In this article I shall focus on some of the important conceptual problems posed by the purported phenomenon of spontaneous generation, showing how these problems are connected with the theoretical question of the origins and ontology of biological species, above all with the problem of their boundaries. I will argue that the important conceptual distinction in the history of generation theory was never that between sexually and spontaneously generated animals, but rather that between animals generated through the cyclical reproduction of form, on the one hand, and through what Descartes would call ‘minor causes’ on the other. For a hylomorphist such as Aristotle, all reproduction is formal, whether sexual or ‘spontaneous’; for a mechanist such as Descartes, all reproduction, including sexual reproduction, is mechanical.
In the first section, I shall begin with a quick overview of the problem of species ontology and spontaneous generation in Aristotle as it has been treated in the secondary literature since David Hull’s well-known attribution of species fixism to the Greek philosopher. In the second section, I turn to a consideration of the more probable candidates for the origins of species fixism, to wit, the natural historians of the early modern period who were concerned with standardization of morphological types within taxonomical systems. In the third section, I discuss the way the newly emerging ontology of species in the 16th century accommodated the widespread account of spontaneous generation that emerged over the course of the middle ages and that was often dubbed ‘Aristotelian’, according to which, in the emergence of creatures from slime or putrescence, it is not that there is no imposition of form upon some matter by an agent, but rather only that the heavens take on the role that the father plays in sexual generation. But astral influx of form was largely replaced in the 16th century by a theory of spontaneous generation as a by-product of putrefaction, and as the new fixist account of species took hold, increasingly a natural philosopher’s degree of libertinism could be measured according to just how high on the scale of being they were willing to propose generation of living kinds out of putrescence might occur. Thus Lucilio Vanini, who affirmed that oxen congeal out of the Nile, and suggested that humans might arise out of putrefaction as well, had his tongue cut out by the Inquisition. In the fourth section I discuss this skeptical and libertine background to certain aspects of the spontaneous generation debate in the early modern period. In the fifth section, matters get more complicated, as we consider the respects in which one prevalent view of sexual generation in the early modern period, that of Descartes, effectively reduces it to spontaneous generation by other means, that is, to the creation of new organisms through a congealing of parts rather than through the imposition of form by an agent. In this respect, I will argue, the ontological status of species is a particular problem for the general mechanist account --and particularly that of Descartes-- not as concerns spontaneous generation alone, but generation simpliciter. For mechanism leaves out entirely any explanation of how or why like consistently begets like, even if, unlike Aristotle’s biology, all early modern generation theorists, save for the libertines, are at least implicitly committed to species fixism.
This article draws heavily on the work of Scott Atran on the cognitive foundations of Western biological taxonomy, while at the same time criticizing his account on certain points. In particular, it will be shown that significant changes in the species concept over the course of the modern period came about not just, or not primarily, as a consequence of new classificatory practices and exigencies, but also as a result of philosophical and theological currents that were not first and foremost preoccupied with natural-scientific practices.
1. Spontaneous Generation and the Ontology of Species in Aristotle
On the basis of a false understanding of Aristotle’s conception of species, David Hull identified a now well-known pseudoproblem concerning the place of spontaneously generated creatures within Aristotle’s metaphysical biology. His worry was that spontaneous generation would constitute a rupture in Aristotle’s fixist account of species. As he put the problem:
Aristotle usually calls an event or thing spontaneous if it fails to occur always or for the most part, but in the case just cited (HA 551a13) and in numerous others, the changes occur regularly whenever the appropriate material is present and the conditions are right… If lower animals can partake in the eternal and divine without the help of efficient, formal, and final causes coinciding, why not all species? And if there is no need for the efficient, formal, and final causes to coincide in any species, nothing stands in the way of accepting evolutionary theory.
Even if this worry is out of place, Hull is nonetheless to be thanked, for his pseudoproblem provides much food for thought as concerns the broader issue of the relationship throughout history between ontologies of biological kinds, on the one hand, and theories of spontaneous generation on the other.
Aristotle was long thought to be a supporter of what has come to be called the ‘Typological Species Concept’, according to which (i) the eternal fixity of species, and (ii) the doctrine that “any individual necessarily comes to be what it is in virtue of its species-specific properties, that is, those properties which define the essence of the kind of being that individual is and which therefore make the individual the particular individual it is.” According to Ernst Mayr, typologism “attempts to assign the variability of nature to a fixed number of basic types at various levels. It postulates that all members of a taxon reflect the same essential nature, or in other words that they conform to the same type… Variation, consequently, is considered by the typologist as trivial and irrelevant.” But to the extent that Aristotle sees species as ‘fixed’, he does not do so in virtue of a belief in underlying universals that would require such fixity, and to the extent that he believes that individuals come to be what they are by virtue of species-specific properties, he does not believe that this happens of necessity. In recent decades, Aristotle scholarship has gone a long way towards overturning the earlier, simplistic attribution of essentialism, as a belief in eternally fixed universals, to Aristotle. In particular, D. M. Balme argues that in Aristotle essentialism,
although apparently supported by various statements in Aristotle’s logic and metaphysics, [is] directly opposed by some of his most mature and carefully argued theories in biology…. Aristotle holds that the animal develops primarily towards the parental likeness, including even non-essential details, while the common form of the species is only a generality which ‘accompanies’ this likeness.”
