Blumenbach and the Epistemology of the Bildungstrieb

Johann Friedrich Blumenbach (1752–1840) introduces the concept of Bildungstrieb (formative drive) in a continually revised short work, first published in 1780.¹ He intends the formative drive to solve the problem of generation, demonstrating once and for all that his theory of epigenesis (and not the competing theory of preformation) is the true representation of organic development. Yet, the success of his theory is by no means unequivocal. The epistemological survey that follows investigates the merits, evidence, and strategy of the Bildungstrieb and Blumenbach’s scientific practice more generally. He himself confesses that he has only recently abandoned preformation theory in favor of epigenesis, and his narrative of conversion grants us insight into the reasons for his theory change. In the first section, we find that Blumenbach’s stated reasons are, in fact, insufficient for decisively overturning preformation theory in favor of epigenesis. That nothing in Blumenbach’s own account would have swayed the already committed adherent of preformation is not due to any fatal flaw in his argument, but rather because he does not introduce anything for which a canned response was not already available. Supporters of preformation had heard his critiques before and were armed to the teeth with rejoinders.

Nevertheless, his Bildungstrieb essay is not without innovation. It does not occur, however, where one might expect, that is, vis-à-vis the tenets of the formative drive itself, but rather with respect to Blumenbach’s methodology. In the second section, we find that his introduction of a simplicity criterion responds effectively to the stalemate in the debate over generation at the time and even anticipates practices in modern biology.²

Despite these innovations and other advances Blumenbach made in the life sciences, his mature formulation of the Bildungstrieb chastens its epistemic reach. While the naturalist can learn the laws of living nature by observing the effects of the Bildungstrieb, he is forever barred from knowing the cause of it. Although there is precedence in eighteenth-century science for Blumenbach’s epistemological modesty, which we review in the final section, he never explains why life as such must be inexplicable, why knowledge of it must lay beyond the mind’s reach.

We do know that the frustration of having only limited answers to the most basic questions about living beings was not lost on Blumenbach. He expresses his own frustration with the lack of progress made in the problem of generation, remarking that already in the seventeenth century Charles Drelincourt, Herman Boerhaave’s teacher, had gathered together 262 “groundless” hypotheses on generation from his predecessors, and Blumenbach adds “nothing is more certain than that [Drelincourt’s] own system amounts to the 263^rd(1789b, 5). Blumenbach adds that the lingering obscurity of this question is all the more embarrassing, since it is one that must have already preoccupied our first parents (6). Deep-seated, then, is the desire to know life, and as flawed as the formative drive may be, it represents one of the best efforts in the late eighteenth century to come to terms with this desire.

From Preformation to Epigenesis: Blumenbach’s Theory Conversion

Although in Über den Bildungstrieb, Blumenbach asserts what came to be recognized as the paradigmatic theory of epigenesis, he had not always been a proponent of that theory. He confesses that just a short time ago he had endorsed preformation, even teaching it and defending it in his writings (1789b, 19). He now wonders how he and others could ever have accepted a theory that retrospectively seems so lacking in evidence. But the wisdom that comes with hindsight is not always forthcoming, and as a result Blumenbach has the opportunity in the first section of his essay to recount the moment of his conversion from preformation to epigenesis.

He recounts taking a walk while on holiday in the country when he happened to find a polyp (now known as Hydra) in a nearby stream. With the intention of amusing his friends with the “wonders” of this animal, Blumenbach takes the creature back to the house to conduct the regenerative experiments already notorious at that time. Fortunate circumstances allowed these experiments to continue over three days, so that he and his friends could observe the regeneration of the polyp, its severed parts becoming so many new polyps as if it were occurring right before their eyes (1789, 21). This result—because he had done the experiments so many times before—was entirely expected. In fact, at the time, he performed the experiments to demonstrate the truth of preformation theory and “den Ungrund der allmäligen Bildung” (20; the baselessness of gradual formation [epigenesis]). Yet, the experiment yielded an unexpected result: the regenerated polyps and their arms were of a much smaller size, even though the creatures had been given ample food. This meant that the new limbs and body could not be the result of an aggregation of matter that merely filled in another preformed germ, because the new limbs were smaller than they had previously been, which could only be the case if they had been gradually formed entirely anew. On his return to the city after the holiday, another fortuitous event allowed Blumenbach to bring the strange case into connection with another. He was called upon as a practicing physician to attend to a patient that was suffering from a deep caries in his femur, just above the knee. Blumenbach observed that as the patient healed and the scar formed over the previous wound that the new or regenerated skin exhibited a shallow but perceptible depression, leading him to remark that this case was, mutatis mutandis, the same as with the polyp (1789b, 23). These two diminutions establish the turning point for Blumenbach: he can no longer uphold a theory of preformation, but must, instead, adopt a theory of epigenesis.³

We can already see why these cases would have deeply complicated the theory of preformation. In general, the polyp’s reproductive power immediately created a problem for the theory when it was first discovered in the 1740s; it even caused preformation’s leading representative, Albrecht von Haller, to briefly reject the theory. Yet, with time, he and other preformationists had been able to adapt to this new phenomenon and present explanations of regeneration that were convincing enough to garner and sustain support for their theory. Though the small polyp had threatened preformation theory, its supporters were not, in the end, defeated by it; however, this new, strangely smaller polyp noticed by Blumenbach had managed to push him over the edge. There did not seem to be any way to account for the diminished size of its regenerated body or parts if one supposed the existence of preformed germs. How could these germs anticipate or respond to the polyp’s accidental severance of limbs or the healed flesh in the caries? This regenerative (or reproductive) capability of living beings, that is, their responsive adaptation to the contingencies of nature, did not seem to be assimilable by preformation theory in any possible guise.⁴ It appears, in fact, wholly anathema to that theory’s essential foundation.

In addition to his personally transformative experiments on the polyp, Blumenbach provides an expansive criticism of preformation in his text in an attempt to discredit preformation beyond any possible doubt. He divides the theory into three versions: ancient Greek (a position represented by Heraclitus and Hippocrates in which germs are strewn about the earth to wander in search of fitting genitals where they can take hold and develop), spermist, and ovist preformation (in weak and strong versions). Although arguments are given against each of these, only the last one—the strong ovist position as advanced by Haller—is considered by Blumenbach to be a true contender for solving the problem of generation. To this version, then, he devotes the bulk of his critical attention.

Blumenbach identifies a lecture delivered by Haller to the Königlichen Societät der Wissenschaften zu Göttingen in May 1758 as containing the “argumentum crucis” for preformation(1789b, 35). It runs as follows: 1. It can be observed that the membrane and blood vessels of a chick embryo are a continuation of the membrane and blood vessels of a yolk in an incubated egg. 2. The yolk, however, is in the hen prior to impregnation. 3. Therefore, the chick embryo, although too small to see, most likely exists prior to impregnation (1789b, 35–7). Because of the continuity of the parts between the yolk and embryo, one can infer the preexistence of the chick. Blumenbach emphasizes “most likely” to highlight the fact that Haller, at least in the initial presentation of his findings, himself remained cautious about his conclusions. It was only with the often overzealous naturalist Charles Bonnet’s declaration of the argument’s infallibility that Haller’s finding achieved the status of the preeminent argument in support of preformation. So much so, in fact, that Haller himself also began to see it as such, relinquishing his earlier caution for a forthright acceptance of the argument’s truth. The preformation community in general thus came to adopt this argument as the best proof of its position. If Blumenbach intended to contradict the most widely held and strongest version of preformation possible, this continuity thesis would have to be his target.

His initial criticism of it rests on the basis that its essential evidence is indeterminate at best. Granting the most scrupulous investigation of the fertilized egg, Blumenbach contends that it remains impossible to determine with any certainty whether the situation is as Haller claims. Yet, even if one grants the continuity of the membrane and vessels between the yolk and chick as Haller maintains, Blumenbach argues that preformation does not necessarily follow because continuity does not imply co-existence, a point for which he adduces two counterexamples (the continuity but non-coexistence of the gall wasp and tree and the formation of new membranes in the animal in response to accidental inflammation). Finally, he closes his criticism of the continuity thesis by showing its inconsistency with another of Haller’s views, in which the latter asserts that the human fetus adheres to the uterus through the formation of new vessels and membranes; that is, they become continuous even though they are admittedly not co-existent.

Blumenbach devotes the remainder of the second section to discrediting other, lesser forms of support for ovist preformation that mainly consist of anecdotal evidence. For example, he relates the case, which had been recorded in the log of the Imperial Academy of Natural Research, where a miller’s wife had been reported to have delivered a daughter with an engorged stomach. The baby suffered so immensely over the next eight days that most of those present thought she was surely to die. Yet, in the meantime this sick baby gave birth to another baby that was, according to another report of the case, “the size of the middle finger” (1789b, 51–2). This case, incredible as it might appear, seems less so if one accepts the theory of preformation and, in fact, then appears to be evidence of it. For this reason, Haller included the case among his evidence for preformation.

