The Molecular Drama
Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology.
by Jacques Monod.
Translated by Austryn Wainhouse. Knopf. 224 pp. $6.95.
Jacques Monod, director of the Pasteur Institute in Paris and winner (with two colleagues, André Lwoff and Francois Jacob) of the Nobel prize for physiology in 1965, calls our attention to the genius of Escherichia coli. Place just one of these bacteria (whose native turf is the bowels of certain animals, including man) in a dish with a little water, a few grains of sugar and a dash of mineral salts, and within thirty-six hours, the broth will be teeming with several billion, virtually identical germs. Little wonder that the facts of life have long strained our capacity to accept a physical explanation. How in the world does a creature weighing less than one trillionth of a gram outperform—in precision, economy, and speed—the best that man’s science of chemistry can deliver? Yet the job gets done, Monod points out, within the constraints imposed by the Second Law of Thermodynamics, which is to say, that the physical-energy changes in the dish conform to ordinary physical principles even as the germs reduplicate themselves into myriads of separate, living existences.
Monod’s book, based on lectures given at Pomona College early in 1969, recounts modern molecular biology’s story about Escherichia coli, and therefore also about the chemical basis of life in general. For, as he says, “To biologists of my generation fell the discovery of the virtual identity of cellular chemistry throughout the entire biosphere.” Clearly a momentous discovery, the chemical unity of life also vastly simplified the task of molecular biology. Now the job called not for a separate account of each living form, but instead merely for the rules by which a single fundamental procedure ramified itself into the phenomenal diversity of creatures. The new task may not be exactly easy, but it could have been (as far as anyone knew thirty years ago) immeasurably harder.
The fertile bacterium poses a dual riddle, says Monod. First, whence the invariance, the capacity to duplicate itself virtually down to the molecular level—at least, most of the time? Inanimate objects do not often (if ever) reveal a comparable flair for self-duplication, so when we marvel at life’s distinctiveness or uniqueness, we must be reacting partly to its invariance. The second half of the riddle, Monod calls teleonomy, the goal-directedness of living beings. In the growth and development of its physical structure, as well as in its behavior, the living organism reveals an inner determination, setting it to some degree free of its immediate circumstances. Each creature develops and performs true to its type, acting and growing so as to sustain itself in its distinctiveness. The environment does not just act upon animate objects, as it does upon inanimate ones like falling stones or cooling cups of coffee, but is acted upon by the creature, for its own purposes. This is not to suggest that Monod believes in a mental life of germs, nor that he is unaware of the physical limits in the environment outside of which any given creature ceases to function typically or at all. Instead, it shows that Monod recognizes the magnitude of the task of reconciling the purposiveness of life with the mechanisms of science.
At least, that reconciliation is what Monod seeks. He scorns easy solutions, which replace ignorance by mere postulation. The vitalists, like Bergson, endow living creatures with élan, a spiritual essence that fortuitously provides just those properties of teleonomy thought to be lacking in the physical body. And the animists, like Teilhard de Chardin, expunge the riddle of teleonomy by professing belief in the unfolding of a universal principle, unknowable by definition. The old struggle between mechanists and anti-mechanists (the vitalists and animists) pervades the book as Monod works through his solution of the dual riddle. The progress of molecular biology since the early 1950’s has closed much of the credibility gap that earlier afflicted mechanistic biology. No longer must the mechanist feebly defend himself with discoveries yet unmade when challenged by the extraordinary precision of biochemistry, its subtle adaptations, or its ability to reproduce itself. Now he can array the chemical code laid down in the genes, along with glimmerings of how it is deciphered into the richer language of amino acids, which concatenate into the thousands of proteins found in all living creatures. By no means has all of the tale been told, but enough bits and pieces so that the anti-mechanist now begins to suffer lack of credibility.
Here and there, molecular biologists have traced through a series of chemical reactions at the microscopic level to show teleonomy in fact, not just in principle. There are, for example, chains of chemical reactions that manufacture “metabolites”—essential chemical components in some structure or process. The speed of the reactions (hence their net productivity per unit of time) gets paced by highly specific chemical agents called catalysts and regulators. (Catalysts, some may remember from their chemistry courses, enter into reactions and speed them up without being consumed or even permanently altered by them.) If, as is sometimes the case, the final outcome of a chain is, at one and the same time, both a metabolite and a regulatory inhibitor for some earlier reaction in the chain, then chemistry has created a self-limiting production line. As the level of metabolite rises, it more and more retards further production. When the level falls, production rises. It is obvious that such negative feedback may sometimes serve a useful purpose. There are other configurations serving other purposes—to retard or advance particular chemical outcomes under particular circumstances so as to promote the vigorous survival of the organism.