In the GA, Balme goes on, Aristotle holds that the animal develops primarily towards the parental likeness, including even non-essential details, while the common form of the species is only a generality which ‘accompanies’ this likeness.” Aristotle treats species, Balme argues, as merely a universal obtained by generalization. While it is true that species-membership may help to explain the features of individuals, this is not because species is an efficient cause of individual formation, but because individuals in like circumstances are advantaged by like features” (ibid).
What is the textual evidence on which Hull bases his argument? Aristotle provides the classic formulation of his concept of kind in the De Anima. Creatures, he says, or at least those “whose mode of generation is not spontaneous,”
produce others of their kind, animals producing animals and plants producing plants, in order that they may share, so far as their several natures allow, in the eternal and divine. That is the ideal for which all creatures strive, and which determines their behavior, so far as their behavior is natural… But since mortal things cannot share continuously in the eternal and divine (because nothing that perishes can preserve its identity nor remain numerically one), they partake of eternity and divinity in the one way that is open to them, and with unequal success; achieving immortality not in themselves, but vicariously through their offspring, which, though distinct individuals, are one with them specifically (De Anima 415a27-b9).
The phrase ‘with unequal success’ is telling here. What Aristotle is in fact concerned with is the functional and morphological analysis of kinds in their ecological context. There is, of course, a theory of ‘underlying’ natures for Aristotle, but in the end, Aristotle’s method is to determine kind membership by appeal to morphological aspect. As Balme puts it, Aristotle makes systematics first in zoology, and morphology first in systematics. Natures develop, in Aristotle’s view, under specified natural conditions, but there is certainly nothing to ensure that an individual organism will necessarily come to be what it is simply in virtue of the inner working of its species-specific nature. It is true that for Aristotle all organisms would turn out as perfect copies of their fathers, who contribute the active principle to reproduction through the vehicle of the sperm, if the offspring did not also require the passive matter contributed by the mother’s menstrual blood in order to develop into a particular embodied substance, and if the development of the offspring were not also influenced by environmental factors.
But this never in fact happens. Environmental and material causes always play a part in embryogenesis. These might be called ‘impeding causes’: they bring about a particular effect by standing as an obstacle to some other active cause --in this case the male sperm-- that would in their absence bring about a very different effect. When the impeding causes prove strong enough, the offspring is sufficiently ‘deformed’ as to come out a female (GA 766a 20-25). At an even greater level of deformity, “when the movements <that came from the male> Relapse and the material <that came from the female> does not get mastered, what remains is that which is most ‘general’, and this is the <merely> ‘animal’” (GA 769b 11-13). Resemblance to another animal species is “resemblance only” and “in no case are they what they are alleged to be” (GA 769b 18-20). For Aristotle, a “monstrosity is really a sort of deformity [kai gar to teras anaperia tis estin]” (GA 769b 30-1), categorically no different from lesser cases of falling-short of the ideal of absolute reproduction of the father. A monster arises whenever the formal nature in reproduction is not able to gain control over the material nature (GA 770b17-18). This is ‘unnatural’ relative to the nature of the animals seeking to reproduce themselves, but there is nothing absolutely unnatural about the monstrous outcome of any two animals’ coupling.
A monster, for Aristotle, is not an abrupt rupture in the order of nature, but is only a case of steresis or ‘falling short’—and indeed, every organism falls short of the reproductive ideal to some extent, since organisms are never exact copies of their fathers. It is against this background that Aristotle can claim that women are deformed—they fall short of the reproductive ideal, indeed somewhat more so than men, but there is nothing exceptional about this. For Aristotle, in an important sense monstrosity is the norm. We might say that for him teratology is just the way one accounts for the diversity of individuals across a kind: every individual falls short of exact duplication of its father; fathers achieve eternity ‘with unequal success’. A very poor stab at eternity would be one in which environmental or maternal influences bring about a creature that not only does not bear the particular traits of the father, but does not even appear to bear the typical traits of the kind to which the parents belong. The kind to which the parents belong is itself, in any case, only “a universal that represents a… possibility for the future course of optimal individual development.” This universal does not have any real being of its own, but is only the derivative or ‘secondary’ substance through which particular primary substances may be cognized.
As Scott Atran explains, the species is a naturally occurring “empirical ‘necessity’ --part of nature’s ontological fold-- that is nevertheless conditional upon an ideal constellation of material circumstances that may never, in fact, obtain.” Thus there is nothing guaranteeing that like will consistently --let alone eternally!-- beget like, even if, for Aristotle, sexual reproduction amounts to a sort of approximation of eternity for mortal, sublunar corporeal substances. Indeed, if we consider Aristotle’s more general account of the relationship between particular primary substances and secondary substances, it is remarkable that Aristotle can continue to be considered a rigid fixist about species. For him, secondary substance such as humanity or bovinity has its reality only derivatively from the existence of actual humans or cows. Whether or not this metaphysical picture constitutes a thorough reversal of the Platonic theory of forms, it is clear that for Aristotle there is no eternal, fixed standard against which an individual can be compared for the determination of its qualification for membership in an unchanging kind. The eternity in Aristotle’s account of sexual reproduction is eternity only in so far as finite corporeal substances are capable of it. Which is to say: not much. Nature only approximates eternity, and environmental circumstances might very well bring it about that, in the case of some species or other, it does so rather poorly.
