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Camera Eyes and Convergence in Creative Evolution

Tano Posteraro

Résumés

Cet article présente un argument pour la théorie de la convergence évolutionnaire de Bergson. La convergence fait référence à l'apparition répétée de caractères similaires, tels que l'œil en forme de caméra, à travers des lignées distantes comme les escargots et les araignées, ou les humains et les pieuvres. C'est un phénomène notoirement difficile à expliquer comme résultant de sélection naturelle pour les variations aléatoires. L'idée de Bergson est que la convergence n'est pas un accident ou une anomalie d'un processus variationnel autrement aléatoire, mais qu'elle révèle plutôt quelque chose d'important sur le fonctionnement de l'évolution. Ce qu'elle révèle, c'est une profonde unité - ou homologie - sous-jacente à la pluralité contingente des êtres vivants, et une sorte de schéma, ou tendance orthogénétique, à leur convergence répétée sur les mêmes organes. Cet article explique cette idée, la relie à l'histoire des théories orthogénétiques de l'évolution et suggère qu'elle peut rester viable selon la science actuelle.

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1One of Bergson’s more striking criticisms of the Darwinism of his time concerned the idea that chance variations producing a random pool of individual differences furnish the conditions requisite for natural selection – the principal cause of evolution – to do its work. Bergson agreed that natural selection works on variations, which are individual differences, and even conceded that these differences most likely consist in what Weismann called the germ line. But Bergson denied that they are chance or accidental occurrences, what today we understand as mutations and copying errors. Life, for Bergson, does not evolve through a series of accidents. It is rather trended by tendencies, and patterned by their materialization. As a result, natural selection should not be considered the omnipotent evolutionary agency that Neo-Darwinians assume it to be. For it can only be so omnipotent if variations are random, playing no efficacious role in the directions evolution takes. And it is precisely that that Bergson contests.

2The historical alternative to the random theory of variation is orthogenesis, the idea that evolution evidences a kind of directionality. The term itself suggests a non-arbitrary trend or trajectory. Like all theories, its particular formulations have varied according to historical context, the usages to which the theory is put and the problems it is intended to address. Though it has largely fallen out of favour, today it is possible to discern a form of qualified orthogenesis at work behind explanations of convergent evolution by developmental constraint. Convergence refers to the repeated appearance of like characters, such as the camera-like eye, across distant lineages like snails and spiders, or humans and octopuses. It is an infamously difficult phenomenon to explain by dint of natural selection for chance variations alone. Convergent evolution exacerbates the improbability that chance changes at an insensible scale could be accumulated over generations in order to come together in the composition of a complex eye in one lineage, since it requires that chance variations succeeding each other in a chance order repeatedly arrive together at the same complex result, the eye, across lineages as distant as cephalopods from vertebrates. Bergson’s idea is that convergence is not an accident or anomaly of an otherwise random variational process, but that it rather reveals something important about how evolution works. What it reveals is a deep unity – or homology – underlying the contingent plurality of life forms, and a kind of pattern, or orthogenetic trend, to their repeated convergence on the same organs and traits. Part of the motivation behind this article is to begin to elaborate an account of Bergson’s theory as a variant of the orthogenesis view, with its own early anticipation of current explanations of convergence by homology and constraint. The variation, as I will show, consists largely in substituting Bergson’s metaphysical idea of tendency for the teleological concept of direction by which orthogenesis has most often been defined.

