The Book of Life
THE DISCOVERY of DNA by James D. Watson and Francis Crick in 1952 revealed that a living creature is an organization of matter orchestrated by a genetic text. Within the bacterial cell, for example, the book of life is written in a distinctive language. The book is read aloud, its message specifying the construction of the cell’s constituents, and then the book is copied, passed faithfully into the future.
This striking metaphor introduces a troubling instability, a kind of tremor, into biological thought. With the discovery of the genetic code, every living creature comes to divide itself into alien realms: the alphabetic and the organismic. The realms are conceptually distinct, responding to entirely different imperatives and constraints. An alphabet, on the one hand, belongs to the class of finite combinatorial objects, things that are discrete and that fit together in highly circumscribed ways. An organism, on the other hand, traces a continuous figure in space and in time. How, then, are these realms coordinated?
I ask the question because in similar systems, coordination is crucial. When I use the English language, the rules of grammar act as a constraint on the changes that I might make to the letters or sounds I employ. This is something we take for granted, an ordinary miracle in which I pass from one sentence to the next, almost as if crossing an abyss by means of a series of well-placed stepping stones.
In living creatures, things evidently proceed otherwise. There is no obvious coordination between alphabet and organism; the two objects are governed by different conceptual regimes, and that apparently is the end of it. Under the pressures of competition, the orchid Orphrys apifera undergoes a statistically adapted drift, some incidental feature in its design becoming over time ever more refined, until, consumed with longing, a misguided bee amorously mounts the orchid’s very petals, convinced that he has seen shimmering there a female’s fragile genitalia. As this is taking place, the marvelous mimetic design maturing slowly, the orchid’s underlying alphabetic system undergoes a series of random perturbations, letters in its genetic alphabet winking off or winking on in a way utterly independent of the grand convergent progression toward perfection taking place out there where the action is.
We do not understand, we cannot re-create, a system of this sort. However it may operate in life, randomness in language is the enemy of order, a way of annihilating meaning And not only in language, but in any language-like system–computer programs, for example. The alien influence of randomness in such systems was first noted by the distinguished French mathematician M.P. Schutzenberger, who also marked the significance of this circumstance for evolutionary theory. “If we try to simulate such a situation,” he wrote, “by making changes randomly . . . on computer programs, we find that we have no chance . . . even to see what the modified program would compute; it just jams.(3)
Planets of Possibility
THIS IS not yet an argument, only an expression of intellectual unease; but the unease tends to build as analogies are amplified. The general issue is one of size and space, and the way in which something small may be found amidst something very big.
Linguists in the 1950’s, most notably Noam Chomsky and George Miller, asked dramatically how many grammatical English sentences could be constructed with 100 letters. Approximately 10 to the 25th power, they answered. This is a very large number. But a sentence is one thing; a sequence, another. A sentence obeys the laws of English grammar; a sequence is lawless and comprises any concatenation of those 100 letters. If there are roughly (1025) sentences at hand, the number of sequences 100 letters in length is, by way of contrast, 26 to the 100th power. This is an inconceivably greater number. The space of possibilities has blown up, the explosive process being one of combinatorial inflation.
Now, the vast majority of sequences drawn on a finite alphabet fail to make a statement: they consist of letters arranged to no point or purpose. It is the contrast between sentences and sequences that carries the full, critical weight of memory and intuition. Organized as a writhing ball, the sequences resemble a planet-sized object, one as large as pale Pluto. Landing almost anywhere on that planet, linguists see nothing but nonsense. Meaning resides with the grammatical sequences, but they, those sentences, occupy an area no larger than a dime.
How on earth could the sentences be discovered by chance amid such an infernal and hyperborean immensity of gibberish? They cannot be discovered by chance, and, of course, chance plays no role in their discovery. The linguist or the native English-speaker moves around the place or planet with a perfectly secure sense of where he should go, and what he is apt to see.
