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1 Introduction: An “Orthodox” Training

Scientists are usually not trained to analyze the intellectual pathways they more or less unconsciously follow during their careers. They may be somewhat aware of the various pitfalls induced by personal remembrances and of the unconscious “reconstructions” or rationalizations linked to autobiographies, not to speak of the pro domo pleading. But it may be profitable in trying to understand patterns of conceptual change. Therefore I will begin with a review of my intellectual background and situation during the years immediately preceding the 1981 Dahlem conference, and how this might explain why I was selected to participate.

I started as an assistant in comparative anatomy at the Science Faculty of Paris University in 1961, after a standard curriculum in biology and geology. Contrary to a long tradition among English (and French) speaking historians of biology who, by and large, convey the simplistic idea that French biologists remained Lamarckian up to the 1960s–70s (e.g., Mayr and Provine 1980), the intellectual situation among evolutionary biologists was much more subtle and interesting in France during the immediate post-war years (Grimoult 2000), the period of my undergraduate education (late 1950s/early 1960s). As well recorded in Grimoult’s extensive and uncompromising survey (2000), every well-known university professor in the various domains of natural history and biology—paleontology, genetics, marine biology, entomology or embryology—were committed evolutionists. But for them this meant a belief in Darwinian “descent with modification” or in the theory of the reality of evolution (Løvtrup 1982), rather than in the all encompassing, almighty explanatory power of the Darwinian mechanism of natural selection (Gayon 1988). This created a very peculiar intellectual situation for students. On the one hand, the data emerging from every quarter of natural history in favor of evolution was conveyed enthusiastically; on the other hand, the underlying mechanisms proposed were viewed with much caution. A pluralistic approach to evolutionary mechanisms was often advocated, with the idea that natural selection was obviously a part of the package but was not working alone; much remained to be discovered about the mechanisms of evolution. To name only one individual of that era, the much-maligned Professor Pierre-Paul Grassé, editor of the great Traité de Zoologie, was an enthusiastic and energetic evolutionist (in the sense just defined), who effectively promoted evolution to the general public through the media. Although he is described as a despiser of genetics, it is critical to underline that Grassé organized in his own laboratory the full practical teaching curriculum about Mendelian genetics in the fruit fly and other models, and this material was mandatory for all biology students in Paris.

It is true that Lamarckism, or more precisely neo-Lamarckism, had been an almost official theory of evolution in the University of the Third Republic, roughly from the 1870s to the 1930s (de Ricqlès 2008, 2010; Loison 2010). But in spite of the supposed influence and power of the “hyper tardive Lamarckians” (as Grimoult depicts them), the practical situation had changed considerably by the late 1950s. First, Mendelian genetics was taught at school on a generalized scale to all pupils. Second, the turmoil caused in France by the “Lysenko affair” and the Communist party enforcing belief in the “heredity of acquired characters” from 1948 to 1953 (cf., de Ricqlès 2006) ultimately had devastating effects on neo-Lamarckism. Third, it is generally not recognized abroad that the synthetic theory of evolution was rather well known in France at the time. It was formally introduced to France by a Rockefeller Foundation sponsored meeting organized by the CNRS as early as 1947 (de Ricqlès 2008). At the meeting, the American paleontologist George Gaylord Simpson explained the synthetic theory to his French colleagues, which acted as a revelation to a new generation of young French scientists in the aftermath of the second world war. They quickly became like apostles of the Modern Synthesis. Among them were paleontologists such as Henry Tintant and Louis Thaler, geneticists like Claudine Petit, and comparative anatomists and developmental biologists like Charles Devillers (Devillers 1991). This generation, in turn, became the mentors of my own generation of students, who thus became intimately familiar with the synthetic theory of evolution; it was taught to us almost as an orthodoxy. This situation was enforced by the translation into French of major books, like Simpson’s Tempo and Mode as early as 1950 (Simpson 1950, 1951); by the publication of the seminal 1947 Meeting (Piveteau 1950); and, by various analyses of the Modern Synthesis, most notably in the masterful historical review of evolutionary theories by Paul Ostoya, the uncle of Louis Thaler, and editor of the respected monthly La Nature (Ostoya 1951).