3Bergson is often considered a vitalist whose infamous “élan vital,” or vital impetus, secured his place on the wrong side of the history of evolutionary science. Vitalism is the position that life is irreducibly different from unorganized matter, and that the difference requires a principle, force, property, or substance superadded to the study of material systems in order to explain their vital organization, individuality, autonomy, creativity, or interiority. Bergson was not a vitalist in this ordinary sense, but in this regard, he was probably his own worst enemy. He repeatedly referred to his theory as a “psychological interpretation” of life in which the élan vital would play the role of evolution’s “psychological cause.” The troubling implication is that there is an “intelligence of nature” responsible for directing its evolution, and safeguarding the autonomy of life from the blind mechanism of material causal interactions. I think this is wrong. I hold instead that Bergson’s élan vital can be understood profitably as part of a qualified theory of orthogenesis, and that its “psychological character” consists in the fact that it is a tendency, what I call a “virtual tendency,” not an actual property, substance, force, or principle. This is a psychological interpretation not because there is any kind of consciousness at work in directing the evolutionary process from beyond it, but because Bergson’s idea was that the best model we have for conceiving of tendencies is a psychological one. Evolution is, in a sense, trended––this is, as I will show, what can be understood as the orthogenetic claim. And it is trended by tendencies––this is the psychological one. Why should anyone accept this position? Because it helps explain convergence. These are the ideas that this short paper brings together.

4Bergson rejected Lamarck’s idea that “the experiences or behavior of the individual in the course of [its] career” could be material for selection and agreed with the Neo-Darwinians that selection acts upon “variations,” or individual differences, inherent in the germ line (Bergson 1998, 85). But he remained unsatisfied with explanations for the cause of these variations as well as of their essential contingency, as accidents. “I have spoken of selection as the paramount power,” Darwin wrote, “yet its action absolutely depends on what we in our ignorance call spontaneous or accidental variability” (Darwin 1868, 236). Natural selection cannot operate without already-existent variations to select; it is derivative, so to speak, on variation’s source. For Darwin, that source was chance, “spontaneous or accidental.” By the 1920s, after the introduction of Mendelian inheritance into evolutionary theory, biologists began to invoke “mutations in genes” as the “source of new, stable variants on which selection can act.” Today recombination, copying errors, and gene immigration are added to the list. Each retains Darwin’s commitment to the accidentality of variation. But some theorists have begun to express dissatisfaction with the idea, in part because there has still never been a documented case of speciation by mutation, for instance, which means that its evolutionary efficacy as a source of variation remains undemonstrated (Margulis and Sagan 2002, 72).

5Bergson’s issue with the chance theory was not its underdetermination, but its improbability. His case in point, as I mentioned, was the widespread convergent evolution of the camera-like eye. Bergson insisted that it was inexplicable by sheer contingency and differential mortality alone.

6Orthogenesis – from the Greek ortho, meaning straight – is the position that evolution is intrinsically directed. This means that evolutionary outcomes are not wholly the consequences of the operation of a neutral mechanism. The term was first introduced by Wilhelm Haacke in 1893, but it was Theodor Eimer’s work on “the impotence of natural selection” in accounting for such phenomena as the colour patterns of butterfly wings, five years later, that would prepare it for popular uptake. Eimer distinguished between adaptive and non-adaptive trends, and privileged the latter. That the consistent action of selection could generate the appearance of a directional development did not mark a break with Neo-Darwinian orthodoxy. Many theorists thought the appearance of directional development was commensurable with random variation. It was eventually given the name of “orthoselection” to signify the compatibility. Eimer’s emphasis on non-adaptive characters and their trends, on the other hand, represented a significant departure from the theory of evolution by natural selection alone.

7Eimer began by observing that even characters with adaptive utility could not always have had it. Adaptive characters would either have had to develop through a process whose early stages were not yet useful, or else come to be out of the assemblage of previously insensible variations, again not themselves originally adaptive. In many cases, adaptive value is a merely hypothetical postulate. Eimer’s own field of animal colouration, for instance, was populated by guesses about the utility of the colour schemes of shells and wings, usually understood as camouflage or for attracting mates. Such hypotheses are difficult if not impossible to confirm. They also leave unaddressed colours that are hidden from view, on the inside of a shell, for example. Eimer argued that these sorts of cases could be better explained by the postulation of “inner forces” whose effects could be stimulated and channeled by external pressures without consisting for that reason in an adaptive response to them (see Eimer 1898, 4, 22, 24-25, 31). Pete Bowler notes that “in the end Eimer was so convinced of the prevalence of directed variation that he claimed there was no random variation at all” (Bowler 1979, 48).

