Showdown on the Burgess Shale
by Simon Conway Morris and
Stephen Jay Gould
lmost a decade ago, Harvard paleontologist and
Natural History columnist Stephen Jay Gould published Wonderful
Life: The Burgess Shale and the Nature of History (W. W. Norton,
1989). In addition to chronicling ongoing work on the Burgess creatures,
Gould used these fascinating fossils to exemplify his view of evolution.
A few months ago, in The Crucible of Creation: The Burgess Shale and
the Rise of Animals (Oxford University Press, 1998), invertebrate
paleontologist Simon Conway Morris, of Cambridge University, a key player
in Burgess research, challenged Gould's interpretations. We invited Conway
Morris to summarize his argument, which we publish here, along with
Gould's reply.—Eds.
The Challenge
by Simon Conway Morris
ew books on paleontology have achieved the wide
readership of Stephen Jay Gould's Wonderful Life, which
popularized research spear-headed by Harry Whittington at Cambridge on
the 520-million-year-old Burgess Shale, found between two peaks in the
Canadian Rockies near Banff. But Gould did much more than chronicle
discoveries concerning these Cambrian fossils; he also set forth his own
deeply held views on the mechanisms and nature of evolution—and
even on humankind's place in the universe—as the "lessons" to be
drawn from the Burgess Shale. In my new book,
The Crucible of Creation,
I argue that the major premises and conclusions of Wonderful Life
must be seriously challenged. Let me begin with some matters of
interpretation of patterns in the fossil record, then move on to
paleontological particulars, and finally offer different "lessons" on what
the Burgess Shale means in the larger reading of evolutionary history.
Gould emphasizes, above all, the apparent weirdness
and diversity of the Burgess fossils. How, he asks, was such an
extraordinary range of anatomies produced, and all apparently in a blink
of geological time? He hints at a special mechanism at work—some
unusual genetic happenstance gone wild—that might account for the
production of so many biological novelties in such a startlingly short
period of time, perhaps only a few million years. And what if we could
"rerun the tape" so that the subsequent history of this maelstrom of
diversification would have taken a different course? We would still have
a planet full of life, he argues, but surely one utterly different from
our familiar world. Notably, this new trajectory of evolution would
probably not have led to the human species and its unique form of
consciousness and self-awareness, which emerged through a series of
contingent accidents in a unique, unrepeatable sequence.
Gould also charges that Charles D. Walcott, the discoverer of the
Burgess Shale, was ill equipped to appreciate how diverse these novel
phyla of sea creatures really were. Committed to the orthodox view that
the range of life-forms must become ever greater over time, Walcott, in
Gould's view, was unprepared to confront a world in which the
proliferation of different kinds of life-forms (phyla) was much greater in
the distant past than in, say, the age of dinosaurs or the more recent age
of mammals. Therefore, he argues, Walcott attempted to "shoehorn" a range
of previously unknown creatures into a few familiar categories to fit his
preconceptions. Gould asserts that paleontologists have only just begun to
appreciate the ever-expanding catalog of bizarre "dead-end experiments"
conducted by nature in ancient seas.
Looking back at the Cambridge group's
classifications of the Burgess Shale, undertaken many decades after
Walcott's pioneering work, my colleagues and I can see that we made
some mistakes. Too often, we thought we had stumbled across yet another
novel body plan (phylum, if you will), and in a few crucial instances,
we did not realize that seemingly unrelated fossils were actually
fragments of a single organism. With the benefit of hindsight, we can
see that we had exaggerated the diversity of these supposedly bizarre
fossils and needed to reconsider their evolutionary relationships.
Recent discoveries in southern China (Yunnan) and northern Greenland
(Peary Land) have provided links that join several of these previously
unconnected fossils and establish them in recognizable phyla.
Let's begin with the animal
Wiwaxia. In
Wonderful Life, it is
described as "another Burgess oddball, perhaps closer to the Mollusca
than to any other modern phylum…but probably not very close."
Ironically, the first breakthrough in establishing Wiwaxia's
affinities came from a postgraduate paleontologist at Harvard who was
inspired by Gould's lectures a decade or so ago. This young researcher,
Nick Butterfield, managed to extract pieces of scalelike armor from the
fossilized creature. When Butterfield studied their microstructure, he
noticed immediately that it was the same as that of the chitinous
bristles (chaetae) that project from the bodies of such modern annelids
as earthworms. His conclusion, published in 1990, was that
Wiwaxia was not a mollusk at all but an annelid. Yet this was
what Walcott had claimed in 1911. In at least this case, Butterfield
concluded, Walcott was not "shoehorning" bizarre animals into familiar
phyla, as Gould had charged; Walcott had got it right the first
time.
