3.1. A general overview

Rignano’s energetical vitalism was concisely elucidated in his final work, The Nature of Life. This publication was divided into two parts. The first was intended to establish “purposiveness” as the essential characteristic of all “vital phenomena,” encompassing processes like assimilation, metabolism, generation, adaptation, lower organism behavior, reflexes, and instincts. For Rignano, moreover, purposiveness, or what is often termed “teleology” today, delineates “the essential difference” between “living entities … [and] non-living entities … the two great categories of phenomena into which man has divided everything in nature which is open to his perception” (Rignano Reference Rignano1930, ix). In other words, Rignano attempted to find a preliminary solution to the enigma of life through the concept of purposiveness.

Take Rignano’s account of assimilation as an example. For Rignano, “assimilation is a selection,” and “as selection the assimilative process has a marked purposive aspect” (Rignano Reference Rignano1930, 3–4, original emphasis). To elaborate, in Rignano’s words, in assimilation living organisms must “select from the extremely complex mixture of chemical substances dissolved in the nutritive liquid just those compounds or radicals or fragments of atomic groups which will reconstruct it in the same specificity as before” (p. 3; original emphasis). Further, Rignano took assimilation to be essentially a vital phenomenon, which is different in kind from any physico-chemical phenomenon, such as “the growth of crystals in a salt solution” (p. 4). For Rignano, in crystal formation only reciprocal attraction between molecules is in operation, and it amounts at best to a simple physico-chemical process of deposition; in sharp contrast, assimilation is “an active process of synthesis and reconstruction by means of materials selected ad hoc and different from the substance which they are to build up again” (p. 4; original emphasis). On the surface, Rignano’s strategy of characterizing the uniqueness of the organic realm appeared to have delivered nothing new, and his appeal was again made to purposiveness, teleology, and final cause. But this is merely his preliminary solution to the problem of the nature of life.

In the second part of The Nature of Life, Rignano introduced his innovative “vitalistico-energetic solution” (p. 130). Convinced that purposiveness is the essential feature of all vital phenomena, Rignano requested that it be further explained, and he recommended his energetical vitalism. Rignano started by blaming mechanists for their narrow interest in physico-chemical aspects of living organisms; for this reason, mechanists “have been directed towards denying the existence of these purposive manifestations of life” (p. 112). Mechanists simply “see everything except life” (p. 121). At the same time, Rignano was equally unsatisfied with traditional vitalists, including Driesch, who abandoned, in Rignano’s opinion, “any attempt to explain the nature of life” and indulged in positing “a vague, undefined and nebulous entity as the cause of the purposive manifestations of life” (p. 125). Rignano believed that neither mechanism nor Driesch’s vitalism succeeded in offering any adequate account of life. Given that “purposive manifestations of life are facts, and indisputable facts” (p. 129), Rignano concluded that only his doctrine of energetical vitalism was able to deliver a “causal and deterministic explanation” (p. 130) of them.

Central to his energetical vitalism were two hypotheses: the hypothesis of vital energy and the centroepigenetic hypothesis. These two will be the focus of the rest of this section.

3.2. The hypothesis of vital energy

The first hypothesis in Rignano’s energetical vitalism postulated the concept of vital energy, or nervous energy (Rignano used these two phrases interchangeably for reasons that will become clear in Section 4), and it suggested that “at the basis of life” there is “a special form of energy” (Rignano Reference Rignano1930, 132). Rignano invoked the concept of vital energy to make sense of the purposive feature of vital phenomena. For him, the essential feature of all vital phenomena lies in “nothing other than the special form of energy which we assume as the basis of life and which alone gives to all its manifestations their purposive imprint” (p. 133), and “it is in life and only in life that a particular form of energy is active, the particular energetic characteristics of which are the sole cause of these purposive manifestations” (p. 159). Notably, while The Nature of Life delineated the progression from purposiveness to vital energy, it did not comprehensively expound upon the vital energy hypothesis. For this, it is necessary to turn to Rignano’s earlier publications.

Rignano explored the hypothesis of vital energy in Upon the Inheritance of Acquired Characters (1911) and Biological Memory (1926). First of all, he argued that the postulate of vital energy, unique to the organic realm and responsible for various purposive manifestations, remains consistent with general energetics principles, including principles of energy conservation and transformation. Within this perspective, Rignano further contended that there is no distinction between vital energy and other energy forms. For instance, vital energy emerges when life is present, much like electric energy exclusively manifests in electric phenomena. Rignano likened vital energy to electric energy, perceiving it as a unique potential energy form that is convertible to kinetic energy or other potential energy forms. He noted that certain cells possess “more potential energy” (Rignano Reference Rignano1911, 25). In Rignano’s words, “vital energy [or] nervous energy … will certainly be a particular case of the more general physico-chemical forms of energy already known or yet to be known, and as such it must necessarily be subject to the laws which control these latter; and also, a fortiori, to the laws which control all energy in general” (p. 337).

Second, Rignano posited that while vital energy adheres to general laws of energetics, it remains distinct from other physico-chemical energy forms. Indeed, living organisms can manifest various potential energy forms (mechanical, chemical, electrical, and vital). In contrast to non-living systems, they uniquely harbor vital energy. Rignano’s belief stemmed from the notion that vital energy observes “further special laws of its own which are only experimentally to be determined and cannot be deduced from the more general laws [of energetics]” (Rignano Reference Rignano1911, p. 336). For Rignano, “it is just these laws of its own which, out of a physico-chemical energy, make it vital energy” (p. 336), and there is little surprise that, referring again to Rignano’s analogy to electric energy, vital energy has some special properties not possessed by electric energy. His commitment to distinguishing vital energy from non-vital forms is evident in his exploration of functional stimulation. For Rignano, phenomena of functional stimulation arise undoubtedly from external forces; however, in his words, it is “absolutely necessary to understand first clearly this distinction between external physical actions and functional stimuli” (p. 302). To clarify, external influences indicate physical energy in nature; even if they can be converted into functional stimuli, received by Rignano as vital energy, they remain intrinsically distinct from the latter.