This new victory for scientific materialism has shown how Darwinian selection reaches down into the molecular substratum of life. “Survival of the fittest”—so graphic a portrayal of the pre-nuptial contests of bull moose or the gradual stretching of the giraffe’s neck—may now be applied with equal, if not greater, validity to the molecular drama. The key to understanding has been the discovery of what Monod calls the “gratuity” of the chemical substratum of life. Because catalysts are tied to certain reactions rather than others by the match of arbitrary spatial features in the component molecules—much like a key in a lock—the opportunities for chemical innovation are as boundless as the endless spatial variations of organic compounds. The catalytic nature of life’s essential chemistry allows regulation to vary relatively freely (by mutation, accident, etc.—the “chance” in the title of the book) without altering the basic chemistry of the system as a whole. If a particular variation is advantageous, it may, through natural selection, establish itself in future generations (by “necessity,” as it follows from the simple arithmetic of Darwinian evolution). The advantageous variation must, of course, originate in the genes in order to be heritable, but Monod shows how the genetic “alphabet” may sometimes turn up with a beneficent misprint. The occasional “errors” are sifted over automatically for the rare, fruitful variation, giving the living system at once both its invariance and teleonomy. Chance and necessity combine to favor the right innovation at the right time.
In the short span of a couple of decades, molecular biology has taken great strides toward deep and significant understanding. It has also added to the vernacular a number of pseudo-words and quasi-phrases—like “DNA” and “RNA” and “polypeptides” and “nucleotides” and “stereochemical complementarity”—incomprehensible to anyone whose last chemistry course is of earlier vintage than about 1955. Part of Monod’s purpose in his lectures must have been simply pedagogic—to attach to those mysterious new labels some concrete meaning for the layman. But that likely was his lesser purpose, for the major themes sound more philosophical than pedagogic. He could actually have made his main points without any chemistry at all, setting the question instead as follows: “Grant me a true science (i.e., like physics or chemistry) of life’s invariance and teleonomy, substantiating once and for all the principles of evolution by natural selection. What broader lessons shall we learn then?” For Monod, of course, the substantive facts of his science have been woven integrally into the fabric of the Weltanschauung he offers. Yet a reader who fails to hang on through the elementary biochemistry early in the book can clamber back on to the train of thought later on.
Star player and articulate popularizer of one of the best games around, Monod should not be too harshly rebuked for his book’s shortcomings. But shortcomings there are, at least two serious ones. When he steps back from molecular biology to take a look at science as a whole, he cannot impart his vision either clearly or persuasively. It will do no reader any good to be told that science seeks “objectivity,” or that it calls for the “confrontation of logic and experience.” The tough problem—to translate those vague and formless guides to action into something concrete and specific—remains unsolved. Was there something especially “objective” about the choice of Escherichia coli as the experimental subject? Doubtless, it was a happy choice, but not any more objective or logical than the many organisms that might have served less well. And, to look at science’s past, was the phlogiston theory of combustion not an elegant confrontation of logic with experience? Monod fails to see the pragmatic core of science, promoting Escherichia coli and rejecting phlogiston by the sole criterion of success. It is an ironic oversight, for the pragmatic standard seems little different in science and in the chemistry of life. In both cases, we see by hindsight how the happy accident (of thought or chemistry) gains ascendancy through natural selection (in predictive power or physiological superiority). Many philosophers, past and present, have come up empty-handed in better style than Monod, when reaching for science’s elusive essence.
But the purely philosophical shortcoming seems, at least to me, the lesser one. When Monod considers the role of a creature’s behavior, he loses the main story in his enthusiasm for a minor subplot. Behavior, he correctly notes, orients the direction of evolution. When some primitive fish first started venturing on land, it was no doubt ill-equipped to do so. However, its tenacious efforts (and those of its descendants) set the scene in which any mutation favoring terrestrial life quickly (relatively speaking) overspread the gene pool in subsequent generations. In the evolutionist’s jargon, terrestrial behavior creates “selection pressure” for terrestrially-adaptive structure. The same argument, Monod notes, applies to all kinds of advantageous behavior. In human beings, the higher mental functions—language, subjective simulation (his term for cognition), the formation of society and culture—presumably exert selection pressure for compatible underlying structures. The universality of language and certain cultural forms suggests to Monod that even those highly conventionalized human activities have innate underpinnings.