Another
recent discovery, in which I was fortunate to play a role, sheds
further light on the place of certain Burgess animals in evolutionary
history. On July 9, 1989, I was with a team in northern Greenland,
collecting at a site containing fauna from Sirius Passet, a regional
variant of the Burgess Shale. It was our first day at the site, and
almost immediately we found an extraordinarily complete fossil, of a
halkieriid—an armored slug with a big shell
at either end. We wondered whether this organism—with such a weird
anatomy, apparently so different from any other animal's—represented
yet another new phylum. But that was only at first sight. |
| 
Posterior shell of a
halkieriid | |
Until then, halkieriids had been known only from the
evidence of isolated scales; with our discovery of this and other
complete specimens, however, we were able to confirm that the creature
was in reality closely related to
Wiwaxia.
In making that connection, we were moving toward
resolving a fundamental problem in evolution: How are body plans
constructed, and how do new phyla actually emerge? To get from
halkieriids, well represented as Lower Cambrian fossils, to
Wiwaxia, which thrived in the Middle Cambrian, there is no need
to postulate macroevolutionary jumps or some sort of genetic
revolution. The halkieriids are not only older than Wiwaxia but
also clearly more primitive. In life, halkieriids crawled across the
seabed, their scales forming a beautifully arranged protective armor.
Wiwaxia looked somewhat similar, but as Butterfield showed, its
scales evolved into chaetae. So is Wiwaxia an annelid? It is
really a matter of definition, but in my opinion, Wiwaxia is a
member of the annelid stem group—a creature still in the process
of becoming an annelid. Once scrutinized, the wiwaxiids
and the halkieriids, despite their seemingly great differences, are
closely related. They may be connected by two simple steps: the scales
of halkieriids are transformed into wiwaxiid chaetae, and lobate,
leglike extensions develop so that the style of locomotion changes
from crawling to a kind of stepping.
| 
A complete
halkieriid. | |
In recent years, the techniques of molecular biology
have profoundly influenced paleontology in ways that bear on Gould's
premise that the Burgess Shale was a seemingly inexplicable explosion of
hundreds of bizarre life-forms, unrelated to anything familiar. One major
surprise concerns the evolutionary position of the phylum Brachiopoda,
a group with bivalved shells. Molecular data, quite unexpectedly, shows
brachiopods to be closely related to annelids. Functional morphology
also indicates that the shells of brachiopods must have originated as
two separate valves; clams, in contrast, derived their familiar double
shells from an ancestor with a single plate, across which developed a
narrow zone of weakness, which became the hinge. Projecting from the
margin of both valves of a brachiopod are delicate, chitinous
bristles—identical to those of annelids. |
Halkieriids also have two prominent shells. In the
pre-brachiopods, I believe, the two shells were probably close to each
other, back to back. To produce a true brachiopod, all that was
necessary was to fold one shell beneath the other. And, interestingly,
exactly this process can be seen in the embryological development of
certain primitive, living brachiopods. So what was once a worm is
transformed into a bivalved animal, the familiar brachiopod. Nor does
the story finish here. If the scales of halkieriids can become
chaetae, surely they can also evolve into the structurally identical
chitinous bristles of a brachiopod. Of course, the origin of
brachiopods is not so simple, but such transformations are
functionally plausible and historically believable.
Although constrained by genetic possibilities, they
are products of convergent evolution. Similar environmental selection
pressures, acting on differing anatomies, can create convergent or
parallel adaptations.
New discoveries and interpretations have altered
our view of arthropod evolution as well. The biggest surprise is
Hallucigenia, exemplar of the bizarre. Or is it? Recent finds
from the Chinese deposit of Chengjiang reveal that my original
reconstruction of this odd-looking, spiky animal had but one simple
mistake: I had envisioned it upside down. Hallucigenia (a name
coined by a colleague and me in an attempt to capture its dreamlike
appearance) may still look strange, but with new discoveries,
especially from southern China, Hallucigenia is now seen to
belong to a group of primitive arthropods. And what about the famous
Anomalocaris, another of Gould's star oddballs?