Third, Rignano sought to decompose vital energy, attributing to it factors of capacity and intensity. Contemporary physics and chemistry no longer recognize this two-factor approach to the concept of energy, but it was influential in Rignano’s time, particularly within the energetics movement (for more, see Section 4). In this approach, various forms of energy are presented as products of two factors, one expressing the factor of capacity and the other that of intensity. To elucidate, Rignano drew parallels with electrical energy, where the capacity factor represents “the quantity of electricity,” and the intensity factor is portrayed by “the potential or electro-motive force” (Rignano Reference Rignano1926, 95). Analogously, for vital energy, he hypothesized that its capacity factor comprises elements he termed “nervions” (akin to “electrons,” but with varying capacities [p. 95]) and the intensity factor is depicted as “will-power” (pp. 98–99), or simply “nervomotive force” (paralleling “electro-motive force,” [p. 99]).

Fourth, in Rignano’s energetical vitalism framework, vital energies are capable of generating vital currents circulating within the entire organism and resulting in diverse purposive phenomena. These vital energies, during their circulation, can be stored, released, and acquired by appropriate accumulators. Rignano’s conception of vital circulation drew heavily from the paradigm of the electric circuit (Rignano Reference Rignano1911, 341–43). In an electric circuit, one can find electric currents and accumulators; and an electric accumulator “is capable of giving back inversely, during its discharge, the same kind of energy which it had previously received, and by which it had itself been deposited” (pp. 290–91). Yet, Rignano underscored the difference between vital and electric systems. While electric accumulators are far more generic as they can restore electric energies via currents of any intensity, their vital counterparts operate with “the greatest delicacy” (p. 291), and each of them only receives, accumulates, and discharges vital energies of “only single definite intensity” (p. 291).

In summary, however, Rignano’s vital energy hypothesis seems excessively speculative. He recognized this shortcoming, elaborating on the challenges of experimental evidence concerning this hypothesis (see Section 3.4). Moreover, Rignano (Reference Rignano1926, 94) expressed his reservations regarding “the nature of [the] specific thing which is susceptible of accumulation”, and also admitted that his hypothesis of vital energy amounted merely to “a few simply provisional conjectures.” Consequently, Rignano invested more in elucidating his centroepigenetic hypothesis, which appeared decidedly less conjectural. This hypothesis aimed to demonstrate how vital energies, currents, and accumulators converge to generate intricate purposive phenomena.

3.3. The centroepigenetic hypothesis

In Rignano’s energetical vitalism, the hypothesis of vital energy postulated a special form of energy as the basis of life; and it was the centroepigenetic hypothesis that solved the problem of how vital energy gives rise to a complex variety of phenomena of purposiveness in the organic realm. In the following the centroepigenetic hypothesis is elaborated through four sub-hypotheses advanced by Rignano.

First, Rignano proposed that a living organism operates through a circulating flow of vital energies. He surmised that these energies are either accumulated in particles on the chromosomes within nuclei or transferred among different nuclei through intercellular protoplasmic bridges. For Rignano, these particles are “specific potential elements,” and they function as “elementary accumulators” of vital energies (Rignano Reference Rignano1926, 85). Moreover, in biological activities vital energies are constantly discharged and received via accumulators, and they produce various vital currents circulating within the whole organism; furthermore, in the organism economy there emerges a general circulation of vital energies mediated by intercellular bridges and nuclei as the nodal points. The multicellular organism turns out to be, in Rignano’s words, “a single voluminous protoplasmic body in which the nuclei are inserted at different intervals as centers or foci of energy” (Rignano Reference Rignano1911, 41). This conception of a living organism as governed by a general vital circulation plays a fundamental role in Rignano’s centroepigenetic hypothesis. For him, an organism remains normally in a state of dynamic equilibrium decided by a specific level of vital circulation in its body; but in its life history the organism experiences various “disturbing influences” (p. 102) and always attempts to reach new states of dynamic equilibrium. Such disturbing influences can be understood as variations in the broadest sense, including both ontogenetic and functional changes, and they might come from different sources (see below).

Second, for Rignano, within every organism there exists a unique central zone of development, which exerts influences on the rest of the organism without undergoing changes itself during (but only during!) the developmental processes. Notably, such influences from the central zone belong to, in Rignano’s view, disturbing influences that are able to break down given states of equilibrium. Additionally, Rignano appeared to have embraced August Weismann’s famous distinction between the germ plasm and the soma. He equated the central zone with the germinative zone housing the organism’s germ plasm, while considering the remaining parts of the organism as the soma governed by the central zone during development. In unicellular organisms, he located their central zones within their nuclei (Rignano Reference Rignano1911, 53). As to multicellular organisms, however, Rignano did not propose that central zones exist in reproductive systems as we might do today; instead, he distinguished “the effective germinal zone,” which aligns with the central zone, from “the apparent geminal zone” where sex cells are formed (p. 17). For example, in a higher plant, Rignano suggested that its central zone is situated within specific nuclei within its “leaf” (p. 71), and for a vertebrate it is located in “the innermost … part of the spinal cord” (p. 75).