To cut a long story short, my generation learned biology within the framework of the Modern Synthesis and Mendelian genetics but—at least for some of us—the intellectual environment did not allow us to easily accept the Modern Synthesis as a fully developed and completely satisfactory answer to the issue of biological evolution. There was an acknowledgement that the synthetic theory was the current “least bad” intellectual package available to account for actual evolutionary mechanisms (e.g., de Ricqlès 1979a), But there was also a reluctance to fully embrace the theory in all of its details for several reasons:

  1. (i)

    The propensity of the theory toward triumphalism. The Modern Synthesis (potentially) explained all biological evolution; there was nothing outside of the theory worth exploring in order to understand the history of life and its current state.

  2. (ii)

    The propensity of the theory toward sclerification. The Modern Synthesis too often turned into dogma. The “right” mutations selected by the “right” pressures from the environment will always account for the observed adaptive results, given ad hoc explanatory scenarios, generally impossible to test (Devillers and Ricqlès 1982). Hence the organism was easily pulverized into various traits, each of them receiving its proper adaptive/selectionist explanation. Nothing could limit the effects of natural selection to exquisitely shape organisms and refine their functions: its explanatory power seemed implausibly boundless.

  3. (iii)

    The organism was neglected and forgotten. Comparative and evolutionary biology before and after Darwin (including Darwin himself) had put great emphasis on the morphologies and functions of individual organisms, shown in the sciences of systematics, comparative anatomy, and physiology. With the advance of population thinking, there was a shift away from the organism. The focus became studying the quantitative fate of genes within populations, thus “jumping over” the organism level. This was resented bitterly by some of us, especially those more interested in comparative morphology and systematics, “the soul of natural history” (as Darwin put it). There was also a palpable tension or paradox because, after all, the individual organism remained the main unit of selection within Darwinian orthodoxy, as well as the end result of the interactions among genes and the environment during ontogeny.

  4. (iv)

    The lack of developmental biology, morphogenesis, and embryology within the Modern Synthesis. In spite of the efforts of some scientists, such as Sir Gavin de Beer, Conrad Waddington, and Richard Goldschmidt, the issue of ontogenesis—the development of the organism—was treated as a “blackbox” of little interest and relevance for the study of animal evolution. In so doing, the Modern Synthesis departed from centuries of intellectual tradition, which had always tried to link and decipher (even through odd and spurious ways) the significance of individual ontogenesis by reference to some larger order “developments” (Mengal 1993). Such ideas took various shapes in pre-Darwinian times, from idealistic metamorphosis, to the speculations of Naturphilosophie. In the framework of evolution, the wider term of comparison for ontogeny finally took the form of phylogeny, the story of species lineages. Thus the idea reached its mature form during Darwin’s life under Haeckel’s “fundamental biogenetic law” that ontogenesis is a brief recapitulation of phylogenesis (1866).

    Even before the emergence of the Modern Synthesis, the Law of Recapitulation, in spite of its popularity and some heuristic value, experienced devastating criticisms that stemmed from both the advances in Mendelian genetics and discoveries surrounding paedomorphosis and neoteny. For instance, Garstang (1922) rephrased Haeckel’s dictum as, “Ontogeny does not recapitulate phylogeny, it creates it.” For all that, the situation of developmental biology relative to the Modern Synthesis from 1940s to 1970s could be best summarized as a form of apartheid, at least in the vertebrate realm (de Ricqlès 2004). Many evolutionary researchers with a deep interest in developmental biology chafed under this situation and sought to integrate development into a wider evolutionary synthesis. This was especially the case with one of my mentors, Professor Charles Devillers (1914–2000), who lamented the lack of developmental biology within the orthodoxy of the Modern Synthesis, and was an advocate for the birth of a new developmental genetics that he was fortunate enough to see dawn well before his life’s end.