Blumenbach, however, thought it all too easy to meet such cases with more cases(1789b, 54, 57). In response to the miller’s wife’s baby’s baby case, he cites one from the Philosophical Transactions of London, where a report is given of a male greyhound that gave birth to a puppy every year. This example is not supposed to prove the truth of epigenesis, but, in fact, of spermist preformation. But why would Blumenbach, supporter of epigenesis, furnish evidence for any version of preformation, the opposing theory? His aim in this passage is not to challenge preformation per se, but rather a type of evidence its supporters use to defend it. To demonstrate the absurdity of their approach, he matches every ovist case with a spermist one, showing that these types of cases prove both versions of preformation equally well. Hence, even though they are published in the reputable journals of the day and vouched for by authorities like natural historians and physicians, these cases are ultimately unconvincing because they prove contradictory views of preformation. This contradiction, Blumenbach thinks, does not refute preformation theory, but rather discredits the use of this type of case altogether. In this instance, then, he is not rebuking preformation as a bad theory, but rather its supporters as practicing bad science.

The failure of preformation theory and the methods used by its supporters leads Blumenbach to conclude, “Keine präformierten Keime präexistiren” (1789b, 24–5; no preformed germs preexist [emphasis in original]). He continues:

In dem vorher rohen ungebildeten Zeugungsstoff der organisierten Körper nachdem er zu seiner Reife und an den Ort seiner Bestimmung gelangt ist, ein besonderer, dann lebenslang tätiger Trieb rege wird, ihre bestimmte Gestalt anfangs anzunehmen, dann lebenslang zu erhalten, und wenn sie ja etwa verstümmelt worden, wo möglich wieder herzustellen.

Ein Trieb, der folglich zu den Lebenskräften gehört, der aber eben so deutlich von den übrigen Arten der Lebenskraft der organisierten Körper (der Kontraktilität, Irritabilität, Sensibilität etc.) als von den allgemeinen physischen Kräften der Körper überhaupt, verschieden ist; der die erst wichtigste Kraft zu aller Zeugung, Ernährung, und Reproduktion zu sein scheint, und den man um ihn von andern Lebenskräften zu unterscheiden, mit dem Namen des Bildungstriebes (nisus formativus) bezeichnen kann. (ibid.)⁵

[In the previously raw unformed generative matter of organized bodies, after the matter has reached maturation and the position of its determination, a particular drive that is operative throughout life becomes active, by which organized bodies receive their determinate form in the beginning, then maintain it throughout life, and, where possible, reproduce it if they somehow become mutilated.

A drive that consequently belongs to the vital forces, but that is just as clearly different from the other kinds of vital force of organized bodies (contractibility, irritability, sensibility, etc.) as from the universal physical forces of the body in general; it appears to be the first, most important force for all generation, nutrition, and reproduction, and can be designated with the name of formative drive (nisus formativus), in order to differentiate it from other vital forces.]

These remarks introduce the Bildungstrieb (formative drive). It is responsible for giving and preserving the form that organized bodies have while alive as well as restoring that form when damaged. In this respect, it is essentially operative in the processes of generation, nutrition, and reproduction, processes that correspond to those just named, that is, the initial determination, subsequent maintenance, and continuous restoration of organic form. It shapes living beings into what they are and what they will be, and reproduces that form when it is mutilated. Although Blumenbach associates it with the other Lebenskräften (vital forces), he intends the formative drive to be considered as distinct from them as well as from physical forces in general. He emphasizes this by using the term “Trieb” (drive, impulse), rather than “Kraft” (force, power), in coining the term “Bildungstrieb.”

The reason that the formative drive is not assimilable to physical forces becomes clear when Blumenbach provides a fuller explanation of the drive in the essay’s third section. He argues that a great divide separates the organic world from the inorganic one and the formative drive only belongs to the former. In identifying this divide, he rejects the thesis of a “great chain of being” in which a gradual ascent is observable throughout all of nature, living and nonliving alike (see Lovejoy 2001). The organic and inorganic are not linked in a continuum, but separated by a gulf. At the same time, though, he admits that an understanding of the inorganic world will undoubtedly help one to understand the organic one and vice versa. To illustrate this claim, he says the existence of the formative drive is confirmed by the fact that a trace of it exists as formative force in the inorganic world, manifest in the regular and invariable forms taken by inorganic bodies like in the process of crystallization (1789b, 72–3).

Part of Blumenbach’s insistence on the difference of force and drive stems from a desire to distinguish his theory from the vis essentialis (essential force) of Caspar Friedrich Wolff, since some readers might have been inclined to conflate them. According to Blumenbach, Wolff’s vis essentialis, as the name suggests, acts like a force—one that is primarily responsible for the distribution of nourishment in the plant or animal—and thus acts uniformly throughout the body.⁶ Hence, it must act uniformly in the most abnormal growths of plants and trees where any principle of regular formation seems to be wholly lacking; and yet, even when the force is weakened in a malnourished organized body, that body will continue to exhibit regular formation (1789b, 29–32). Therefore, Blumenbach thinks the vis essentialis is not capable of doing what Wolff intended, that is, explain the progressive formation of organized beings by epigenesis. It fails in this regard because the needed connection between formation and the intensity of the force does not exist, resulting in the conclusion that the vis essentialis is not essential to generation. While it plays a part in formation through the distribution of nutriments and other vital functions, it cannot be the principle of formation itself, as Wolff intended.⁷

Conversely, the formative drive is just this principle. In the third section, Blumenbach returns to the conversional experiment he described in the first section (1789b, 84–5). The diminished size of the first mutilated and then restored polyp can be explained if one supposes that the creature, in losing its arm, also loses part of its formative drive. This explanation implies that while the formative drive is not determined by the body’s matter, it does require this matter for its existence and energy. It depends on matter, but is not determined by it. Therefore, because the drive has been diminished, one must also suspect that the reproduced part would also be similarly diminished—but, importantly, reduced only in size, not in form. Moreover, Blumenbach does not think that this reconstitution can be explained solely through a mechanical aggregation of new matter that has been nutritionally gleaned because in its injured state the polyp does not consume as much as it normally would and certainly not enough to account for the restored limb. Its nutritional input is less than, and hence not equal to, the regenerated parts. Therefore, Blumenbach concludes, the matter for the regeneration must be taken from some other part of the animal and then reconfigured into a consequently diminished limb or body.⁸ This process is inexplicable according to a simple force like Wolff’s vis essentialis because it requires the ability to repurpose existing matter for ends entirely different from those for which it was first formed.⁹

In addition to indicating the inadequacies of a force to explain the diminished state of the polyp, Blumenbach also anticipated the counterargument that proponents of preformation would likely make(1789b, 85–9). It goes as follows: in each part of the polyp, there exist innumerable germs in a dormant state that will remain so until the naturalist makes this or that cut, rousing the germ into growth. Although Blumenbach finds this hypothesis dubious, he performs two experiments meant to confound it. First, he describes an experiment in which half a brown polyp is fused together with half a green one, forming a mixture of the two. Second, he recounts an experiment where the polyp is not dismembered, but rather only cut across its body. In this case, the polyp does not generate any new limbs, but is still restored to its original state. Preformation theory cannot account for these cases because it cannot explain how a preformed germ allows for the bicolored-fused polyp or its much greater regenerative power (relative to other animals). Blumenbach’s reliance on these further experiments is necessary, for without them, he appears to remain in an identical position as the preformationist: he has postulated a principle of generation that is, just like the preformed germ, unobservable. Although the formative drive avoids the pitfalls of preformation in accounting for the polyp’s regenerative power, its existence continues to be precarious, since the observer only has access to its effects, but never to the drive itself. We will return to this point below.

Blumenbach supplements his theory and foregoing criticisms by invoking several more problems that discredit preformation: he recalls the difficulty the theory has in explaining the accidental origin and growth of preternatural parts; that is, living beings can adapt responsively to ectopic pregnancies, hydrocephalus, broken bones, and so forth. Preformation is not capable of explaining this adaptability. He also refers to the problem of hybridity with respect to the mule and Kölreuter’s then-recent work on the tobacco plant, for, again, the preformed germ does not seem capable of anticipating or producing such mixtures.¹⁰ Yet, as Blumenbach himself acknowledges, even if he does not find them convincing, preformation theorists were already outfitted with solutions to all these kinds of problems. These challenges were nothing new, and hence they alone could not be expected to overturn the theory’s longstanding support.

Blumenbach also adduces the “consistently confirmed experience” that even to the “most-armed [bewaffnetesten] eye” no trace of the developing living being can be seen until a relatively long time after fertilization(1789b, 58). Because no trace of it can be observed, he argues that there cannot be any preformed germ, since it would have been visible. Yet, one might ask whether this observation advances at all over those anecdotes decried by Blumenbach above, in which the preformationist claimed to have witnessed this or that case in support of his theory, given that Blumenbach’s justification—that his experience differs by being “consistently confirmed” by any unprejudiced observer—could have been equally employed by the preformationist. Moreover, is not Blumenbach guilty of the old aphorism that the “absence of evidence is not evidence of absence” inasmuch as he claims that no trace of a living being exists for such and such a period of time? The proponent of preformation would undoubtedly counter that the initial unobservability of the preformed embryo is not proof of its nonexistence, but only of its minute size and consequent invisibility. Blumenbach’s experience would then seem to be acceptable only to those who were already convinced of the inadequacies of preformation. Although Blumenbach rightfully challenged the use of spurious cases to defend preformationism and undermined Haller’s argumentum crucis, has he yet provided any criticism that would have been absolutely devastating to the theory? Has he provided anything to prevent recourse to the defense that the preformed germs are always, already present—but just too small to see?

