Darwin's Dangerous Idea (6 page)

or
carnivore
be as important a classifier as
warmblooded creature?
Although We post-Darwinians are so used to thinking in historical terms about the the broad outlines and most of die specific rulings of taxonomy were development of life forms that it takes a special effort to remind ourselves undisputed (and remain so today, of course), there were heated controversies that in Darwin's day species of organisms were deemed to be as timeless as about the problem cases. Were all these lizards members of die same species, the perfect triangles and circles of Euclidean geometry. Their individual or of several different species? Which principle of classification should members came and went, but the species itself remained unchanged and

"count"? In Plato's famous image, which system "carved nature at the unchangeable. This was part of a philosophical heritage, but it was not an idle joints"?

or ill-motivated dogma. The triumphs of modern science, from Copernicus Before Darwin, these controversies were fundamentally ill-formed, and and Kepler, Descartes and Newton, had all involved the application of precise could not yield a stable, well-motivated answer because there was no back-mathematics to the material world, and this apparently requires 38 AN IDEA IS BORN

Natural Selection
—
an Awful Stretcher
39

ground theory of
why
one classification scheme would count as getting the in, so in the conclusion of his book he went so far as to beseech the support joints right—the way things
really
were. Today bookstores face the same sort of his younger readers: "Whoever is led to believe that species are mutable of ill-formed problem: how should the following categories be cross-will do good service by conscientiously expressing his conviction; for only organized: best-sellers, science fiction, horror, garden, biography, novels, thus can the load of prejudice by which this subject is overwhelmed be collections, sports, illustrated books? If horror is a genus of fiction, then true removed"
(Origin,
p. 482).

tales of horror present a problem. Must all novels be fiction? Then the Even today Darwin's overthrow of essentialism has not been completely bookseller cannot honor Truman Capote's own description of
In Cold Blood
assimilated. For instance, there is much discussion in philosophy these days (1965) as a nonfiction novel, but the book doesn't sit comfortably amid either about "natural kinds," an ancient term the philosopher W. V. O. Quine the biographies or the history books. In what section of the bookstore should (1969) quite cautiously resurrected for limited use in distinguishing good the book you are reading be shelved? Obviously there is no one Right Way to scientific categories from bad ones. But in the writings of other philosophers, categorize books—nominal essences are all we will ever find in this domain.

"natural kind" is often sheep's clothing for the wolf of real essence. The But many naturalists were convinced on general principles that there were essentialist urge is still with us, and not always for bad reasons. Science does real essences to be found among the categories of their Natural System of aspire to carve nature at its joints, and it often seems that we need essences, living things. As Darwin put it, "They believe that it reveals the plan of the or something like essences, to do the job. On this one point, the two great Creator; but unless it be specified whether order in time or space, or what kingdoms of philosophical thought, the Platonic and the Aristotelian, agree.

else is meant by the plan of the Creator, it seems to me that nothing is thus But the Darwinian mutation, which at first seemed to be just a new way of added to our knowledge"
(Origin,
p. 413).

thinking about kinds in biology, can spread to other phenomena and other Problems in science are sometimes made easier by adding complications.

disciplines, as we shall see. There are persistent problems both inside and The development of the science of geology and the discovery of fossils of outside biology that readily dissolve once we adopt the Darwinian manifestly extinct species gave the taxonomists further curiosities to con-perspective on what makes a thing the sort of thing it is, but the tradition-found them, but these curiosities were also the very pieces of the puzzle that bound resistance to this idea persists.

enabled Darwin, working alongside hundreds of other scientists, to discover the key to its solution: species were
not
eternal and immutable; they had evolved over time. Unlike carbon atoms, which, for all one knew, had been around forever in exactly the form they now exhibited, species had births in 2. NATURAL SELECTION—AN AWFUL STRETCHER

time, could change over time, and could give birth to new species in turn.

This idea itself was not new; many versions of it had been seriously
It is an awful stretcher to believe that a peacock's tail was thus formed;
discussed, going back to the ancient Greeks. But there was a powerful
but, believing it, I believe in the same principle somewhat modified
Platonic bias against it: essences were unchanging, and a thing couldn't
applied to man.

change its essence, and new essences couldn't be born—except of course by

—CHARLES DARWIN, letter quoted in Desmond and

God's command in episodes of Special Creation. Reptiles could no more
turn
Moore 1991, p. 553

into
birds than copper could turn into gold.

It isn't easy today to sympathize with this conviction, but the effort can be Darwin's project in
Origin
can be divided in two: to prove
that
modern helped along by a fantasy: consider what your attitude would be towards a species were revised descendants of earlier species—species had evolved—

theory that purported to show how the number 7 had once been an even and to show
how
this process of "descent with modification" had occurred. If number, long, long ago, and had gradually acquired its oddness through an Darwin hadn't had a vision of a mechanism, natural selection, by which this arrangement whereby it exchanged some properties with the ancestors of the well-nigh-inconceivable historical transformation could have been ac-number 10 (which had once been a prime number). Utter nonsense, of course.

complished, he would probably not have had the motivation to assemble all Inconceivable. Darwin knew that a parallel attitude was deeply ingrained the circumstantial evidence that it had actually occurred. Today we can among his contemporaries, and that he would have to labor mightily to readily enough imagine proving Darwin's first case—the brute historic fact overcome it. Indeed, he more or less conceded that the elder authorities of his of descent with modification—quite independently of any consideration of day would tend to be as immutable as the species they believed Natural selection or indeed any other mechanism for bringing these brute events about, but for Darwin the idea of the mechanism was both the 40 AN IDEA IS BORN

Natural Selection
—
an A wful Stretcher
41

hunting license he needed, and an unwavering guide to the right questions to of years, we can be sure that only a fraction of the elephants born in any ask.1

period have progeny of their own.

