Darwin's Untimely Burial
Dispite reports to the contrary, the theory of natural selection remains
very much alive.
by Stephen Jay Gould
n
one of the numerous movie versions of A Christmas Carol, Ebenezer
Scrooge, mounting the steps to visit his dying partner, Jacob Marley,
encounters a dignified gentleman sitting on a landing. "Are you the doctor?"
Scrooge inquires. "No," replies the man, "I'm the undertaker; ours is a very
competitive business." The cutthrought world of intellectuals must rank a
close second, and few events attract more notice than a proclamation that
popular ideas have died. Darwin's theory of natural selection has been a
perennial candidate for burial.
Tom Bethell held the most recent wake in a piece called
"Darwin's Mistake (Harper's, February 1976): "Darwin's theory,
I believe, is on the verge of collapse.…Natural selection was quietly
abandoned, even by his most ardent supporters, some years ago." News to me,
and I, although I wear the Darwinian label with some pride, am not among the
most ardent defenders of natural selection. I recall Mark Twain's famous
response to a premature obituary: "The reports of death are greatly
exaggerated."
Bethell's argument has a curious ring for most practicing
scientists. We are always ready to watch a theory fall under the impact of new
data, but we do not expect a great and influential theory to collapse from a
logical error in its formulation. Virtually every empirical scientist has a
touch of the Philistine. Scientists tend to ignore academic philosophy as an
empty pursuit. Surely, any intelligent person can think straight by intuition.
Yet Bethell cites no data at all in sealing the coffin of natural selection,
only an error in Darwin's reasoning: "Darwin made a mistake sufficiently
serious to undermine his theory. And that mistake has only recently been
recognized as such.…At one point in his argument, Darwin was mislead."
Although I will try to refute Bethell, I also deplore the
unwillingness of scientists to explore seriously the logical structure of
arguments. Much of what passes for evolutionary theory is as vacuous as
Bethell claims. Many great theories are held together by chains of dubious
metaphor and analogy. Bethell has correctly identified the hogwash surrounding
evolutionary theory. But we differ in one fundamental way: for Bethell,
Darwinian theory is rotten to the core; I find a pearl of great price at the
center.
Natural selection is the central concept of Darwinian
theory—the fittest survive and spread their favored traits through
populations. Natural selection is defined by Spencer's phrase "survival of
the fittest," but what does this famous bit of jargon really mean? Who are
the fittest? And how is "fitness" defined? We often read that fitness involves
no more than "differential reproductive success"—the production of more
surviving offspring than other competing members of the population. Whoa!
cries Bethell, as many others have before him. This formulation defines
fitness in terms of survival only. The crucial phrase of natural selection
means no more than "the survival of those who survive"—a vacuous tautology.
(A tautology
is a phrase—like "my father is a man"—contain no information in the
predicate ("a man") not inherent in the subject my ("my father"). Tautologies
are fine as definitions, but not as testable scientific statements—there
can be nothing to test in a statement true by definition.)
But how could Darwin have made such a monumental, two bit
mistake? Even his sincerest critics have never accused him of crass stupidity.
Obviously, Darwin must have tried to define fitness differently—to find
a criterion for fitness independent of mere survival. Darwin did propose an
independent criterion, but Bethell argues quite correctly that he relied upon
analogy to establish it, a dangerous and slippery strategy. One might think
that the first chapter of such a revolutionary book as origin of Species would
deal with cosmic questions and general concerns. It doesn't. It's about
pigeons. Darwin devotes most of his first forty pages to " artificial
selection" of favored traits by animal breeders. For here an independent
criterion surely operates. The pigeon fancier knows what he wants. The
fittest are not defined by their survival. They are, rather, allowed to
survive because they possess desired traits.
The principle of natural selection depends upon the
validity of an analogy with artificial selection. We must be able, like
the pigeon fancier, to identify the fittest beforehand, not only by their
subsequent survival. But nature is not an animal breeder; no preordained
purpose regulates the history of life. In nature, any traits possessed by
survivors must be counted as "more evolved"; in artificial selection,
"superior" traits are defined before breeding even begins. Later
evolutionists, Bethell argues, recognize the failure of Darwin's analogy
and redefined "fitness" as mere survival. But they did not realize that
they had undermined the logical structure of Darwin's central postulate.