"Nothing…about Anomalocaris suggests a linkage with arthropods,"
he writes. Now we know better. The discovery, in different species,
of lobopod-like legs and jointed appendages along the length of the
body not only establishes a link between Anomalocaris and the
more primitive Hallucigenia but also is crucial for
understanding the appearance of the first arthropods—a group
that would eventually radiate into crabs, spiders, and the millions
of species of insects.
So the Burgess creatures do not form an exception
to the orthodox mechanisms and patterns of evolution, as I believe
Gould has implied. The new evidence suggests that not only did the
sheer number of species increase since the Cambrian (as nearly
everyone agrees), but, more significantly, the total number of phyla
has been maintained and has not, contrary to, what Gould has
written, shown a catastrophic decline. But now we come to the most
egregious misinterpretation of the Burgess Shale in Gould's
book—a conclusion drawn not from the evidence of paleontology
but from Gould's personal credo about the nature of the
evolutionary process.
Gould sees contingency evolutionary history based
on the luck of the draw—as the major lesson of the Burgess
Shale. If you rerun the tape of evolution, he says, the results
would surely come out differently. Some creature similar to
Pikaia, a small eel-like animal with a rudimentary head, may
have survived in Cambrian seas to become the ancestor of all
vertebrates. If it hadn't, Gould says, perhaps other—entirely
different—major animal groups would have evolved instead from
one of the Burgess Shale's other "weird" body plans. Such a view,
with its emphasis on chance and accident, obscures the reality of
evolutionary convergence. Given certain environmental forces, life
will shape itself to adapt. History is constrained, and not all
things are possible.
To understand how creatures that are descended
from very different groups can evolve similar forms and functions,
consider that dolphins, which evolved from doglike mammals, are
shaped like fish because there exists an optimal shape for moving
through water—a classic example of convergent evolution. Or
consider another example: both placental mammals and marsupials
produced a large, saber-toothed carnivore on separate continents.
If such a quality as intelligence can arise both in human beings
and in the octopus—an eight-armed sea animal without a bone
in its body—then perhaps there is a course and a direction to
evolution that would be achieved despite diverse anatomical
starting points.
Contingency or no, I believe that a creature with
intelligence and self-awareness on a level with our own would surely
have evolved—although perhaps not from a tailless, upright ape.
Almost any planet with life, in my view, will produce living
creatures we would recognize as parallel in form and function to our
own biota. But first, life must arise, and we have no idea how rare
an event that might be. If we are honest, despite our exciting
fancies about extraterrestrials, we must admit the real possibility
that life arose but once, and that we are alone and unique in the
cosmos—with an awesome and, to many, unanticipated role as
stewards of all other living things. But were we to let evolution
take another route than it did, why not grant (as, Gould will not)
that another kind of being would have evolved to fill our special
place in nature?
The Reply
by Stephen Jay Gould
he recorded history of life on earth extends from
3.5-billion-year-old bacteria to our modern biota of oak trees, great
white sharks, people, and many other organisms of stunning diversity. If
evolution had followed a path of smoothly rising complexity, then our
cultural preferences for progress would be fulfilled and paleontology
would validate our deepest hopes and expectations. But life's bumpy and
unpredictable course challenges us at every turn. Why did unicellular
organisms of bacterial grade hold exclusive sway for nearly 2 billion
years—more than half of life's duration on earth? When multicellular
animals of modern design finally entered the fossil record, why did
nearly all phyla make their initial appearance in an internal
so brief
(perhaps no more than 5 to 10 million years) that paleontologists call
this episode the Cambrian explosion?
The Burgess Shale, in the Canadian Rockies, contains
the world's most important fossil fauna—a detailed and exquisite
record (with rarely preserved soft parts included) of marine life about
520 million years ago, just following the Cambrian explosion and
therefore permitting us to census the results of this seminal episode
in the history of animal life on earth. Charles
D. Walcott, a great American paleontologist, discovered the Burgess
Shale early in our century but failed to appreciate its full
significance. Beginning in the 1960s, Cambridge University
paleontologist Harry Whittington, in eventual partnership with two
remarkable graduate students, Derek Briggs and Simon Conway Morris,
restudied Walcott's extensive collection in conjunction with new
material from their own fieldwork and developed a novel
interpretation with profound implications for our understanding of
evolution and the history of life.