Third, Rignano designed a peculiar mechanism for the formation of a central zone. According to his hypothesis, the germ plasm of a living organism is initially stored in the nucleus of the fertilized egg; however, during embryogenesis, certain nuclei derived from the division of the original nucleus gradually gain dominance and constitute the central zone by being transformed into germinal nuclei, while others are reduced to somatic nuclei. More specifically, Rignano speculated that at a particular stage “embryonal development can no longer proceed after the same fashion in all cells” (Rignano Reference Rignano1911, 25). Cells possessing by accident (e.g. better nutrition) “more potential energy” (p. 25) will prevail and constitute the central zone of development. Conversely, other cells will be influenced by vital energies emanating from the central zone, leading to replacement of their original specific potential elements with new ones of a somatic nature. In Rignano’s words, “with the progressive somatization … the mass of their [somatic nuclei’s] respective specific elements to which is due the persistence … of their germinal energies, will gradually diminish and finally disappear” (p. 25).

Fourth, for Rignano, very interestingly, although germinal nuclei from a central zone govern somatic nuclei by discharging vital energies during organic development, somatic nuclei are capable of influencing germinal nuclei in exactly the same manner after development is “completed at the moment when all the germinal elements have achieved activation” (Rignano Reference Rignano1911, 101). This point is fascinating, and it warrants a closer exposition. In Rignano’s view, during development the central zone exerts almost complete control over the organism, because new developmental stages arrive exclusively through “the continuous activation of new specific potential elements” (p. 101) from its (the central zone’s) germinal nuclei; however, once development is complete and sex cells are formed, disturbing influences or variations originate no longer from the central zone, which has exhausted all possibilities of germinal activation. Instead, many of these influences stem from functional stimuli caused by external environmental factors. A functional stimulus, for Rignano, also leads to “a different distribution of the general nervous energy” (p. 102) like its ontogenetic counterpart and takes the adult organism to a new stage of dynamic equilibrium. In other words, after development is complete, in the general vital circulation of the organism somatic nuclei might also discharge vital energies of specific intensities to germinal nuclei that accumulate resultantly new specific potential elements. Through this perspective, Rignano essentially broke down the Waismann barrier that isolates the germ plasm from the soma. Contra Waismann, Rignano allowed for the possibility that somatic variations might also be inheritable as long as they can be incorporated into the germ plasm.

With his centroepigenetic hypothesis and its more flexible implications for the germ plasm/soma distinction, Rignano was confident that he could resolve several intricate controversies in contemporary biology, particularly the longstanding debate between preformation and epigenesis. By drawing upon various theoretical and experimental sources of his time, Rignano provided a comprehensive analysis of this controversy (which will be discussed further in Section 3.4). Additionally, Rignano aimed to address the dispute between neo-Darwinism and neo-Lamarckism through his centroepigenetic hypothesis. This dispute centered around whether acquired characters could be inherited or not. While Rignano generally leaned towards neo-Lamarckism, he found common ground with the renowned neo-Darwinian Weismann on several points. Notably, he acknowledged Weismann’s observation that “the great and justifiable desire to find for this inheritance some proof which should be irrefutable and not open to any objections has remained so far unfulfilled” (Rignano Reference Rignano1911, 159). Like Weismann, Rignano examined alleged cases of the inheritance of acquired characters and conceded that many of them could potentially be explained by neo-Darwinian mechanisms. However, Rignano was less inclined to dismiss the possibility of the inheritance of acquired characters for two reasons. First, despite the lack of conclusive experimental evidence, there were “a very large number of facts” (p. 169) supporting it. Second, he found neo-Darwinian arguments against it from Weismann and his followers to be either equally lacking in evidence or logically untenable at worst. To illustrate his point, Rignano referred to Weismann’s well-known amputation experiment where he observed that tail amputation in rats was not inherited. However, Rignano believed that Weismann’s experiment proved “nothing against the inheritance of functional adaptations” (p. 169). He argued that his centroepigenetic hypothesis could easily explain Weismann’s results, suggesting that a drastic variation such as amputation merely disrupts a “local” equilibrium, which the organism quickly restores without affecting its germ plasm at all (p. 169).

Considering these factors, Rignano concluded that neo-Darwinism did not possess a clear advantage over neo-Lamarckism, and he advocated for a reconciliation between the two. This was where Rignano believed his centroepigenetic hypothesis held one of its main virtues. As demonstrated earlier, Rignano adopted a more flexible interpretation of the germ plasm/soma distinction, allowing for the possibility of somatic influences on the germ plasm. According to his viewpoint, while the germ plasm from a living organism plays fundamental roles in both inheritance and development, its soma also participates in evolution when new potential elements are introduced to the germ plasm through functional stimuli. As suggested by the centroepigenetic hypothesis, not all acquired characters are inheritable, because, in Rignano’s words, “elements, new as well as old, deposited in the somatic nuclei will … be lost with the death of the individual” (Rignano Reference Rignano1911, 290). However, elements associated with “the simple addition of a new specific potential element to the germinal substance” can be inherited and ultimately contribute to species evolution (p. 290).

3.4. The problem of experimental evidence

Rignano was well aware of the primary challenge that his energetical vitalism faced from an empirical standpoint. In The Nature of Life, Rignano endeavored to address the issue of experimental evidence, particularly concerning his hypothesis of vital energy: “Who has seen this nervous energy which is assumed at the basis of life?” (Rignano Reference Rignano1930, 135). Surprisingly, Rignano openly acknowledged that “no one has ever seen it, no one has ever touched it in his laboratory” (p. 135). However, he swiftly attributed this lack of evidence to the absence of appropriate experimental instruments. Once again, Rignano drew a parallel with electric energy. Just as empirical evidence for electric energy is unavailable without the relevant instruments, he argued that the same applies to vital energy. Consequently, Rignano believed that “only when the physiologist has invented instruments capable of recording it, will nervous energy become perceptible to his senses” (p. 135).