But what does this revised understanding of species in Aristotle have to do with our understanding of his account of spontaneous generation? Jim Lennox has vividly brought out the connection between these two problems. In his view, the fundamental difference between the two modes of generation is that there is no teleological causation involved in the spontaneous variety. Sexual generation is formal replication which generates teleological explanations, that is, “explanations of processes by means of their outcomes.” In the case of sexually generated species, their ‘nobility’ is ranked in terms of “the internal vital heat characteristic of the species.” In spontaneous generation, in contrast, “the exact amount and strength of the pneuma, and consequently the vital heat, that an enclosure would ‘capture’ would be a function of the locale where it took shape.” As Aristotle explains in the GA:
Animals and plants come into being in earth and in liquid because there is water in earth, and air in water, and in all air there is vital heat; so that in a sense all things are full of soul. Therefore living things form quickly whenever this air and vital heat are enclosed in anything. When they are so enclosed, the corporeal liquid’s being heated, there arises as it were a frothy bubble. The differentiae which determine whether the kind is more or less honorable are determined by the organization of the vital principle in the enclosure. And both the places and the enclosed material are causes of this organization (GA 762a18-27).
This same account is in the relevant details repeated at numerous points in the Historia Animalium. The pattern of development is a function of the amount of pneuma relative to earthen and liquid material in the enclosed mix. That mix, which can change depending on climatic and geographic variables, will determine whether the enclosure comes to be a sea urchin or an oyster. The vital heat that is productive of a species member is thus not derived from anything one in form with that species member. To put this another way, “there is no description of the course of such a process that identifies it as for the production of a specific kind of organism.” Lennox concludes that spontaneous processes should not be contrasted with orderly ones, but rather with those that involve formal replication. It is not, in short, that a barnacle has no form. It simply has no father.
In sexual generation, we have the unique phenomenon of formal replication, in which an abstract universal ideal is approximated in the generation of like by like, but again, here the form is not guiding the process nor guaranteeing any outcome. Quite the contrary, the form or secondary substance may be said to exist only to the extent that like individuals in fact continue to generate their like. In spontaneous generation, the regular, orderly, generation of what appear to be members of kinds --the oyster-kind, the barnacle-kind, etc.-- is made possible by the relative constancy of environmental circumstances. There is nothing guaranteeing that environmental circumstances will stay the same, and so nothing guaranteeing that there will always be barnacles. But what Lennox perhaps underemphasizes, in marked contrast with Atran, is that there is also nothing guaranteeing that local circumstances will obtain that permit Spoonbills to keep generating either, and thus nothing ensuring formal replication will continue. Spoonbills approximate eternity through formal replication as best they are able, and their ability depends on environmental circumstances no less than does the spontaneous generation of barnacles.
And so spontaneous generation creates no real problem for Aristotle’s philosophy of biology, since there is no reason to believe that Aristotle was committed to the sort of typological essentialism for which spontaneous generation would constitute a threat. Hull’s worry nonetheless highlights a very interesting point about the connection between spontaneous generation and the ontology of species in Aristotle. Indeed, far from constituting a rupture in Aristotle’s biology, the fact that he is so committed to the reality of spontaneous generation should have clued us in to the fundamental inadequacy of our earlier treatment of him as a rigid fixist.
2. The Origins of Fixism
In Atran’s view, the first steps towards a systematic global classification of biological kinds came in the 16th century when botanists such as Andrea Cesalpino sought to fix the species as an eternally self-perpetuating entity. As a consequence of the effort to develop a comprehensive and universal system of classification in the early modern period, it was, as Atran argues,
necessary to fix a criterion for the species even in advance of future discoveries. Without such a criterion there could be no principled justification for uniting basic-level sorts originating in different climes within the same genus. Such a criterion must, therefore, establish that morphological characters usually perceived to be constant are, in fact, those that ought to be constant according to God’s eternal plan.
In 1571 the Italian botanist writes that “Eternity can only arise from the eternal: since the proper work of the vegetative soul is to engender its like, which makes for the eternity of the species, it is necessary that its substance not be corruptible. The reason for the eternal lies neither in corruptible existences taken individually, nor in their totality.” Species must, in other words, be understood independently of ecological context, and as not subject to transmutation as a result of any ecological change; the species essence must be conceived as reliably transmitted from one generation to the next through sexual reproduction. Variation in a population under new ecological circumstances must now be conceived as intraspecific phenotypic drift rather than as transformation of one species into another. A creature’s species essence is determined exhaustively by who its parents are. “[F]or like everywhere engenders like,” as Cesalpino puts it, “according to nature and of the same species.”
Interestingly, Cesalpino takes Aristotle to task for his view that ‘the sun and man generate man.’ But the Italian botanist sees his disagreement with the Greek philosopher more as an emendation than a rejection. For Cesalpino, it is man that generates, and it is thus superfluous to mention the sun in this connection. If the sun plays a part in generation, it is as an auxiliary to the act of reproduction, and not as a parent. The requisite elements for the continuity of species reproduction have been placed in the first parents of the species at the creation, and even if the sun is requisite for the post-Creation successio of generations, this does not diminish the fact that the continuous existence of the species was guaranteed at the prima creatio. Cesalpino is not such an Aristotelian that he is unwilling to confront the fundamental point of difference that Aristotle acknowledged no Creation, but that he, as a Christian, must. The upshot of Cesalpino’s divergence from Aristotle would be a conception of species not all that different from Aristotle’s, according to which species essences were fixed at the Creation, and according to which subsequent generations unfold by necessity from their first parents, regardless of alterations in environmental circumstances. Nearly two centuries later, Linnaeus would put it even more unambiguously: “Constans, immo constantissima, naturae lex est, quod similes procreentur a similibus, nec imbellem feroces progenerent aquilae columbam.”
