Antonine Nicoglou

In 1956, in his Principles of Embryology, Conrad Hal Waddington explained that the word “epigenetics” should be used to translate and update Wilhelm Roux’ German notion of “Entwicklungsmechanik” (1890) to qualify the studies focusing on the mechanisms of development. When Waddington mentioned it in 1956, the notion of epigenetics was not yet popular, as it would become from the 1980s. However, Waddington referred first to the notion in the late 1930s. While his late allusion clearly reveals that Waddington readily associated the notion of epigenetics with the developmental process, in the contemporary uses of the notion this developmental connotation seems to have disappeared. The advent and success of molecular biology have probably contributed to focusing biologists’ attention on the “genetic” or the “non-genetic” over the “developmental”. In the present paper, I first examine the links that exist, in Waddington’s work, between the classical notion of epigenesis in embryology and those of epigenetics that Waddington proposed to connect, and even synthesize, data both from embryology and genetics. Second, I show that Waddington’s own view of epigenetics has changed over time and I analyze how these changes appear through his many representations (both schematic or metaphorical images) of the relationships between genetic signals and developmental processes.

The paper describes the context and the origin of a particular debate that concerns the evolution of phenotypic plasticity. In 1965, British biologist A. D. Bradshaw proposed a widely cited model intended to explain the evolution of norms of reaction, based on his studies of plant populations. Bradshaw’s model went beyond the notion of the “adaptive norm of reaction” discussed before him by Dobzhansky and Schmalhausen by suggesting that “plasticity” – the ability of a phenotype to be modified by the environment – should be genetically determined. To prove Bradshaw’s hypothesis, it became necessary for some authors to identify the pressures exerted by natural selection on phenotypic plasticity in particular traits, and thus to model its evolution. In this paper, I contrast two different views, based on quantitative genetic models, proposed in the mid-1980s: Russell Lande and Sara Via’s conception of phenotypic plasticity, which assumes that the evolution of plasticity is linked to the evolution of the plastic trait itself, and Samuel Scheiner and Richard Lyman’s view, which assumes that the evolution of plasticity is independent from the evolution of the trait. I show how the origin of this specific debate, and different assumptions about the evolution of phenotypic plasticity, depended on Bradshaw’s definition of plasticity and the context of quantitative genetics.

In this chapter, I analyze how the effort to bring together " nature " and " nurture " has put forward " plasticity " as a key concept in biology. While the notion of plasticity appeared in the field of genetics in the early 20 th century as a solution to the debate between " nature " and " nurture " – the notion of plasticity proved a key concept in articulating those genes and environment –, in social science the opposition seems to persist (probably because the meaning of plasticity itself has not remained stable or uncontroversial among the different fields of biology). In order to understand the issues raised by the nature-nurture debate, it therefore appears necessary to provide a comprehensive view of the history of plasticity within the debate.

The question of whether it is possible to fit together the developmental and evolutionary explanations raises a number of difficulties. In a sense, it is possible to consider that the problems concerning the development of the individual have nothing to do with those related to the evolution of organisms over time (Wallace B, Can embryologists contribute to an understanding of evolutionary mechanisms? In: Bechtel W (ed) Integrating scientific disciplines: case studies from the life sciences. Springer. pp 149–163. Retrieved from http://​link.​springer.​com/​content/​pdf/​10.​1007/​978-94-010-9435-1_​9.​pdf, 1986). If one describes the development as the temporal trajectory of an individual from the zygote to adult, then the timescale of the individual development appears to be radically different from the evolutionary time scale. This chapter aims to show that the time dimension is an essential element to explain the proximal mechanism of development, and that it remains unspecified if not still largely ignored by biologists. I suggest that by focusing on the characters rather than on the “developmental stages”, developmental biology, while approaching evolution, nonetheless and paradoxically lost sight of the actual temporal dimension its process (Beer, G.R. (de) 1930. Embryology and evolution. Gloucestershire: Clarendon Press; Hamburger V, Hamilton HL, J Morphol 88(1):49–92, 1951). Therefore, consideration and characterization of the timing of development remain to be done: it requires to analyze its peculiarities and the way they have been, or may be apprehended. This focus on the developmental time will allow us to emphasize the importance of time for the explanation of the developmental process.