As to his centroepigenetic hypothesis, Rignano spoke with greater confidence. In Upon the Inheritance of Acquired Characters, Rignano (Reference Rignano1911) discussed a formidably large number of experiments, demonstrating his proficiency in contemporary biological literature. To begin with, he pointed out several phenomena that provided evidence for the presence of intercellular protoplasmic bridges and the resulting circulation of vital or nervous energy within organisms. As an illustration, Rignano cited a series of experiments conducted by Wilhelm Pfeffer, a pioneering botanist in plant physiology. In the first experiment, Pfeffer removed the cell membrane from a plant cell, and then divided it into halves, one with a nucleus and one without. Two outcomes were reported by Pfeffer regarding the fate of these two parts: First, only the nucleated half was capable of forming a new cell membrane; second, if the anucleate portion remained connected to the nucleated part “even by only a very fine protoplasmic filament” (Rignano Reference Rignano1911, 31), it could also generate a small cell membrane. The second experiment conducted by Pfeffer involved attaching an anucleate mass of protoplasm to a neighboring cell “by means of thin filaments piercing the cell” (p. 31), and he discovered that a membrane could be formed around the anucleate fragment.

Moreover, Rignano believed that the presence of a central zone of development was strongly supported by numerous experimental findings. Specifically, he referred to an experiment conducted by the American biologist Helen Dean King on regeneration in Asteria Vulgaris (Rignano Reference Rignano1911, 61–62). In this experiment, it was observed that when certain arms of an organism of the species were severed, it failed to regenerate those specific parts. However, when all arms were completely removed, the organism demonstrated the ability to regenerate all arms, albeit with incomplete restoration of their original sizes. According to Rignano’s interpretation, these experimental results provided compelling evidence that the germ plasm is not uniformly distributed throughout the body but rather localized in a specific region, namely, the central zone.

These isolated experimental findings indeed provided support for certain aspects of Rignano’s centroepigenetic hypothesis. However, to truly appreciate how his hypothesis could better accommodate a range of contemporary experimental results compared to alternative theories, it is essential to examine his attempt to reconcile the longstanding controversy between preformation and (simple) epigenesis. Rignano outlined his strategy for substantiating the hypothesis as follows:

Then, to start, Rignano presented a series of experimental phenomena that would challenge hypotheses of both simple epigenesis and preformation. By simple epigenesis, Rignano indicated processes of development in which “no part whatever should ever be considered different in anyway, in so far as its formative action on the other parts is concerned, from these other parts, but rather all are to be regarded as equally necessary and of equal value in this respect” (pp. 106–7). Such simple epigenetic processes can be categorized into two types: those with preformistic germs and those without (“epigenesis proper” [p. 107]). As for preformation, Rignano specifically referred to Weismann’s doctrine, which postulated “infinitely numerous particles constituting the different determinants or groups of determinants” (p. 121). In his refutation, Rignano relied heavily on experimental results on embryological formation, regeneration, and instances of anachronic or abnormal development. A particularly insightful set of experiments was conducted by the German embryologist Gustav Born, who successfully produced artificially induced double monsters using tadpoles (namely, double-headed tadpoles).Footnote ¹ Born’s experiments involved removing specific parts from two tadpoles and then joining the cut surfaces together. He observed that a complete union resulting in double monsters formed shortly after their fusion. Inspired by Born’s results, Rignano believed that these successful cases of fusion:

Moreover, recognizing the significance of these results (p. 68), Rignano promptly put forth his centroepigenetic hypothesis as a suitable explanation. According to Rignano, by postulating two central zones of development with distinct nodal points, his hypothesis effectively accounted for the production of double monsters, better than both the theories of simple epigenesis and preformation.

Finally, Rignano (Reference Rignano1930, 139–54) posited that the centroepigenetic hypothesis has the potential to stimulate a range of novel experiments. According to this hypothesis, the germ plasm is positioned along the chromosome axis, “as a columnar stratification” (p. 142). Rignano suggested that this proposition could inspire investigations into the composition of chromosomes. He noted that contemporary observations already indicated that “the chromosomes often appear to be composed of superimposed discs” (p. 142), but cautiously remarked that “further observation might lead to fresh evidence on this point” (p. 142). A more pertinent example involves the inheritance of acquired characters, which is also implied by the centroepigenetic hypothesis. Consequently, Rignano proposed the following experiment for contemporary neo-Lamarckian biologists:

4.1. The energetics movement

The idea of vital energy emerged during the formative period of energy physics, when the notion of vital force received an energetical reinterpretation (Carpenter Reference Carpenter1850). However, it was not until the rise of the energetics movement that energetical vitalism gained public attention (Deltete Reference Deltete and John2003). Among the notable figures associated with this movement was Wilhelm Ostwald, an esteemed physical chemist who received a Nobel Prize in 1909 for his groundbreaking work on catalysis, chemical equilibrium, and reaction velocities. Starting from the 1880s, Ostwald actively promoted energetics as the fundamental science underlying all others. In his distinctive manner, he sought to demonstrate that key principles in physics and chemistry could be derived from more fundamental principles within energetics. Later in life, Ostwald shifted his focus away from experimental research in physical chemistry and developed a strong interest in natural philosophy and philosophy as a whole. During the early twentieth century, he dedicated himself to elaborating energetical principles applicable to various disciplines such as physics, chemistry, biology, sociology, and economics (Ostwald Reference Ostwald1908).