Atran argues that this new conception of species essences rooted in sexual reproduction is one that developed in conjunction with the work of the early modern botanists. Whereas for traditional biology, including that of Aristotle, the primary interest had always been in determining and grouping species according to morphological aspect and ecological proclivity, natural history after Cesalpino, and then more clearly after Linnaeus, gradually came to focus on determining species’ genealogically-related affinities. For Cesalpino, essence is communicated through reproduction, through like’s begetting of like, and it is this process that ensures the eternity of species, rather than merely approximating to eternity, as was the case for Aristotle:
Eternity can only arise from the eternal: since the proper work of the vegetative soul is to engender its like, which makes for the eternity of species, it is necessary that its substance not be corruptible. The reason for the eternal lies neither in corruptible existences taken individually, nor in their totality.
On Atran’s view, Cesalpino’s metaphysics of plant kinds is a consequence of certain exigencies in the project of systematic classification. Plant kinds came to be seen as fixed, and plant essences as reliably and unchangingly transmitted from one generation to the next, in a way that was no longer concerned with the kind’s ecological context, in large part because conceiving them in this way was useful to the project at hand.
Put succinctly, we may say that the view just outlined, which emerged in the early modern period as a result of certain new exigencies of scientific classification, was later projected back unjustly upon Aristotle himself, who was admittedly the acknowledged forefather of Cesalpino et al., but who did not, for all that, agree with the early modern naturalists on all points, including the question of the ontology of species.
3. Astral Influx as Formative Agent and the Non-Spontaneous Character of Non-Sexual Generation
While Atran makes a compelling case, it may be worth revising his thesis concerning the importance of the 16th-century botanists for the emergence of the modern species concept, to the extent that it was not just new methods of scientific classification that brought about a new ontology of species, but the scriptural tradition as well. To cite just one example, in his commentary on Genesis Martin Luther writes that, in forming Eve, God created for Adam an “associate in generation and in the conservation of the species” [socia generationis et conservationis speciei]. God thereby ensures that future humans will be generated in the manner of the beasts, as opposed to being forged from mud: “Neither did God wish for [Adam’s] descendants to be born in the same way as Adam, namely, from the earth. Rather, he wanted man to have generation just as the other beasts have it [voluit, ut haberet generationem, qualem aliae bestiae habent].” After this moment, the criterion of species membership, for both men and beasts, is clear: “Whatever living thing is generated, is generated from the male and the female, in such a way that it is brought into the world by the female [sic ut per foeminam edatur in lucem].” On this view, the first man is generated out of the earth, with God playing the role, quite literally in Aristotelian terms, of the father, to the extent that God communicates to the appropriately receptive clod of matter some form of which he, God, has an intellectual idea. Subsequently, the mode of generation changes, so that God need not see to every act of generation himself, but instead may impart the generative role to Adam’s male descendents working in conjunction with human females.
The fact that in the Christian tradition, as opposed to the Aristotelian, the first man is born from the earth, is worth some reflection. On the face of it, this should not count as an instance of spontaneous generation, since after all Adam is supernaturally created by a God who has a clear idea of what he is creating. In other words, Adam’s creation admits of teleological explanation. But if not with respect to Aristotle, then certainly with respect to later medieval, Renaissance, and early modern ideas about earthborn creatures, the distinction between their mode of generation and that of Adam is not so clear, since they too come to be seen as generated as a consequence of heavenly or astral influx into terrestrial matter. Of course, the Christian God is meant to be ‘heavenly’ only in a figurative sense, yet God’s role in the first generation of the human and animal species bears a remarkable resemblance to medieval and early modern ideas about the celestial ‘fertilization’ of terrestrial matter. The standard 19th- and 20th-century triumphalist accounts of spontaneous generation generally leave out the role of the sun and other heavenly bodies, yet these are almost always invoked by those seeking to define this mode of generation, even critically, in the era in which it was still an option. Thus for example a rather late entry in a reference work of 1728 tells us that
EQUIVOCAL Generation, is a Method of producing Animals and Plants, not by the usual Way of Coition between Male and Female, but I know not what plastic Power, or Virtue in the Sun, &c…Thus Insects, Maggots, Flies, Spiders, Frogs, &c. have usually been supposed to be produced by Equivocal Generation, i.e. by the Heat of the Sun warming, agitating and impregnating the Dust, Earth, Mud, and putrified Parts of Animals. This Method of Generation, which we also call spontaneous, was commonly asserted and believed among the antient Philosophers: But the Moderns, from more and better Observations, unanimously reject it, and hold that all Animals, nay and Vegetables too, are Univocally produced, that is, by Parent Animals, and Vegetables of the same Species and Denomination.
