A New Darwinism?
by Tim Flannery
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astonishing fact about Charles Darwin's theory of evolution is that it was conceived
in the absence of two major kinds of support that would have been helpful to
it—evidence from the then meager fossil record and knowledge of the mechanism
of inheritance. The endurance of a theory so conceived—almost from first
principles—has excited the admiration of generations of biologists. It has
also given them the opportunity, as discoveries in genetics and paleontology have
been made, to determine if this new evidence merits a revision of Darwinism, as
the theory is now known.
The Structure of Evolutionary Theory is the latest—and
perhaps the grandest—of such attempts. In effect it is a summation of Stephen
Jay Gould's life work, building on Darwinism to provide a novel synthesis of how
evolution has shaped the living world. Explaining his motivation in writing it,
Gould, who was trained as a paleontologist, says it
does fire my very best shot in the service
of…general theory. I am a child of the streets of New York City; and although
I reveled in a million details of molding on the spandrel panels of Manhattan
skyscrapers…I guess I always thrilled more to the power of coordination than
to the delight of a strange moment—or I would not have devoted 20 years and
the longest project of my life to macroevolutionary theory rather than
palaeontological pageant.
Gould employs two metaphors to assist the reader in
understanding the complex theory that the book develops: the Duomo of Milan and a
fossil coral. The Duomo, Gould says, is similar to Darwin's evolutionary theory
in that it has been built on in ways that add significantly to it but nonetheless
leave the original form and intent recognizable. The fossil coral (see
illustration on page 54), which was discovered near Messina and figured in
Agostina Scilla's La vana speculazione disingannata dal senso, published
in 1670, has special significance for Gould because its branches mimic Gould's
theoretical structure.
Gould envisages the trunk and each branch of the coral as
representing a hierarchy within Darwinism. The trunk is Darwin's theory of
evolution by natural selection itself. The first three branchings represent the
three fundamental principles of Darwinian logic, which Gould characterizes as
"agency [the central branch], efficacy [the left branch] and scope [the right
branch]." The three fundamental principles so characterized arise from Darwin's
thesis that evolution produces new species by natural selection (efficacy)
acting on individuals (agency), resulting in small changes that accumulate
over very long periods of time (scope).
The potentially confusing structure of The Structure of
Evolutionary Theory itself can only be understood in these terms. Gould
says of his book that it "cycles through the three central themes of Darwinian
logic at three scales—by brief mention of a framework in [the
introduction], by full exegesis of Darwin's presentation in Chapter 2, and by
lengthy analysis of the major differences and effects in historical (part 1)
and modern critiques (part 2) of these three themes in the rest of the volume."
To many readers, the arguments that Gould mounts in support of his evolutionary
synthesis will not be new. Most have appeared in articles and exchanges over
the past quarter-century.[1] Here, they are brought
together for the first time.
The historical overview presented in Part One consists of a
reflective commentary on thought relating to evolution as it has developed over
the past three hundred years. Gould provides an admirably comprehensive review
of the literature, dealing with great scientists such as Richard Owen, Georges
Cuvier, and Étienne Geoffroy St. Hilaire, as well as many lesser-known but
interesting and worthy contributors. This section includes many fresh insights
into how thinking about evolution slowly changed, and who built on whose prior
work. Central to the discussion is an exegesis of Darwin's work, where
considerable emphasis is given to the idea that Darwin was a gradualist; that is,
that he saw evolution resulting from the aggregation of countless small changes
over a vast period of time. This is followed by a discussion of the ideas of
Darwin's "brilliant and eccentric cousin" Francis Galton, who challenged Darwin's
concept of gradualism by suggesting that species come into existence almost
instantaneously. Galton illustrated his idea with the metaphor of the polyhedron;
a shape that rests stably on any of its facets, but that when disturbed switches
rapidly from one resting position (facet) to another. Species, Galton argued,
are likewise stable, not changing or evolving until something happens; then they
are rapidly transformed into new (stable) species. Here Gould finds an
intellectual predecessor, for his theory of punctuated equilibrium (of which more
presently) is more akin to Galton's polyhedron than to Darwin's gradualism.
One fascinating aspect of evolutionary thought to which Gould
gives prominence is the idea that Darwin's concept of natural selection owes much
to Adam Smith's economic arguments as presented in The Wealth of
Nations. It is known that Darwin devoted much time in the late 1830s to
studying Smith. Gould goes so far as to say that "the theory of natural selection
is, in essence, Adam Smith's economics transferred to nature," adding that while
"Adam Smith's economics doesn't work in economics," it does admirably well in
"amoral nature."