The eerie and unexpected presence of an alphabet in every living creature might suggest the possibility of a similar argument in biology. It is DNA of course, that acts as life’s primordial text, the code itself organized in nucleic triplets, like messages in Morse code. Each triplet is matched to a particular chemical object, an amino acid. There are twenty such acids in all. They correspond to letters in an alphabet. As the code is read somewhere in life’s hidden housing, the linear order of the nucleic acids induces a corresponding linear order in the amino acids. The biological finger writes, and what the cell reads is an ordered presentation of such amino acids-a protein.
Like the nucleic acids, proteins are alphabetic objects, composed of discrete constituents. On average, proteins are roughly 250 amino acid residues in length, so a given protein may be imagined as a long biochemical word, one of many.
The aspects of an analogy are now in place. What is needed is a relevant contrast, something comparable to sentences and sequences in language. Of course nothing completely comparable is at hand: there are no sentences in molecular biology. Nonetheless, there is this fact, helpfully recounted by Richard Dawkins: “The actual animals that have ever lived on earth are a tiny subset of the theoretical animals that could exist.” It follows that over the course of four billion years, life has expressed itself by means of a particular stock of proteins, a certain set of life-like words.
A COMBINATORIAL COUNT is now possible. The MIT physicist Murray Eden, to whom I owe this argument, estimates the number of the viable proteins at 10 to the 50th power. Within this set is the raw material of everything that has ever lived: the flowering plants and the alien insects and the seagoing turtles and the sad shambling dinosaurs, the great evolutionary successes and the great evolutionary failures as well. These creatures are, quite literally, composed of the proteins that over the course of time have performed some useful function, with “usefulness” now standing for the sense of sentencehood in linguistics.
As in the case of language, what has once lived occupies some corner in the space of a larger array of possibilities, the actual residing in the shadow of the possible. The space of all possible proteins of a fixed length (250 residues, recall) is computed by multiplying 20 by itself 250 times (20 to the 250th power). It is idle to carry out the calculation. The numbers larger by far than seconds in the history of the world since the Big Bang or grains of sand on the shores of every sounding sea. Another planet now looms in the night sky, Pluto-sized or bigger, a conceptual companion to the planet containing every sequence composed by endlessly arranging the 26 English letters into sequences 100 letters in length. This planetary doppelganger is the planet of all possible proteins of fixed length, the planet, in a certain sense, of every conceivable form of carbon-based life.
And there the two planets lie, spinning on their soundless axes. The contrast between sentences and sequences on Pluto reappears on Pluto’s double as the contrast between useful protein forms and all the rest; and it reappears in terms of the same dramatic difference in numbers, the enormous (20 to the 250th power) overawing the merely big (10 to the 50th power), the contrast between the two being quite literally between an immense and swollen planet and a dime’s worth of area. That dime-sized corner, which on Pluto contains the English sentences, on Pluto’s double contains the living creatures; and there the biologist may be seen tramping, the warm puddle of wet life achingly distinct amid the planet’s snow and stray proteins. It is here that living creatures, whatever their ultimate fate, breathed and moaned and carried on, life evidently having discovered the small quiet corner of the space of possibilities in which things work.
It would seem that evolution, Murray Eden writes in artfully ambiguous language, “was directed toward the incredibly small proportion of useful protein forms. . . ,” the word “directed” conveying, at least to me, the sobering image of a stage-managed search, with evolution bypassing the awful immensity of all that frozen space because in some sense evolution knew where it was going.
And yet, from the perspective of Darwinian theory, it is chance that plays the crucial–that plays the only role in generating the proteins. Wandering the surface of a planet, evolution wanders blindly, having forgotten where it has been, unsure of where it is going.
The Artificer of Design
RANDOM MUTATIONS are the great creative demiurge of evolution, throwing up possibilities and bathing life in the bright light of chance. Each living creature is not only what it is but what it might be. What, then, acts to make the possible palpable?
The theory of evolution is a materialistic theory. Various deities need not apply. Any form of mind is out. Yet a force is needed, something adequate to the manifest complexity of the biological world, and something that in the largest arena of all might substitute for the acts of design, anticipation, and memory that are obvious features of such day-to-day activities as fashioning a sentence or a sonnet.