In the GA, Aristotle himself mentions, without much explanation, that the pneuma in animal semen is ‘analogous’ to the material of the stars (GA II 3 736b29). As one commentator notes, while Aristotle did not mean by this that the pneuma originated from the aether, we do find this view springing up in the later Aristotelian tradition. Avicenna describes the pneuma as a ‘virtus informativa’ not just analogous to, but in fact of the same kind as, the virtue of the heavenly bodies. Throughout Scholastic philosophy, there is a common presumption that the formative power at work in nature in general is but a different manifestation of the formative faculty traditionally held to govern biological growth and development. This formative power filters down from the celestial to the terrestrial sphere, and in this respect we may say that in all cases of natural growth and development, including the emergence of fossils and crystals as well as of ‘spontaneously’ generated organisms, there is in fact an agent whose role is analogous to the father’s in sexual generation: the heavens.
We see just such a conception of the emergence of forms in terrestrial matter in the standard Scholastic account of the origins of fossils. The Dominican Antoine Goudin, in his Philosophy, Following the Principles of Saint Thomas, argues that there are both efficient and final causes at work in the earth’s production of rocks that resemble animals or parts of animals. Their efficient cause is a sort of cooking brought about by exhalations from the depth of the earth that makes the strata where fossils are found into a furnace of sorts. Their final cause, in turn, is
a certain force earth itself possesses variously, following the different places in which the mixed body is formed. This force, similar to the maternal bosom from which animals arise, assuredly plays a great role in the formation of these bodies; this is why, according to Aristotle and Saint Thomas, earth and water furnish to everything arising from the bowels of the earth their matter and bosom, as would a mother, while heaven and the stars fulfill the office of the father, who imparts the form.
A ‘male’ formative principle exercises its influence over the ‘maternal’ matter of the earth and thereby gives rise to forms in earth that resemble living beings. A fossil, for Goudin, is simply a ‘spontaneously’ generated creature whose form is imposed in the wrong sort of material --stone, say, rather than pliable mud-- and so is unable to live and move as an animal does, even if it partakes of an animal form.
This cosmic force is also a commonplace in the Platonic tradition, extending from Marsilio Ficino in the 15th century to Cambridge Platonist figures such as Henry More in the 17th century. Ficino asks rhetorically: “From the beginning of any thing that is to be generated, do not celestial influences bestow wonderful gifts in the concoction of the matter and its final coming together?” Spontaneous generation, then, is nothing other than what occurs when the rays of the heavens concoct suitably disposed matter into complex organisms. Thus Ficino goes on to ask: “Do not innumerable frogs and similar animals often, when the face of the heavens favors it, leap forth out of the sand in a moment? Such is the power of the heavens in well-disposed material.” Ficino goes on to adduce a number of other earthly phenomena involving the influence of power of vision and imagination in order to make the case that, a fortiori, celestial rays have the power to influence the form of earthly things.
I pass over fascinations achieved by a sudden glance and very passionate loves instantly kindled by rays from the eyes… Nor will I mention how quickly an inflamed eye afflicts whoever looks at it and how a menstruous woman affects a mirror by looking in it… What can a mad dog accomplish even without an apparent bite?… In the light of all this, are you going to deny that the celestials with the rays of their eyes with which they both look at us and touch us, achieve wonders in an instant? But now a pregnant woman instantly by touch stamps a bodily part of the person who is about to be born with a mark of something she desires. Are you then going to doubt nevertheless that rays touching in this way or that accomplish diverse things?
Ficino maintains that “the immense size, power, and motion of celestial things brings it about that all the rays of all the stars penetrate in a moment the mass of the earth.” These rays penetrate to the center of the earth. “By the rays’ intensity, the material of the earth there --being dry and far from any moisture-- is immediately kindled and once kindled, is vaporized and dispersed through channels in all directions and blows out both flame and sulfur.” He describes this fire as “very dark,” and “like a flame without light,” using the same vivid phrase that Descartes would later echo in describing the ‘fire’ that burns in the heart at the moment the fetus is quickened. Ficino continues: “Finally, diverse powers come into being in the combinations of rays with each other of one sort or another, here and there… instantly with an emission of rays forces are imprinted in images, and divers forces from a different emission.”
This account of celestial influence is echoed in the 17th century by the Cambridge Platonist Henry More. In The Immortality of the Soul More maintains that the sun and the stars are the most “Intellectual Beings in the world,” and that these have
filled the whole Earth with vital Motion, raising innumerable sorts of Flowers, Herbs and Trees out of the ground. These have also generated the several Kinds of living Creatures. These have filled the Seas with Fishes, the Fields with Beasts, and the Aire with Fowles; the Terrestrial matter being as easily formed into the living shapes of these several Animals by the powerful impress of the Imagination of the Sun and Stars, as the Embryo in the womb is marked by the strong fancy of his Mother that bears him.”
In the same work More argues for a sympathy between earthly and astral bodies as a consequence of their mutual subjection to the “Spirit of Nature.” The universal spirit, More maintains, “is ready to change his own Activity and the yielding Matter into any mode and shape indifferently as the occasion engages him, and so to prepare an edifice, at least the more rude strokes and delineaments thereof, for any Specifick Soul whatsoever, and in any place where the Matter will yield to his operations.”