Nature provides no independent criterion of fitness; thus, natural
selection is tautological.
Bethell then moves to two important corollaries of his
major argument. First, if fitness only means survival, then how can natural
selection be a "creative" force, as Darwinians insist. Natural selection can
only tell us how that "a given type of animal became more numerous"; it
cannot explain "how one type of animal gradually changed into another."
Secondly, why were Darwin and other eminent Victorians so sure that mindless
nature could be compared with conscious selection by breeders. Bethell argues
that the cultural climate of triumphant industrial capitalism had defined
any change as inherently progressive. Mere survival in nature could only be
for the good: "It is beginning to look as though what Darwin really
discovered was nothing more than the Victorian propensity to believe in
progress."
I believe that Darwin was right and that Bethell and his
colleagues are mistaken: criteria of fitness independent of survival can be
applied to nature and have been used consistently by evolutionists. But let
me first admit that Bethell's criticism applies to much of the technical
literature in evolutionary theory, especially to the abstract mathematical
treatments that consider evolution only as an alteration in numbers, not as
a change in quality. These studies do assess fitness only in terms of
differential survival. What else can be done with abstract models that
traced the relative successes of hypothetical genes A and B in populations
that exist only on computer tape? Nature, however, is not limited by the
calculations of theoretical geneticists. In nature, A's "superiority" over
B will be expressed as differential survival, but it is not
defined by it—or, at least, it better not be so defined, lest
Bethell et al. triumph and Darwin surrender.
My defense of Darwin is neither startling, novel, nor
profound. I merely assert that Darwin was justified in analogizing natural
selection with animal breeding. In artificial selection, a breeder's desire
represents a "change in environment" for a population. In this new
environment, certain traits are superior a priori; (they survive and spread
by our breeders choice, but this is a result of their fitness, not a
definition of it). In nature, Darwinian evolution is also a response to
changing environments. Now, the key point: certain morphological,
physiological, and behavioral traits should be superior a priori as designs
for living in new environments. These traits confer fitness by an engineer's
criterion on a good design, not by the empirical fact of their survival and
spread. It got colder before the woolly mammoth evolved its shaggy coat.
Why does this issue agitate evolutionists so much? OK,
Darwin was right: superior design in changed environments is an independent
criterion of fitness. So what? Did anyone ever seriously propose that the
poorly designed shall triumph? Yes, in fact, many did. In Darwin's day
many rival evolutionary theories asserted that the fitness (best designed)
must perish. One popular notion it—that theory of radical life
cycles—was championed by a former inhabitant of the office I now
occupy, the great American paleontologist Alpheus Hyatt. Hyatt claimed that
evolutionary lineages, like individuals, had cycles of youth, maturity, old
age, and death (extinction). Decline and extinction are programmed into
the history of species. As maturity yields to old age, the best-designed
individuals die and the hobbled, deformed creatures of phyletic senility
take over.
Another anti-Darwinian notion, the but he theory of
orthogenesis, held that certain trends, once initiated, could not be halted,
even though they must lead to extinction caused by increasing inferior
design. Many nineteenth-century evolutionist did (perhaps a majority) held
that Irish elks became extinct because they could not halt their evolutionary
increase in antler size; thus, they died—caught in trees or bowed
(literally) in the mire. Likewise, the demise of saber-toothed "tigers" was
often attributed to canine teeth grown so long that the poor cats couldn't
open their jaws wide enough to use them.
Thus, it is not true, as Bethell claims, that any traits
possessed by survivors must be designed as fitter. "Survival of the fittest"
is not a tautology. It is also not the only imaginable or reasonable reading
of the evolutionary record. It as testable. It had rivals that failed under
the weight of contrary evidence and changing attitudes about the nature of
life. It has rivals that may succeed, at least in limiting its scope.
If I am right, how can Bethell claim, "Darwin, I suggest,
is in the process of being discarded, but perhaps in difference to the
venerable old gentleman, resting comfortably in Westminster Abbey next to
Sir Isaac Newton, it is being done as discreetly and as gently as possible
with a minimum of publicity." I'm afraid I must say that Bethell has not
been quite fair in his report of prevailing opinion. He cites the gadflies
C. H, Waddington and H. J. Muller as though they epitomized a consensus.
He never mentions the leading selectionists of our present generation—E.
