, who needs "ancestral survival" as
evidence
of descent.

of particular genotypes within a

His explanation is interesting. The fossil record is loaded with cases in which one form abruptly stops and another, quite different, form abruptly appears "in its place." Which of these are cases of swift sideways leaps of 7. For a similar criticism of Gould, see Ayala 1982. See also G. Williams 1992, pp. 53-evolution, and which are cases of simple displacement due to sudden im-54; Williams, who defines cladogenesis as the isolation, however short-lived, of any migration of a rather distant relative? You can't tell. It is only when you can gene pool, also points out the triviality to evolutionary theory of short-term cladogenesis see what you take to be the parent species coexisting for a while with what (pp. 98-100).

298 BULLY FOR BRONTOSAURUS

Tinker to Evers to Chance
299

population, look at the differential extinction rate of whole species and the neo-Darwinism? Darwin's account of speciation, as we have just recalled, differential "birth" rate of species—the rate at which a lineage can speciate invoked competition between close relatives.

into daughter species.

This is an interesting idea, but it is not, as it first appears to be, a denial of New species usually win an address by driving out others in overt com-the orthodox claim that whole species undergo transformation via "phy-letic petition (a process that Darwin often described in his notebooks as "wedg-gradualism." Let it be true, as Gould proposes, that some lineages spawn lots ing" ). This constant battle and conquest provides a rationale for progress, of daughter species and others don't, and that the former tend to survive since victors, on average, may secure their success by general superiority longer than the latter. Look at the trajectory through Design Space of each in design. [Gould 1989b, p. 8.]

surviving species. It, the whole species, is at any period of time either in Gould does not like this image of the wedge. What is wrong with it? Well, it stasis or undergoing punctuated change, but that change itself is a "slow invites ( he claims ) a belief in progress, but this invitation, we have already transformation of a lineage," after all. It may be true that the best way of seen, is as easily declined by neo-Darwinism as it was by Darwin himself.

seeing the long-term macroevolutionary pattern is to look for differences in Global, long-term progress, amounting to the view that things in the biosphere

"lineage fecundity" instead of looking at the transformations in the individual are, in general, getting better and better and better, was denied by Darwin, and lineages. This is a powerful proposal worth taking seriously, but it neither although it is often imagined by onlookers to be an implication of evolution, it refutes nor supplants gradualism; it builds on it.8

is simply a mistake—a mistake no orthodox Darwinians fall for. What else (The level shift Gould proposes reminds me of the level shift between might be wrong with the image of the wedge? Gould speaks in the same hardware and software in computer science; the software level is the right article ( p. 15 ) of "the plodding predictability of the wedge," and I suggest level at which to answer certain large-scale questions, but it does not cast any that this is exactly what offends him in the image: like the ramp of doubt on the truth of the explanations of the same phenomena at the hardware gradualism, it suggests a sort of
predictable, mindless trudge
up the slopes of level. You would be foolish to try to explain the visible differences between Design Space (see, e.g., Gould 1993d, ch. 21). The trouble with a wedge is WordPerfect and Microsoft Word at the hardware level, and perhaps you simple: it is not a skyhook.

would be foolish to try to explain some of the visible patterns of diversity in the biosphere by concentrating on the slow transformations of the various lineages, but that does not mean that they did not undergo slow 4. TINKER TO EVERS TO CHANCE: THE BURGESS SHALE

transformations at various punctuation marks in their history.) 9

The relative importance of species selection of the sort Gould is now DOUBLE-PLAY MYSTERY

proposing has not yet been determined. And it is clear that however large a role species selection comes to play in the latest versions of neo-Darwinism,
Even today a good many distinguished minds seem unable to accept or
it is no skyhook. After all, the way new lineages come onto the scene as
even understand that from a source of noise natural selection alone and
candidates for species selection is by standard gradualistic micro-mutation—

unaided could have drawn all the music of the biosphere. In effect
unless Gould does want to embrace hopeful monsters. So Gould may have
natural selection operates
upon
the products of chance and can feed
helped discover a new crane, if that is what it turns out to be: a heretofore
nowhere else; but it operates in a domain of very demanding conditions,
unrecognized or unappreciated mechanism of design innovation, built out of
and from this domain chance is barred.

the standard, orthodox mechanisms. Since my diagnosis, however, is that he

—JACQUES MONOD 1971, p. 118

has all along been hoping for skyhooks, not cranes, I must predict that he will keep on looking. Could there perhaps be something
else
about speciation that is so special that it cannot be handled by

9. "Tinker to Evers to Chance" is a baseball meme, immortalizing the double-play combination of three Hall of Fame infielders, Joe Tinker, Johnny (the Crab) Evers, and Frank Chance, who played together for Chicago in the National League from 1903 to 1912. In 1980, Richard Stern, a freshman in my introductory philosophy course, wrote an excel-8. Gould's ideas about "higher level species sorting" must be distinguished from some lent essay for me, an update on Hume's
Dialogues,
this time between a Darwinian lookalike neighbors: the ideas about group selection or population selection currently (Tinker, of course) and a believer in God (Evers, of course), ending up, appropriately, under intense and controversial scrutiny among evolutionists. Those ideas will be dis-with Chance. The serendipitous multiple convergences of that title, given Gould's own cussed in the next chapter.

encyclopedic knowledge and love of baseball, is simply irresistible.