Darwin's Dangerous Idea (8 page)

these effects. Skeptics were presented with a challenge: Could they show that Before anyone jumps on this and pronounces that I have just conceded that his arguments were mistaken? Could they show how natural selection would Darwinism is just as much an unprovable faith as natural religion, it should be incapable of producing the effects?5 Or could they even describe be borne in mind that there is a fundamental difference: having declared their allegiance to natural selection, these scientists have then proceeded to take on the burden of showing how the difficulties with their view could be overcome, and, time and time again, they have succeeded in meeting the 4. As is often pointed out, Darwin didn't insist that natural selection explained everything: challenge. In the process, Darwin's fundamental idea of natural selection has it was the "main but not exclusive means of modification"
(Origin,
p. 6).

been articulated, expanded, clarified, quantified, and deepened in many 5. It is sometimes suggested that Darwin's theory is systematically irrefutable ( and hence ways, becoming stronger every time it overcame a challenge. With every scientifically vacuous), but Darwin was forthright about what sort of finding it would take to refute his theory. "Though nature grants vast periods of time for the work of natural success, the scientists' conviction grows that they must be on the right track.

selection, she does not grant an indefinite period"
(Origin,
p. 102), so, if the geological It is reasonable to believe that an idea that was ultimately false would surely evidence mounted to show that not enough time had elapsed, his whole theory would be have succumbed by now to such an unremitting campaign of attacks. That is refuted. This still left a temporary loophole, for the theory wasn't formulatable in suffi-not a conclusive proof, of course, just a mighty persuasive consideration.

ciently rigorous detail to say just how many millions of years was the minimal amount required, but it was a temporary loophole that made sense, since at least some proposals One of the goals of this book is to explain why the idea of natural selection about its size could be evaluated independently. (Kitcher [1985a, pp. 162-65], has a appears to be a clear winner, even while there are unresolved controversies good discussion of the further subtleties of argument that kept Darwinian theory from about how it can handle some phenomena.

being directly confirmed or disconfirmed.) Another famous instance: "If it could be demonstrated diat any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down" (
Origin,
p. 189 ). Many have risen to this challenge, but, as we shall see in chapter 11, there are good reasons why they have not succeeded in their attempted demonstrations.

48 AN IDEA IS BORN

Natural Selection as an Algorithmic Process
49

4. NATURAL SELECTION AS AN ALGORITHMIC PROCESS

consists of two sorts of demonstrations-, the logical demonstration that a certain
sort
of process would necessarily have
a
certain sort of outcome, and
What limit can be put to this power, acting during long ages and rigidly
the empirical demonstration that the requisite conditions for that sort of
scrutinising the whole constitution, structure, and habits of each crea-process had in fact been met in nature. He bolsters up his logical dem-ture,
—
favouring the good and rejecting the bad? I can see no limit to
onstration with thought experiments—"imaginary instances"
{Origin,
p.

this power, in slowly and beautifully adapting each form to the most
95)—that show
how
the meeting of these conditions
might
actually account
complex relations of life.

for the effects he claimed to be explaining, but his whole argument extends to book length because he presents a wealth of hard-won empirical detail to

—CHARLES DARWIN,
Origin,
p. 469

convince the reader that these conditions have been met over and over again.

Stephen Jay Gould (1985) gives us a fine glimpse of the importance of this The second point to notice in Darwin's summary is that he presents his feature of Darwin's argument in an anecdote about Patrick Matthew, a principle as deducible by a formal argument—
if
the conditions are met,
a
Scottish naturalist who as a matter of curious historical fact had scooped certain outcome is
assured.6
Here is the summary again, with some key Darwin's account of natural selection by many years—in an appendix to his terms in boldface.

1831 book,
Naval Timber and Arboriculture.
In the wake of Darwin's ascent If, during the long course of ages and under varying conditions of life, to fame, Matthew published a letter (in
Gardeners' Chronicle?)
proclaiming organic beings vary at all in the several parts of their organization, and I his priority, which Darwin graciously conceded, excusing his ignorance by think this cannot be disputed; if there be, owing to the high geometric noting the obscurity of Matthew's choice of venue. Responding to Darwin's powers of increase of each species, at some age, season, or year, a severe published apology, Matthew wrote:

struggle for life, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other To me the conception of this law of Nature came intuitively as a self-and to their conditions of existence, causing an infinite diversity in struc-evident fact, almost without an effort of concentrated thought. Mr. Darwin ture, constitution, and habits, to be advantageous to them, I think it here seems to have more merit in the discovery than I have had—to me it would be a most extraordinary fact if no variation ever had occurred did not appear a discovery. He seems to have worked it out by inductive useful to each being's own welfare, in the same way as so many variations reason, slowly and with due caution to have made his way synthetically have occurred useful to man. But if variations useful to any organic from fact to fact onwards; while with me it was by a general glance at the being do occur, assuredly individuals thus characterized will have the scheme of Nature that I estimated this select production of species as an a best chance of being preserved in the struggle for life; and from the strong priori recognizable fact—an axiom, requiring only to be pointed out to be principle of inheritance they will tend to produce offspring similarly admitted by unprejudiced minds of sufficient grasp. [Quoted in Gould characterized. This principle of preservation, I have called, for the sake of 1985, pp. 345-46.]

brevity, Natural Selection.
[Origin,
p. 127 (facs. ed. of 1st ed.).]