In fact, if we return to Blumenbach’s doctor-on-holiday narrative, we may ask whether a strong enough impetus exists within it to elicit his conversion. Although the narrative of the doctor on holiday who happens to observe this peculiar characteristic of the notorious polyp, which had somehow escaped the notice of other naturalists, is quite compelling, and even more so when it is connected shortly afterward with the case of the patient suffering from a caries in his femur, we might ask whether these events are really enough to explain Blumenbach’s conversion. That is, there are two questions. First, has Blumenbach decisively refuted preformation? And, in particular, has he conclusively dealt with the seemingly unassailable strategy of preformation to appeal to an ever smaller and always invisible preformed germ? Second, even if he has refuted preformation, has Blumenbach proved the truth of epigenesis? Although Blumenbach might have been converted through his experiments on the polyp as detailed in his narrative, these experiments alone offer no clear advance over the counterexamples and criticisms of preformation; he has not yet sunk the invisible preformed germ, and the truth of epigenesis remains outstanding. To the contrary, though, Blumenbach’s introduction of Conferva fontinalis in the 1781 edition of his essay solves these difficulties. Whereas many of the examples above had problematized preformation through examples of extraordinary generation (for example, the regenerative capacity in the polyp) or through exhibiting regularity under irregular conditions (for example, hybrids and monsters), the virtue of C. fontinalis lay in its utter simplicity.

Conferva fontinalis and the Simplicity Criterion

Nothing could make the existence and activity of the formative drive clearer to the impartial eye, Blumenbach proposes, than an organized body that grows and reproduces quickly as well as having a structure that is semi-transparent (1789b, 74–5).¹¹ How this is the case becomes clear in his example of C. fontinalis.¹² He writes:

Ein Beispiel der Art aus dem Gewächsreiche gibt die überaus einfache Fortpflanzungsweise einer eben so einfachen Wasserpflanze, die, zumal im Frühjahr gar häufig am Ausfluss der Röhrenwasser, an Quellen, in Gräben, Teichen etc. zu finden ist, und deren sich auch wohl unbotanische Leser leicht aus der bloßen Beschreibung werden erinnern können. Das ganze Gewächs besteht nämlich aus einem einfachen, (nie geteilten) meist geraden, etwa einen halben Zoll langen, feinen Faden von hellgrüner Farbe, der gewöhnlich mit seinem untern Ende im Schlamme eingewurzelt ist. (1789b, 75–6; my emphasis)

[An example of this kind in the plant kingdom is given in the extremely simple sort of generation of a just as simple water plant, which is frequently found, especially in the springtime, etc., and from whose mere description even the unbotanical reader will be able to be reminded of it. The whole plant is comprised of a simple, (never divided) mostly straight, nearly half-inch long, bright-green fine filament that usually roots itself in the mud with its bottom end.]

In this short passage, Blumenbach employs the adjective “simple” twice to describe the plant itself and once to describe its reproductive process. The alga is essentially a straight line that is internally and externally identical, a fact known because of the plant’s translucency(1789b, 77). These features of the alga—coupled with a quick reproductive cycle (completed in around 48 hours), every stage of which is easily visible—make it exceptionally observable. Whereas the chick embryo, the locus of the debate over generation between Haller and Wolff, has the disadvantage (relative to observation) of beginning not just within an egg, but within an egg within a hen, nothing of C. fontinalis is barred from view. Blumenbach writes, “Auch bei der stärksten Vergrößerung und im hellsten Lichte, ist in der ganzen Pflanze schlechterdings nichts weiter als ein blasiges Gewebe, (beinahe wie ein grüner Gesicht oder Schaum) zu erkennen, das durch eine äußerst feine, kaum merkliche äußere Haut umschlossen wird” (1789b, 77–8; Even under the strongest magnification and in the brightest light, absolutely nothing further is to be found in the whole plant other than a fine, vesicular texture [almost like a green froth or foam], which is enclosed by an extremely fine, hardly noticeable external skin). The charge against Haller’s argumentum crucis, that the continuity argument has indeterminate evidence at best because of the difficulty of observation, is not one that can be brought against Blumenbach’s algae. Importantly, an implication of this structural simplicity is that nothing lays beyond what meets the eye. There is nothing further to be seen here. This means that if preformed germs are not observed during generation, then they cannot be involved in reproduction at all. The plant’s generation must be due to something else: Blumenbach proposes the formative drive.

The choice of this algae vis-à-vis the simplicity criterion is thus an attempt to forestall preformation’s rejoinder that preformed germs are present but unobservable, a claim that remains tenable as long as one can appeal to the germ’s more basic, underlying structure. But if the algae’s most basic structure is already visible on account of the organized being’s simplicity, as Blumenbach insists, then the rejoinder is futile. Algae also benefits the researcher by being attained simply (from ditches, springs, ponds, etc.) and by reproducing over a short time span, so that anyone with a microscope can observe the whole process many times over without a large commitment of time or resources. Although Blumenbach’s choice of algae (he gives the polyp as a correlate in the animal kingdom) might appear as a somewhat obvious strategy to rebut evidence of preformation, selecting a living being because of its simplicity represents a novel approach at the time. It anticipates modern biology’s later use of experimental and model organisms.

While previous naturalists had observed and experimented on a wealth of living beings, the selection of what to observe had not yet been dictated so emphatically by the criterion of simplicity. For instance, Joseph Gottlieb Kölreuter, who performed 65 hybridity experiments in his remarkable Vorläufige Nachricht von einigen das Geschlecht der Pflanzen betreffenden Versuchen und Beobachtungen (1761; Preliminary Report on Some Observations and Experiments Concerning the Sex of Plants), chose different species of tobacco plants(Olby 1966, 21). He was able to cross the different species of tobaccos plants (Nicotiana rustica x Nicotiana paniculata) and obtain hybrids, from which he was able to back cross and obtain a second generation of hybrids. We already saw above that these relatively recent experiments had influenced Blumenbach and that he had mentioned them in his text as part of the evidence against preformation. From the perspective of facility, tobacco was a good choice because it was “easy to grow, easy to castrate and cross, and they set numerous seeds”(Olby 1966, 46). Yet, Kölreuter’s success notwithstanding, the tobacco plant, because of its polyploidy, is a poor choice for the study of hybridity, since he was then not only observing hybridity, but also polyploidy, which resulted, in retrospect, not in the purported hybrid but in a triploid(ibid.). In the end, this confusion prevented Kölreuter from formulating any decisive laws regarding hybridity or explanations of heredity, which had been his intention.

Conversely, Gregor Mendel’s use of Pisum in the next century, since the plant exhibits simple binary traits, is much more conducive to the investigation of hybridity. In his “Versuche über Pflanzen-Hybriden” (1865), after giving his introductory remarks, Mendel devotes the first body section of his essay, “Auswahl der Versuchspflanzen” (Choice of Experimental Plants), to enumerating the reasons for selecting the pea plant for his experiments. He writes, “The value and validity of any experiment is conditioned by the suitability of the means used for it as well as by its expedient implementation. In the present case it also cannot be indifferent, which kinds of plants were chosen as means for the experiments and in which ways they were conducted”(1865, 5). Mendel is exceedingly aware of the importance of choosing Pisum, yet his remark, “it cannot be indifferent,” suggests that this awareness is not something given or obvious. He presents two criteria as guiding his choice of the pea plant: the presentation of constant differentiating characteristics and the plant’s resistance to the influence of foreign pollen. He will also add that the pea plant is easy to grow and that it grows relatively quickly. This last addition resembles Blumenbach’s remarks concerning the advantage of the alga. Mendel’s two initial criteria are also akin to Blumenbach’s insofar as they both revolve around simplicity. That the plant must present constant differentiating characteristics means that they must be simple (not too many) and easy to identify; that it is resistant to the influence of foreign pollen means that its reproductive process is not susceptible to adventitious and contingent factors that would be difficult or impossible to anticipate or recognize. Mendel differs from Blumenbach in placing much more emphasis on consistency. He expected the numerous plants used in various experiments to behave the same way. While Blumenbach also had this expectation, consistency was not as much of an issue, since his experiments did not require a comparison between different species of the genus and the algae did not seem susceptible to contamination. Kölreuter’s choice of plant, however, though it was motivated in part by ease of use, differed from Blumenbach’s and Mendel’s explicit acknowledgement of the simplicity criterion in the use of their respective plants. Indeed, simplicity of the organic being is not a principal criterion for most of the naturalists and physiologists of the early and middle eighteenth century. By highly estimating the criterion of simplicity and focusing on a living being based on the presumption that it is illustrative of a theory intended to apply to all living beings in general, Blumenbach anticipates what will become standard procedure in the life sciences.