This need is met in evolutionary theory by natural selection, the filter but not the source of change. “It may be said,” Darwin wrote,
that natural selection is daily and hourly scrutinizing, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good: silently and insensibly working, whenever and wherever opportunity offers, as the improvement of each organic being in relation to its organic and inorganic conditions of life.
Natural selection emerges from these reflections as a strange force-like concept. It is strange because it is unconnected to any notion of force in physics, and it is force-like because natural selection does something, it has an effect and so functions as a kind of cause.(4)
Creatures, habits, organ systems, body plans, organs, and tissues are shaped by natural selection. Population geneticists write of selection forces, selection pressures, and coefficients of natural selection; biologists say that natural selection sculpts, shapes, coordinates, transforms, directs, controls, changes, and transfigures living creatures.
It is natural selection, Richard Dawkins believes, that is the artificer of design, a cunning force that mocks human ingenuity even as it mimics it:
Charles Darwin showed how it is possible for blind physical forces to mimic the effects of conscious design, and, by operating as a cumulative filter of chance variations, to lead eventually to organized and adaptive complexity, to mosquitoes and mammoths, to humans and therefore, indirectly, to books and computers.
In affirming what Darwin showed, these words suggest that Darwin demonstrated the power of natural selection in some formal sense, settling the issue once and for all. But that is simply not true. When Darwin wrote, the mechanism of evolution that he proposed had only life itself to commend it. But to refer to the power of natural selection by appealing to the course of evolution is a little like confirming a story in the New York Times by reading it twice. The theory of evolution is, after all, a general theory of change; if natural selection can sift the debris of chance to fashion an elephant’s trunk, should it not be able to work elsewhere–amid computer programs and algorithms, words and sentences? Skeptics require a demonstration of natural selection’s cunning, one that does not involve the very phenomenon it is meant to explain.
No sooner said than done. An extensive literature is now devoted to what is optimistically called artificial life. These are schemes in which a variety of programs generate amusing computer objects and by a process said to be similar to evolution show that they are capable of growth and decay and even a phosphorescent simulacrum of death. An algorithm called “Face Prints,” for example, has been designed to enable crime victims to identify their attackers. The algorithm runs through hundreds of facial combinations (long hair, short hair, big nose, wide chin, moles, warts, wens, wrinkles) until the indignant victim spots the resemblance between the long-haired, big-nosed, wide-chinned portrait of the perpetrator and the perpetrator himself.
It is the presence of the human victim in this scenario that should give pause. What is he doing there, complaining loudly amid those otherwise blind forces? A mechanism that requires a discerning human agent cannot be Darwinian. The Darwinian mechanism neither anticipates nor remembers. It gives no directions and makes no choices. What is unacceptable in evolutionary theory, what is strictly forbidden, is the appearance of a force with the power to survey time, a force that conserves a point or a property because it will be useful. Such a force is no longer Darwinian. How would a blind force know such a thing? And by what means could future usefulness be transmitted to the present?
If life is, as evolutionary biologists so often say, a matter merely of blind thrusting and throbbing, any definition of natural selection must plainly meet what I have elsewhere called a rule against deferred success.(5)
It is a rule that cannot be violated with impunity; if evolutionary theory is to retain its intellectual integrity, it cannot be violated at all.
But the rule is widely violated, the violations so frequent as to amount to a formal fallacy.