  • 1 Bergson is more often compared with evolutionary theorists such as the Neo-Lamarckian Edward Cope. (...)

8It is from Eimer that Bergson inherits his own understanding of orthogenesis.1 Bergson thinks that orthogenesis is clearest in convergent evolution. He correctly observed that the same organs are converged upon not only evolutionarily, but developmentally or ontogenetically as well. The evolutionary histories of sapiens and cephalopods eventually arrive at the same form and function of the same organ, the camera-like eye, 500 million years after diverging from the last ancestor they had in common. This is phylogenetic convergence.

9But the eye is not only converged upon in the evolutionary event when two distinct species arrive at the same complex result. The vertebrate eye, for instance, is formed out of brain tissue, while the cephalopod eye is formed out of the epidermis. The eye is therefore converged upon every single time it is developed in individuals of each species as well. “Every moment, right before our eyes, nature arrives at identical results, in sometimes neighboring species, by entirely different embryogenic processes” (Bergson 1998, 74-75). This is ontogenetic convergence, or what is typically referred to as structural analogy. If the “production of the same effect by two different accumulations of an enormous number of small causes is contrary to the principles of mechanistic philosophy,” then more than phylogenetic convergence, it is ontogenetic convergence that presents the strongest challenge for mechanist biology (Bergson 1998, 76; cf. 74 for the terminology of ontogeny and phylogeny in this context). For “here we have, indeed, the same effect,” as Bergson says, “obtained by different combinations of causes” (Bergson 1998, 76). The more traditional distinction between structural analogy and functional homology captures only part of what is at stake here. It is not only the case that different structures (such as the wings of a butterfly and the wings of a bird) can be analogous without being derived from the same evolutionary lineage or embryogenic processes. Even when the structures are homologous, derived from the same processes, they can be constituted in different ways, or produced out of two series of causes, as Bergson says. The point is that homology cannot be captured adequately by mechanistic analysis.

10Bergson concludes that Eimer may have been right to base a theory of orthogenesis on the directional character of variation but was likely wrong to insist that it could be explained via the concatenation of mechanical causes alone. Bergson affirms that “variations of different characters continue from generation to generation in definite directions,” but denies that “physical and chemical causes are enough to secure the result [of the definite directedness of evolution]” (Bergson 1998, 86). Not because orthogenesis requires the postulation of “some supernatural force,” but because mechanical causes alone seem inadequate to the explanation of widespread onto- and phylogenetic convergence, functional homology included.

11In order to understand Bergson’s alternative to Eimer’s theory of orthogenesis, we have to look to Bergson’s conception of life. When Bergson says “life,” he means “evolution,” and by “evolution,” he means the unity or continuity of a single, unfolding event. Life is an event because it is not a kind; if it were a kind, there would be instances of it – but every possible instance of life, like a spider, is an instance of a species. There are no instances of life. Life is a word for a process, and it scales according to whether you are talking about organisms – in which case life designates metabolic processes of self-organization – or species – in which case life designates the source of variation and its consolidation in the differentiation of species. Ultimately it is the latter that Bergson considers primary. It is the latter that is impelled or trended by tendency, the élan vital. Individual organisms are its products and medium.

12What is a tendency? Tendency is directional puissance without a pre-specified end. Tendencies tend toward actualization, like potentialities, but they are not defined in terms of the actual states that they are supposed to realize. An equally important distinguishing feature is their virtual unity. Individuated tendencies are like “psychic states, each of which, although it is itself to begin with, yet partakes of others, and so virtually includes in itself the whole personality to which it belongs” (Bergson 1998, 118). Tendencies are both differentiated and co-implicated at the same time. This is what defines a qualitative or heterogeneous multiplicity. The modal status of such a multiplicity is what, in my other work, I have called virtual – in contradistinction to the possible and potential, both of which involve teleological presuppositions (see Posteraro 2022, 120-123). Evolution is a single, still-happening event, directed by the materialization of tendencies over time. Its tendency, as a single process, is what Bergson calls the élan vital.