Besides Ostwald, Georg Helm (Reference Helm1887) stood as another primary proponent of the energetics movement. While Helm may not have enjoyed the same historical prominence in physics and chemistry as Ostwald, he showcased a deeper understanding of mathematics and articulated the foundational principles of energetics with greater precision (Deltete Reference Deltete2012). Moreover, Helm preceded Ostwald in endeavors to reduce various physical sciences—including thermodynamics, chemistry, and mechanics—to the principles of energetics. As previously mentioned, Rignano associated the factors of capacity and intensity with the notion of vital energy, and this two-factor approach was offered first through Helm’s factorization principle. Helm postulated that every form of energy could be mathematically dissected into two components: the intensity factor and the capacity factor (Helm originally termed this “extensivity”). Concerning the intensity factor, Helm introduced the law of intensity as the second law of energetics, complementing the first law, recognized as the energy conservation principle. According to Helm’s second law of energetics, every form of energy had the tendency to pass from higher to lower intensity. Lastly, while Helm exhibited more restraint than Ostwald in venturing beyond his expertise to champion general energetics, he fundamentally supported efforts to recognize non-physical energy forms, notably in sociology and economics (Helm Reference Helm1887, 71–75).

At a meeting in Lübeck in 1895, however, Max Planck and Ludwig Boltzmann voiced significant critiques of the energetical theories presented by Ostwald and Helm, leading to a diminished appeal of the energetics movement within the realms of physics and chemistry (Deltete Reference Deltete1999). Nevertheless, the broader conception of energetics garnered substantial interest from disciplines outside of the physical sciences. Within psychoanalysis, the idea of mental energy thrived, with Sigmund Freud prominently utilizing it in the development of psychoanalytical frameworks (Tran The, Magistretti, and Ansermet Reference Tran The, Magistretti and Ansermet2018). Several neo-classical economists active during the marginalist revolution of the late nineteenth century, notably Francis Ysidro Edgeworth, drew parallels between utility or pleasure and mental energy, with some even making bold proclamations regarding their equivalence (Mirowski Reference Mirowski1989, 210–75). The advocacy for energetical sociology extended beyond esteemed figures like Ostwald. It also included the renowned Belgian industrialist and philanthropist Ernest Solvay, whose affluence allowed him to establish an institute of sociology dedicated to exploring the possibility of reducing social relations to energetical relations (Carrosio Reference Carrosio, Magnani and Carrosio2021).

Given the incorporation of energy concepts into social sciences, it is unsurprising to witness its adoption in biology around the turn of the twentieth century. A noteworthy illustration is found in the widely referenced physiology textbook of that era, Principles of General Physiology, authored by the eminent physiologist, William Bayliss (Reference Bayliss1924). Within this work, Bayliss dedicated an entire chapter to energetics, elaborating on its foundational principles. Furthermore, he embraced the two-factor approach, a hallmark of the energetics movement: “Energy is composed, then, of two factors, which are known as the ‘intensity’ and ‘capacity’ factors, and is equal to the product of the two factors, properly chosen” (Bayliss Reference Bayliss1924, 28). Bayliss also exhibited a clear awareness of Rignano’s energetical vitalism doctrine when he wrote:

While he maintained strong reservations about the vital energy hypothesis, Bayliss sought a more balanced stance, concurring in principle with Rignano that emerging instruments could potentially substantiate the hypothesis through novel experimental evidence.

Concurrently, Hans Driesch, now recognized as the last prominent biologist ardently supporting vitalism, also demonstrated a keen awareness of energetical vitalism. Mirroring Bayliss, Driesch incorporated the general laws of energetics—those delineated by energeticists like Helm and Ostwald—into his overarching philosophy of nature (Driesch Reference Driesch1908). Despite expressing a congenial tone towards Rignano in his foreword to the latter’s Man not a Machine (Driesch Reference Driesch and Rignano1926), Driesch directed incisive critiques at energetical vitalism in The Science and Philosophy of the Organism (Driesch Reference Driesch1908). He initiated his critique by posing the question: “How stands entelechy to the concept of energy”? (Driesch Reference Driesch1908, 164). Driesch’s response split into two segments. On the affirmative front, he endeavored to illustrate that entelechies can influence physical systems by either inhibiting or redirecting physical energy (pp. 221–22). However, the more intriguing aspect lay in his counterargument, where he firmly repudiated a perspective he explicitly labeled as “energetical vitalism” (p. 170). For Driesch, this doctrine suggested that “in cases of morphogenesis, and probably in nervous phenomena too, some unknown potential forms of energy may be at work; and … that the specificity of vital phenomena and their autonomy is due to the peculiarities which that unknown energy possesses” (p. 167), and in Driesch’s summary, in this doctrine entelechies were perceived as “a sort of subsidiary or potential energy” (p. 168). Yet, Driesch unambiguously dismissed this notion: “I decline … any kind of ‘energetical’ vitalism whatever” (p. 170). Driesch anchored his rejection on two grounds. First, “in all cases where the economic equation [the principle of energy conservation] is fulfilled there would seem to be no place for a ‘new’ energy” (p. 168). Second, compared to energies that “are quantities” (p. 168), “entelechy lacks all the characteristics of quantity” (p. 169).

4.2. The neo-Lamarckian movement

In the historiography of Darwinism, the influential eclipse thesis posited that the Darwinian paradigm of evolution by natural selection underwent a decline towards the late nineteenth century, giving way to several competing evolutionary doctrines. Notably, one such alternative was the neo-Lamarckian doctrine, which embraced the concept of the inheritance of acquired characters (Bowler Reference Bowler1992, 58–106). As illustrated earlier, through his energetical vitalism—specifically, the centroepigenetic hypothesis—Rignano sought to bridge the gap between neo-Lamarckism and neo-Darwinism. Contrary to the eclipse thesis’s assertion, Rignano perceived neo-Darwinism as the prevailing doctrine of the era and endeavored to carve out a niche for the less dominant neo-Lamarckism via his centroepigenetic hypothesis. Rignano’s comprehensive understanding encompassed not only experimental evidence bolstering neo-Lamarckism during his period, but also theoretical frameworks put forth by both antecedent and contemporary biologists (Rignano Reference Rignano1911, 224–88). It was these biologists who laid the groundwork for what can aptly be termed the neo-Lamarckian movement at the dawn of the twentieth century (Bowler Reference Bowler1992, 58–106; Schacter Reference Schacter2011, 98–106; Gliboff Reference Gliboff, Snait and Jablonka2011).

