See Jacques Monod, Chance and Necessity: an essay on the Natural Philosophy of Modern Biology, trans. Austryn Wainhouse, London: Collins, 1972, pp. 109-113

Summary

"In modern biological research some of the work most outstanding in methodology and significance is that known as molecular genetics (Benzer, Yanovsky, Brenner, Crick).  This work has, in particular, made it possible to analyse the different types of discrete accidental alterations a DNA sequence may suffer.  Various mutations have been identified as due to: We say that these events are accidental, due to chance.  And since they constitute the only possible source of modifications in the genetic text, itself the sole repository of the organism's hereditary structures, it necessarily follows that chance alone is at the source of every innovation, of all creation in the biosphere.  Pure chance, absolutely free but blind, at the very root of the stupendous edifice of evolution: this central concept of modern biology is no longer one among other possible or even conceivable hypotheses.  It is today the sole conceivable hypothesis, the only one compatible with observed and tested fact.  And nothing warrants the supposition (or the hope) that conceptions about this should, or ever could, be revised.  There is no scientific position, in any of the sciences, more destructive of anthropocentrism than this one, and no other more unacceptable to the intensely teleonomic creatures that we are.  So for every vitalist or animist ideology this is the concept or rather the spectre to be exorcised at all costs.  It is therefore most important to say something about the words chance and random, and to specify in what sense they may and must be used with regard to mutations as the source of evolution.  The idea of chance is not a simple one, and the word itself is employed in a wide variety of contexts. A few examples will help.
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 Dice and roulette are called games of chance, and the theory of probability is used to forecast their outcome.  But chance enters into these purely mechanical and macroscopic games only because of the practical  impossibility of governing the throw of the dice or the spinning of the little ball with sufficient precision.  A highly precise mechanical thrower might conceivably be invented which would go far to reduce the uncertainty of the outcome.  Let us say that in roulette the uncertainty is purely operational and not essential.  It is easy to see that the same holds for the theory of numerous phenomena where the concept of chance and the theory of probability are used for purely methodological reasons.
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 But in other situations the idea of chance takes on an essential and no longer merely operational meaning.  This is the case, for instance, in what may be called "absolute coincidences", those which result from the intersection of two totally independent chains of events.  Suppose that Dr Brown sets out on an emergency call to a new patient.  In the meantime Jones the carpenter has started work on repairs to the roof of a nearby building.  As Dr Brown walks past the building, Jones inadvertently drops his hammer, whose (deterministic) trajectory happens to intercept that of the physician, who dies of a fractured skull.  We say he was a victim of chance.  What other term fits such an event, by its very nature unforeseeable ?  Chance is obviously the essential factor here, inherent in the complete independence of two causal chains of events whose convergence produces the accident.
    Now, between the occurrences that can provoke or permit an error in the replication of the genetic message and its functional consequences there is also complete independence.  The functional effect depends on the structure, on the actual role of the modified protein, on the interactions it ensures, on the reactions it catalyses - all things which have nothing to do with the mutational event itself nor with its immediate or remote causes, regardless of the nature, whether deterministic or not, of those "causes".
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 Finally, on the microscopic level there exists a source of even more radical uncertainty, embedded in the quantum structure of matter.  A mutation is in itself a microscopic event, a quantum event, to which the principle of uncertainty consequently applies.  An event which is hence and by its very nature essentially unpredictable.
    The principle of uncertainty was never entirely accepted by some of the greatest modern physicists, including Einstein, who was unwilling to admit that "God plays at dice".  Certain schools have retained the principle for its operational usefulness but denied it the standing of an essential concept.  However, all the efforts made to replace quantum theory by a "finer" structure from which uncertainty has vanished have ended in failure, and today very few physicists seem disposed to believe that this principle will ever disappear from their discipline. 
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 However this may be it must be stressed that, even were the principle of uncertainty some day abandoned, it would remain true that between the determination, however complete, of a mutation in DNA and the determination of its functional effects on the plane of protein interaction, one could still see nothing but an "absolute coincidence" like that defined above by the parable of the workman and the physician.  The event would still belong to the realm of chance.  Unless of course we go back to Laplace's world, from which chance is excluded by definition and where Dr Brown was always fated to die knocked out by Jones's hammer.
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 It will be recalled that Bergson saw evolution as the expression of a creative force, absolute in the sense that it was directed to no end except creation in itself and for its own sake.  In this he differed radically from the animists (whether Engels, Teilhard de Chardin, or optimistic positivists like Spencer), who all regarded evolution as the majestic unfolding of a programme woven into the very fabric of the universe.
    For them, consequently, evolution was not really a creation but uniquely the "revelation" of nature's hitherto unexpressed designs.  Whence the tendency to see in embryonic development an emergence of the same kind as evolutionary emergence.  According to modern theory, the idea of "revelation" applies to epigenetic development, but not of course to evolutionary emergence, which, owing to the fact that it arises from the essentially unforeseeable, is the creator of absolute newness.  Might this apparent meeting of the ways between Bergsonian metaphysics and scientific thought be yet another effect of sheer coincidence ?  Perhaps not: artist and poet that he was, and also very well informed on the natural sciences of his day, Bergson could not fail to respond to the dazzling richness of the biosphere and the amazing variety of forms and behaviour it displays, which indeed seem to bear almost direct witness to an inexhaustible, wholly untrammelled creative prodigality.
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    But where Bergson saw the clearest proof that the "principle of life" is evolution itself, modern biology recognizes, instead, that all the properties of living beings are based on a fundamental mechanism of molecular invariance.  For modern theory evolution is not a property of living beings, since it stems from the very imperfections of the conserving mechanism which indeed constitutes their unique privilege.  It must, then, be said that the same source of fortuitous perturbations, of noise, which in a nonliving (i.e. nonreplicative) system would gradually lead to the disintegration of all structure, is the progenitor of evolution in the biosphere and accounts for its unrestricted liberty of creation, thanks to the replicative structure of DNA: that registry of chance, that tone-deaf conservatory where the noise is preserved along with the music.
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