13When Bergson says that evolution is directed by an élan, he has the psychology of effort in mind, whose details he elaborated five years earlier. The feeling of effort is supposed to consist for him in the psychological act of straining to dissociate distinct parts, acts, or images, from out of their implication in the unity of an abstract idea, an indistinct feeling, a cluster of memories, or a confused multiplicity of psychic dispositions. “Impetus” is an image for “effort” depersonalized, closer to unconscious drive than to intentional mental strain. Bergson says that while “it is only an image” for life, “no image borrowed from the physical world can give more nearly the idea of it” (Bergson 1998, 257). This is because “the essence of the psychical is to enfold a confused plurality of interpenetrating terms,” and in this sense it should be said that “life is of the psychological order” (Bergson 1998, 257).

14Here is one statement of Bergson’s argument. “The more two lines of evolution diverge, the less probability is there that accidental outer influences or accidental inner variations bring about the construction of the same apparatus upon them, especially if there was no trace of this apparatus at the moment of divergence. But such similarity of the two products would be natural, on the contrary, on a hypothesis like ours…” (Bergson 1998, 54). The question of how to conceive convergence occurs at the intersection between internalist and externalist accounts of evolutionary agency. Externalism is the position that locates agency, or what Stephen Jay Gould calls “the motor of organic change,” in selection pressures external to a random proliferation of biological variations (Gould 1977, 2). Internalism is the position that selection is not the only evolutionary force driving organic change. Internalists posit constraints on the development of individual organisms that function to limit and bias the production of variations. These internal constraints shape the pool of variations on which external selection acts, mediating the force of selection and driving evolution from the inside.

15To each position corresponds an explanation for the appearance of like traits in divergent lineages: internalism conceives them as instances of “parallelism,” while externalism conceives them as instances of “convergence.” Similar traits are “parallel” in two species if they have been evolved from out of a shared ancestral character or condition. Though the similar traits did not exist in the ancestor, descendant species inherited a developmental potential for those traits that each expressed in parallel after diverging. Selection pressure alone would not explain the resultant similarity, for it would have been derived from a shared origin. Similar traits are considered “convergent” when they are independently evolved in different species that did not share a recent ancestor. In such cases, the resultant similarity would be an effect of congruent selection pressures acting to bring about a like solution to like environmental problems in descendants that did not previously have anything relevant in common.

16For parallelism, there are two dimensions to the process by which similar characteristics arise on independent lineages: there is the manifest trait itself, as well as the developmental pathway responsible for manifesting it. Gould distinguishes between “underlying generators” and “realized structures.” Parallelism consists in the inheritance of the same “underlying generators” in divergent species; the traits they have in common are the “realized structures” of those generators (Gould 2002, 1078). The generators are called “homologous,” which means that their similarity is due to derivation from a common source. Characteristics whose similarity was independently evolved are called “homoplastic” instead. Homology is similarity by shared origin; homoplasty is similarity by other means. Parallelism involves the homology of underlying generators in connection with the homoplasty of realized structures, while convergence eschews homology and posits structural homoplasty as a result of non-homologous underlying generators selected for via external pressures.

17Bergson speaks only of the generation of “the like apparatus, by unlike means, on divergent lines of evolution” (Bergson 1998, 54). By that definition, he seems to intend convergence in the externalist sense, for “unlike means” imply non-homologous generators. The “like apparatuses” that are their homoplastic products would seem then to arise along divergent lines independently of the ancestral qualities shared across them (Bergson 1998, 54-55). Yet we know that it cannot be selection pressure, on Bergson’s account, that is primarily responsible for their production. He posits a positive “motor of organic change” that makes the appearance of convergent forms a natural bias of a trended evolutionary movement: “such similarity of the two products [of convergence] would be natural,” he writes, for “one should find even in the last rivulets [or evolutionary lineages] something of the impulsion received at the source” (Bergson 1998, 54 tm). This shared impulsion seems to correspond to internalism’s idea of constraints on the parallel development of pathways. Bergson’s “motor of organic change” is, of course, the virtual impulsion of the élan vital. It is common across all of life because it is what runs through each living form. It cannot be equated with internalism’s underlying generators because it is not inherited at any particular point in evolutionary history, derived from any particular ancestral quality. It is beyond the genome of any already constituted species, for it resides in the movement through which each species is constituted as such.