The biologist Ignaz Doellinger offers confirmation of the continuation and refinement of this method in the early 1820s. In his “Von den Fortschritten welche die Physiologie seit Haller gemacht hat” (On the Progress Physiology Has Made since Haller), he writes:

Natur der Erforschung des Ursprunges des menschlichen Leibes eine Grenze, welche auch der festeste Wille zu überschreiten nicht im Stande ist. Die ersten Anfänge des Embryo sind in ein geheimnisvolles Dunkel gehüllt, und es ist nicht abzusehen, wo sich Gelegenheit finden sollte, zu ihnen zu gelangen; kann der Forscher das Hindernis nicht überwinden, so sucht er es doch umgehen, seine Untersuchungen erstrecken sich nun auf die Tiere, wo die erwünschte Gelegenheit sich leichter darbietet, sogar gesucht werden kann; allein auch hier kommt ihm manche Beschwerde entgegen; die Säugetiere, deren Zeugungsgeschäft noch die meiste Ähnlichkeit mit dem des Menschen hat, können nur sparsam, und nach Überwindung der ungünstigsten Umstände in solcher Menge untersucht werden, dass ein bestimmtes Resultat zu erwarten wäre; er muss sich daher an jene Tierclassen wenden, bei welchen die Entstehung und Entwicklung des Jungen in einem Ei außer dem Mutterleibe vor sich geht, und wo mit Leichtigkeit die Beobachtung so oft wiederholt werden kann, also es nur immer die Sicherheit der Erfahrung fordert. Am nächsten den Säugetieren stehe die Vögel; bei der Verschiedenheit der Zeugungsweise und der äußern Gestalt des Tieres, treffen wir bei ihnen noch immer dieselben Gebilde, in derselben Verknüpfung, wie selbst im menschlichen Leibe an, während nur Form und Größenverhältnisse verändert sind; mit ziemlicher Sicherheit kann also, sind uns einmal die Verhältnisse in der Entwicklung der Organe des Vogelleibes bekannt, davon ein Schluss auf die erste Bildung des menschlichen Embryo gezogen werden, wenigstens mag mit Leichtigkeit das, was wir in zerrissenen Bruchstücken von diesem kennen, durch solche Hülfe zu einer zusammenhängenden Lehre verknüpft werden. (Doellinger 1824, 12)

[Nature sets limits to the exploration of the human body’s origin, which even the most determined will cannot surpass. The first beginnings of the embryo are shrouded in a secret obscurity, and it is not foreseen where an occasion is supposed to be found to arrive at them. If the researcher cannot overcome this barrier, then he looks to circumvent it: his investigations extend themselves to the animals that can actually be sought, where the desired opportunity more easily presents itself. Only, even here several difficulties are encountered. Mammals, whose generative ability has the most similarity to the human’s, can only be investigated sparingly and only after overcoming the most unfavorable conditions in great number if a determinate result is to be expected. He must appeal to those classes of animal in which the genesis and development of the young occurs in an egg outside the mother’s body, and where the observation can be often repeated with ease, as it always requires the certainty of experience. Birds stand next to mammals. In the difference in generative capacity and external form of the animal, we still always encounter the same formations in the same combination in them as even in the human body, while only shape and proportions are altered. With fair certainty, therefore, once the relations in the development of the organs of the bird’s body are known to us, a conclusion can be drawn from it about the first formation of the human embryo, at least what we know in disjointed fragments from this may easily be combined by such assistance into a coherent theory.]

Doellinger (as well as Blumenbach, Kant, and generally all natural researchers of this period) desired first and foremost to understand the human being and how he came to be. Hence, the human being was always the desired subject of investigation. However, as Doellinger remarks, the question of human generation is highly obscure. The human ovum, after all, had still not been discovered at the time that Doellinger is writing. To navigate this obscurity, Doellinger proposes that one examine the generation of birds. Observation of them is facilitated by the fact that their embryos develop, in part, outside of their bodies and are thus more easily accessible. Although the bird’s generation will not be identical to the mammal’s, Doellinger argues that one encounters the same formations in each. Therefore, a universal theory of generation that also applies to human beings can be inferred from the more easily observed chick. The rationale of this method is the same as Blumenbach’s, except that he looked to a still simpler life form to advance his claim, considering even the chick, as the contentious locus in the preformation epigenesis debate, to be too complex to deliver conclusive evidence.

For Blumenbach, the simplicity of the species reigned supreme, and his introduction of this criterion into the life sciences, as reaffirmed and justified by Doellinger and stated explicitly by Mendel, became de rigueur in twentieth- and twenty-first-century biology. Yet, the meaning of simplicity changes. The biologist no longer only looks for life forms that are simple, but also looks to make life forms that are simple.

In Lords of the Fly: Drosophila, Genetics, and the Experimental Life, Robert E. Kohler investigates one of the first of these simplified life forms or “standard organisms,” which he describes as “dramatically designed and constructed,” so that they “most resemble spectrometers, bubble chambers, ultracentrifuges, and other physical instruments”(1994, 6). Since the 1900s, because of these changes, the fruit fly (Drosophila melanogaster and other species) has become a staple of laboratories, most notably that of T. H. Morgan at Columbia University, who pioneered the study of genetic mutations in the early twentieth century (ibid.). Around the same time research began on and with Drosophila, another one of the first standard organisms also appeared: the laboratory rat. Bonnie Tocher Clause has detailed the “purposeful and systematic intervention … required to mold these feral animals, unreliable and unpredictable, into biological entities that could be counted on to consistently and invariably yield a productive day’s work”(1993, 330). This intervention occurred at the Wistar Institute in Philadelphia from 1906 until the 1940s. It was there that the ubiquitous white lab rat, the WISTARAT, was born, or better, manufactured, for its production was not an essay task, requiring significant advances in animal breeding techniques. The goal of the institute was to produce a standardized animal that possessed enhanced traits and superior health, and whose structure and development were consistent enough to offer a baseline control in experiments (Clause 1993, 344–5). The simplicity of the fruit fly and WISTARAT is similar to the simplicity of Blumenbach’s algae in that these animals were chosen for their availability and ease of use as well as their relatively rapid rate of growth. As most have likely experienced at one time or another, Drosophila will appear wherever fruit begins to rot and yeast to grow, and the rat is a frequent, nearly ubiquitous resident of cities (from which it was first caught and brought to the lab). However, as already suggested and as Kohler’s and Clause’s work makes clear, these animals had to be altered in order to become standard organisms suitable for laboratory experiments. It is only when these animals take on this new standardized form that they exhibit a simplicity similar to the C. fontinalis, for it is here that they gain a uniformity of structure. The further advantage of the WISTARAT and Drosophila is that their uniformity of structure extended across the species, constituting a simplicity that was not limited to a single individual, but rather made each individual identical. These animals might not have possessed the internal, individual, and structural simplicity as Blumenbach’s C. fontinalis did, but they were engineered toward it as a species.

In looking for something to bolster his formative drive theory against the proponents of preformation, Blumenbach introduced the simplicity criterion through his example of the algae with hopes of forestalling appeal to preformed germs that could always remain just out of sight. The introduction and appreciation of simplicity anticipates trends in modern experimental biology, but with two important differences. First, in the case of the fruit fly and rat, their simplicity must be manufactured. It is not there from the start. “When drosophilas crossed that threshold, they crossed from one ecosystem to another one, with different rules of selection and survival,” Kohler writes. “Once in the laboratory they were physically reconstructed and adapted to experimental uses”(1993, 282). Moreover, the initial reason for the fly’s implementation in the lab—it was a cost-effective organism for students—differed from what would end up keeping it there as a celebrated experimental subject: “Melanogaster was the best adapted to the conditions of experimental production: it was vigorous, fertile, prolific, easy to manipulate, tolerant, and hardy. It was not a fussy feeder and was quick to recover from such recurring disasters of a genetics laboratory as heat or cold waves, epidemics of mites, and neglect” (ibid., 295, 309). In similar language, Clause describes the approach the director of the Wistar Institute, Milton J. Greenman, took in developing its rats: “In the era when biology was being defined, he recognized in the rat the potential to be a living analog to the pure chemicals that legitimated experimental science. From management literature he extracted the ideals of uniformity of product, standards of quality, and efficiency of production, applying them to scientific practice to generate an animal model that thrives as standard equipment in laboratories throughout the world today”(1993, 348–9).

Blumenbach, on the contrary, did little to alter the algae he collected, attempting, rather, to present them in the purest state possible. Adulterating his specimen, in fact, would have given his colleagues reason to doubt his findings. He thus plucked the algae right from their source, placing them straightaway into glass jars without change to the living beings themselves, at least not in the kind of manipulations required for the fruit fly and rat.¹³ Second, and more importantly, Blumenbach presented this algae in order to demonstrate the incontrovertible absence of preformed germs and thereby prove the existence of the Bildungstrieb. His institution of the simplicity criterion anticipates the practices of modern biology in its need for standard organisms as subjects of extensive experimentation; however, while these standard organisms are useful because they have become so uniform that they could be used like “pure chemicals,” Blumenbach’s algae were intended to secure the categorical difference of the organic world from the inorganic one. His efforts were not to show that living beings could be transformed into machines, but to demonstrate the opposite: vital organization occurred according to—and only according to—a unique formative drive.