This chapter starts with a short history of the concept of phenotypic plasticity (from the seventeenth century to present) in order to distinguish two distinct conceptions of plasticity: one more dynamic (or Aristotelian) according to which the notion has been described as a property inherent to life whose very organization depends upon it, and an other conception, more passive, according to which “plasticity” means the capacity to express different phenotypes for a single genotype depending on environmental conditions. The chapter shows then how Darwinian theories have first favored the second conception, before the emergence of a renewed interest for the first one, which plays the role of an explanans, while the second conception would rather be an explanandum. In so doing, the chapter describes in depth the role of the concept in micro- and macroevolution study.

The phrase “nature and nurture” in its modern sense was coined by Francis Galton, in 1869, in discussion of the influence of heredity and environment on social advancement based on his reading of Charles Darwin. For the first time, what was inherited and what was acquired appeared as two independent causal domains, referring to two distinct supports and processes. Discussions in biology, psychology and social sciences about nature and nurture are mainly associated with the relative importance of an individual’s innate qualities (“nature”) as compared to an individual’s personal experiences, also considered as acquired qualities (“nurture”), in causing individual differences for physical and behavioral traits. “Nurture” may correspond to education, to culture, to what is acquired, or even to environment, depending on how one defines “nature” in each case. In biology, these discussions have focused on the relative importance of inherited factors (genes) compared to environmental factors in causing the apparent features of the organism (that biologists call “phenotypic traits.”)
Since both types of factors are known to play interacting roles in development, some contemporary scientists consider the question as representing an outdated state of knowledge (Barnes & Dupré 2008, Rutter 2006, Ridley 2003, Holdrege 1996). While social scientists agree on considering that social interactions are crucial in the rise of many cultural relevant trait, some evolutionary biologists and evolutionary anthropologists would enlighten the strong impact of gene differences onto any trait, be it morphological or behavioral, and therefore contest the importance of the interaction between factors through development (Dawkins 1976, 1982). Lumsden & Wilson (1981) have argued that genes are keeping a leash on culture, the difference between authors being only on the length of the leash. Therefore, it appears still difficult to get rid of the old nature-nurture debate.
In this presentation, I will present my current project, which is an attempt to provide a reconceptualization of the nature-nurture debate in a new framework, which brings development to the fore, in order to throw new light on our current understanding of the evolution of individual’s traits formation in life. More precisely, the project aims at offering a clarification of developmental process through different disciplines (from developmental biology but also evolution, and until disciplines for which the implications of evolutionary theory may be important, such as developmental psychology and child psychoanalysis). Such a rapprochement should allow a clarification of the relationships, but also of the differences between these disciplines concerning the question of individual’s development in the nature-nurture debate.

The writings of the plant ecologist Anthony Bradshaw, published in the mid-1960s, have been  particularly influential in the development of evolutionary ecology. His theoretical work has changed the way biologists use to see “phenotypic plasticity” – the ability of an organism to respond morphologically, physiologically or behaviorally to the changes in its environment – and it has also changed the way breeders use to consider the problems of genotype and environment interaction. Before him, this interaction was mainly seen through the “norm of reaction” model – the sum total of all the possible phenotypic curves expressed for a same genotype submitted to changing environments (Woltereck 1909). From now on, the norm of reaction was redefined as a phenotypic function which represents the multiple varying reactions determined by a genotype interfering with the totality of all incident (environnemental) factors (Johannsen, 1911); the “norm of reaction” gradually becoming synonymous with the concept “genotype” (Dobzhansky, 1955).
Through an analysis of Bradshaw’s works in plant ecology and what distinguishes him from his predecessors, we will enlighten some of the important causes that have led to a sustainable implementation of the concept of “phenotypic plasicity” in most of the contemporary studies that examine the evolution of interactions between the genotype and its environment. We argue that such an analysis should have important theoretical impacts for our current undestanding of phenotypic plasticity.