18The camera eye, first offered forty years ago as a case study in evolutionary convergence, remains a textbook case of the phenomenon today. It has evolved to similar degrees of complexity, in comparable form and function, across mammals and cephalopods, gastropods, and some arthropods as well. Bergson thinks this testifies to the unity of life. “From its origin, [life] is the continuation of one and the same impetus, divided into divergent lines of evolution” (Bergson 1998, 53). Life evolves by radiating outward across a ramifying series of directions, but each direction retains the history from which it diverges. That retention of a common past is what unifies the process. It follows that when the same trait appears across divergent lineages, it is in one sense a result of parallel evolution, not convergence. Adaptive benefit provides the opportunity for homologous pathways to materialize the same characters in each case. But Bergson does not restrict himself to the claim that only species sharing a recent common ancestor can manifest like characteristics by deriving underlying generators from it. The strength of his account is supposed to be “proportional both to the divergency between the lines of evolution thus chosen and to the complexity of the similar structures found in them” (Bergson 1998, 55).

19According to Bergson, what divergent evolutionary lineages have in common is more primary – more basic in a metaphysical sense – than the generation of any one of them, for the “common impulsion” that is divided across each species is coextensive with the evolutionary movement of all life. Bergson implies that the tendency that manifests itself in the realized structure of a convergent organ metaphysically prior to the developmental pathways that channel it.

20If homology is a correlate of shared generators, then Bergson’s account of convergence is, ultimately, a non-homologous one. For he nests the parallel evolution of homoplastic traits from out of homologous generators within the larger evolution of the generators from out of more elementary tendencies still. When the convergent organ in question is the camera-like eye, researchers today agree that the developmental pathway responsible for its parallel evolution is a genetic cascade controlled by Pax-6 – the so-called master control gene for visual organs, present in every species that has them. This gene was first cloned in mice using Drosophila probes, a fly species, in the early 90s, and was soon afterward linked to mutations in the form and function of eyes. Further studies established that it was the expression of a homolog to Pax-6 that induced eye development and deformation in the flies as well. Conservation between the mammalian and insect sequences turned out to be over 90 percent. Their functional homology was then affirmed by inducing the mouse gene in Drosophila and finding that the mammalian version could still induce the formation of normal eyes in the fly. A genetic homology between the two phyla was thus uncovered in the form of a shared developmental constraint on the formation of their eyes (i.e., through the Pax family of genes).

21The idea is that over time, the “instructions” that arose from differently spliced variants of a single Pax-6 increased, diversified, and integrated a set of associated genes responsible for the formation and patterning of the membranes, muscles, proteins, chemicals, and glands that come together in the realization of the complex eye (see Tahar 2022). But for Bergson the pathway channels a tendency that predates its genetic constitution. Wherever that tendency is able to begin materializing itself, it will eventually come to be embodied in like genetic pathways, controlled by Pax-6, which can be leveraged to realize increasingly complex structures. But more fundamentally than the pathway, it is the virtual lineage of the tendency that is common across all appearances of a like organ.

22No matter how complex, every visual organ is an apparatus for seeing. The tendency operative behind the convergence of like traits is not a tendency towards the formation of those traits as organic forms, but a tendency towards the realization of the one function channeled through each of them. Bergson contends that “no matter how distant two animal species may be from each other, if the progress toward vision has gone equally far in both, there is the same visual organ in each case” (Bergson 1998, 96). This is because “the form of the organ only expresses the degree to which the exercise of the function has been obtained” (96 tm). If eyes of like complexity appear in molluscs and chordata alike, it is because the same tendency towards vision has made a similar progress in each phylum. But what is the tendency towards vision?