I
told the story, following their views of the
Burgess fauna quite strictly (while presenting my own best judgment
about larger implications), in my book Wonderful Life. Simon
Conway Morris (who has since rejected his original interpretation
and reached a nearly opposite conclusion — in general, an
admirable stance for a scientist, although in this particular case,
I think that Conway Morris was right the first time around)
recently challenged my reading in The Crucible of Creation,
the impetus for this dialogue. |
| 
This Burgess Shale scene features the predator
Anomalocaris, which has captured a
trilobite. | |
Interpreting the fauna of the Cambrian explosion
raises two deep and distinct issues, often confused in Conway Morris's
commentary but providing a good framework for exemplifying our
differences. First, a question of origins: How could so much
anatomical variety evolve so quickly? In particular, must novel
evolutionary mechanisms be proposed for such a burst of activity?
Second, a question of consequences: How many distinct lineages arose
in the Cambrian explosion? How many survived to leave modern organisms
as descendants? Why have no new animal phyla (with the single
exception of Bryozoa) evolved in more than 500 million years since the
Cambrian explosion? Did surviving lineages prevail for predictable
reasons of superior biomechanical design or ecological adaptation? Or
did nature (to speak metaphorically) play a grand lottery with this
initial diversity, issuing just a few winning tickets effectively at
random—thus implying that modern groups, including our own
lineage of vertebrates, owe their current success to an initial luck
of the draw, combined with good fortune along the meandering paths of
history's later contingencies?
The question of origins: I devoted only a
few pages to this fascinating topic in Wonderful Life because
so little meaningful evidence exists, and fruitful science must be
defined by palpable and potentially decisive data, not by our
subjective sense of intrigue or importance. (For this reason,
questions about intelligent extraterrestrial life remain scientifically
vacuous, although no issue could be more important in principle.)
As a framework for tackling the puzzle of why so
much anatomical variety arose so rapidly at this unique time, I
suggested that two basic approaches should be explored (with a full
answer undoubtedly requiring a balance of both). An "external," or
ecological, perspective would focus upon the uniquely "empty"
ecological barrel of potential environments for mobile multicellular
animals at the dawn of Cambrian time; almost any "experiment" might
work for a while during an initial "filling"—at least until
Darwinian forces sorted the workable from the suboptimal and placed
a brake upon subsequent change of such magnitude. By contrast, an
"internal" genetic or developmental perspective might view the
Cambrian as a time of unique flexibility, before definite patterns
of growth from egg to adult became so locked into the embryology of
complex organisms that fundamental reconstructions became nearly
impossible.
I suggested in Wonderful Life (and still
maintain) that scientists should devote more attention to the
unconventional internal arguments than to the more familiar
ecological claims. I proposed no bizarre or novel evolutionary
mechanisms but only emphasized a potentially greater efficacy for
ordinary processes at a unique time of organic flexibility, before
major developmental pathways became irrevocably set. I therefore
feel that Conway Morris has misrepresented my views by vague
allusion (for he can cite no true source for arguments I never made)
when he states that I hint "at a special mechanism at work—some
unusual genetic happenstance gone wild" or when he floats an even
vaguer charge about unorthodox mechanisms that he "believes" I have
"implied."
The question of consequences: This second
key issue does call upon a large and juicy reservoir of testable
evidence and therefore does become subject to scientific
adjudication and fruitful debate. I based Wonderful Life
almost exclusively upon this issue. Two basic questions, with
different judgments and implications, have been widely debated
within this general theme:
1. How much anatomical variety did the Cambrian
explosion generate? Did the number of early experiments exceed (or
overshoot) our current range of organic architecture? Wonderful
Life argues for greater disparity during the explosion, with
subsequent trimming on the "lottery model"—thus raising the
interesting implication (and central theme of my book) that if we
could perform the great undoable thought experiment of "rewinding
the tape of life" back to the Cambrian and "distributing the
lottery tickets" at random a second time, the history of animals
would follow an entirely different but equally "sensible" course
that would almost surely not generate a humanoid creature with
self-conscious intelligence.
Most of Conway Morris's commentary properly
focuses on a crucial and testable point. He denies my claim for a
Cambrian overshoot by arguing that most Burgess "oddballs" really
belong to modern groups (or to formative stages of modern designs)
when properly interpreted. Therefore, the Cambrian did not generate
enough anatomical variety to fuel a markedly different outcome for
any hypothetical replay of life's tape.