This mode of generation, again, is not properly speaking ‘spontaneous’ at all, to the extent that the heavens very literally function as the father, imposing form upon suitably receptive matter. The theory of spontaneous generation as imposition of form from without seems to meet its demise at precisely the same time that the theory of sexual generation transforms from one of imposition of form by a paternal agent, into either a purely thermomechanical process (Descartes) or the triggering of some primordium (Harvey and later both the ovist and the spermist preformationists). In other words the generation of frogs from cosmic rays falls out of favor not because it is preposterous, but because the rays had been thought to play a role too analogous to the formal, active principle once attributed to semen but increasingly seen as superfluous. Non-sexual generation, then, was prior to mechanism never conceived as strictly spontaneous; and, conversely, mechanist sexual generation is conceived as spontaneous in at least one important respect. With the rise of mechanism, spontaneous generation comes to be seen for the most part as heterogenesis, purely a consequence of putrefaction: here, new organisms are not developed out of previously formless matter, but are rather merely the by-products of the decay --that is, the loss of functional unity once explained by the inherence of a form-- of dead organisms.
4. Heterogenesis and the Descent of Kinds
“Every living thing,” Athanasius Kircher writes vividly in his Scrutinium pestis of 1658:
produces from its own decay some congruous animal and different from all others. This we have proved by actual experiment for species of different herbs, and it is true for grain quickened into winged worms. It is just as certain among animals whether highly organized or simple. A dead and rotting ox is quickened into bees… Horses living and dead produce wasps and beetles which for food then suck the blood of the animals that gave them life, to their great annoyance. Human beings (as well as some Bruta) generate bedbugs, lice and fleas, which are thus as intimate companions provided by nature to draw off corrupted blood. A dead body, foul with decay, becomes a nursery for worms. Remains of insects, when they rot, produce animals of a similar nature.
Emphasis such as Kircher’s, on heterogenesis as opposed to cosmically induced emergence of form in suitable matter, we might suggest, is largely the result of two distinct developments in the early modern period. The first of these was the invention of the microscope and the consequent awareness of the ubiquity of organic life. This discovery had an important influence on the way people thought about the question concerning the ultimate starting point of generation, and indeed seems to have motivated some to rethink the scope of the predicate ‘living’ in nature: after the discovery of microorganisms in mud, pond-scum, food, blood, and perhaps most significantly, semen, it easily began to appear that any new spontaneously generated creature could only be generated from another creature or from its remains. The second factor, alluded to briefly above, was that the emphasis on generation as the imposition of form --whether from a father or from the heavens-- on previously formless matter, came to be downplayed, as microscopic observation revealed that what looks formless to the unaided eye often has an intricate structure, a partedness where earlier only homogeneity was perceptible. When this change occurs, there is correspondingly less emphasis (Henry More and a few others aside) on spontaneous generation as cosmic agency, and a new understanding of it as the coming-to-the-fore of some clump of putrescent waste that was previously a subordinate part of some now perished organism.
One important factor in the new conception of spontaneous generation we’ve described was the rise of microscopic technology. Another important factor was skeptical libertinism, which flirted with precisely that possibility that Hull claims Aristotle should have guarded against, namely, that biological kinds have earthly, rather than divine, origins, and that the multifarious life-forms we see around us are but the result of chance. In the 16th century, Girolamo Cardano and Julius Scaliger both entertained the possibility that the corpses of large animals could produce new, perfect animals, perhaps even human beings. In the following century, many would be inspired by the discovery of microorganisms to identify a wide variety of microscopic changes as instances of heterogenesis. Thus Leibniz writes in 1669 to his mentor Jakob Thomasius “that iron rust is a minute forest which has sprung up; to rust is therefore an alteration of iron but a generation of little bushes.” Whether some natural change is alteration or generation, in other words, is a matter of perspective. Some decades later, Margaret Cavendish explains that the ‘generation’ of certain organisms may be accounted for entirely as an alteration in their source material:
I have mentioned in my Philosophical Letters that no animal creature can be produced by the way of metamorphosing, which is a change of motions in the same parts of matter; but (as I do also express in the same place) I mean such animals which are produced one from another, and where the production of one is not caused by the destruction of the other; such creatures, I say, it is impossible should be produced by a bare metamorphosis, without transmigration or translation of parts from the generator: but such insects, as maggots, and several other sorts of worms and flies, and the like, which have no generator of their own kind, but are bred out of cheese, earth and dung, etc. their productions is only by the way of metamorphosing, and not translation of parts.
Heterogenesis would seem to provide a sufficient reason why it is only smaller organisms that arise in such a fashion: since corruption involves disintegration into smaller component parts, any organism that is generated from the corruption of another organism will be smaller than its source. But not all putrescent matter can be traced to one deceased organism: bogs and swamps are often just plain putrid, but not because some particular creature or other crawled in and died. Because there is no upper limit to how much putrescent matter could collect in a bog or mudbank, it was presumed by some that the upper boundary for the size, if not the nobility, of a spontaneously generated organism was set largely by environmental circumstances, in particular, by the extent of the concentration of putrescent matter, on the one hand, and the heat of the sun causing it to transform into new life-forms on the other. Repeating a prejudice that goes back at least to Herodotus, many early moderns presumed that the environmental circumstances ideal for the spontaneous generation of large animals, as well as of new animal kinds, were most likely to obtain in Africa.
At the same time as theories of spontaneous generation were transformed from accounts of the imposition of form by cosmic forces onto terrestrial matter, into theories of heterogenesis as a by-product of decay, these theories became elided in certain libertine circles with theories of natural, as opposed to supernatural, origins of species, including the origins of humans. According to the historian Giuliano Gliozzi in his monumental study of early modern theories of racial difference, the majority of defenders of human spontaneous generation in the 16th century were Paduans heavily immersed in Aristotelian biology. Among the more prominent and controversial of these was Giulio Cesare Vanini, whom Gliozzi sees as “connecting the polygeneticism expressed in 16th-century naturalism with the version that would take on new forms in the milieux of French libertinism in the first half of the 17th.” Polygeneticism, the view that different human racial groups had distinct origins, implied in most of its variations, a commitment to the natural origins of at least some human groups, since the only divine creation was the one described in Genesis. In other words, Jews and Christians were created, but heathens congealed out of mud, or emerged as a by-product of putrescence. This is a moderate view by at least one measure: it saves human beings, properly speaking, from terrestrial as opposed to supernatural origins, but restricts the class of human beings to a much smaller group than the missionaries and their colonialist backers would have liked.
In one dialogue, Vanini has the character ‘Julius Caesar’ report the opinion of Diodorus of Sicily, according to whom “the first man was born by chance from the mud of the earth.” Even though Vanini uses narrative distancing techniques to appear as though he is not asserting the view himself, it is nonetheless something he is intent on inserting into the legitimate debate. Julius Caesar responds to the objection, that we only ever see small animals such as frogs and mice arising spontaneously, that this is more a question of the quantity of putrid matter available for the generation than any inherent limitation on what may be produced in this way. He cites in corroboration of this yet another variation on the adage, Ex Africa semper aliquid novi, suggesting that in the Nile there are mudbanks sufficiently large to produce “enormous animals” when heated by the sun. He proposes, again through Julius Caesar, that “the first man was generated by the corruption of apes, pigs, and frogs,” since there is a great resemblance between these species “as concerns their flesh and their customs. Subsequently, he modifies this view to suggest that perhaps it is only the Ethiopians who are descended from apes, since they have, so he thinks, a similar pigmentation. The manifest racism of this suggestion should not prevent us from discerning its true motivation, namely, to adopt a compromise position between the truly blasphemous view that all human beings, including Christian Europeans, arose by chance, and the view that all human beings, notwithstanding racial diversity, are the descendents of Adam.
Vanini’s rather cryptic view seems to be that animals are generated from the decaying matter of other animals which are like their ‘offspring’ in some respects, but not members of the same species. In this respect, his heterogenesis is at the same time an account of the descent of life-forms. The rotting organic matter that was a monkey can give rise to a man in virtue of the shared properties of both species. Vanini never spells out what he takes the different lines of descent to be, but he at least reveals the interconnection of the possibility of creatures arising from earth or slime, on the one hand, and of creatures sharing lines of descent on the other: if a creature can emerge de novo from rotting matter without being the result of some ‘conception’ either heavenly or seminal, then effectively supernatural creation is disproved repeatedly all over the world at every moment.
Vanini is not the only libertine to discern the connection between spontaneous generation, on the one hand, and natural origins for humanity on the other. Some, such as François de la Mothe le Vayer, believe that it is only by appeal to spontaneous generation that we can explain the variety of humanlike, yet evidently soulless, creatures thought to dwell at the edges of the known world. As he writes, “nature is capable of producing on her own --without man’s falling into execrable bestiality-- animals that resemble us to such an extent that they force us to say that sometimes there is a greater difference from one man to another than between us and them.” La Mothe le Vayer claims that this is not so hard to conceive if we are willing to draw on the authority of many ancient and medieval authorities, among them Plato, Aristotle, Epicurus, Lucretius, and Avicenna, who all acknowledged that “the Earth had [earlier] produced us from herself as [she does] the animals. La Mothe le Vayer does not simply repeat the heterogenetic theory of the 16th-century naturalists, but instead offers a developmental account according to which “men did not come into being originally in the perfect state in which we see them.
5. Mechanical Embryogenesis as Spontaneous
We have seen that in the early modern period, spontaneous generation ceases to be conceived so much as the imposition of form by the heavens upon suitably receptive terrestrial matter, and instead comes to be thought of as a chance consequence, or what we might call a by-product, of putrefaction, and that it came to be emphasized by those wishing to promote the possibility of the natural origins of biological kinds, in contrast with their heavenly creation ex nihilo. Interestingly, though, a very similar reconceptualization of sexual generation took place simultaneously: for what is Descartes’ account of embryogenesis but an effort to explain how, through a series of mechanical causes, homogeneous fluids can clot and grow, separate out into specialized organs, and, in the end, become an animal? Indeed, Descartes thinks this is the most fitting way to both vindicate God from responsibility for abnormal births, as well as to properly exalt God by attributing to him the wisdom to make all phenomena flow from just a few eternal laws of nature. Thus he summarizes his approach to embryology in the Primae cogitationes as follows:
I expect some will say disdainfully that it is ridiculous to attribute such an important phenomenon as human procreation to such minor causes. But what greater causes could be required than the eternal laws of nature? Do we need the direct intervention of a mind? What mind? God himself? Why then are monsters born?
That this is what Descartes wished to do is well known. What has been less noted in recent scholarship is that this effort was perceived by many to reduce sexually generated species to the ontologically sketchy level many were happy to allow barnacles and mice to live at, that is, Cartesian embryogenesis effectively makes all biological kinds the product of minor causes, and in so doing puts species into something of a crisis. This much is recognized quickly by Malebranche, who notes that while Descartes might be able to account for the formation of organs in general,
nevertheless, it seems to me that… women and animals could not easily bring forth young of the same species. For although one can give some explanation of the formation of the fetus in general, as Descartes has tried successfully enough, nevertheless it is very difficult… to explain why a mare does not give birth to a calf, or a chicken lay an egg containing a partridge or some bird of a new species.
Leibniz, shortly after, praises Leeuwenhoek’s discovery of spermatozoa, and his theory that the preexisting creature is hosted by this little ‘worm’, on the grounds that the Dutch microscopist had restored dignity to men, against those earlier thinkers --i.e., the mechanist embryologists-- who had said that the father ‘does nothing more than the rain’. For Leibniz, to accept mechanical epigenesis, as opposed to his own favored spermist preformationism, is really no different than accepting Vanini’s view that animals can emerge from suitable matter given the right environmental and meteorological circumstances. Even if this could happen, there would seem to be no sufficient reason why like regularly begets like: where there is a possibility of new organisms emerging from non-living matter as a result of a thermomechanical process, then organic life forms can no longer be seen as the products of the kind-preserving transmission of an immaterial species essence from generation to generation.
To make matters worse, it is not only not clear why, for a mechanist, there should be species, but also why, within a species, there should be two different sexes. In this connection, Catherine Wilson has noted that if there is no longer a matter-form dichotomy onto which the male-female one may be mapped, then why is there not simply universal parthenogenesis instead of distinctly sexual reproduction? How do we explain sexual dimorphism within the context of mechanism? For a hylomorphist, one sex is responsible for the form of offspring and the other provides its matter. But within the context of mechanism, it is not clear why God could not have arranged for either epigenesis or preformation in one basic kind of body.
In sum, it is Descartes, and not Aristotle, who ought to be at least a bit concerned about the problem Hull pointed out, and not just with respect to spontaneously generated creatures, but to the sexually generated ones as well. For if he were to take the problem of species on, Descartes could only have concluded, with Darwin, that their origins are as ‘minor’ as the origins of each individual organism. Aristotle had a satisfactory way of explaining a wide range of natural phenomena: all natural things are a combination of matter and form; there are all sorts of ways some particular form can come to inhere in some suitably receptive matter, among these sexual generation, solar concoction, etc. Form always separates itself from matter to the extent possible, in imitation of the purely formal divine, and thus the more noble organisms --those capable of reuniting through self-motion to copulate when necessary-- will be separated out into male and female. But with the matter-form metaphysics gone, there is no clear reason why, for Descartes, there is either dimorphism in sexually generating species, or regular species reproduction --what in the old days could have been described as formal replication-- among the males and females of a species. Before Descartes, a Scholastic Aristotelian could have argued in one of two ways: either that eels and barnacles are mere rearrangements of matter that do not require any transmission of form, and that these thus differ fundamentally from horses and men, whose generation is also always reproduction; or that eels and barnacles are generated through the transmission of form by way of astral influx. But Descartes could take neither of these tacks to account for eels and barnacles, let alone for horses and men. The generation of any creature is only by ‘minor causes’, without any transmission of form.
6. Conclusion
Why is the prospect of generation by minor causes troubling? Darwin himself diagnoses the problem insightfully when he notes in his The Descent of Man that “[t]he birth both of the species and of the individual are equally parts of that grand sequence of events, which our minds refuse to accept as the result of blind chance.” Aristotle was untroubled in this regard, since for him in any case species of either spontaneously or sexually generated creatures are not supernaturally reified eternal kinds, but rather morphological regularities emerging in response to environmental ones. Eternal species reification begins with the exigencies scripture imposes upon the speculative science of origins, and is consolidated by the new ‘applied metaphysics’ of principally botanical taxonomy beginning in the 16th century. Even on the fixist account of species, however, ‘spontaneous’ generation does not necessarily constitute a rupture in the order of nature, since, as theories of cosmic influx show, there is an available account of non-sexual generation in terms of the communication of form by an agent-- just not a biological agent. The real rupture comes with mechanist embryology, which deprives all instances of generation, sexual as well as spontaneous, of any teleological explanation, and strongly militates towards the view that all individual creatures, human as well as animal, have natural as opposed to supernatural origins. And as Darwin observes, once natural origins are admitted for individual generations, creationism loses its footing and it becomes possible to think of entire species as having natural origins. Such a possibility seems to be what was in fact behind the heterogenetic theories of megafauna origins among early modern libertines such as Vanini and La Mothe le Vayer: their aim was not first and foremost to promote a racist account of the origins of non-Europeans, nor were they simply lapsing into fantasy by vouching for a natural phenomenon they had clearly never seen. Rather, with the conceptual resources available to them, they sought to introduce a naturalistic alternative to the supernatural species origins dictated by Genesis. The fact that that spontaneous generation played such an important role in this shift, from supernaturalism to naturalism, should compel us to re-think the relationship in history between the problem of the generation of living things, on the one hand, and, on the other, that of the origins of living kinds.
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