The neo-Lamarckian movement gained momentum in the late nineteenth century as certain biologists and philosophers began earnestly promoting ideas subsequently categorized as neo-Lamarckian. However, as historians have compellingly demonstrated, while Lamarck championed the inheritance of acquired characters, he neither claimed originality for the idea nor actively sought to promote it; paradoxically, it was Charles Darwin who ardently advocated for the inheritance of acquired characters, emerging as a more zealous Lamarckian than Lamarck himself. Compared to Lamarck, Darwin not only “offered a theory to explain how characters acquired as the result of use and disuse were transmitted from one generation to the next,” but also “allowed that he had provided more evidence on the effects of use and disuse than anyone before him” (Burkhardt Reference Burkhardt2013, 803). Throughout his lifetime, Darwin perceived no discord between natural selection and the inheritance of acquired characters. Evidently, Rignano’s interpretation of Darwin highlighted Darwin’s Lamarckian tendencies, noting that Darwin “draws especial attention to the inheritance of characters acquired by domestic animals” (Rignano Reference Rignano1911, 160).

By the close of the nineteenth century, the concept of inheriting acquired characters was labeled either Lamarckian or neo-Lamarckian. This notion was contrasted against an evolved doctrine of all-sufficient natural selection, touted as neo-Darwinism, predominantly by Weismann. With his strict distinction between the germ plasm and the soma, Weismann contended that the inheritance of acquired characters was implausible since these characters manifested somatically and, consequently, fail to influence the germ plasm. Nonetheless, a considerable cohort of biologists and philosophers of the time remained skeptical, challenging the neo-Darwinian stance and advocating for the inclusion of the inheritance of acquired characters, a position increasingly termed neo-Lamarckian.

As has been pointed out (Schacter Reference Schacter2011, 98–106; Gliboff Reference Gliboff, Snait and Jablonka2011), early twentieth-century neo-Lamarckians, including Rignano, were less antagonistic towards natural selection; their primary grievance lay with the dogmatic neo-Darwinian assertion of natural selection as the sole evolutionary mechanism. Given the multifaceted nature of evolutionary and developmental processes, neo-Lamarckians were open to exploring alternative mechanisms, with the inheritance of acquired characters being a primary contender. Regrettably, the broader trajectory of evolutionary biology did not align with their perspective. By the mid twentieth century, the doctrine endorsed by modern evolutionary synthesis championed the neo-Darwinian narrative, leading to neo-Lamarckism’s decline. The resurgence of Lamarckian theories, buoyed by epigenetic inheritance, has materialized only recently. Although this resurgence has remained controversial, it provides a potential platform for considering Rignano’s possible contributions to modern molecular genetics (for more, see Sections 5 and 6).

4.3. The mnemic movement

A third important movement that shaped Rignano’ vitalism was the mnemic movement in biology at the onset of the twentieth century. This movement expounded biological heredity by ascribing memory as an inherent property to all living entities (Schacter Reference Schacter2011, 106–20). Expectedly, this movement exhibited significant overlap with the neo-Lamarckian movement, wherein acquired characters were aptly perceived as “remembered” characters. Richard Semon, a key proponent of this movement, introduced the notion of the mneme in his work The Mneme (1921), originally published in German in 1904. For Semon, the mneme represented “the capability” of preserving residual effects even when “the excitement produced by the stimulation has apparently ceased” (Semon Reference Semon1921, 12). Notable contributors to this movement included Ernst Haeckel, Francis Darwin, Ostwald, and Rignano, with the latter two providing an energetical lens to the mneme concept.Footnote ²

It is worth noting the distinctive stance of the philosopher and sociologist Edgar Zilsel, as helpfully chronicled by Monica Wulz (Reference Wulz2012). Whereas the majority of biologists and philosophers demarcated living from non-living entities via the mneme concept, Zilsel expanded this idea into the inorganic domain. For Zilsel, matter was not synonymous with static entities but rather with evolving processes. Even inanimate processes, in his view, could manifest mnemonic attributes, with memory in this context alluding to material constellations of equilibrium. By adopting this perspective, Zilsel homogenized physical, biological, and cognitive processes, anchoring them in a singular dynamic understanding of matter. Moreover, Zilsel contended that these constellations or memories could never be replicated with absolute precision, and this inherent imprecision underscored the unidirectional nature of all natural (physical, biological, and cognitive) processes. In consequence, Zilsel posited that “knowledge … is the enterprise of building epistemic objects from fluctuating matter producing mutable empirical constellations over the course of time” (Wulz Reference Wulz2012, 101). Self-identifying as a Marxist, Zilsel believed that this conception of knowledge aligned seamlessly with the tenets of historical materialism.