Part Two of The Structure of Evolutionary Theory returns
to the three principles of Darwinian logic in the context of contemporary
evolutionary debate. Here the author and his collaborators take center stage as
the reformulators of two of these three principles. The theory of punctuated
equilibrium, conceived by Niles Eldredge and Gould, is seen as having revised the
principle of agency, because Gould believes that it lays the theoretical
groundwork for natural selection to act upon species as well as individuals. Gould
and E.S. Vrba's ideas on internal constraint are said to have performed the same
service for efficacy, because they challenge the omnipotence of natural selection
in shaping species. Of the remaining principle, that of scope, Gould says that
although his contribution to the understanding of mass extinction and catastrophic
events which challenge Darwin's concept of gradualism "cannot claim much
novelty.… I do explicate [their significance] perhaps more fully than
before."
Niles Eldredge and Gould first coined the term "punctuated
equilibrium" in 1971 and published it the following year. The theory seeks to
explain a persistent pattern in the fossil record whereby a species suddenly
appears, then persists unchanged for a very long time before going extinct. This
pattern is seen in a wide variety of contexts, from marine creatures such as
shellfish and sea urchins to mammals and birds. Punctuated equilibrium posits that
these species come into existence relatively rapidly (over tens of thousands of
years), though just how (and indeed if) this happens is hotly debated. An opposing
explanation is that these species have evolved much more slowly somewhere else,
and their "sudden" appearance is the result of migration. While, as Galton's
polyhedron suggests, the concept of punctuated equilibrium was not entirely new
to paleontology, Eldredge and Gould's formulation of it was timely and coherent.
Even among its supporters, however, argument has raged over its significance,
with many questioning whether it really challenges Darwin's concept of gradualism.
(After all, tens of thousands of years is sufficient time for species to evolve
"gradually.") Most researchers, though, recognize that the concept has been
invaluable in encouraging paleontologists to examine the fossil record with a
rigor and attention to detail that previously was largely lacking.
Punctuated equilibrium has forced paleontologists to focus not
only on the origin of species, but also on their often long, unchanged persistence
in the fossil record. Before punctuated equilibrium, this phenomenon tended to be
accepted as simply the way things were—yet it is an intriguing problem. One
of the best examples given by Gould concerns the mammals (including rhino, pig,
and camel relatives) of the White River Chronofauna of the American West, which
endured almost unchanged through a period of astounding climatic upheaval. During
this time the rain forests of Nebraska were transformed into forested grassland
and the mean annual temperature dropped by 13 degrees Celsius. Revelations such
as this remind us of how much we have to learn about our planet's past.
What is particularly satisfying about reading Gould's views of
punctuated equilibrium is the sense he gives that a fundamental problem—that
of how species originate and then persist over geological time—is not yet
fully understood. If young biologists ever reach deep into his vast tome, they
may find here materials with which to build careers.
Following a thorough treatment of the literature relating to
punctuated equilibrium in nature, Gould brings his discussion into the social
realm, debating how the concept might apply to changing human cultures and even
to businesses in complex societies. He notes, not without some chagrin, that
creationists have welcomed the theory because it has enabled them to argue that
the fossil record does not show us "evolution in action" and that therefore
evolution does not exist. The first part of this observation is indeed a
corollary of the theory, which posits that the changes leading to new species
usually happen so rapidly that they go undetected, but the second is clearly an
unwarranted "leap of faith."
Gould's discussion of punctuated equilibrium concludes with
an overview of nonscientific objections to the theory, including
the accusation that he developed it as
part of a Marxist political agenda. Gould resents "this absurd misreading,"
writing that his politics are "a private matter that I do not choose to discuss
in this forum." Under the heading "THE MOST UNKINDEST CUT OF ALL" he discusses
the dismissal of his theory as both "trivial and devoid of content," a charge he
intensely resents and feels is deeply unfair.
On the twenty-first anniversary of the publication of the
theory of punctuated equilibrium, Gould and Eldredge wrote in Nature: "In
developing punctuated equilibrium, we have either been toadies and panderers to
fashion, and therefore destined for history's ashheap, or we had a spark of
insight about nature's constitution." In The Structure of Evolutionary
Theory Gould appears to have revised this view, perhaps as a result of the
criticism that the theory is extraordinarily difficult to test, because life is
so diverse and so many differing interpretations of the fossil record are possible.
He now believes that no one expects an either-or result, but only (eventually) a
sense of what proportion of life's diversity evolves gradually and steadily, and
how much in leaps and bounds.