O. Wilson or D. Janzen, for example. And he quotes the architects of
neo-Darwinism—Dobzhansky, Simpson, Mayr, and J. Huxley—only
to ridicule their metaphors on the "creativity" of natural selection. (I
am not claiming that Darwinism should be cherished because it is still
popular; I am enough of a gadfly to believe that uncriticized consensus is
a sure sign of impending trouble. I merely report that, for better or
worse, Darwinism is alive and thriving, despite Bethell's obituary.)
But why was natural selection compared to a composer by
Dobzhansky; to a poet by Simpson; to a sculptor by Mayr; and to, of all
people, Mr. Shakespeare by Julian Huxley? I won't defend the choice of
metaphors, but I will uphold the intent, namely, to illustrate the essence
of Darwinism—the creativity of natural selection. Natural selection
has a place in all anti-Darwinian theories that I know. It is cast in a
negative role as an executioner, a headsman for the unfit (while the fit
arise by such non-Darwinian mechanisms as the inheritance of acquired
characters or direct induction of favorable variation by the environment).
The essence of Darwinism lies in its claim that natural selection creates
the fit. Variation is ubiquitous and random in direction. It supplies the
raw material only. Natural selection directs the course of the
evolutionary change. It preserves favorable variants and build fitness
gradually. In fact, since artist fashion their creations from the raw
material of notes, words, and stone, the metaphors to not strike me as
inappropriate. Since Bethell does not accept a criterion of fitness
independent of mere survival, he can hardly grant a creative role to
natural selection.
According to Bethell, Darwin's concept of natural
selection as a creative force can be no more than an illusion encouraged
by the social and political climate of his times. In the throes of
Victorian optimism in imperial Britain, change seemed to be inherently
progressive; why not equate survival in nature with increasing fitness
in the nontautological sense of improved design.
I am a strong advocate of the general argument that
"truth" as preached by scientists often turns out to be no more than
prejudice inspired by prevailing social and political beliefs. I have
devoted several essays to this theme because I believe that helps to
"demystify" the practice of science by showing its similarity to all
creative human activity. But the truth of the general argument does not
validate any specific application, and I maintain that Bethell's
application is badly misinformed.
Darwin did two very separate things: he convinced the
scientific world that evolution had occurred and he proposed the theory
of natural selection as its mechanism. I am quite willing to admit that
the common equation of evolution with progress made Darwin's first claim
more palatable to his contemporaries. But Darwin failed in the second
quest during his own lifetime. The theory of natural selection did not
triumph until the 1940s. It's Victorian unpopularity, in my view, lay
primarily in its denial of general progress as inherent in the workings
of evolution. Natural selection is a theory of local adaptation to
changing environments. It proposes no perfecting principles, no guarantee
of general improvement; in short, no reason for general approbation in a
political climate favoring inmate progress in nature.
Darwin's independent criterion of fitness is, indeed,
"improved design," but not "improved" in the cosmic sense that contemporary
Britain favored. To Darwin, improved meant only "better designed for
immediate, local environment." Local environments change consistently:
they get colder or hotter, wetter or drier, more grassy or more
forested. Evolution by natural selection is no more than a tracking of
these changing environments by differential preservation of organisms
better designed to live in them: hair on a mammoth is not progressive in
any cosmic sense. Natural selection can produce a trend that tempts us
to think of more general progress—increase in brain size does not
characterize the evolution of group after group of mammals. But big
brains have their uses in local environments; they do not marked intrinsic
trends to higher states. And Darwin delighted in showing that local
adaptation opted produces "degeneration" in design—anatomical
simplification in parasites, for example.
If natural selection is not a doctrine of progress,
then its popularity cannot reflect the politics that Bethell invokes. If
the theory of natural selection contains an independent criterion of fitness,
then it is not tautological. I maintain, perhaps naïvely, that its
current, unabated popularity must have something to do with its success
in explaining the admittedly imperfect information we now possess about
evolution. I rather suspect that we'll have Charles Darwin to kick
around for some time.
Stephen Jay Gould teaches biology, geology, and the
history of science at Harvard University.
[ Stephen Jay Gould, "Darwin's Untimely Burial," Natural
History 85 (Oct. 1976): 24-30. ]
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