4.4. Moral and political messages

Historians have widely recognized that early twentieth-century vitalists frequently (though not universally) endeavored to derive moral and political implications from their teachings. As Anne Harrington (Reference Harrington1996, xix) has noted succinctly, “life and soul … served as key symbols in this time of cultural and spiritual regeneration.” Consequently, several German scientists and philosophers of the early twentieth century vocalized moral and political tenets under the banner of science. A prominent example is the physiologist Jakob von Uexküll (Harrington Reference Harrington1996, 34–71). Hailing from an aristocratic German Baltic lineage, Uexküll’s childhood fostered a robust German nationalist sentiment. As he matured, Uexküll became disenchanted with the Weimar Republic’s tumultuous inception, cultivating a persistent skepticism towards mass democracy. Drawing from his vitalistic or holistic biology, Uexküll proposed an organic characterization of the state, likening it to a living entity. In this paradigm, he emphasized state authority over its citizenry. Uexküll’s organic interpretation later found favor with the Nazi regime. However, it must be emphasized that the links between scientific tenets and moral or political pronouncements could be ambiguous. For example, despite largely concurring with Uexküll on biological specifics and sharing a united front against mechanistic perspectives in biology, Driesch diverged significantly in his sociopolitical outlook. A committed cosmopolitan and pacifist, Driesch’s contrasting views led to his forced “retirement” in 1933, despite his close association with Uexküll (Harrington Reference Harrington1996, 188–93).

Similarly, energeticists, such as Ostwald, eagerly sought moral and political interpretations from their principally scientific propositions. Ostwald, more ambitious than Rignano, formulated an energetical sociology within his energetical worldview, aspiring to elucidate social dynamics through the universal laws of energetics. Ostwald did not hesitate to offer moral guidance, proclaiming an energetic imperative: “Do not waste energy: make it useful” (Ostwald, quoted from Hakfoort Reference Hakfoort1992, 536). In parallel, Solvay proposed his own version of energetical sociology, advocating for the optimization of socially utilizable energies.

In the neo-Lamarckian discourse, similar moralizing sentiments prevailed. Herbert Spencer, for instance, drew from Lamarckian principles to highlight the potential for moral and social progress via the enhancement of cognitive and ethical faculties (Weinstein Reference Weinstein and Edward2024). However, with the emergence of the mnemic movement, certain neo-Lamarckians leveraged the heredity/memory analogy to endorse nationalist and occasionally racist ideologies. Their approach was rather direct: They perceived nations and races as human collectives shaped by a prolonged accumulation of inheritable memories (Otis Reference Otis1994). Yet, drawing a direct line between the mnemic movement and nationalist or even racist ideologies can be challenging. For instance, the aforementioned Marxist socialist, Zilsel, extended the mneme concept to inorganic entities, drawing parallels with historical materialism that undoubtedly bolstered his Marxist convictions (Wulz Reference Wulz2012).

Nevertheless, in 1909, the eminent sociologist Max Weber ([Reference Weber, Brunn and Whimster1909] Reference Weber, Brunn and Whimster2012) provided a scathing critique of such interpretations, pinpointing Ostwald’s and Solvay’s energetical sociology as primary culprits. Weber contended that Ostwald erred egregiously, particularly in his attempt to “derive value standards … from the facts found in his area of specialization” (p. 253). Contrarily, as far as I read, Rignano consistently refrained from retroactively attributing his economic and sociological theories to energetical rationales. Unlike Ostwald and Solvay, he did not intend to elaborate his version of energetical sociology. Despite short remarks on social purposiveness, justice, and morality, no evidence indicates Rignano’s allowance of elusive derivations of moral and political directives from his integrated energetical vitalism framework, tailored specifically for biology.

5.1. On the hypothesis of vital energy

Regarding the hypothesis of vital energy, it is clear that its validity is questionable due to the absence of corroborating experimental evidence. Specifically, consistent experimental results supporting the effects of vital energies have been elusive since the hypothesis was proposed. However, Rignano might argue that the deficiency in experimental evidence stems from contemporary limitations of scientific instruments and may be addressed in the future. Although such a counterpoint could prematurely conclude the debate and perhaps irk some, it must be acknowledged that, logically, the argument is not inherently flawed. The aforementioned physiologist Bayliss concurred on this point, although with strong reservations. According to Bayliss, “the fact that we have no instrument by which it can be measured directly is not a serious argument against its existence, since we have no direct means of measuring chemical energy” (Bayliss Reference Bayliss1922, 294).

An ancillary observation is that, unlike vital energy, various forms of physical energy, such as kinetic energy, thermal energy, and electric energy, have all been well established in contemporary physics (Smith Reference Smith1998). Notably, these energy constructs have been indirectly verified and invariably accompanied by mathematical formulations facilitating precise experimental validation. Therefore, it seems plausible that, should the notion of vital energy ever gain traction in biology, it too would necessitate a mathematical representation. This would not only enable accurate measurements but also foster theoretical paradigms for modeling exchanges between physical and vital energy forms.

It is also imperative to underscore that the outright dismissal of vitalism based on a presupposition of various forms of physicalism contravenes the foundational ethos of scientific inquiry and is, thus, intrinsically unsound. It is a pity that analytical philosophers of biology today often oppose vitalism, defaulting to a physicalist metaphysical standpoint (Brigandt and Love Reference Brigandt, Love and Edward2023). Nevertheless, the essence of scientific progress lies in bold hypothetical proposals and careful experimental investigations, and such progress is of little relevance to the grand struggle between vitalism and physicalism. Put succinctly, there exists no inherent metaphysical rationale precluding the proposition of hypotheses bearing vitalistic elements, such as that of vital energy.

The principle of energy conservation’s impact on vitalism further elucidates this point. Today physicalists frequently herald the articulation of the conservation principle as a pivotal moment in the history of physicalism (Papineau Reference Papineau, Gillett and Loewer2001). Such a standpoint appears to strengthen the conviction that vitalism can be excluded by physicalism, given the eminent scientific polymath Hermann Helmholtz’ assertion in the late nineteenth century that vitalism inherently suggests the feasibility of perpetual motion of the first kind and violates therefore the principle of energy conservation (Caneva Reference Caneva2021, 1–4). However, while Helmholtz’ critique aptly addresses early vitalistic doctrines posited by natural philosopher-physiologists like Georg Stahl and Albrecht Haller, it scarcely debilitates the vital energy hypothesis. Energetical vitalists can deftly counter that the vital factor is a special form of energy, i.e., vital energy, and for this reason, it essentially observes the principle of energy conservation. Indeed, one is entirely free to advance the hypothesis of vital energy (although experimental confirmation is another matter), and the principle of energy conservation (not to say physicalism) could do little to eradicate entirely possible forms of vitalism.