23One way to make sense of this progress is to ask what the species that realise it have in common, other than their eyes. Besides vertebrates and cephalopods, such as the octopus, camera eyes are convergent in Cubozoan box jellyfish, Portia and Dinopis spiders, and some Gastropods, including snails of the Strombus genus as well (see Morris 2003, 151-157). These species are agile, coordinated, and fast. The spiders are dexterous hunters with impressive motor control. The box jellyfish are skilled swimmers, manifesting complex, visually guided response behaviour (see Skogh et al. 2006). The snails are adept at registering threats quickly and, somewhat surprisingly, rapidly evading their predators as a result. When Bergson says that similar visual organs represent similar levels of progress in the realisation of vision, he means that each species has evolved to a similar level of coordination between its ability to perceive and its ability to act with precision in response. Vision is not sensory, but sensorimotor. A sophisticated ability to see is incomprehensible apart from a complex capacity to act on visual data. Sophisticated vision and sophisticated motor control are two facets of the same fact. It is towards that fact, the intensification of action, that evolution is oriented. The tendency channelled through the visual apparatus is a particularised variant of the tendency towards action, indetermination, or choice.

24The convergent evolution of complex vision in humans and octopuses is among the most impressive cases of convergence. Our last common ancestor was a sightless worm in the Ediacaran era, 500 million years ago. Since then, we have evolved eyes comparable in structural complexity and functional sophistication. Octopuses are visually guided predators with close, responsive control of their tentacles. Their dexterity is impossible to understand independently of their eyes and the way they make use of what they can see. Perception, on the Bergsonian view, is virtual action, no matter the species. Sophisticated perception is a correlate of sophisticated action capacity. Externalists are wrong to suggest that complex vision evolves and proves adaptive for some species on the ultimate basis of selection pressures and external environments. The evolution of vision in the form of the camera-like eye also depends on the neurology and morphology that coordinates visual information with motor control, coupling action with the perception that it makes use of. When the conditions are right, when the channel towards vision is available and beneficial, complex eyes can become increasingly likely, no matter how divergent the evolutionary trajectory or dissimilar the external environment. That is the idea.

25Conservation, constraint, and convergence imply that evolution has trends. Trends imply a form of directionality, or at least a non-randomness, which is what the idea that biology involves tendencies is meant to capture. Directionality, or orthogenesis etymologically defined, is not an indication that there is something outside of or beyond the evolutionary process that guides or directs it, like an intelligence, as it may have been for most of the history of the orthogenesis view. The sort of directionality at issue here is rather an immanent effect of the insistence of the past in the present of a process of change. It is neither reducible to the action of selection, nor does it require the postulation of an external principle. The trends that regularise the evolutionary process are not derived from pre-existent ends, but from what Bergson called a “vis a tergo,” a force from behind, developing through divergent channels as it is differentiated over time (Bergson 1998, 103). “One assumes,” says Robert Wesson, “that the octopus eye resembles the vertebrate eye because there are not many ways to make a cameralike apparatus” (Wesson 1991, 189) If this is true, it is because there are not so many channels for the development of the complex eye. If that is true, it is because those channels are outlined in the form of developmental potentialities that constrain how and in what forms they can be realised. If that is true, it is because evolution con- serves itself over time, re-employing the same sequences in an increasing variety of developmental processes. This demonstrates, finally, that complex eyes are not the result of adaptation building organs in the only way that they can be built, but rather that the history of life canalises its own evolutionary unfolding, deriving a set of directions as potentials from the past and realising them along a select number of channels that lead to a similar set of organs.