Unprejudiced minds may well resist a new idea out of sound conservatism, The basic deductive argument is short and sweet, but Darwin himself however. Deductive arguments are notoriously treacherous; what seems to described
Origin of Species
as "one long argument." That is because it stand to reason" can be betrayed by an overlooked detail. Darwin appreciated that only a relentlessly detailed survey of the evidence for the historical processes he was postulating would—or should—persuade scientists to abandon their traditional convictions and take on his revolutionary vision, 6. The ideal of a deductive ( or "nomologico-deductive" ) science, modeled on Newtonian even if it was in fact "deducible from first principles."

or Galilean physics, was quite standard until fairly recently in the philosophy of science, so it is not surprising that much effort has been devoted to devising and criticizing various axiomatizations of Darwin's theory—since it was presumed that in such a formalization lay scientific vindication. The idea, introduced in this section, that Darwin should be seen, rather, as postulating that evolution is an algorithmic process, permits us to do justice to the undeniable
a priori
flavor of Darwin's thinking without forcing it into the Procrustean (and obsolete) bed of the nomologico-deductive model. See Sober 1984a and Kitcher
Gardeners' Chronicle,
April 7, I860. See Hardin 1964 for more details.

1985a.

50 AN IDEA IS BORN

Natural Selection as an Algorithmic Process
51

From the outset, there were those who viewed Darwin's novel mixture of ing, using any symbol system you like. The power of the procedure is detailed naturalism and abstract reasoning about processes as a dubious and due to its
logical
structure, not the causal powers of the materials used inviable hybrid. It had a tremendous air of plausibility, but so do many get-in the instantiation, just so long as those causal powers permit the rich-quick schemes that turn out to be empty tricks. Compare it to the prescribed steps to be followed exactly.

following stock-market principle. Buy Low, Sell High. This is guaranteed to (2)
underlying mindlessness:
Although the overall design of the proce-make you wealthy. You cannot fail to get rich
if you
follow this advice. Why dure may be brilliant, or yield brilliant results, each constituent step, doesn't it work? It does work—for everybody who is fortunate enough to act as well as the transition between steps, is utterly simple. How simple?

according to it, but, alas, there is no way of determining that the conditions Simple enough for a dutiful idiot to perform—or for a straightforward are met until it is too late to act on them. Darwin was offering a skeptical mechanical device to perform. The standard textbook analogy notes world what we might call a get-rich-slow scheme, a scheme for creating that algorithms are
recipes
of sorts, designed to be followed by
novice
Design out of Chaos without the aid of Mind.

cooks. A recipe book written for great chefs might include the phrase The theoretical power of Darwin's abstract scheme was due to several

"Poach the fish in a suitable wine until almost done," but an algorithm features that Darwin quite firmly identified, and appreciated better than many for the same process might begin, "Choose a white wine that says 'dry'

of his supporters, but lacked the terminology to describe explicitly. Today we on the label; take a corkscrew and open the bottle; pour an inch of could capture these features under a single term. Darwin had discovered the wine in the bottom of a pan; turn the burner under the pan on high; ...

power of an
algorithm.
An algorithm is a certain sort of formal process that

"—a tedious breakdown of the process into dead-simple steps, can be counted on—logically—to yield a certain sort of result whenever it is requiring no wise decisions or delicate judgments or intuitions on the

"run" or instantiated. Algorithms are not new, and were not new in Darwin's part of the recipe-reader.

day. Many familiar arithmetic procedures, such as long division or balancing (3)
guaranteed results:
Whatever it is that an algorithm does, it always your checkbook, are algorithms, and so are the decision procedures for does it, if it is executed without misstep. An algorithm is a foolproof playing perfect tic-tac-toe, and for putting a list of words into alphabetical recipe.

order. What is relatively new—permitting us valuable hindsight on Darwin's discovery—is the theoretical reflection by mathematicians and logicians on It is easy to see how these features made the computer possible.
Every
the nature and power of algorithms in general, a twentieth-century
computer program is an algorithm,
ultimately composed of simple steps that development which led to the birth of the computer, which has led in turn, of can be executed with stupendous reliability by one simple mechanism or course, to a much deeper and more lively understanding of the powers of another. Electronic circuits are the usual choice, but the power of computers algorithms in general.

owes nothing (save speed) to the causal peculiarities of electrons darting The term
algorithm
descends, via Latin
(algorismus)
to early English about on silicon chips. The very same algorithms can be performed (even
(algorisme
and, mistakenly therefrom,
algorithm),
from the name of a faster) by devices shunting photons in glass fibers, or (much, much slower) Persian mathematician, Muusa al-Khowarizm, whose book on arithmetical by teams of people using paper and pencil. And as we shall see, the capacity procedures, written about 835 A.D., was translated into Latin in the twelfth of computers to run algorithms with tremendous speed and reliability is now century by Adelard of Bath or Robert of Chester. The idea that an algorithm permitting theoreticians to explore Darwin's dangerous idea in ways is a foolproof and somehow "mechanical" procedure has been present for heretofore impossible, with fascinating results.

centuries, but it was the pioneering work of Alan Turing, Kurt Godel, and What Darwin discovered was not really
one
algorithm but, rather, a large Alonzo Church in the 1930s that more or less fixed our current understanding class of related algorithms that he had no clear way to distinguish. We can of the term. Three key features of algorithms will be important to us, and now reformulate his fundamental idea as follows: