Chance and Directionality in Contemporary Evolution
Is evolution a creative process? And is it possible to answer in the affirmative without positing a god to provide the creative impetus? Bergson’s 1907 masterpiece argues in the affirmative, and despite most of a century that conspired to prove him wrong, recent findings in evolutionary biology may vindicate the core of his argument. In this paper I hope to show that some of Bergson’s most pointed criticism of evolution can be answered by the most recent developments in theory, but not in a way that he or the creators of the neo-Darwinian synthesis might have expected. While some of these scientific ideas are as speculative as Bergson’s own, they offer a tantalizing way to answer some of the perennial questions of evolutionary theory: viz., How have complex lifeforms evolved from unicellular structures, and how can we account for both the astonishing diversity and the many common features found in animal life to-day?
For Bergson this was clearly a function driven forward by life itself, and he imagined it as a life-force, an élan vital, which coursed through organic beings and spurred on their ability to divide and differentiate themselves. There could be no question of animal life having developed by chance, or having so effectively adapted itself to the conditions of its environment through a process of random mutations selected negatively. While we cannot take seriously as science his model of a vital metaphysical force, we may be able to envision what actually occurs in a metaphorically Bergsonian manner. While not indicative of a life force per se, we can now perceive in life a certain positive tendency to evolve in particular ways according to internal, regulatory mechanisms such as the newly-discovered genetic “tool kit” and the “core conserved processes” described below. As this paper hopes to show, these processes may lend some weight to Bergson’s underlying concern, and grant a certain lasting utility to a quasi-vitalistic language for biology.
Bergson and the Revolt Against Chance
Henri Bergson is not taken seriously as an evolutionary thinker in standard works on the history of science, in large measure because his most important theoretical innovations are essentially indemonstrable, lying outside the realm of science and firmly within that of post-Kantian metaphysics. Yet his criticism of evolution remains surprisingly strong if one considers it only in light of the mid-twentieth century formulation of neo-Darwinism, and has only been answered definitively in the past two decades. Moreover, two of his central claims — that random mutation was insufficient to explain the emergence and proliferation of life, and that changes proceed according to internal direction — might even be validated by more recent theories in biology.
Before we go too far in support of Bergson’s views of life, it is perhaps useful to place his ideas in context. Much has transpired in the life sciences since his day, and it is perhaps unfair to subject his theories to facts which were unavailable to him, but there are some important consequences attached to a few of them. Were we to make a more thorough defence of him we would need to address many of these problems more thoroughly than is possible here, even if they are deployed in a more-or-less purely metaphorical or rhetorical context. Chief amongst these are his determination to “attribute to man a privileged place in nature, to hold that the distance is infinite between the animal and man”, and his belief that “consciousness is distinct from the organism it animates, although it must undergo its vicissitudes.”1 The former could have been comprehensively refuted even in Bergson’s day, yet is still troubling to most people to-day; and the latter is still hotly debated, with many philosophers and some scientists attempting to maintain a kind of mind-body dualism in order to retain a truly libertarian notion of free will. Although it would require a complete engagement with the roots of his dispute with mechanism, it might even be possible to reconcile Bergson’s temporally-derived conception of life with a compatibilist view of determinism and the will, but this must of necessity be attempted elsewhere.
Our principal concern in this paper will be to work around these metaphysical landmines in order to find a use for arguments that retain their relevance when placed against the older models of evolution. In this section I will outline a few of Bergson’s more interesting critiques of evolution and of biological mechanism, and describe some the clever counter-arguments he puts forward in Creative Evolution. Bergson addresses himself in that work to an abiding problem of philosophy, which manifests in the recent resurgence in thought on the ontological questions of life.2 He very perceptively lays out the heart of the problem in the introduction, where he claims that
not one of the categories of our thought — unity, multiplicity, mechanical causality, intelligent finality, etc. applies exactly to the things of life: who can say where individuality begins and ends, whether the living being is one or many, whether it is the cells which associate themselves into the organism or the organism which dissociates itself into cells?3
Yet he refuses to flinch in the face of such questions, and categorically rejects Herbert Spencer’s notion of the “Unknowable” and the Kantian limitations on human knowledge, and he intends his foray into evolutionary biology to address these concerns in some positive sense. He boldly predicts that we can learn something of life as the “maker of the stereotype-plate” and of the intellect’s ability to “touch something of the absolute”.4 Although he rejects Hegel’s dialectic, he also posits a dynamic conception of life as perpetual becoming; “that we change without ceasing, and that the state itself is nothing but change.”5 In this model changes in the phenotype do not emerge at random, nor do they appear as a response to external events; rather, “variation… is being produced every moment, continuously and insensibly, in every living being”.6
This points to an interesting part of Bergson’s critique: his efforts to temporalize evolutionary development. Building on his theorization of memory, he argues that all the past moments must be counted into any account of the organism. “Continuity of change, preservation of the past in the present, real duration — the living being seems… to share these attributes with consciousness.”7 Yet he is certain that change could not come to life in a truly random, undirected fashion, as implied in the traditional Darwinian synthesis, and asks if “we can go further and say that life, like conscious activity, is invention, is unceasing creation?”8 Bergson points out that Darwinism (i.e., natural selection) is a fundamentally negative force, winnowing the field of competitive organisms and species, and is entirely unable to account for progressive development in the first place. Against the standard reliance on chance mutations in the materialist theories of the late nineteenth century, Bergson argues that all roads do not lead to Rome:
An accidental variation, however minute, implies the working of a great number of small physical and chemical causes. An accumulation of accidental variations, such as would be necessary to produce a complex structure [in organisms on two entirely different lines of evolution], requires therefore the concurrence of an almost infinite number of infinitesimal causes. Why should these causes, entirely accidental, recur the same, and in the same order, at different points of space and time?9
Until the unravelling of the genetic code, this presented a formidable challenge to Darwinism, and still crops up in most creationist critiques. The best counter-argument would suggest the common descent of all creatures with similar structures, but until one can peruse the genetic similarities themselves it is difficult to appreciate the commonalities between apes and arthropods! And Bergson makes his case against Darwinism precisely at its weakest link: the development of new and beneficial changes which can then be selected for. “The struggle for life and natural selection can be of no use to us in solving this part of the problem. For we are not concerned here with what has perished, we have to do only with what has survived.”10
Critical both of mechanistic, naturalistic theories such as the neo-Darwinism of his day (which leaned in Weismann’s direction, towards a fully materialistic, non-Lamarckian interpretation), and of the overtly teleological systems like that of Kant or Hegel, Bergson hopes instead for a middle way. In common with Kant, he was driven by an epistemology that rejected approximation of the universe based in human ways of thinking, arguing: “We must get beyond both points of view, both mechanism and finalism being, at bottom, only standpoints to which the human mind has been led by studying the work of man.”11 He aimed to do this by radicalizing to some degree the notion of finalism; not only did he think teleology in some form inevitable (if only for psychological reasons), but held that it must be “external or it is nothing at all.”12 Against the kind of internally-derived telos found in Kant’s third Critique, Bergson argues that “it is of no use to try to restrict finality to the individuality of the living being. If there is finality in the world of life, it includes the whole of life in a single indivisible embrace.”13
Bergson seems to argue that life itself is a totality of force striving to realize itself in ever-changing forms. He claims that
life is like a current passing from germ to germ through the medium of a developed organism. It is as if the organism itself were only an excrescence, a bud caused to sprout by the former germ endeavouring to continue itself in a new germ.”14*
By taking account of this long-term process he proposes not a return “to the old notion of finality” (i.e., philosophical notions of teleology), but instead for a “progress toward” a given thing without the requirement of a “conscious idea of an end to be attained.”15 He argues instead that a telos in some abstract sense is “effected in virtue of the original impetus of life; it is implied in this movement itself”, and is fundamental to his conception of life as “a tendency to act on inert matter.”16 As he argues in the definition of his own evolutionary theory, the unfolding or
direction of this action is not predetermined; hence the unforeseeable variety of forms of life which, in evolving, sows along its path. But this action always presents, to some extent, the character of contingency; it implies at least a rudiment of choice. Now a choice involves the anticipatory idea of several possible actions. Possibilities of action must therefore be marked out for the living being before the action itself.17
It is just these notions of possibility and choice that we will see emerging in the discussion of genetic “tool kits” and “facilitated variation” in the next section.