In drawing comparisons between fruit flies and lab rats with Blumenbach’s algae, we have emphasized how the latter anticipated the former, while maintaining that an important conceptual difference separated the two. It is necessary, though, to introduce another conceptual distinction. We have called the fruit flies and lab rats experimental or standard organisms because of the features detailed above. There is another class of organisms, however, essential to modern biology: model organisms.

The easiest way to introduce model organisms is by way of example, and specifically by way of those recognized by the U. S. National Institute of Health. These include the rat and fruit fly, as already mentioned, but also the mouse, zebrafish, nematode worm, and thale cress. E. coli and yeast, among others, could also be included. More generally, model organisms are non-human species that are used to investigate a host of biological phenomena(Ankeny and Leonelli 2011, 313). These investigations are intended to yield data and theories that are applicable to other organisms or to the organic world as a whole. By investigating simpler model organisms, researchers hope to gain knowledge of more complex ones. What is true of the fruit fly might reveal something true of the fish, dog, and human.

Experimental and model organisms, however, are not identical. Although they agree in several ways, they importantly differ according to social conditions and epistemological features. Because the social conditions of model organisms are mostly inapplicable in Blumenbach’s case, we will focus on the epistemological features.¹⁴ There are two ways in which model organisms differ epistemologically from experimental ones. These differences rely on the concepts of representational scope and representational target. Representational scope is how far the results from one organism can be applied to a wider groups of organisms(Ankeny and Leonelli 2011, 315). In philosophical terms, this is the question of how far a type can be extended to a token; that is, what does the results concerning this bike reveal about bikes in general or all vehicles as a whole. Second, the representational target is the phenomena to be investigated in the organism (ibid.). Ankeny and Leonelli illustrate these concepts through the example of Marcello Malpighi’s experiments on the frog concerning respiration. The representational target of his investigation is respiration, since it is the phenomenon to be studied. The representational scope, however, is respiration in all animals. The intention is that the findings concerning the frog will also be applicable to animals in general. The difference between model organisms and experimental organisms is constituted through the difference in relation to these concepts (ibid., 315–6):

1. Model organisms are always taken to represent a larger group of organisms beyond themselves. This means that a model organism relies on specific claims regarding its representational scope. But this does not hold for experimental organisms, the representational scope of which need not be considered at all. A scientist might be investigating the physiology of fur growth in poodles without concern for its applicability to other breeds or species. Model organisms never have such a limited scope.
2. While experimental organisms have a specific representation target—that is, there is a determinate phenomenon to be understood (like fur growth in the previous example), model organisms are not limited to a single phenomenon, but rather serve to explicate the organism as a whole in each of its processes, like its development and physiology.¹⁵

In sum, research on model organisms is intended to extend to a wide class of organisms and wide class of phenomena within those organisms. The representational scope and target of Blumenbach’s experiments and observations on the alga thus suggest that it is as much a model organism as an experimental one, for the representational scope that he intends for his research is living beings in general; that is, it refutes preformation as a viable theory and confirms an epigenesist one by demonstrating the gradual development of algae. If this organized being is confirmed to reproduce gradually, then all organisms will also be confirmed to reproduce gradually. Moreover, the representational target is of a wide scope. Blumenbach is not interested solely in the reproduction of C. fontinalis, but reproduction as it occurs in general. He intends his results sufficient enough to show that every living being exhibits the formative drive in its generation.

Bildungstrieb as Occult Quality

Although the Bildungstrieb extends to every living creature, it is also distinct. We recall the pains Blumenbach took to differentiate it from all known kinds of physical and vital forces. Its specialty might lead us to think that he has effectively priced himself out of the market: the drive is so sui generis and operates according to such unique principles that it is essentially inscrutable. Yet, Blumenbach closes his essay by proposing six laws that may be inferred from the observation of the formative drive’s effects in nature. These laws show that the drive is more than a product of empty speculation, offering valuable insights into living nature. They are as follows:

1. The strength of the Bildungstrieb stands in an inverse ratio with the age of the organized body (Blumenbach 1789b, 93–7). Once the formative drive takes hold in the generative matter, it begins its vigorous process of formation, explaining the rapid growth and development of organized bodies in their earliest years. As they age, however, the Bildungstrieb becomes weaker; growth and development slow and eventually cease altogether.¹⁶
2. The formative drive is more active in embryos of viviparous animals than in those of oviparous ones because, Blumenbach explains, “Es scheint die Natur eilt bei den lebendig gebärenden Tieren der Frucht so früh also möglich gleich bestimmte Ausbildung zu geben, und sie dadurch für vielen zufälligen Verunstaltungen von gewaltsamen Druck u. a. dergl. Gefahren zu sichern, denen hingegen das in seiner Eierschale festverwahrte Kügelchen bei weiten nicht so leicht ausgesetzt ist” (ibid.; It appears nature hastens to give in the animals born living an immediately determinate formation to the progeny as early as possible, and it thereby protects against many contingent deformities by violent force as well as similar dangers, to which, on the contrary, the globule firmly secured in its eggshell is by and large not so readily exposed).
3. With some organs, the Bildungstrieb expresses more variation, but with others much less(ibid.)For example, Blumenbach mentions that while the brain always maintains the same structural physiology, the kidneys are consistently varied.¹⁷
4. The principal kind of variation consists in the formative drive adopting one kind of organized body for the course of another, as when hares are observed to have small horns(ibid.).
5. “Eine andre ebenso merkwürdige Abweichung des Bildungstriebes ist, wenn bei Ausbildung der Sexualorgane, die beim einen Geschlecht mehr oder weniger von der Gestaltung des andern annehmen”(ibid.; Another just as remarkable derivation of the Bildungstrieb is, when in the formation of the sexual organs, those of one sex more or less adopt the form of the other).
6. Finally, Blumenbach mentions those cases that differ from the previous ones in that they are not just variations or deviations from the course of nature, but ones in which the formative drive acts entirely against nature, producing “monsters” (Misgeburten)(ibid.). He continues, “Und dennoch ergibt sich bei einer nähern Beleuchtung aus der bewundernswürdigen Gleichförmigkeit die unter vielen Arten von Monstrositäten herrscht, dass doch auch selbst die Ursachen, die in diesen Fällen dem Bildungstriebe die falsche Richtung geben, dennoch an sehr bestimmte Gesetze gebunden sein müssen” (ibid.; And, nevertheless, with closer scrutiny an admirable uniformity results that rules among the different kinds of monstrosities, that even the causes, which give the formative drive the wrong direction in these cases, must nonetheless be bound to very determinate laws). The classification of these laws that reign in the realm of monstrosity are stated more fully by Blumenbach in his Handbuch der Naturgeschichte(1788, 15).

After the careful, extended argumentation Blumenbach presents throughout his essay, these laws appear, admittedly, underwhelming, almost like an afterthought.¹⁸ It is clear that the main effort of the essay is to establish the formative drive’s existence against the falsity of preformation theory, leaving only a few pages (15 of 108 in the second edition) to enumerating these laws. In fact, they do not even appear along with the discussion of the Bildungstrieb in Blumenbach’s other texts. Yet, these laws, three through six, in particular, reveal an effort to demonstrate that even in those places where nature seems to be irregular—even where it appears contrary to itself—order still prevails. Formative drive and the generation, growth, and reproduction that it directs never act with absolute caprice, but rather always abide by certain guidelines. Living nature, too, is bound by laws.

These laws, which are inferred from observation of the Bildungstrieb’s effects, raises an epistemological question: if the Bildungstrieb is the main ground of all generation, nutrition, and regeneration, then what is its ground? What is the cause of the Bildungstrieb? The supporter of preformation, in response to this question of origins, is well-equipped, since he may appeal to the preformed germ that has been present since the time of Creation. What appeal, though, is open to Blumenbach? Immediately after introducing the formative drive, perhaps in anticipation of such questions, Blumenbach writes,

Hoffentlich ist für die mehresten Leser die Erinnerung sehr überflüssig, dass das Wort Bildungstrieb, so gut, wie die Worte Attraktion, Schwere, etc. zu nichts mehr und nichts weniger dienen soll, als eine Kraft zu bezeichnen, deren konstante Wirkung aus der Erfahrung anerkannt worden, deren Ursache aber so gut wie die Ursache der genannten, noch so allgemein anerkannten Naturkräfte, für uns qualitas occulta ist. Es gilt von allen diesen Kräften was Ovid sagt: —caussa latet, vis est notissima. Das Verdienst beim Studium dieser Kräfte ist nur das, ihre Wirkungen näher zu bestimmen und auf allgemeinere Gesetze zurück zu bringen. (1789b, 25–6)

[Hopefully, for the majority of readers the reminder is entirely superfluous that the word Bildungstrieb as well as the words attraction, gravity, etc. should serve neither more nor less than to designate a force whose constant effect has been recognized from experience, but whose cause as well as the cause of the generally recognized natural forces is for us a qualitas occulta. What Ovid says is true of all these forces: caussa latet, vis est notissima. The merit in studying these forces is only to ascertain their effects more closely and to bring them under more general laws.]