I accept and applaud some of Conway Morris's
arguments, while regarding the tone of his rhetoric as peculiar
in several key places. Why, for example, does he label as ironic
the fact that Butterfield's more orthodox reinterpretation of
Wiwaxia began with an interest in my lectures? I don't know
what could bring a scientist greater pleasure—the very
antithesis of irony—than the honor of having his ideas act as
a spur to important advances in knowledge, whatever the impact
upon any initially favored and necessarily tentative hypothesis.
And why does Conway Morris imply that I have been soft-pedaling
the revised interpretation of Hallucigenia, when I applauded this
discovery as soon as it was announced by writing an entire essay
for this magazine entitled "The Reversal of
Hallucigenia" (January 1992)?
Nonetheless, I think my central argument has
fared well in the decade since the publication of Wonderful
Life, for both a general and a specific reason. For the
general argument, my colleague Mike Foote, of the University of
Chicago, and I engaged in a technical debate with Conway Morris's
colleagues (published in our major professional journal
Paleobiology) on the quantitative assessment of
comparative degrees of anatomical variety in the Burgess Shale
versus modern oceans. Even our staunchest critics agreed that
the Burgess range equaled the modern scope (while we argued for
a greater variety in Burgess times). In other words, even our
strongest opponents admit that in less than 20 million years
from the inception of the Cambrian explosion to the deposition
of the Burgess Shale, marine invertebrate life reached a fully
modern range—and that more than 500 million years of
subsequent evolution has not at all enlarged the scope of basic
anatomical variety. In this context, how can the early Cambrian
be viewed as anything other than a unique time of explosive and
unparalleled diversification?
For
the specific argument, I believe that many Burgess and other early
Cambrian creatures are weirder than Conway Morris allows and that
several of his linkages to modern groups remain fanciful at best.
For example, he blithely speaks about connecting wiwaxiids and
halkieriids—rather dissimilar creatures, to my eyes—by
"two simple steps" that seem both complex and improbable to me.
How can Conway Morris view the evolution of lobopods (leglike
extensions present in hameriids but not in wiwaxiids) from no
prior structure at all in supposedly ancestral halkieriids as a
simple and obvious step? I am even more surprised by Conway
Morris's confidence that the two plates at either end of an
elongated Halkieria
can overcome their several centimeters of separation to become
the two connected valves of a brachiopod. |
| 
Wiwaxia corrugata—an ancestral annelid? |
|
(I must also ask readers' indulgence for a
paragraph that Robert's Rules of Order would call a "point of
personal privilege": Conway Morris has chosen, less in this article
than in his book, to be imperiously dismissive of my ideas, as if
no sensible or experienced person could ever advocate such
prejudiced nonsense. But he never tells us that Wonderful
Life treats him, in his radical days as a graduate student, as
an intellectual hero. I developed my views on contingency and the
expanded range of Burgess diversity directly from Conway Morris's
work and explicit claims, and I both acknowledged my debt and
praised him unstintingly in my book. I even suggested—although
it's surely none of my business—that Whittington, Conway
Morris, and Briggs should receive the Nobel Prize for their
exemplary work. Conway Morris is certainly free to change his mind,
as he has done. Indeed, such flexibility can only be viewed as
admirable in science. But it is a bit unseemly never to state that
you once held radically different opinions and to brand as
benighted, in some obvious and permanent sense, a colleague who
holds the views you once espoused. I do therefore object to Conway
Morris's strategy of working out his own ontogenetic issues at my
expense. Lest readers think I am being either peevish or
idiosyncratic, may I cite our British colleague Richard Fortey, who
generally sides with Conway Morris on the scientific debate, from
the October 10 issue of the London Review
of Books: "What is peculiar about [The Crucible of
Creation] is that the casual reader…would never guess from
it that Conway Morris ever entertained views different from those he
now holds.…It is this selective amnesia which accounts for the
passion of his disillusion with Gould, for Gould has preserved in
the print of a best-seller ideas that Conway Morris…now
repudiates. He is furious that his past misinterpretations have
been so eloquently placed on record.…The way Conway Morris
goes about biting the hand that once fed him would make a shoal of
piranha seem decorous.")
2. How repeatable is the history of life? In
particular, did lineages that survived after Burgess times
prevail for predictable reasons of adaptive superiority or by the
luck of the draw? If we could replay life's history from Burgess
beginnings, would the same trends occur, and would a self-conscious
species arise again on earth? Conway Morris rests his claim for
substantial predictability upon the important evolutionary
phenomenon of convergence, or the independent origins of similar
and highly adaptive designs in separate lineages—with the
wings of bats, birds, and pterosaurs (flying reptiles of dinosaur
times) or the eyes of squid and vertebrates as classic examples.