Facilitated Variation and Evolutionary Developmental Biology
Darwin’s evolutionary argument had from the start three distinct elements: natural selection, heredity, and variation; but only the first of these was definitively solved in The Origin of Species. Heredity would await the neo-Darwinian Synthesis in the 1930s and ’40s, and especially the unravelling of DNA’s secrets in the 1950s. Variation, however, has remained difficult to account for, and has been the most consistent target of Darwinism’s critics. Even to-day proponents of creationism will ask how it is possible for a structure as complex as the eye to developed entirely by chance. Traditionally biology has had recourse to the infinitely-long timeframe of evolutionary change, suggesting — in effect — that anything was possible over millions of years of generation. Yet it remains a difficult leap of the imagination to see a very large number of eventually-beneficial mutations occur and remain in place without a noticeable benefit in each instance in order to guarantee their heritability. As Kirschner and Gerhart argue: “Without some account of how complex novelty arises, mere refuge in the sufficiency of time is unconvincing.”18
The modern renaissance of embryology, now called evolutionary developmental biology or evo-devo for short, has revolutionized our understanding of phenotypic change, and this new evidence may warrant a revision of the standard model of evolution. This section will briefly examine the revisions suggested in a pair of recent books, Sean B. Carroll’s Endless Forms Most Beautiful: The New Science of Evo-Devo, and Marc W. Kirschner and John C. Gerhart’s The Plausibility of Life: Resolving Darwin’s Dilemma, both published in 2005. In the first part I will use Carroll’s book to examine the shape of this revitalized field, and point to some of the ways it might answer a central objection of Bergsonism. The second half will describe one new theory that takes a major discovery of evo-devo very seriously, and posits a mechanism for the internal facilitation of evolutionary change, which may go a long way towards palliating the fear and/or rational rejection of random processes in the origin of life.
Nearly all of the science described here was produced in the past twenty years, and very little of it is commonly known to-day. In part this reflects an ignorance that goes back to Darwin’s own day; in September 1860 he was to write American supporter Asa Gray that “Embryology is to me by far the strongest single class of facts in favour of change of forms, and not one, I think, of my reviewers has alluded to this.”19 Evolution was to prove so powerful an idea, able to explain so much of biology, that the extreme difficulty encountered in working out the ways in which the foetus develops went largely unnoticed, and by the time the Modern Synthesis was formulated in the 1930s embryology was fading from significance. In the last twenty years this field has staged a magnificent comeback, spurred on by discoveries in molecular biology and genetics, and there are now increasing calls for a more modern synthesis that adds developmental biology to such stalwarts of the field as natural selection, heredity, and population genetics.