Significantly, Blumenbach reveals here that the formative drive’s cause is hidden; all that is known of it are its effects as gleaned from experience. Investigation of the Bildungstrieb (in addition to other natural forces) will never yield knowledge about its causes, but only allow the researcher to know the effects in more detail and to bring them under fewer, more general laws. This framework provides a better understanding of Blumenbach’s conclusion in his essay. The six laws Blumenbach specifies represent a codification of the formative drive’s effects.

Besides the quote from Ovid’s Metamorphoses, the stated inspiration, or perhaps warrant, for taking this position is Newton. Blumenbach’s invocation of “occult qualities” indicates this provenance because it is a term Newton sanctioned in his natural philosophy. We are confirmed in this supposition by Blumenbach’s direct reference to the natural philosopher’s Opticks in the footnote to the quoted passage. In fact, one of the few major changes from the second (1789b) to the third edition (1791) of the Bildungstrieb essay is the inclusion of a further reference to Newton and the addition of two citations from Voltaire’s popularization of him regarding occult qualities.

This use of occult qualities, however, is lacking from the earliest editions (1780, 1781a) of the essay, in which Blumenbach grants a quite different epistemological status to the Bildungstrieb. He writes that it “eine der ersten Ursache aller Generation, Nutrition, und Reproduktion zu sein scheint” (1781a, 13; seems to be one of the first causes of all generation, nutrition, and reproduction). He will change this line in the 1789 edition and those editions thereafter to “die erste wichtigste Kraft” (1789b, 25; the first, most important force).¹⁹ In fact, the one time that he does mention occult qualities in these earlier editions, he does so dismissively, arguing that the formative drive is wholly different from the vis plastica and not “an empty word” like “occult quality”(1781a, 15). He associates this unsatisfactory usage of “occult qualities” with the Aristotelians in general and Franz Bonamico, a seventeenth-century Aristotelian professor from Florence, in particular. Therefore, Blumenbach’s position dramatically shifts between the editions of his texts concerning the meaning of occult qualities; this shift, coincidentally, recapitulates the term’s own historical shift in meaning initiated in the transition from Medieval and Renaissance Aristotelian natural philosophy to modern mechanism.

In those earlier eras, occult qualities were contrasted with manifest ones. Whereas the former—planetary influences, magnetism, chemical and pharmacological potencies, etc.—were denied truth, the latter—tastes, colors, or whatever was immediately apprehensible by the senses—constituted the entire domain of natural science. Hence, the limits of manifest qualities were the limits of sensibility; what was intelligible was what was sensible. In this respect, Thomas Aquinas, for instance, argued that God had not created any creature or element that surpassed the threshold of human sensibility, or that if He did, it was because human sensibility had suffered corruption after expulsion from Eden(Hutchison 1982, 236–7).

One might suppose, then, that the Scientific Revolution would be predicated on a rejection of occult qualities tout court, especially insofar as the “occult,” beyond signifying the insensible, also connoted the supernatural and mystical, notions that seem inimical to the rise of modern science. However, the objection takes a different form: mechanical natural philosophy continued to maintain that occult qualities were unintelligible, but it rejected that this was due to their insensibility. In fact, mechanical philosophy even recognized that those qualities thought to be manifest might actually be occult, because they recognized that “one’s psychological perception of a sensible quality is of a different order of reality from the physical cause of that quality”(ibid., 243). In short, seventeenth-century natural philosophers divorced insensibility from unintelligibility, so that they no longer entailed one another. The meanings of manifest and occult were also reconfigured. These changes allowed for a study of nature’s effects, which were detectable even if not immediately apprehensible, without concern for their causes, since these remained occult or unintelligible. This new position is one completely unfathomable for Aristotelian natural science.

Although Newton was not the first natural philosopher to adopt this approach, he did state it paradigmatically, insisting on an epistemic separation between the study of effects and causes(Henry 1986, 351). His statement of it, moreover, clarifies the benefit of this reconfiguration.For Newton, because the existence of gravity, for example, can be demonstrated from the effects of nature or phenomena, it is admissible to the study of natural philosophy without “feigning hypotheses” or admitting something that could not be deduced from nature (1986, 362). In the “Queries”appended to hisOpticks, Newton explains his position, revealing at the same time the necessary reconfiguration of the Aristotelian meaning of occult qualities. He writes:

These Principles [of gravity, fermentation, or the cohesion of bodies] I consider, not as occult qualities, supposed to result from the specific Forms of Things, but as general Laws of Nature, by which the Things themselves are formed; their Truth appearing to us by Phenomena, though their Causes be not yet discovered. For these are manifest Qualities, and their Causes only are occult. And the Aristotelians gave the name of occult Qualities, not to manifest Qualities, but to such Qualities only as they supposed to lie hid in Bodies, and to be the unknown Causes of manifest Effects: Such as would be the Causes of Gravity, and of magnetic and electric Attractions, and of Fermentations, and if we should suppose that these Forces or Actions arose from Qualities unknown to us, and incapable of being discovered and made manifest. Such occult Qualities put a stop to the Improvement of natural Philosophy, and therefore of late years have been rejected. To tell us that every Species of Things is endowed with an occult specific Quality by which it acts and produces manifest Effects, is to tell us nothing: But to derive two or three general Principles of Motion from Phenomena, and afterwards to tell us how the Properties and Actions of all corporeal Things follow from those manifest Principles, would be a very great step in Philosophy, though the Causes of those Principles were not yet discovered: And therefore I scruple not to propose the Principles of Motion above-mentioned, they being of very general Extent, and leave their Causes to be found out. (Newton 1979, 401–2)

Newton’s remark, stated in the same Query which Blumenbach cites, reveals the new sense of occult qualities, its difference from the Aristotelian usage, and the methodological importance of this shift. Because gravity’s effects can be known and general laws drawn therefrom, it is acceptable that its cause remains unknown or occult, since the attempt to explain an effect in terms of a thing’s specific quality that is unknowable will never yield an explanation. Instead, Newton proposes to derive some general laws from the phenomena and then to explain the properties of individual things therefrom. This approach represents for him a “very great step in Philosophy,” even if it leaves the causes that actually produce the phenomena or effects of nature unknown. The gamble, then, is that the sacrifice of not pursuing nature’s causes will still yield knowledge of its laws in the end.

By describing the Bildungstrieb as an occult quality, like Newton’s gravity, Blumenbach is taking the same gamble as the natural philosopher, even if an Aristotelian would doubt its soundness. Even Aristotle himself claims “we think we do not yet know each thing until we have taken hold of the why of it (and to do this is to come upon the first cause)”(1995, 194b19–20). The difficult question of which position yields the better, more satisfying explanation of a thing, and specifically, what, in our case, constitutes an explanation of a living being must be postponed until our discussions in the next two chapters of the epistemological limitations of biological knowledge recognized by Kant in his third Critique. Nevertheless, we can say here that although Newton emphasized the strategic virtue of his approach, his great popularizer, Voltaire, whom Blumenbach also cites in support of characterizing the Bildungstrieb as an occult quality, emphasized a different aspect of occult qualities in his Elements of Newton’s Philosophy and in an extended passage in A Philosophical Dictionary. In the latter, Voltaire writes, “What is the centripetal force, the force of gravitation, which acts without contact at such immense distances? … You know nothing about it, and the cause will be eternally occult to you. All that surrounds us, all within us, is an enigma which it is not in the power of man to divine”(1824, 130). Voltaire’s description forgoes Newton’s “causes be not yet discovered” for a much starker interpretation: the causes will be eternally unknown, for they are beyond the human intellect altogether. Blumenbach himself emphasizes this same skeptical tone when later describing the Bildungstrieb in the third edition of the Institutiones Physiologicae (1810; 1^st ed. 1787): “I have used the expression—nisus formativus, merely to distinguish it from the other orders of vital powers, and by no means to explain the cause of generation, which I consider equally involved in Cimmerian darkness as the cause of gravitation or attraction that are merely terms given to effects known, like the nisus formativus, a posteriori”(1828, 376n1). With each later edition of the Bildungstrieb essay, the epistemological reach of the formative drive shortens and Blumenbach ultimately relinquishes its cause to the unknowable depths of Cimmerian darkness.²⁰

Having documented in part this shift in epistemological reach, we can now complete the record. In the first editions of “Über den Bildungstrieb” of 1780 and 1781, Blumenbach defines the formative drive as what “seems to be one of the first causes [Ursachen] of all generation, nutrition, and reproduction”(1781a, 13). Yet, already in the Handbuch der Naturgeschichte [Manual of Natural History] from 1782, he changes the formulation: the Bildungstrieb now “seems to be the Hauptgrund [principal reason]”(1782, 15). This change is ambiguous. Although he has dropped the explicit use of “cause,” “Hauptgrund” could still be interpreted to retain this sense. Moreover, he has not yet invoked Newton or the occult qualities with respect to the drive. In the Handbuch from 1788, he maintains the use of Hauptgrund; however, Blumenbach here adds the following remark, which betokens a transformation of his thinking:

Die Ursache dieses Bildungstriebes lässt sich freilich eben so wenig als die der Attraktion oder der Schwere und anderer noch so allgemein anerkannten Naturkräfte angeben. Genug dass es eine eigentümliche Kraft ist, deren unleugbare Existenz und ausgedehnte Wirksamkeit sich durch die ganze Natur in der Erfahrung offenbart, und deren so konstante Phänomene einen weit leichtern und helleren Ausschluss über das Zeugungsgeschäft und viele andere der wichtigsten Gegenstände der Naturgeschichte geben, als andere zu deren Erklärung vorgeschlagene Theorien. (1788)

[The cause of this formative drive can be indicated, admittedly, just as little as that of attraction or gravity and of other of the generally recognized natural forces. Enough that it is a particular force, whose undeniable existence and ample activity manifests itself through the whole of nature in experience, and whose constant phenomena give a much lighter and brighter conclusion about generation and many other of the most import objects of natural history than other theories proposed for their explanation.]