The issue of whether and how a gathering of developmental and evolutionary explanations should be achieved raises difficulties. In a certain way, one could consider that “problems concerned with the orderly development of the individual are unrelated to those of the evolution of organisms through time” (Wallace 1986). Since development can be depicted as the trajectory of an individual from the zygote stage
to the adult stage, in a process in time, at least its timescale appears
clearly decoupled from the evolutionary timescales (Hall & Olson
2006). Furthermore, the developmental process may include various
processes at distinct time and space scales (molecular, cellular, etc.),
which can be further analyzed on its own. I suggest that by focusing
on the character instead of the developmental stage (de Beer 1940),
developmental biology has lost the temporal dimension of its process.
I argue that a way to reassess the importance of time in developmental
process (in order maybe to achieve afterwards a gathering of development and evolution) is to addresses the specifics of the developmental timing, its specificities and its relation to other time scales. This would, first, offer a clarification of the separation between evolutionary and developmental timescales and then show how a developmental theory might integrate the various processes at distinct space and time scales that I identify.

In this presentation I will describe the context and the origin of a particular debate that concerns the evolution of phenotypic plasticity. In 1965, British biologist Anthony Bradshaw proposed a widely-cited model intended to explain the evolution of norms of reaction, based on his studies of plant populations. Bradshaw's model went beyond the notion of the “adaptive norm of reaction” discussed by Theodosius Dobzhansky and I. I. Schmalhausen by suggesting that “plasticity” (the ability of a phenotype to be modified by the environment) could be under direct genetic control. To prove Bradshaw’s hypothesis, it became necessary for some authors to identify the pressures exerted by natural selection on phenotypic plasticity in particular traits, and thus to analyse its evolution. In this presentation I will contrast two different views, based on quantitative genetic models, propsoed in the mid-1980s: Russell Lande and Sara Via’s conception of phenotypic plasticity, which assumes that the evolution of plasticity is linked to the evolution of the plastic trait itself, and Samuel Scheiner and Richard Lyman’s view, which assumes that the evolution of plasticity is independent from the evolution of the trait. I will show how the origin of this specific debate, and different assumptions about the evolution of phenotypic plasticity, depended on Bradshaw’s definition of plasticity and the context of quantitative genetics.

The assumption that plasticity is nothing more than a property of the genotype and that it is specific to particular traits within a given range of environments is based on the idea that the precise scientific – genetic – notion of “phenotypic plasticity” and a more general – sometimes metaphorical – notion of “plasticity” used across different disciplines of biology (in evolution, behavioral ecology or in cellular biology) can be assimilated. By focusing on the theoretical analysis of phenotypic plasticity, biologists have mainly addressed the issue of what its mechanistic bases are (Schlichting & Smith 2002) and they have tried to reach a general consensus assuming that phenotypic plasticity should be considered as an explanandum – its explanans being the process of natural selection to which is added the assumption of a genetic basis for plasticity. However, theoreticians of the Extended Synthesis – whose aim is to offer an extended view of evolutionary theory based on recent data – have assumed that the same phenomenon of phenotypic plasticity is not only an explanandum of evolution but that it is also an explanans of evolution (Pigliucci 2010). This assumption has led to a certain confusion concerning the explanatory status of phenotypic plasticity.

In this presentation, I will show how a general notion of plasticity (distinguished from the specific notion of “phenotypic plasticity”) might either be considered as an explanans of variation or as an explanandum of natural selection. I will argue that a distinction between “phenotypic plasticity” and a more general notion of “plasticity” is important in order to offer a clarification on the explanatory status of plasticity. I will argue that this clarification sheds light on the reasons for a recurrent use of a general notion of plasticity in all disciplines of biology alongside the existence of the genetic notion of phenotypic plasticity.

The notion of plasticity appears to be a key term for the study of development. First, the notion has a long history in the field (it was already used in 1928 by vitalists such as Hans Driesch). And second, it puts on various meanings depending on its field of use (i.e., in morphogenesis, developmental genetics, zoology!). The old disciplinary tradition considers that development stops at a certain point of the lifetime (at the end of embryogenesis, with birth or with sexual maturity of the organism). But more recently development has been considered, by a growing number of biologists and philosophers alike, as a process that “never stops” (Gilbert 2010) during the lifetime of an organism. In this conception, development would have no sharp-cut boundaries.
My purpose here is to show in which ways the notion of plasticity –defined as the “ability of an organism to react to an environmental input with a change in form, state, movement or rate of activity” (West Eberhard MJ 2003)- has been used as a heuristic tool to develop a conception of development that “never stops”. By making some distinctions in the different understandings of plasticity in biology, I would like to investigate a more restrictive definition of plasticity and its consequence for our understanding of developmental process. References Gilbert SF (2010) Developmental Biology. Sunderland : Sinauer Associates. West-Eberhard MJ (2003) Developmental Plasticity and Evolution. Oxford : Oxford university Press.