Carroll argues matter-of-factly that the bewildering array of new discoveries in embryology and evo-devo “devastate lingering remnants of stale anti-evolution rhetoric about the utility of intermediate forms or the probability of evolving complex structures.”20 Yet in addition to providing a new layer of evidence for the basic model of evolutionary change, evo-devo offers intriguing possibilities for theoretical engagements with life science. Indeed, the surging interest in the science of German Romantics like Schelling and Goethe dovetails nicely with the aesthetic emphasis of evo-devo, where the visualization of forms is an integral part of the explanatory model. Carroll notes that some of the “greatest ‘eurekas’ in science combine both sensual aesthetics and conceptual insight.” He quotes physicist and pianist Victor Weisskopf:
What is beautiful in science is the same thing that is beautiful in Beethoven. There’s a fog of events and suddenly you see a connection, It expresses a complex of human concerns that goes deeply to you, that connects things that were always in you that were never put together before.21
One such discovery is the recognition of so-called tool kit genes. We have now been able to observe the embryonic development of a wide variety of organisms in combination with the record of gene-triggers fired at each point. What this has shown us is that the same tool kit genes are used in widely diverse animals in order to build homologous structures, by controlling the direction and duration of various construction tasks. These genes act like a molecular orchestra conductor, signalling the way in which various developmental tasks will be performed.22 Crucial insights into diversity and complexity thus arise from understanding these genetic switches. “Because individual genes can be and are governed by numerous independent switches, mutations in one switch can be selected for that have no effect on other switches or the function of the protein encoded by the gene.”23 This means that the key to endless diversity lies “in the astronomical number of possible combinations of regulatory inputs and switches.”24
These genes are common to all forms of animal life, and appear to have been present in almost identical forms for millions of years:
all of the genes for building large, complex animal bodies long predated the appearance of those bodies in the Cambrian Explosion. The genetic potential was in place for at least 50 million years [prior to the Cambrian], and probably a fair bit longer, before large, complex forms emerged. This means that while the genetic tool kit was not evolving, the rapid appearance of and changes in body forms tells us that animal development was evolving a great deal.25
But the tool kit provides much more than a body of
entirely new and profound evidence for one of Darwin’s most important ideas — the descent of all forms of life from one (or a few) common ancestor. The shared genetic tool kit for development reveals deep connections between animal groups that were not at all appreciated from their drastically different morphologies.26
The discovery of the tool kit has forced scientists to revise two long-held beliefs about evolution. Where we once thought that complex organs were the “independent analogous inventions of different animals”, we now understand that instead of “being invented repeatedly from scratch, each eye, limb, or heart has evolved by modification of the same master gene or genes.”27
Stephen Jay Gould has defended Darwin’s “weak and negative force” of natural selection as incapable of playing its “creative rôle” unless “variation met three crucial requirements: copious in extent, small in range of departure from the mean, and isotropic (or undirected towards adaptive needs of the organism).”28 Yet the new evidence of a genetic tool kit capable of responding to changes in the life-circumstances of the developing organism have led Kirschner and Gerhart provocatively to ask: “What if evolutionary biologists were wrong to think of phenotypic variation as random and unconstrained, even though genetic variation was random and unconstrained?”29
Like Bergson, Kirschner and Gerhart point to the inadequacy of that “weak and negative force”, arguing that:
There are limits on what selection can accomplish. We must remember that it merely acts as a sieve, preserving some variants and rejecting others; it does not create variation. If genetic change were random, what could ensure that enough favorable phenotypic variation had taken place for selection to have produced the exquisite adaptations and variety we see on the earth today?30
Grounding their new theory of “facilitated variation” on the shores of evo-devo, Kirschner and Gerhart argue that “Whatever bias there is to alter the amount and kind of phenotypic variation must arise out of the construction of the organism itself.”31 Carroll’s survey of evo-devo has shown us that while the “genetic tool kit represents possibility” the “realization of its potential is ecologically driven.”32 What Kirschner and Gerhart have done is extend this neo-Lamarckian insight to view the organism as a mixture of conserved and non-conserved processes, noting the fundamental genetic similarity of all complex lifeforms, and the infinite variety possible through creative recombination of the same few genes.