But I think that Conway Morris has given too prominent a role to an
admittedly interesting principle for three reasons:
a) As a striking phenomenon, convergence
draws our attention, but I think that we often overestimate its
sway. Nearly all textbooks stress the admittedly remarkable
convergences of several Australian mammals with their independently
evolved counterparts in northern continents (for example, the
marsupial "mole" with the denizens of our gardens, and the extinct
Australian marsupial thylacine, otherwise known as the Tasmanian
wolf, with doglike carnivores). When I first visited Australia, I
expected to be overwhelmed by these demonstrations of convergence,
but I encountered just the opposite phenomenon: uniqueness and
difference, with convergence as an oddity singled out for textbook
illustration. The mammalian fauna of Australia, after all, is
dominated by upright and effectively "three-legged" herbivores
known as kangaroos—a group with no evolved counterpart
elsewhere.
b) Most outstanding examples of
convergence build upon an inherited anatomical substrate that
evolved by ordinary routes of highly contingent and unrepeatable
historical circumstance. For example, the wings of bats, birds, and
pterosaurs are convergent but all these structures evolved from
vertebrate forelimbs of similar inherited design, not from scratch.
In replaying life's tape from Burgess beginnings, what odds would
anyone place on the evolution of such forelimbs if no ancestral
creature had the precursors for these structures?
c) Evidence for convergence requires
multiple cases of independent evolution, while the example that we
all carry closest to our hearts (and that engenders the emotional
oomph in this debate)—the evolution of consciousness in Homo
sapiens—remains an outstanding singleton in the only
history of life we know: the story of our own planet. (I am not
impressed by Conway Morris's citation of octopuses, a group that I
deeply admire and respect but that hasn't, and presumably can't,
return the compliment via any higher mental functioning of its own.
Consciousness at our level of language and conceptual abstraction
has evolved but once on earth—in a small lineage of primates
(some 200 species), within a small lineage of mammals (some 4,000
species, while the more successful beetles now number more than half
a million), within a phylum that prevailed by contingent good fortune
from the Burgess draw. If complex consciousness has evolved but once
in the admittedly limited domain of known evidence, how can anyone
defend the inevitability of its convergent evolution?
Finally, Conway Morris charges that my arguments
for contingency arise "not from the evidence of paleontology but from
Gould's personal credo about the nature of the evolutionary process."
This claim, however ungenerously stated, is—and must
be—true, for any general view of life must read evidence in the
light of a favored theory. I would, however, label my view as a valid
reading of paleontological evidence in the context of a theory about
life's evolution and history that I have worked out by considerable
thought, practice, and intellectual struggle, and that I always
explicitly identify as tentative, undoubtedly wrong in places (but
not, I hope, in general approach), and embedded (as all ideas must
be) in my own personal and social context.
I am puzzled that Conway Morris apparently,
doesn't grasp the equally strong (and inevitable) personal
preferences embedded in his own view of life—especially when
he ends his commentary with the highly idiosyncratic argument that
life might be unique to Earth in the cosmos, but that intelligence
at a human level will predictably follow if life has arisen
anywhere else. Most people, including me, would make the opposite
argument based on usual interpretations of probability: The origin
life seems reasonably predictable on planets of earthlike
composition, while any particular pathway, including consciousness
at our level, seems highly contingent and chancy.
I don't know how
else to interpret the cardinal fact that life did originate on earth
almost as soon as environmental conditions permitted such an
event—an indication, although surely not a proof, of reasonable
expectation and predictability; whereas consciousness has evolved
only once, and in a marginal lineage among so many million that
have graced our planet's history—an indication, although again
not a proof, that such a phenomenon is not inevitably meant to be.
Conway Morris's peculiar and undefended reversal
of these usual arguments about probability can arise only from a
"personal credo"—and I would value his explicit attention to
the sources of his own unexamined beliefs. All scientific greatness
must integrate external data with the internal power of a fruitful
view of life—the more iconoclastic the better, for Lord only
knows that hidebound tradition and stupidity stand as the greatest
barriers to enlarged understanding. But we cannot appreciate and
use our own mental power if we do not follow the earliest and
greatest advice of our classical forebears: Know thyself.
[ Simon Conway Morris and Stephen Jay Gould, "Showdown on
the Burgess Shale," Natural History magazine, 107 (10):
48-55. ]
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