26“It is not that evolution proceeds toward a goal,” Wesson writes, “but that it carries on in a direction that has been adaptive in the past” (Wesson 1991, 192). “This implies,” as a result, “something like orthogenesis” (Wesson 1991, 194). This view that is “something like orthogenesis” is one, as I have shown, that can be understood as seeking to explain direction on the basis of tendency. Tendency is directionality without direction. The orthogenesis-like directionality of evolution is derived from the past, from a shared history inherited in the form of conserved developmental tendencies that facilitate a definite set of available trajectories for the evolutionary future. The result is the appearance of trend, pattern, and coherence; not chance, accident, and mechanical reaction. The appearance is confirmed by “the development in different groups of similar improbable organs and instincts” (Wesson 1991, 192). That is Bergson’s position more or less.

27Here, by way of conclusion, are some the implications for the contemporary study of evolution. Adaptation is not the sole or only agent at work in evolution. In fact, it is better understood as a negative filter or contouring force operating on a more primary production. Selection does not act only upon the chance proliferation of variations, but rather on the directionality imparted to evolution by the tendencies that trend it and the developmental history that it retains (through conservation and developmental constraint). Finally, there is a deep unity underlying the extant plurality of life forms, which reveals itself in the convergent evolution of like characters across divergent evolutionary lineages. Each of these claims remain challenging, if not viable, for the contemporary study of variation, homology, and convergence. Bergson’s “psychological interpretation” of tendencies should not distract from that fact.

28Bergson, Henri. 1998. Creative Evolution. Trans. Arthur Mitchell. Mineola: Dover.

29Bowler, Peter J. 1979. “Theodor Eimer and Orthogenesis: Evolution by ‘Definitely Directed Variation’”. Journal of the History of Medicine and Allied Sciences 36(1): 40-73.

30Darwin, Charles. 1868. The Variation of Animals and Plants under Domestication. London: John Murray.

31Eimer, Theodor Gustav Heinrich. 1898. On Orthogenesis and the Impotence of Natural Selection in Species Formation. Translated by J. M. McCormack. Chicago: Open Court.

32Gould, Stephen Jay. 1977. “Eternal Metaphors of Palaeontology.” Patterns of Evolution as Illustrated by the Fossil Record. Edited by A. Hallam, 1-26. Amsterdam: Elsevier.

33Gould, Stephen Jay. 2002. The Structure of Evolutionary Theory. Cambridge: Belknap.

34Margulis, Lynn and Dorion Sagan. 2002. Acquiring Genomes. New York: Basic Books.

35Morris, Simon Conway. 2003. Life’s Solution: Inevitable Humans in a Lonely Universe. Cambridge: Cambridge University Press.

36Posteraro, Tano S. 2022. Bergson’s Philosophy of Biology: Virtuality, Tendency, and Time. Edinburgh: Edinburgh UP.

37Skogh, C., A. Garm, D. E. Nilsson and P. Ekström. 2006. “Bilaterally Symmetrical Rhopalial Nervous System of the Box Jellyfish Tripedalia Cystophora.” Journal of Morphology. 267(12): 1391-1405.

38Tahar, Mathilde. 2022. “The History of the Bergsonian Interpretation of Charles Darwin’s Theory of Evolution.” Bergsoniana 2: 73-90.

39Wesson, Robert. 1991. Beyond Natural Selection. Cambridge: MIT.

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Notes

1 Bergson is more often compared with evolutionary theorists such as the Neo-Lamarckian Edward Cope. By centering Eimer in this article, I do not mean to suggest that Bergson has more in common with the latter than the former, for instance. Instead, I want to clarify the role played by Eimer in Creative Evolution, with particular reference to Eimer’s theory of orthogenesis. This is the only way to understand Bergson’s otherwise enigmatic remark that his own élan vital and the view of evolution associated with it comes close to “a hypothesis like Eimer’s” (1998: 86).

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Tano Posteraro, « Camera Eyes and Convergence in Creative Evolution »Bergsoniana [En ligne], 4 | 2024, mis en ligne le 01 janvier 2024, consulté le 14 février 2026. URL : http://journals.openedition.org/bergsoniana/1578 ; DOI : https://doi.org/10.4000/bergsoniana.1578

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