The idea of natural selection was not itself a miraculously novel creation of So the normal state of affairs for any sort of reproducers is one in which Darwin's but, rather, the offspring of earlier ideas that had been vigorously more offspring are produced in any one generation than will in turn repro-discussed for years and even generations (for an excellent account of this duce in the next. In other words, it is almost always crunch time.3 At such a intellectual history, see R. Richards 1987). Chief among these parent ideas crunch, which prospective parents will "win"? Will it be a fair lottery, in was an insight Darwin gained from reflection on the 1798
Essay on the
which every organism has an equal chance of being among the few that
Principle of Population
by Thomas Malthus, which argued that population reproduce? In a political context, this is where invidious themes enter, about explosion and famine were inevitable, given the excess fertility of human power, privilege, injustice, treachery, class warfare, and the like, but we can beings, unless drastic measures were taken. The grim Malthusian vision of elevate the observation from its political birthplace and consider in the ab-the social and political forces that could act to check human overpopulation stract, as Darwin did, what would—must—happen in nature. Darwin added may have strongly flavored Darwin's thinking (and undoubtedly has flavored two further logical points to the insight he had found in Malthus: the first was the shallow political attacks of many an anti-Darwinian ), but the idea Darwin that at crunch time, if there was significant variation among the contestants, needed from Malthus is purely logical. It has nothing at all to do with then any advantages enjoyed by any of the contestants would inevitably bias political ideology, and can be expressed in very abstract and general terms.

the sample that reproduced. However tiny the advantage in question, if it was Suppose a world in which organisms have many offspring. Since the off-actually an advantage (and thus not absolutely invisible to nature), it would spring themselves will have many offspring, the population will grow and tip the scales in favor of those who held it. The second was that
if
there was a grow ("geometrically" ) until inevitably, sooner or later—surprisingly soon,

"strong principle of inheritance"—if offspring tended to be more like their in fact—it must grow too large for the available resources (of food, of space, parents than like their parents' contemporaries—the biases created by ad-of whatever the organisms need to survive long enough to reproduce). At that vantages, however small, would become amplified over time, creating trends point, whenever it happens, not all organisms will have offspring. Many will that could grow indefinitely. "More individuals are born than can possibly die childless. It was Malthus who pointed out the mathematical inevitability survive. A grain in the balance will determine which individual shall live and of such a crunch in
any
population of long-term reproducers— people, which shall die,—which variety or species shall increase in number, and animals, plants (or, for that matter, Martian clone-machines, not that such which shall decrease, or finally become extinct"
{Origin,
p. 467).

fanciful possibilities were discussed by Malthus). Those populations that What Darwin saw was that if one merely supposed these few general reproduce at less than the replacement rate are headed for extinction unless conditions to apply at crunch time—conditions for which he could supply they reverse the trend. Populations that maintain a stable population over long ample evidence—the resulting process would
necessarily
lead in the direc-periods of time will do so by settling on a rate of overproduction of offspring tion of individuals in future generations who tended to be better equipped to that is balanced by the vicissitudes encountered. This is obvious, perhaps, for deal with the problems of resource limitation that had been faced by the houseflies and other prodigious breeders, but Darwin drove the point home individuals of their parents' generation. This fundamental idea—Darwin's with a calculation of his own: "The elephant is reckoned to be the slowest dangerous idea, the idea that generates so much insight, turmoil, confusion, breeder of all known animals, and I have taken some pains to estimate its anxiety—is thus actually quite simple. Darwin summarizes it in two long probable minimum rate of natural increase:... at the end of the fifth century sentences at the end of chapter 4 of
Origin.

there would be alive fifteen million elephants, descended from the first pair"

(
Origin,
p.
64
).2 Since elephants have been around for millions If during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organization, and I 1. This has often happened in science. For instance, for many years there was lots of 3. A familiar example of Malthus' rule in action is the rapid expansion of yeast evidence lying around in favor of the hypothesis that the continents have drifted—that populations introduced into fresh bread dough or grape juice. Thanks to the feast of Africa and South America were once adjacent and broke apart—but until the mechanisms sugar and other nutrients, population explosions ensue that last for a few hours in the of plate tectonics were conceived, it was hard to take the hypothesis seriously.

dough, or a few weeks in the juice, but soon the yeast populations hit the Malthusian 2. This sum as it appeared in the first edition is wrong, and when this was pointed out, ceiling, done in by eir own voraciousness and the accumulation of their waste Darwin revised his calculations for later editions, but the general principle is still products—carbon dioxide (which forms the bubbles that make the bread rise, and the unchallenged.

fizz in champagne) and alcohol being the two that we yeast-exploiters tend to value.

42 AN IDEA IS BORN

Did Darwin Explain the Origin of Species?
43

think this cannot be disputed; if there be, owing to the high geometric doesn't even purport to offer an explanation of the origin of the
first
species, powers of increase of each species, at some age, season, or year, a severe or of life itself; he begins in the middle, supposing many different species with struggle for life, and this certainly cannot be disputed; then, considering many different talents already present, and claims that starting from such a the infinite complexity of the relations of all organic beings to each other mid-stage point, the process he has described will inevitably hone and di-and to their conditions of existence, causing an infinite diversity in struc-versify the talents of the species already existing. And will that process create ture, constitution, and habits, to be advantageous to them, I think it would still further species? The summary is silent on that score, but the book is not.