Though he has not yet explicitly named Newton or occult qualities, the reference is already suggested by his comparison of the Bildungstrieb’s epistemological status to that of attraction and gravity, which are the Newtonian forces as occult qualities par excellence. He completes this transition by changing the formulation again in the second edition (1789b) of the Bildungstrieb essay, which went unchanged in its third and final edition (1791): as noted, he no longer describes the drive as a “Hauptgrund,” but now as the “die erste wichtigste Kraft” (1789b, 25; the first, most important force). And although Blumenbach will continue to modify the formulation of the Bildungstrieb over the twelve editions of the Handbuch der Naturgeschichte, with the last appearing in 1830, its epistemological status does not significantly depart from that articulated in his texts at the end of the 1780s: the cause of the formative drive cannot be known. The life scientist is thus in a position analogous to the natural philosopher’s study of gravity and other natural forces the causes of which are occult. And, like Newton, Blumenbach claims that this inability to know the cause of the Bildungstrieb neither puts its existence into question nor does it make the deduction of laws concerning it impossible. To the contrary, one can, through the observation of its effects, come to deduce laws important to life science.

What, though, causes Blumenbach to alter the formulation of the Bildungstrieb? The cause of this shift, much like the occult quality itself, seems inexplicable, for, of Blumenbach’s texts available to survey from the early 1780s, none seem to provide reason for it.²¹ That being said, Blumenbach’s revision to his theory aligns him more closely with his life science forebears and contemporaries than if he had retained his original formulation of the Bildungstrieb as having a knowable cause. In “On Biological Analogs of Newtonian Paradigms” (1968), Thomas S. Hall documents several cases in which physiologists compared their conception of living forces to Newtonian forces; that is, they used a variety of “inexplicable explicative devices” or “physiological unknowns” in imitation of Newton’s natural philosophy and mathematics that allowed them to reduce a variety of phenomena to a single force whose cause was unknowable. Blumenbach is included in Hall’s account as is the physiologist Haller (Hall 1968, 13–20).

Haller read two papers in 1752 to the Royal Society of Sciences at Göttingen. These papers were published the following year under the title De partibus corporis humani sensibillibus et irritabilibus. This text contains Haller’s irritability and sensibility theory, which held the former to pertain to any part of the body that contracts upon being touched (for example, muscles) and the latter to any part of the body that upon being touched transmits that impression to the soul (that is, nerves)(Haller 1936, 8–9).²² His theory became immensely influential and any eighteenth-century physiologist worth his salt would have been intimately familiar with it (Blumenbach not excluded). The theory, though, was not influential because Haller had first discovered the irritable and sensible properties, for they had already been more (irritability) or less (sensibility) documented before his treatise; rather, the influence laid in the fact that he had explained them mechanically (as opposed to vitally) and delimited them experimentally. Haller thus provided more than a finding—he provided a method and a proven one at that.

Because of the importance of his theory and method, Haller’s response to the question of the cause of irritability and sensibility is revealing:

But the theory, why some parts of the human body are endowed with these properties, while others are not, I shall not at all meddle with. For I am persuaded that the source of both lies concealed beyond the reach of the knife and microscope, beyond which I do not choose to hazard many conjectures, as I have no desire of teaching what I am ignorant of myself. For the vanity of attempting to guide others in paths where we find ourselves in the dark, shows, in my humble opinion, the last degree of arrogance and ignorance. (1936, 8)

The cause of irritability and sensibility is beyond the reach of the microscope and knife and hence is also beyond the limits of our knowledge; or, in other words, Haller makes the knowledge of living beings coextensive with the instruments used to investigate it, and he condemns anyone who transgresses this boundary. Later in the text, Haller provides further justification for his method, at least insofar as it pertains to irritability. He is in the process of arguing that irritability is a property of animal gluten, when he asks:

What therefore should hinder us from granting Irritability to be a property of the animal gluten, the same as we acknowledge attraction and gravity to be properties of matter in general, without being able to determine the cause of them. Experiments have taught us the existence of this property, and doubtless it is owing to a physical cause which depends upon the arrangement of the ultimate particles, though the experiments that we can make are too gross to investigate them. (1936, 42)

Haller thus compares irritability to the Newtonian forces of attraction and gravity, arguing that they are acknowledged properties of matter, even though their causes cannot be known, and Haller again attributes this epistemological inability to the coextensive limits of instrument and knowledge.²³

We have thus found, even if not in the same explicit language, what would have been a widely-known precedent for describing a vital force as an occult quality, in the same respect as Newton did with gravity. Blumenbach would have been familiar with this highly-regarded model for the reformulation of his own Bildungstrieb. (We, too, could speculate that Blumenbach does not explicitly mention Haller’s usage as his model because he would thus be affirming his opponent’s method and then, perhaps, undermining his own efforts.)

Yet, the unknowability of the formative drive’s cause differs from that of Haller’s irritability. For Blumenbach, the limits of knife and microscope do not appear to be what makes the Bildungstrieb’s cause unknowable. These limits, after all, must be temporary and mobile insofar as improvements in instruments would also be improvements in our knowledge. Nonetheless, recalling his citations of Voltaire and his own remark on Cimmerian darkness, this unknowability appears impermeable to advances in instruments or techniques. Indeed, in Blumenbach’s formulation, there appears to be something necessarily and inherently inexplicable about its cause, which, if the Bildungstrieb is supposed to be the first and most important force of all generation, nutrition, and reproduction, means that there would be something necessarily and inherently inexplicable about life itself.

But Blumenbach does not offer any clue to why this is the case. Such an outcome should not be unexpected, though, for his intention, especially as a life scientist, is not to demonstrate why certain causes about life are unknowable, but rather to explicate what is knowable and known. The knowable extends from the more general, universal laws deducible from observable phenomena (like the six laws of the Bildungstrieb listed above) to the more specific details about the living world that fill the more than 700 pages of his Handbuch der Naturgeschichte, not to mention the rest of his voluminous corpus. Despite the development of Blumenbach’s thought explicated above—the architecture of his conversion from preformation to epigenesis and the lingering complications that the introduction of C. fontinalis resolved—it does not seem to get the fly out of the ointment: what is the cause of the formative drive? This question is tantamount to another: What is the cause of life? Is it necessarily unknowable? And if this is the case, are we at least able to know why?

Such questions, once asked, are not so easily dismissed. Blumenbach offers no answers to these questions, but partially because of him, Immanuel Kant is prompted to investigate them and even provide an answer. In the following two chapters, we will explicate the relationship between Blumenbach and Kant, and the latter’s paradoxical contribution to the science of life.

1Blumenbach published the earliest version of the work as an essay, entitled, “Über den Bildungstrieb (Nisus formativus) und seinen Einfluß auf die Generation und Reproduction” (1780), in the Göttingisches Magazin der Wissenschaften und Litteratur. The essay became the basis for a book that would be published in three subsequent editions, each of which saw substantial revisions and additions. The first of these editions, which incorporated new research and expanded the original arguments, is published in the following year (1781a), the second in 1789, and the third and final edition, to which Blumenbach made minor changes but also important additions, in 1791. Blumenbach also published a Latin translation of the essay in 1787. The only English translation, often unreliable, is based on the third edition and appeared in 1792. This historiographic presentation provides more than a selected bibliography, for it offers a record by which we can better understand Blumenbach’s Bildungstrieb and ascertain its epistemological limits. This approach allows us to see how Blumenbach’s formulations changed over time, which complements an analysis of those features of the Bildungstrieb that remained consistent across each edition. In general, I have quoted from the second edition because it represents the mature formulation of his theory and is the edition he sent to Kant, a fact important for the next chapter.

2 We note, however, that this criterion did not contribute to Blumenbach’s theory conversion, for the research leading to its introduction occurred after the formulation of the Bildungstrieb.

3 McLaughlin claims that these experiments and their interpretation represent a crucial moment for Blumenbach and thereby for life science in the late eighteenth century in general. He writes, “The experimental research and the explanation of regenerative activities of the polyp formed the starting point of Blumenbach’s epigenetic theory and vitalism” (1982, 360).

