Dialectical thinking has been pervasive in philosophy of developmental biology. After the paradigm of the “genetic program” (Jacob, 1970) according to which an organism is the expression of an authoritative program engraved in heredity, the late 20th and early 21st centuries have emphasized that biological systems result from a dialectical process taking place between genes and environment (Lewontin, 2001; Gilbert & Tauber, 2016). Evolutionary biology has also engaged into a dialectical turn, notably through the studies dedicated to selective niche construction. These studies have shown that not only natural selection shapes organisms, but that organisms also shape natural selection (Odling-Smee et al., 2003), and therefore participate in evolutionary processes. This contribution aims at highlighting that dialectical thinking can also impact researches about heredity, a process that can be conceived as a point of junction between development and evolution.
Heredity is a universal biological phenomenon that has been the object of scientific research since the second part of the 19th century. Traditionally, heredity refers to the “like-begets-like phenomenon” (Darwin, 1859), namely to the transmission of traits such as morphologies, metabolic capacities or behaviors, across generations. At first sight, heredity therefore refers to what is stable in living beings. It denotes something static in the biological world. As early noted by Susan Oyama (2000), the traditional descriptions of heredity invite adopting a static perspective, in which traits appear as relays that are passed on unchangedduring a race.
Genetics, the first unified science of heredity born at the dawn of the 20th century, has obviously contributed to ground this static perspective. According to Mendelian geneticists, traits are passed on through the transmission of theoreticalstable units called genes. This statement appears in line with the 19th century’s idea according to which the vehicles of hereditary transmission are small and fixed particles (see for example Galton’s units of « stirps » and De Vries’ «pangenes  »).
The identification of genes with DNA strands by the middle of the 20th century has hardened the static perspective of heredity, insofar as it has led to explain the like-begets-like phenomenon by the duplication of an inert material, transmitted intact across generations and equally controlling the development of traits in parents and offspring. According to this updated version, the vehicle of heredity is a stable molecule that can be divided into discrete units. This molecule has a life on its own. It self-replicates and determines the features of organisms in virtue of a specific and unidirectional causal power, generation after generation.
Some authors have nevertheless early questioned the static and atomistic approach. They have proposed dynamical (behavioral) accounts, in which heredity appears as the property of a set of elements and of their collective actions, rather than as a property of a specific object (for a general appraisal, see Gayon 1992). For example, D’Arcy Thompson (1942) considered that it was a mistake to attribute to material particles properties that depend on their collective action (“the energy of their collocation”, Gayon, 1992, p. 432). In the same vein, Nanney (1956), envisioned a process of cellular stability due to molecular interactions. In the context of his research about cytoplasmic heredity, he described a dynamic self-perpetuation of a variety of molecular species.
By the end of the 20th century, the putative specific properties of DNA and its full responsibility in the maintenance of biological forms have been subject to serious criticism. Fox Keller (2000, p. 26-27) has highlighted that the molecule does nothing by itself. She emphasized  that DNA stability requires the work of a full cellular machinery that notably performs DNA repair across cell divisions, but also that self-replication is a myth, given that DNA replicates thanks to specific cellular enzymes.  Lewontin, as for him, insisted on the fact that if anything has the power to replicate in the biological world, it is nothing but organisms (1993).
All these views put forward the idea that biological stability, and notably the stability of traits across generations, is not a property that can be attributed to a single molecule – causally responsible for the stability of other elements – but rather to a system in which parts collaborate. Thereby, they opened a path to introduce a dialectical thinking in research about heredity.
Such a path has been explored by Developmental System Theory (DST) tenants. These philosophers stated that biological stability and replication are collective phenomena. Their dialectical vision of heredity was connected to their dialectical vision of development. DST tenants’ argument can be summarized as follows : contrary to the idea conveyed by the metaphor of the genetic blueprint, ontogenesis is not the effect of a single molecule that has a specific causal and informational power. It rather results from the interactions of different genetic and non-genetic developmental resources (causal parity). And if life cycles reoccur in a similar way in parents and offspring, it is because all these resources are made available at each generation. As a result, heredity cannot be restricted to genes, but should include all those elements that constitute the replicated “developmental matrix”.
DST studies facilitated the emergence of the idea of extended heredity. The latter refers to the fact that the like-begets-like phenomenon is not underpinned by the replication of DNA alone, but by the transmission of multifarious elements – DNA, epigenetic marks, microorganisms, behaviors, representations, etc. – that are today highly documented in the literature (see for example Jablonka & Lamb, 2005; Bonduriansky & Day, 2018). Extended heredity can be conceived in a static and cumulative way. In this view, expanding heredity merely consists in adding all those elements that are transmitted across generations, namely the genotype plus some elements of the phenotype (see for example Bonduriansky, 2012).
However, studies about extended heredity also constitute an opportunity to elaborate a new dialectical and dynamic perspective of the like-begets-like phenomenon. Such perspective is at the core of the organizational approach to (extended) heredity that has been developed during the last few years (Pontarotti, 2015; Pontarotti 2016; Mossio & Pontarotti, 2019). This approach articulates the concept of heredity and the concept of organization  . It more precisely intends to link extended heredity with a Kantian flavored conception of organization, in which the latter is thought in terms of closure of constraints (Moreno & Mossio, 2015; Montevil & Mossio, 2015; Bich, 2016).