  5. (v)

    The lack of a distinction between evolutionary patterns and evolutionary processes within the Modern Synthesis, including independent methodologies to study them. Because the only level where actual evolutionary process could take place were populations, specific groupings were favored and supra-specific taxa were viewed as practical artifacts destined to express biodiversity through formal Linnean categories. Accordingly, the Modern Synthesis emphasized the construction of scenarios to explain evolutionary processes only at the infra- or peri-specific levels (de Ricqlès 1997). Conversely, macroevolution merely described the end-result of microevolutionary processes accumulated over geological time. And since macroevolution only described patterns, no distinct evolutionary processes could exist at such supra-specific levels. Nevertheless, generalizations such as “mammals evolved from reptiles” were a part of the common phraseology within the vulgate of the Synthesis. The philosophy of phylogenetic systematics (cladistics) provided a basis to question these premises and the practices of the Modern Synthesis (the so called “new systematics”) as soon as the work of Willy Hennig (1965, 1966) became known outside of the German-speaking realm (mid-1960s).

During the 1960s and 1970s, my own technical expertise became histology, comparative anatomy, and vertebrate paleontology. Because I was especially interested in “lower” tetrapods, I first focused my histological knowledge on the morphogenesis of the skeleton in extant amphibians (de Ricqlès 1964–65). Later, I developed methods in paleohistology to study developmental features of paleozoic and mesozoic tetrapods. This was accomplished within a broad comparative framework, taking into account the Synapsids (mammalian lineage) and, subsequently, reptilian lineages including crocodiles, dinosaurs, and birds (e.g., de Ricqlès 1975, 1976, 1980).

2 Conceptual Perspectives on Evolution and Development Circa 1981

Many of the grounds for dissatisfaction with the Modern Synthesis described above, and the themes of research interest shared by those of us discontented with it, were central elements of the 1981 Dahlem conference. For example, I met Stephen Jay Gould in 1977, having exchanged correspondence with him earlier, and his involvement in the Dahlem conference mirrored my own dissatisfaction with the synthesis and interest for research subjects outside of it. Among the subjects of common interest to us was—first and foremost—the importance of heterochronies in evolution (a subject interest also shared with Dave and Marvalee Wake). The use of urodele amphibians as an extant model to analyze heterochronies as possible evolutionary processes among fossil stegocephalians and amniotes has remained an important subject of study ever since (e.g., de Ricqlès 1975, 1979b, 1989). The possibility of pursuing informative analyses of late development among fossil vertebrates followed thanks to skeletal histology and paleohistology. Some examples of this work are the skeletal heterochronies in the secondary adaptation of tetrapods to aquatic habitats (e.g., de Ricqlès and Buffrenil 2001; Houssaye et al. 2008) and growth patterns among archosaurs (e.g., Horner et al. 2001; de Ricqlès et al. 2001; Main et al. 2005).

Much more generally, the relevance of heterochronies for the study of relationships between developmental and evolutionary biology, and the integration of development into evolutionary thinking, has blossomed as a most important consequence of Dahlem 1981 (e.g., Ricqlès 2004; see also Hanken, Ch. 4, this volume). Important monographs, popular textbooks, and hundreds of specialized research papers have followed on the heels of this inspiration, bringing an important input of the morphological sciences into the current Evo-devo synthesis.

Some Dahlem 1981 participants (including myself) also shared views on very general, even philosophical, aspects of evolutionary biology. These included the repudiation of simple, linear deterministic causation as a relevant explanation of evolution. Historical contingencies and the chance convergence of multiple causal factors were viewed as essential aspects of evolutionary history, following views already clearly expressed by Cournot (1872). Accordingly, even if retrospective explanations can be formulated, predictions of evolutionary trajectories are hardly possible (other than the trivial-mechanistic). This conclusion was linked to the contrast between nomological (law-seeking) and palaetiological (historical) sciences, and the need for evolutionary analysis to integrate both of them. An intrinsic unpredictability stemmed from the historical component of evolution, and a similar unpredictability (but one that could ultimately be reduced to causal explanations) was reflected in the emergence of new properties along the succession of ascending levels of biological organization.