Central to our argument is that these processes, many of which have been conserved for hundreds of millions or even billions of years, have very special characteristics that facilitate evolutionary change. They have been conserved, we suggest, not merely because change in them would be lethal (although that might be a factor), but because they have repeatedly facilitated changes of certain kinds around them.33
They describe these conserved genetic components as akin to conceptual LEGO blocks, which can be creatively re-arranged readily by the organism to instantiate structural changes. “Although the phenotype may play out at the gross anatomical and physiological level, the real locus of change is in the cellular processes that generate these anatomies and physiologies”, and taking account of these processes allows us to “explain anatomy and physiology in terms of the cell’s adaptive response to differing conditions.”34 “Phenotypic variation,” therefore, “and along with it evolutionary change, is facilitated by simple regulatory tweaks to existing physiological and developmental processes that long ago were designed so that the organism could adapt to its environment.”35*
The notion of “adaptive cell behaviours” has been around since at least the 1930s, when the pioneering population geneticist Sewall Wright first invoked it, but until recently it was not possible to speak of what these behaviours might be or what rôle they played in evolution. It is now known that “there is only a limited, though large, set of core cell behaviors”, and Kirschner and Gerhart argue that “Novelty usually comes about by the deployment of existing cell behaviors in new combinations and to new extents, rather than in their drastic modification or the invention of completely new ones.”36 They claim than true novelty is extremely rare, and call these long-term, stable cell behaviours “conserved core processes” for whom adaptability is the characteristic trait.37 Their argument for the reuse of these processes “implies that [they] are constructed in such a way as to facilitate phenotypic variation.”38
These conserved elements lie behind the mechanisms which the organism “uses day to day to vary its phenotype to meet new physiological demands”, and in neo-Lamarckian fashion Kirschner and Gerhart argue that these “mechanisms can be easily modified in evolution to yield new phenotypes.”39 While such arguments may have been unconvincing in the past, new understandings of embryology and of biological functions at the molecular level add much weight to the argument. Kirschner and Gerhart imply that changes in the phenotype occur not only from the response of the developing foetus to conditions in the womb, but from the long-term adaptations of the organism to its external environment. But whereas Lamarck conceived of the organism in a fundamentally reactive capacity, changing itself in direct relation to the vicissitudes of its environment, facilitated variation goes well beyond this by arguing that these conserved processes direct changes in ways likely to be beneficial to the organism. Metaphorically, then, why not think of these processes as the creative force of life itself?
Élan Vital and the Progress of Difference
Organized life is, for Bergson, marked out from the inorganic world by two main criteria — adaptability, and the capacity to store and release energy — and he locates both of these in the organism’s connexion with élan vital. Bergson’s most famous formulation, the élan vital makes the tendency to change an inherent feature of species, and gives this tendency a definite directionality. Through élan vital Bergson provides to evolution a vis a tergo, a non-random impelling force, but he seems not to be overly concerned with the problem of intentionality that this notion creates. Might we not view the élan vital as no more or less than the tendency of life to unfold along certain identifiable paths? Bergson himself knew that the theory of mutation asserts “that at a given moment… the entire species is beset with tendency to change”, but — he argued — the “tendency to change” itself “is not accidental.”40
All of these scientific ideas above may have brought us perceptively closer to unravelling the mystery of life’s origins and proliferation, and if some theory of facilitated variation is proven accurate, we can then “perhaps say we understand how evolutionary change occurs, based on the organism’s capacity to generate novelty, without reference to particular selective conditions or catastrophic events”, or indeed in terms of random accident and fortuitous chance.41 The genetic tool kit is a conserved process that has now been proven experimentally, and Kirschner and Gerhart’s research indicates that there may be other processes that remain with the organism throughout many generations, subtly tweaking the organism within, and according to, certain constraints. Under facilitated variation, mutations would still occur on a random basis, but only within well-defined areas, and perhaps according to an identifiable logic determined by the organism in question.
Bergson had argued “that the spontaneity of life is manifested by a continual creation of new forms succeeding others.”42 And, in one of his temporalizing moments, he states that “it is evident that even the sudden ‘mutations’ which we now hear of are possible only if a process of incubation, or rather of maturing, is going on throughout a series of generations that do not seem to change. In this sense it might be said of life, as of consciousness, that at every moment it is creating something.”43 By locating the constraints on mutation that leave the organism in a continuous state of development, adapting itself to new conditions and experimenting with new forms, we have come closer to validating this belief in evolution as a creative force. Bergson knew that the “indetermination” implied in a theory of consistently-creative expression “cannot be complete; it must leave a certain part to determination. An organ like the eye, for example, must have been formed by just a continual changing in a definite direction.”44 And this is exactly what we find in facilitated variation; the constraints placed on genetic drift ensure that new mutations will provide a useful improvement on the previous forms, lending a certain amount of directionality to the evolutionary record that we can observe through palaeontology, genetics, and comparative anatomy. Whether or not this constitutes a useful expression of élan vital I will leave to the reader.