In this theoretical context, biological systems are conceived as objects displaying differentiated and interdependent parts. These parts are called organizational constraints and are said to perform (organizational) functions. This means that they collectively channel flows of matter and energy (processes) so as to contribute to the maintenance of the system to which they belong and, thereby, to their own maintenance, in virtue of circular causality. Organizational constraints can be enzymes, but also organs such as hearts, or functional systems such as vascular ones. Organizational closure refers to the loop of interdependencies that can be identified between all the constraints constituting a biological system.
The organizational perspective of heredity defines heredity as the conservation of functional patterns across generations, or as the transgenerational maintenance of networks of organizational constraints. This approach is fully compatible with an extended vision of heredity, and actually appears as particularly adequate to make sense of it. In this perspective, the networks of biological constraints are not limited to genes and to organs produced “out of genes” in a given environmental context. They include epigenetic marks, microorganisms, hormones, socially acquired behavior (involving or not the use of specific tools), etc. As a result, biological systems appear as extended functional networks. For example, in some birds, the pattern of food channeling can be determined by constraints as diverse as enzymes produced out of DNA, microorganisms acquired early in development and feeding behaviors transmitted through social interactions. The transgenerational conservation of this pattern will involve the collaboration of diverse channels of transmission (genetic, epigenetic, behavioral, etc.).
The organizational perspective of heredity contributes to introducing dialectical thinking into the studies about biological heredity. Indeed, it is based on the assumption that the stability of biological objects, across generations, cannot be explained by pointing at the power of a single molecule, but should be explained by the collective action of a network’s components. In doing so, this approach meets other contemporary proposals introducing a dynamic dimension into the field of heredity or into biological studies in general. Beyond the above mentioned DST approach, one can evoke Griesemer’s contribution (2000), in which heredity is a phenomenon taken in the dynamic of developmental processes. Besides, the organizational perspective of heredity partially meets “process ontology” (Nicholson and Dupré, 2018), insofar as it participates in rejecting atomistic and substantialist visions of living beings.
However, the organizational approach presents some specificities. First, it extends heredity while keeping the phenomenon limited and distinct from environmental stability. Indeed, it restricts the range of interactants responsible for biological stability to the constitutive constraints of a biological system. In doing so, it clearly departs from the DST perspective. Second, the literature dealing with organization as “closure of constraints” contrasts constraints with processes, and thereby takes some distance with process ontology . In the view outlined in this literature, biological beings cannot fully be conceived as made of processes. They are rather thought as constituted by constraints channelling processes. Third, and importantly, the organizational approach to heredity annihilates the relevance of the distinction between genotype and phenotype, namely between hereditary causes and hereditary effects (Pontarotti, Mossio and Pocheville, 2022). From an organizational point of view, the distinction between causes and effects within a biological system makes no sense, insofar as, as early stated by Kant, parts of organized beings are reciprocally causes and effects of each other. The annihilation of the distinction between genotype and phenotype somehow echoes the collapse of the replicator/interactor dichotomy in evolutionary biology, which is justified by the fact that replication always implies interaction (Griffiths and Gray, 1994).
The organizational approach to heredity may also have significant consequences in evolutionary thinking. First, it may allow overcoming the debate about whether evolutionary biology should pay attention to the evolution of genotypes (Modern synthesis) or to the evolution of phenotypes (Extended synthesis). From an organizational point of view, what matters is neither the fate of genotypes or that of phenotypes, but the differential maintenance, through space and time, of functional networks that can include heterogeneous parts (including  tools and microorganisms). Fitness, in this view, is not about making more offspring; it is about making more of oneself in space and time, either through maintenance, growth or multiplicative reproduction. Second, the organizational approach to heredity may bring some new material to the dialectical turn in evolutionary biology   . This turn is based on the hypothesis that evolutionary causality is not fully assumed by natural selection, but rather shared with organisms – and other biological systems – able to produce evolutionary relevant variation. In claiming that hereditary elements are reconstructed across generations in a dynamic way in the context of an organized system, the organizational approach clearly open some room to think about the conditions of emergence and stabilization of multifarious heritable variation (epigenetic, behavioral, symbiotic, etc.) with potential impact on evolutionary processes. At this point, it might be important to remember that organizational closure does not mean immutability and that organization rather appears as a condition of (stable) variation (Mossio, Montévil, Longo, 2016).
To conclude, I would like to remind the reader that heredity is originally a metaphor. It refers, indeed, to the transmission of goods from parents to offspring, to a global heritage. While the traditional approaches suggest that this heritage is static, the challenge, now, is to propose theoretical tools to make sense, in tomorrow’s biology, of this heritage’s dynamic and dialectical nature.
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Comments on “Dialectical thinking in the science of heredity: yesterday, today and tomorrow”
Rasmus S. Haukedal says:
Great article! However, there’s an issue with the endnotes, as only the first  is present below the text.