The emphasis on punctuated equilibrium opens the way for The
Structure of Evolutionary Theory's most audacious proposal—the idea of
species selection. Gould sees punctuated equilibrium as a prerequisite for species
selection because it bestows on species some of the properties inherent in
individuals. Thus Gould envisages a sort of life cycle of species: born via
punctuated equilibrium, they live a life in mature (stable) form, and then die
through extinction. Species selection is a central aspect of the book, and by it
Gould means that species as a whole—not just individuals or
populations—are being acted on by natural selection.
Gould admits that few (if any) examples of species selection
have come to light—but argues that this is because scientists have not
looked hard enough. Consequently we must make do with hypothetical examples, of
which the author gives us one of his own making. It has to do with variability
within species, which Gould sees as the best example of a "species character."
This is a necessary prerequisite of species selection since otherwise natural
selection at the level of species would have nothing to act on:
Suppose that a wondrously optimal fish, a marvel
of hydrodynamic perfection, lives in a pond. This species has been honed by
millennia of conventional Darwinian selection, based on fierce competition, to
this optimal organismic [individual] state. The gills work in an exemplary
fashion, but do not vary among individual organisms for any option other than
breathing in well-aerated, flowing water. Another species of fish— the
middling species—ekes out a marginal existence in the same pond. The gills
don't work as well, but their structure varies greatly among organisms. In
particular, a few members of the species can breathe in quite stagnant and
muddy waters.
Organismic selection favors the optimal fish, a proud creature
who has lorded it over all brethren, especially the middling fish, for ages
untold. But now the pond dries up, and only a few shallow, muddy pools remain.
The optimal fish becomes extinct. The middling species persists because a few of
its members can survive in the muddy residua. (Next decade, the deep,
well-aerated waters may return, but the optimal fish no longer exists to
reestablish its domination).
Gould argues that the persistence of the more variable,
middling species and the extinction of the less variable, optimal form result
from natural selection acting upon entire species rather than individuals,
because the outcome ensues from the greater variability (a character of the
species) of the surviving "middling fish." While it is true that entire species
die out because they cannot adapt to new circumstances (such as dinosaurs during
large asteroid impacts), this is not, of itself, an argument for species
selection. For me, this particular example raises more questions than it
resolves. For instance, the supposed "species character" of greater variability
of the middling fish is itself eliminated by the drought-caused natural
selection, because just a few individuals at the extreme end of variation
survive. Does this mean that the survivors constitute a new species, with
different "species characters"? Not even punctuated equilibrium posits such
virtually instantaneous generation of species.
Gould's concept of species selection is embedded within a
second concept of a hierarchy of selection, which leads from the gene to
(presumably) the whole of life itself. This brings him into direct conflict
with that formidable Gouldian nemesis Richard Dawkins, whose selfish gene
theory posits that natural selection acts on genes rather than on individuals
or groups of individuals. By way of illustration, on the subject of sexual
selection among birds, Dawkins says, "'Pressure' from choosy females drove the
evolution of male pheasants' sumptuous feathers. What this means is that a
gene for a beautiful feather is especially likely to find itself riding a
sperm into a female's body."[2] Dawkins's hypothesis has
arguably revolutionized evolutionary theory, and while actively contested, it
enjoys widespread acceptance.
One of the more controversial aspects of Dawkins's work is
the concept of "memes," which he defines as being the cultural equivalent of
genes. The concept is intriguing because it suggests a new way of examining how
ideas "behave" in human societies. Interestingly, Gould dismisses Dawkins's
selfish gene theory as "an impotent meme," claiming that the entire concept is
based on a flaw of logic—that of confusing what Gould calls "bookkeeping"
with "causality." I have tried to tease out exactly what Gould means by this,
but find it hard to pin down. At its base, though, is Gould's idea that natural
selection acts on individuals or groups (such as species) and only by way of
them on genes themselves. Not only does Gould see a fatal flaw of logic here,
but he goes on to argue that the recent discovery that organisms possess fewer
genes than previously thought is a death knell to Dawkins's hypothesis. Yet
this is such a new and rapidly changing field of research— particularly
on the structure and function of proteins—that announcing the demise of
the selfish gene theory on these grounds seems premature.
As I pondered the Gould–Dawkins rivalry, it occurred
to me that Gould's hypothetical example of the pond's two fish species might
explain more about Gould and Dawkins than it does about evolution. Read at
another level (and surely the playful Gould is mischievous enough to have
given it a second meaning), the "wondrously optimal fish" might be Richard
Dawkins and his successful selfish gene theory (which indeed takes a narrow
focus on natural selection), while the "middling fish" could be the author
himself (who sees natural selection operating on a wide field). This left me
wondering what revolution Gould thinks will muddy the waters and eliminate the
competition, thus permitting the Gould-ian "middling fish" to triumph? While I
suspect that the concept of species selection is destined not to survive, at
least in its present form, this is such a strongly contested field of biology
that I would certainly not lay money—even at short odds—against
Gould's eventual triumph.