Advent of the Head Monkey
IT IS Richard Dawkins’s grand intention in The Blind Watchmaker to demonstrate, as one reviewer enthusiastically remarked, “how natural selection allows biologists to dispense with such notions as purpose and design.” This he does by exhibiting a process in which the random exploration of certain possibilities, a blind stab here, another there, is followed by the filtering effects of natural selection, some of those stabs saved, others discarded. But could a process so conceived–a Darwinian process–discover a simple English sentence: a target, say, chosen from Shakespeare? The question is by no means academic. If natural selection cannot discern a simple English sentence, what chance is there that it might have discovered the mammalian eye or the system by which glucose is regulated by the liver? A thought experiment in The Blind Watchmaker now follows. Randomness in the experiment is conveyed by the metaphor of the monkeys, perennial favorites in the theory of probability. There they sit, simian hands curved over the keyboards of a thousand typewriters, their long agile fingers striking keys at random. It is an image of some poignancy, those otherwise intelligent apes banging away at a machine they cannot fathom; and what makes the poignancy pointed is the fact that the system of rewards by which the apes have been induced to strike the typewriter’s keys is from the first rigged against them.
The probability that a monkey will strike a given letter is one in 26. The typewriter has 26 keys: the monkey, one working finger. But a letter is not a word. Should Dawkins demand that the monkey get two English letters right, the odds against success rise with terrible inexorability from one in 26 to one in 676. The Shakespearean target chosen by Dawkins–“Methinks it is like a weasel”–is a six-word sentence containing 28 English letters (including the spaces). It occupies an isolated point in a space of 10,000 million, million, million, million, million, million possibilities. This is a very large number; combinatorial inflation is at work. And these are very long odds. And a six-word sentence consisting of 28 English letters is a very short, very simple English sentence.
Such are the fatal facts. The problem confronting the monkeys is, of course, a double one: they must, to be sure, find the right letters, but they cannot lose the right letters once they have found them. A random search in a space of this size is an exercise in irrelevance. This is something the monkeys appear to know. What more, then, is expected; what more required? Cumulative selection, Dawkins argues–the answer offered as well by Stephen Jay Gould, Manfred Eigen, and Daniel Dennett. The experiment now proceeds in stages. The monkeys type randomly. After a time, they are allowed to survey what they have typed in order to choose the result “which however slightly most resembles the target phrase.” It is a computer that in Dawkins’s experiment performs the crucial assessments, but I prefer to imagine its role assigned to a scrutinizing monkey-the Head Monkey of the experiment. The process under way is one in which stray successes are spotted and then saved. This process is iterated and iterated again. Variations close to the target are conserved because they are close to the target, the Head Monkey equably surveying the scene until, with the appearance of a miracle in progress, randomly derived sentences do begin to converge on the target sentence itself.
The contrast between schemes and scenarios is striking. Acting on their own, the monkeys are adrift in fathomless possibilities, any accidental success-a pair of English-like letters-lost at once, those successes seeming like faint untraceable lights flickering over a wine-dark sea. The advent of the Head Monkey changes things entirely. Successes are conserved and then conserved again. The light that formerly flickered uncertainly now stays lit, a beacon burning steadily, a point of illumination. By the light of that light, other lights are lit, until the isolated successes converge, bringing order out of nothingness.
The entire exercise is, however, an achievement in self-deception. A target phrase? Iterations that most resemble the target? A Head Monkey that measures the distance between failure and success? If things are sightless, how is the target represented, and how is the distance between randomly generated phrases and the targets assessed? And by whom? And the Head Monkey? What of him? The mechanism of deliberate design, purged by Darwinian theory on the level of the organism, has reappeared in the description of natural selection itself, a vivid example of what Freud meant by the return of the repressed.
This is a point that Dawkins accepts without quite acknowledging, rather like a man adroitly separating his doctor’s diagnosis from his own disease.(6) Nature presents life with no targets. Life shambles forward, surging here, shuffling there, the small advantages accumulating on their own until something novel appears on the broad evolutionary screen-an arch or an eye, an intricate pattern of behavior, the complexity characteristic of life. May we, then, see this process at work, by seeing it simulated? “Unfortunately,” Dawkins writes, “I think it may be beyond my powers as a programmer to set up such a counterfeit world.”(7)
This is the authentic voice of contemporary Darwinian theory. What may be illustrated by the theory does not involve a Darwinian mechanism; what involves a Darwinian mechanism cannot be illustrated by the theory.