It is worth noting that the aforementioned physical energy concepts were postulated nearly concurrently with vital energy. Historically, prior to the establishment of the principle of energy conservation, various non-mechanical systems, ranging from electric to biological ones, were deemed candidates of perpetual machines of the first kind (Drysdale Reference Drysdale1870, 9–10; Caneva Reference Caneva2021, 78). Given this context, it is plausible that concepts of both physical and vital energies emerged in response to the challenge presented by the conservation principle. However, their subsequent trajectories diverged markedly. As previously highlighted, constructs like electric energy have endured experimental scrutiny with mathematical precision and are now entrenched in modern physics, a fate not shared by vital energy.

Further, the reality is that vitalism has been proposed and re-proposed by drawing resources from contemporary sciences, and its fecundity surpasses what most physicalists recognize (Chen Reference Chen2024). As evidenced in this article, figures like Rignano deftly wove intricate energetical vitalism theories, intriguingly bridging energy and vitalism. The editors of Nature once highlighted a recurring theme they termed “chronic vitalism” (Anonymous 2007, 1032), where vitalistic doctrines wax and wane yet persist throughout the history of science. Contrary to physicalist assumptions, advancements in the physical sciences have not eradicated vitalism but have instead occasionally invigorated it in unforeseen ways, paving avenues for novel vitalistic hypotheses. Energetical vitalists discerned connections between energy and life, and, perhaps more notably, Driesch (Reference Driesch1908, 225), despite his critique of energetical vitalism, invoked Maxwell’s demon and its possible violation of the second law of thermodynamics to elucidate the role of his entelechy! Given such recurring endeavors to rejuvenate vitalism, their potential implications for addressing the enigma of life warrant further consideration.

5.2. On the centroepigenetic hypothesis

In Rignano’s energetical vitalism, the centroepigenetic hypothesis emerges as more congruent with contemporary biology. Though it might be contestable to conflate life with a distinct energy form through the vital energy hypothesis, the centroepigenetic hypothesis is notable for two primary reasons. First, it posits that certain chromosomal entities are pivotal during organic development. Rignano’s idea of specific potential elements on chromosomes echoes contemporary notions of genes, characterized by unique nucleotide sequences, and vital energy mirrors genetic information. Second, the centroepigenetic hypothesis suggests a mechanism where the soma impacts the germ plasm, aligning with current understandings of epigenetic inheritance.

However, some might argue that this interpretation of Rignano’s centroepigenetic hypothesis is excessively generous, potentially misconstruing Rignano’s intent within his energetical vitalism. Addressing this contention, it is imperative to note that while Rignano’s centroepigenetic hypothesis resonates with current molecular genetics in facets, it also encompasses diverse elements (like vital energy). Nevertheless, it is defensible to assert that facets of Rignano’s doctrine presaged later molecular genetics breakthroughs. At their core, both specific potential elements and genes are posited to reside on chromosomes, directing organic development via either vital energy or genetic information, despite their divergent operational mechanisms.

This evaluation is informed by Hasok Chang’s perspectives on outdated doctrines in the history of science (Chang Reference Chang2012, Reference Chang2021). According to Chang, concepts like phlogiston from chemistry have never really disappeared but maintained their presence “under different names”; notably, phlogiston can be interpreted as the predecessor of both “chemical potential energy” and “electrons” (Chang Reference Chang2012, 65). Although it is perhaps misleading to claim that the concept of phlogiston still exists under different names, Chang’s insight can be received in a less mysterious and also more insightful manner. In my view, to do full justice to apparently outdated concepts like phlogiston, it is possible to suggest a more nuanced history of differentiation: Phlogiston, embedded within eighteenth- and nineteenth-century scientific discourse with diverse connotations, was eventually supplanted by more refined concepts, with only some facets retained in modern constructs like “chemical potential energy” and “electron.” Thus, historically “outdated” doctrines can be reincorporated into contemporary scientific discourse. To put it even more explicitly, these seemingly obsolete concepts “have displayed significant meanings and utilities in various experimental and theoretical contexts”, and for this reason they are quite likely to have potential contemporary analogs (Chang Reference Chang2021, 227).

To emphasize, it is judicious to reevaluate historical scientific concepts and theories more charitably. To illustrate further, the notion of mental energy briefly mentioned in Section 4 offers insight. The evolution of energy physics and the resultant energetics movement birthed ideas of both vital energy and mental energy. In the late nineteenth century, mental energy was sometimes received as a form of energy only available in the realm of mind, but observing equally the laws of energetics like its physical and even vital counterparts. At the time, for instance, pioneering neo-classical economists, such as Edgeworth, were enamored by the idea of mental energy, equating it occasionally with economic concepts of utility and pleasure (Mirowski Reference Mirowski1989, 218). However, despite neo-classical economics drawing heavily from energy physics, especially in mathematical constructs, the identification of mental energy with utility proved awkward, because no principle of energy conservation could be meaningfully formulated in economics for mental energy (Mirowski Reference Mirowski1989, 222–31). Consequently, this connection waned, and the nascent conceptual history of utility and mental energy is largely forgotten today.Footnote ³ However, for a comprehensive understanding of mental energy, its historical connection with utility is pivotal: Mental energy intriguingly prefigured utility or pleasure, serving as a historical conduit between energy physics and neo-classical economics.