Is plasticity relevant to define development?

Antonine Nicoglou, IHPST & Paris Pantheon-Sorbonne University

The notion of plasticity appears to be a key term for the study of development. Indeed, the notion has a long history in the field (it was already used in 1928 by embryologists such as Hans Driesch). And nowadays the notion of plasticity puts on various meanings depending on its field of use (in morphogenesis, developmental genetics, zoology…). The old disciplinary tradition considers that development stops at a certain point of the lifetime (alternatively at the end of embryogenesis, at birth or when the organism reaches sexual maturity). But more recently development has been considered, by a growing number of biologists and philosophers alike, as a process that “never stops” (Gilbert 2010, see also Oyama, Griffiths & Gray (eds.) 2001) during the lifetime of an organism. In this conception, development would have no sharp-cut boundaries. My purpose here is to show in which ways the notion of plasticity –defined as the “ability of an organism to react to an environmental input with a change in form, state, movement or rate of activity” (Mary Jane West-Eberhard 2003)- has been used as a heuristic tool to develop a conception of development that “never stops”. The conventional dichotomy pervasive in evolutionary theory, between environment and genotype will be discussed and revisited. By making some distinctions in the different understandings of plasticity in biology, I would like to demonstrate that a restrictive definition of plasticity might help to define more precisely what development is.

References
Gilbert SF (2010) Developmental Biology. Sunderland : Sinauer Associates.
Oyama S, Griffiths PE, Gray RD (2001) Cycles of Contingency : Developmental Systems and Evolution. Cambridge(MA): MIT Press.
West-Eberhard MJ (2003) Developmental Plasticity and Evolution. Oxford : Oxford university Press.

Les écrits du phytoécologiste Anthony Bradshaw, parus au milieu des années 1960, sont considérées comme ayant particulièrement influencé l’écologie évolutionnaire. Ils ont changé la manière dont les biologistes envisageaient l’évolution de la plasticité phénotypique – la capacité qu’a un organisme à répondre morphologiquement, physiologiquement ou comportementalement aux changements dans son environnement – mais ils ont également modifié la manière dont les sélectionneurs envisageaient les problèmes soulevés par la question de l’interaction entre le génotype et l’environnement. Auparavant cette interaction était principalement envisagée par le biais de la « norme de réaction » – l’ensemble des courbes phénotypiques possibles pour un même génotype soumis à des environnements variant (Woltereck) – bientôt définie comme les fonctions phénotypiques représentant la réponse d’un génotype à une variable environnementale (Johannsen) ; la « norme de réaction » devenant progressivement synonyme de « génotype » (Dobzhansky).
L’analyse des travaux de Bradshaw (en écologie végétale) et de ce qui les distingue de ses prédécesseurs, qui se réfèrent à la notion de norme de réaction (principalement en génétique animale), nous permettra d’éclairer les raisons probables de l’implantation durable de la notion de « plasticité phénotypique » dans les études contemporaines diverses qui examinent l’évolution des interactions entre le génotype et l’environnement.

In this presentation, I examine the issue of regulation in biology in order to clarify when regulation might be considered as a source of variations in living systems. In biology, references to regulation have first appeared in embryology about regeneration. In  physiology, by contrast, “regulation” mainly referred to metaphors about physics and was linked, for Claude Bernard for instance (1878), to the intrinsic properties of living systems. Just before him, Auguste Comte had introduced the idea of a regulation of the “inside through the outside”(1851).
These two views – an intrinsic conception of regulation vs. regulation as an emergent property – permeate the current conception of regulation in biology. First, I argue that regulation may either appear as 1) the self­regulation ability of living systems or as 2) the observable outcome of the interaction of living organisms within their environments. Then, I examine these two views in the light of induction in development (i.e. the developmental process, which generates a new embryonic organization). Finally, I indicate which criteria should be used to determine when regulation is a source of variations in living systems.