4 Blumenbach always uses the term “reproduction” to designate what we would now usually call “regeneration.”

5 Wherever possible, I have updated German and English texts to their modern spellings, except for titles, where I have retained original spellings.

6 Shirley Roe presents a lucid summary of Wolff’s position: “Wolff’s philosophy of biology thus rests on his separation of ‘vegetative’ processes in living organisms from both mechanical processes and those, like sensation and thought, that depend on the soul. Wolff consistently used the term ‘vegetative’ to refer to the activities of nourishment, maintenance, growth, and development in the living organism, that is, the vital functions. Clearly, it is the essential force that is the key to these vegetative processes and thereby the key to Wolff’s philosophical views on the nature of life. Denying total reductionism, yet unwilling to ascribe to vitalism either, Wolff sought to create an explanation for life processes that was mechanical in its own right yet also unique to living creatures” (1981, 110).

7 Wolff did not sit on his haunches in the face of Blumenbach’s criticism, but attacked the formative drive by using the same arguments that Haller had used against him (see Roe 1981, 116).

8 This explanation, however, appears to contradict Blumenbach’s initial one in the essay’s first section, where he had said that the polyp had ample food and one should thus not suppose that the diminished limb was a product of less nutrients. Yet, in the present explanation, Blumenbach says that the injured polyp does not eat as much as a healthy one, which would seem to make the amount of food available irrelevant and mean that the polyp’s reduced intake could explain its diminished limbs. I believe, however, that the contradiction can be resolved as follows. Although the polyp is given ample food, this fact is irrelevant because of its reduced appetite. Therefore, a disparity remains between what the polyp consumes and the size of its regenerated parts in that its consumption provides less matter than is needed, which requires the formative drive’s repurposing of existent matter.

9 Lenoir attributes Blumenbach’s rejection of the vis essentialis to a form of vitalism that superimposes a soul onto the matter (1982, 21). Yet, according to the present analysis, such a conclusion cannot be accepted, for it was not Wolff’s vitalism to which Blumenbach objected but the lack of it! Roe contends that Wolff was not even a vitalist (1981, 110). Nonetheless, for Blumenbach, the vis essentialis was too much of a physical force and not enough of a living drive. It could never be a principle of regular formation, for it could not respond to the contingencies of nature, as in the case of the polyp.

10 Although these examples of hybridity are important for Blumenbach’s rejection of preformation, they do not occupy a central position in his text. For this reason, I cannot agree with Lenoir, who claims the rejection is based on precisely these grounds: “Reflection on two problems led Blumenbach to abandon the preformation theory. The first was that the production of fertile varieties, such as mulattos, was completely inexplicable on Haller’s model. In terms of a consistent application of the preformation theory, the mixture of two different races should not exhibit a blend or Mittelschlag. The second and decisive factor was Blumenbach’s realization that Kölreuter’s experiments absolutely refuted the preformationist scheme. Kölreuter had not only produced fertile hybrid offspring by crossing nicotina rustica with nicotina paniculata; more importantly, he had succeeded in reverting the hybrid offspring to the paternal form (paniculata) after several generations” (1980, 82).

11 Blumenbach publishes his initial work on the Conferva fontinalis in the Göttingen Magazin (1781b). He titles it, “Über eine ungemein einfache Fortpflanzungsart” (On an Extraordinarily Simple Kind of Reproduction), and says that it was his work on the formative drive that first led him to inquire into this organism, an inquiry that then incidentally yielded evidence of the drive’s existence.

12 Although it was common practice at the time to apply the name “moss” to a wide variety of plants that have small leaves, no flowers, and grow on certain surfaces, I have determined that Blumenbach’s C. fontinalis was not a moss at all, but rather a yellow-green algae in the genus Vaucheria. Based on the archival and morphological work of Christensen (1968), Blumenbach likely had the species V. fontinalis before him; however, because of limited evidence, an infallible species identification is impossible. Further description of Vaucheria can be found at AlgaeBase, an online repository which maintains a continually updated taxonomy of algae (Guiry 2017).

13 Without doubt the act of collecting, transportation, and microscopic observation alters if not the subject investigated, then at least the context under which that subject was originally found. Nevertheless, the point here is that the manufactured experimental organism is distinct from Blumenbach’s algae.

14 These social conditions, which includes, e.g., the large research community surrounding Arabidopsis, complicates the interpretation of Blumenbach’s algae as a model organism, since a research community devoted to it never emerged in the same sense. It is best, then, to consider Blumenbach’s algae as a proto model organism insofar as it shares some but not all of the features of modern model organisms. On the reception of C. fontinalis in the late eighteenth century, see my essay, “Visions of Algae in Eighteenth-Century Botany” (2016).

15 In light of this distinction, I will reiterate that experimental and model organisms share some features: the chosen organism must be tractable, i.e., simple to acquire, simple to maintain, simple to manipulate, and relatively simple in structure. Moreover, every model organism is an experimental organism, but not every experimental organism is a model organism.

16 Brandon C. Look identifies a contradiction in the first law in relation to the polyp case (2006, 359-60). If the formative drive is strongest in the early years of development and the weakest at the end, then it would inversely correlate with the amount of matter in the being, which is inconsistent with Blumenbach’s claim in the polyp’s case, since its reduction in matter correlated directly with a reduction in formative drive. To the contrary, one could respond that this state of affairs only attests to how much stronger the Bildungstrieb must be in early development given the paucity of matter and how much it must decrease in old age given the relative abundance of it then. This, of course, does not explain why the drive diminishes over time nor why it must diminish at all.

17 For a brief, modern consideration of anatomical variation and its differentiation from anomaly or deformity, see Sañudo (2003).

18 Denise Gigante gives a potential explanation for why Blumenbach’s laws seem so underwhelming. She writes, “Biologists compared vital power to forces like electricity and magnetism, but the key difference was that their power could not be quantified or mathematically predicted in the same manner as physical force” (2009, 17). Even if it were the case that vital powers could not be quantified, Gigante’s response only begs the question, for it says nothing about why vital powers (Lebenskräfte) could not be quantified. What makes a law of nature so different from a law of living nature? Although Blumenbach intimates an answer to this question insofar as the Bildungstrieb cannot act blindly like a natural force and must, instead, determine form and respond to contingent events, he does no more than intimate. It will be Kant who provides a reason for why the laws must be different, which will the subject of the next and following chapters. In looking ahead, we can also say that C. F. Kielemyer presents the organic forces of nature as having a determinate proportion among each other, arguing that there are discernible laws of organic forces.

19 We will return to this change in more detail below.

20 Peter McLaughlin (1982) provides one of the most perceptive analyses of Blumenbach’s use of Newton, especially as this use changes over different editions of his essay.

21 Robert J. Richards suggests that Blumenbach might have been brought to the comparison with Newton via Michaelis Birkholz’s doctoral dissertation, in which a comparison is made between the Bildungstrieb and Newton’s principium trahens (2000, 24n56). This suggestion, though, is less than plausible. First, the comparison to Newton occurs much before the 1791edition of Über den Bildungstrieb, yet the citation of Birkholz only appears in the this third and last edition. If Blumenbach had been so influenced by him, then it would be curious that he omitted the reference from earlier editions. Second, Blumenbach uses the citation is to adduce a different point than one about occult qualities; that is, he wishes to dissuade those who might be inclined to find the Bildungstrieb theory already articulated in precisely the same way in the most ancient of writers, admitting at the same time that elements of it will be found in earlier writers, a fact shown already by Birkholz and hence the reason for the citation. If one looked, however, to the citation that directly precedes that one, then one would find much better evidence for what might have induced Blumenbach to draw the comparison to Newton, if the cited work had not just been published in 1788. Although it could not have spurred Blumenbach’s invocation of Newtonian occult qualities, it remains useful to consider the citation in detail. Blumenbach quotes the Scottish physician George Fordyce, who “sagte kürzlich bei Gelegenheit einer ähnlichen physiologischen Untersuchung (said recently on the occasion of similar physiological research): ‘although the study of causes of original powers be totally absurd and futile, yet the laws of their action are capable of investigation by experiment and applicable to the evolving much useful knowledge’” (Blumenbach 1791, 34n). By resembling von Haller’s remark, inasmuch as experiment and application delimit knowability, Fordyce’s claim further emphasizes the influence of the De partibus on eighteenth-century life scientists and again indicates a possible source for Blumenbach’s own comparison. Adopting this source would allow response to another of Richard’s claims. He argues that Blumenbach’s quotation from the Opticks as well as the (now questionable) comparison source in Birkholz suggests that Blumenbach’s knowledge of Newton was “less than comprehensive” (ibid.). Yet, Blumenbach’s knowledge of Newton is beside the point, because we are not looking for a model concerning physical forces in general, as in natural philosophy, but rather for physiological forces. For this purpose, von Haller fits the bill, as he was quite knowledgeable of Newton and also included the particular comparison in one of his most famous works, with which Blumenbach would have been more than familiar.

22 Haller’s irritability and sensibility theories are explained in more detail in the Introduction.

23 The comparison, however, is asymmetrical, for Newton’s forces extend to all of matter, whereas irritability is strictly limited to animal gluten.