Gould's discussion of the second of the fundamental Darwinian
principles, efficacy, centers on the importance of historical and structural
constraints on development, and the curious phenomena of spandrels and
"exaptation," of which spandrels are an example. A principal theme here is that
many features of organisms do not arise through natural selection, but through
contingency or the inherent nature of the organisms themselves. One of Gould's
favored examples concerns male nipples and the clitoris, both of which, he
argues, exist not because of their function, but because they are necessary
elements of the essential body plan from which adult males and females
differentiate.
Gould argues that historical constraint (the legacy of all
that has gone before in a biological lineage, including its genes) is important.
While this may seem self-evident, there are other factors to consider, not the
least of which is ecology. Gould attacks Theodosius Dobzhansky's ecologically
based theory of "adaptive peaks" because it cedes too much ground to natural
selection and ecology. To illustrate the point, Gould uses the example of cats
and dogs. Dobzhansky argues that cats and dogs exist as discrete types, with
not much in between, because ecological niches exist for dog-like and cat-like
creatures, but not for in-between kinds. Gould, however, argues that the two
discrete types owe their existence to historical constraint in the form of
their own, separate inheritances from an ancestral dog-like and cat-like
creature.
There is a simple test of these competing theories. If
ecology were responsible, it would be reasonable to expect that other mammal
groups would have thrown up cat- and dog-like forms during their evolution,
with little in between—and indeed, this is precisely what we see. Both
South America's and Australia's marsupials have given rise to dog-like and
cat-like species, while Madagascar's carnivores (which are related to ferrets)
have given rise to the cat-like fossa. Here is good evidence that Dobzhansky's
theory, in this instance at least, is preferable.
If the word "exaptation" is unfamiliar to some readers, it
is because it has been only recently coined, by Gould and Vrba in 1982. To use
Gould's definition, it denotes "features coopted for a current utility
following an origin for a different function (or for no function at all.)" By
way of example, he cites the case of an African lizard whose extremely
flattened head is an adaptation to life in crevices, but which also assists
the creature in gliding. Spandrels—an architectural term that Gould has
introduced to biology—are an extreme form of exaptation, in that they
may not result from natural selection at all. Like the spandrels on the
interior surface of a cathedral dome, they just have to be there as a result
of the underlying structure of a dome atop four supports; yet whether in snails
or mammals or other animals, we find spandrel-like structures that have
acquired functions.
Perhaps the best example comes from snails, Gould's own
special subject. Certain groups of snails have co-opted the umbilicus (a tube
around which the shell coils) as a chamber for protecting their eggs. The
umbilicus must exist if the shell is to coil, yet it had no internal function
of its own until a few species co-opted it as an egg chamber. Much later in
The Structure of Evolutionary Theory, Gould discusses how his sense
that the inherent properties of organisms (such as spandrels), rather than
deterministic and all-explaining adaptation, is important personally to him
because it allows room for individuality and essential humanity in his own
worldview.
The third Darwinian principle, scope, is dealt with more
cursorily than the other two. At the heart of the matter for Gould is the
existence of seemingly random events such as mass extinctions and other
similar catastrophes. He explains that they are "more frequent, more rapid,
more intense, and more different" than Darwin ever imagined. Moreover, their
discovery represents an important extension of Darwinian logic, because they
further disrupt Darwin's concept of "gradualism." Yet these events are not
strictly biological in nature—and thus outside Gould's own
expertise—so he deals with them only briefly.
This year also marks the publication of a very different
Gouldian production. I Have Landed is Gould's tenth and final volume
of collected essays, most of which were written for Natural History
magazine. These essays have entranced millions, from company presidents to
penitentiary inmates, with the wonders of evolution. For the past twenty-five
years Gould has produced an essay a month for Natural History, not
stopping, as he says, for "cancer, hell, high water or the World Series." In
between he has also found time to write for Science, Time,
The New York Times, The New York Review, and antiquarian book
catalogs, as well as completing ten monographs on various aspects of
evolution. But human energy is not limitless, and in I Have Landed
Gould indicates that this prodigious flow of words is slowing down.
The book's introduction celebrates his fascination with
numerical coincidence. In earlier works, Gould's interest in this topic was
often concerned with baseball, but here it becomes altogether more personal.