Monod thus takes his place in the vanguard of the swing back toward nativistic theories of human behavior. For a couple of generations after World War I, at least in the United States, the pendulum swung almost friction-free toward the environmentalist pole. John B. Watson’s book Behaviorism (1924) was heralded in a review in the New York Times as the beginning of a new epoch, with its argument that each man’s character and behavior was simply a lifetime’s worth of conditioned reflexes. Although the psychological substance has actually been much refined, the mass-culture rendition of B. F. Skinner’s recent Beyond Freedom and Dignity sounds much the same, in content and as portent. Yet in the interval between Watson and Skinner, the simpleminded environmentalism of elementary textbooks and popular magazines has taken a beating, in the laboratory and in philosophical analysis. Behavior is not infinitely malleable; people are not equally talented or motivated or psychically sound. Moreover, some of the limitations, predispositions, and differences are surely genetic. And so, with the customary lag, the pendulum is swinging back, receiving a fair impetus from Monod. It is easy to imagine his message blending with Robert Ardrey’s, Noam Chomsky’s, Konrad Lorenz’s, Desmond Morris’s, and with all the others that now stand for nature as opposed to nurture in the account of man.
While Monod is doubtless right about the contribution of behavior to selection pressure, he fails to uncover a crucial precondition. Consider again the primitive fish flinging itself awkwardly upon the land. A bulging appendage or two to stabilize its thrashings would be very helpful, but only if the fish has the wits to use them. What good would it do the fish to have its new appendages without any inkling of how to use them? It may, to be sure, inherit just the right behavior to go along with each new structural modification. But not only is such dual mutation vastly less probable, it tacitly rules out the impact of behavior on selection pressure. New behavior must, at least sometimes, arise within an individual’s lifetime, guided by the individual’s own successes or failures, in order to influence the course of evolution. There needs to be a provision for fruitful non-genetic and individual variation, in addition to genetic variation, if Monod’s hypothesis is to work. For only then, with behavior exploiting the opportunity, will selection pressure follow in the wake of individual variation. Similarly, picture the proto-man whose proto-larynx first fashioned coherent gruntings. Selection pressure for language presupposes that our ancestor had some capacity to press his advantage within his own lifetime, otherwise the potential for language would have languished unused.
To play the major role in phylogeny that Monod accords it, behavior must be responsive in ontogeny. But saying that behavior is ontogenetically responsive acknowledges a substantial part of the environmentalist canon. The more familiar name for the study of ontogenetic responsiveness is “learning theory,” the branch of psychology devoted to how creatures get their behavior changed by their experience. Monod, having missed the environmentalist ingredient in his scheme, fails to note that the study of the learning process has not lagged far behind molecular biology in recent years. For Watson, all learning was a version of Pavlovian conditioning. Skinner and most contemporary environmentalists know that Pavlovian conditioning is not enough. Not very much complex behavior is cast in the mold of a dog salivating at the sound of the dinner bell. In addition, behavior often echoes its past in accordance with a process known as “operant” or “instrumental” conditioning. The laboratory rat hungrily pressing a lever for a bit of food exemplifies such learning. Even in human beings, behavior of all degrees of complexity can be shaped by this process, which accounts for much of the current excitement over “teaching machines” and “behavior therapy.” The essential principle could hardly be simpler—out of the stream of movement, certain movements are selected for repetition, if they lead to particular outcomes (like food for a hungry rat or a successful putt for a golfer). The clear parallel between this kind of learning and phylogenetic selection has been noted often in the hundred-odd years since Herbert Spencer and Charles Darwin. In both mechanisms, adaptive, teleonomic outcomes arise from purely automatic rules for selection.
Environmentalists, impressed by the power with which surroundings mold behavior, implore us to make the most of the plasticity. Nativists, recognizing the tie between behavior and physiology, caution us against too bland a disregard of biology. Both, of course, are right, and, often, wrong, when carried away by excesses of enthusiasm. Monod, in the grip of nativism, fails to tie together the strands of his argument, depriving it of a solidity it could have had. He acknowledges the role of behavior in creating selection pressure. And he is hardly unconscious of the learning process in some contexts, for, when discussing mankind, he notes that ontogenetic adaptation substitutes to some degree for biological evolution, making adjustments possible within single lifetimes. But he misses the impact of ontogenetic adaptation on evolution itself, for once creatures acquired the capacity to learn, their behavior became the cutting edge of phylogeny as never before, creating selection pressure wherever a new behavior conferred some advantage over one’s kind. Had he spotted the parallel yet interacting mechanisms of selection in behavior and in the germ-plasm, he would have seen ontogeny and phylogeny playing off one another in endless spirals of chance and necessity.