The book's title derives from the coincidence of the author's grandfather's
arrival in New York on September 11, 1901, and Gould's interrupted pilgrimage
to Ellis Island on the terrible centenary of that day. Other numerical
coincidences are at play in Gould's pattern of publication. His three
hundredth essay appeared in the millennial issue of Natural History,
followed in 2002 by his tenth book of essays and his tenth monograph. On
realizing this, he "felt the double whammy of an equally 'exact' and notable
twenty-five years (a quarter of the square of our decimal base) between two
odd and fortuitous conjunctions in life's passage." He took this to mean
that "something must be beaming me a marching order to move on."
The new collection of essays brings us up to date with
the thinking—and indeed even the personal experience —of one of
America's best-loved scientists. Gould has fashioned a admirable "second"
career as a historian and philosopher of science, and this material dominates
the compilation. Topics range from the nature of excellence as illustrated by
the operas of Gilbert and Sullivan to Freud's concepts of mental development,
and the brief friendship between Karl Marx and the biologist E. Ray Lancaster
("Resolving Evolution's Oddest Coupling"). In comparison with Gould's earlier
collections, many of the essays in I Have Landed lack an urgent
scientific point; the prose is more detailed and less intense in tone.
While there is rarely the sense that Gould has stepped out
of his depth, the essay I found least satisfying is the twenty-fourth, titled
"An Evolutionary Perspective on the Concept of Native Plants." Arguing that
indigenes may be less well adapted to their local conditions than introduced
organisms, Gould bases his case on the observation that introduced plants and
animals can be wildly successful, often to the detriment of the locals. What
is astonishing about this argument is that it takes no account of ecology.
Gould fails to consider, for example, that California's eucalyptus trees may
have succeeded because they left behind in Australia all of their predators
(such as koalas, which can kill trees), diseases, and competitors. Nor does
he consider that Australia's marsupials may have been disadvantaged, and the
introduced placental mammals given an advantage, by the land management
practices introduced by European colonists. These seem fundamental
oversights.
In the closing lines of the title essay, Gould talks of
his "own childhood dream—something that once seemed so mysteriously
beyond any hope of realization to an insecure little boy in a garden apartment
in Queens—to become a scientist and to make, by my own effort, even the
tiniest addition to human knowledge of evolution and the history of life." No
one can deny Stephen Jay Gould this achievement, and there will be many who
have been inspired by the spark of his particular genius as an essayist and
popular communicator of the fascination of science.
How are we to judge Stephen Jay Gould's additions to the
knowledge of evolution and the history of life, particularly as presented in
The Structure of Evolutionary Theory? I could not help but feel that
the diverse matter fails to gel into a cohesive theory; yet remarkably Gould
leaves us with a self-acknowledged paradox that may explain why this is so.
He says that one of his principal themes has been the importance of
nonadaptational features of evolution such as spandrels, and of the effects
of accidents such as asteroid-induced mass extinctions on the course of
evolution. By their very nature such phenomena resist being part of an
inclusive evolutionary theory, yet they remain central to Gould's view. If
he is correct, then evolution may be one field of science that is not
amenable to the application of a grand, overarching theory. This seems an
entirely plausible if disconcerting possibility.
One could wish that the editors of The Structure of
Evolutionary Theory had been more concerned about the book's own
structure. At 1,433 densely printed pages and almost five pounds in weight,
Gould's mammoth book takes too long to make its points. A very large book
can, of course, be justified for those wishing to understand Gould's corpus
of ideas; but the lack of a clear, succinct summary of his work and the
mostly unhelpful index (which even lacks an entry for Gould's beloved
Tyrannosaurus) frustrate this goal. Still, one of the joys of
reading about good science is the chance not only to observe how scientific
theory works, but also to participate in the workings of the mind behind
the words. In Gould's I Have Landed and The Structure of
Evolutionary Theory, the reader will find such joy in abundance.
Notes
See, for example, the following:
Stephen J. Gould, "The Confusion over Evolution," The New York Review,
November 19, 1992; Daniel C. Dennett, John Maynard Smith, and Stephen Jay
Gould, "'Confusion over Evolution': An Exchange," The New York
Review, January 14, 1993; Stephen J. Gould,
"Darwinian Fundamentalism,"
The New York Review, June 12, 1997; Stephen J. Gould,
"Evolution: The Pleasures of Pluralism,"
The New York Review, June 26, 1997; Daniel C. Dennett and Stephen
Jay Gould, "'Darwinian Fundamentalism': An
Exchange," The New York Review, August 14, 1997.
Richard Dawkins, Climbing Mount Improbable
(Viking, 1996), p. 180.
[ Tim Flannery, "A New Darwinism?"
The New York Review of Books,
49 (May 23, 2002): 52–54. ]
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