There was also a conviction that not all biological structures could be understood merely as actual (or past) adaptations resulting from the operation of natural selection, which paved the way for the concept of exaptation (Gould and Vrba 1982). Other substantial issues underplayed by the Modern Synthesis were (a) the significance of structural conditions and properties of biological materials (e.g., architectural, topological, geometrical, and dimensional), as previously expressed by Seilacher (1970), and, (b) the actual historical (phylogenetic) situations that acted as pre-established “constraints” from which (and within which) natural selection had to operate. Finally, there was discomfort with the way proponents of the Modern Synthesis contrasted microevolution and macroevolution. Here there were a variety of opinions, including some that restricted macroevolution to patterns only, and others who regarded the span of microevolution to macroevolution as a hierarchy of processes rather than a doctrinal opposition or dichotomy.

Gould (and others) had already published on important aspects of these approaches and views by the time of Dahlem 1981 (Alberch et al. 1979; Gould 1977, 1980a, b). Over the next three decades Gould elaborated on these themes (e.g., de Ricqlès 2002, 2010), culminating in his magnum opus (Gould 2002). But Dahlem 1981 was far from simply a meeting for expressing a consensus of dissent. For example, I disagreed with Gould about the appropriate theoretical perspective for an evolutionary approach to systematics. Gould accepted a version of “Mayrian” evolutionary systematics, whereas I was an advocate in favor of cladistics. I never understood why Gould did not readily embrace cladistics, which seemed to me a necessary part of his hierarchical view of evolution. If macroevolutionary processes above the species levels exist, then they require (in my view) treating historical/genealogical/genetical entities (clades) as realities in (or of) nature. As a consequence, material processes, such as clade selection, could apply to them. If supra-specific groupings are only convenient “Linnean pigeon holes” or formal categories for taxa (e.g., poly- or paraphyletic), then they do not convey a material, genetic kinship and hence cannot behave as entities that are subject to unique (macro) evolutionary processes.

3 Conceptual Stasis and Change Since Dahlem 1981

As noted above, many aspects of these evolutionary subjects and the issues they raised were discussed at the time of the 1981 Dahlem conference. They have remained an inspiration for many of us during the intervening decades. But the constraints of careers have extensively modulated what each of us has done and how much we have published in the various fields considered. I concentrated on the comparative histology of bone and developed paleohistology as a method to introduce the study of late ontogenetic development and natural history traits into the realm of tetrapod paleobiology (e.g., de Ricqlès 1992; de Ricqlès et al. 2004). Rather than elaborate on these scientific developments in more detail (cf. Stockstad 2004; Erickson 2005), it is more useful to focus here on the contextual background in which they occurred over the decades following Dahlem 1981. To be frank, it has been a constant strain and struggle for me to keep the natural history oriented parts of biology (e.g., systematics, morphology, paleontology, organismal biology, and ecology) alive and evolving within the university ecosystem. This persistent effort was required because of the overwhelming pressure from cell physiology, molecular biology, pharmacology, and other allied approaches that strove to seemingly swallow everything within the framework of a biomedical and applied vision of biology. Seen in retrospect, the necessary nurture and care of our particular “intellectual” problems (e.g., phylogenetics, phenotypic plasticity, gene regulation, and evolvability) was downplayed in light of the preeminent sociological problem of disciplinary survival and renewal. In these science wars, where the niches in a Darwinian academic ecosystem were limited, internecine battles in evolutionary theorizing were not the most pressing concern.

The 1970s were dominated by the hard-fought campaign to introduce modern phylogenetics (cladistics) into the curriculum. Simultaneously, it became more and more obvious that the western pattern of economic development, viewed so far as an unquestionable fact of progress in all its aspects (even by the Soviet Union, which tried to compete with it under a different political system), would sooner or later bring the world ecosystem to a dead end. It was thus time to introduce new curricula integrating ecology, inventory systematics, and conservation biology alongside of the more traditional subjects. This has blossomed along a variety of pathways (and not always satisfactorily), but at last evolutionary ecology appears to be well integrated with other aspects of evolutionary science.

During the early 1980s, and following the inspiration of Dahlem 1981, those of us in the Paris university context introduced a new evolutionary biology cursus (from Masters Degree to PhD) based on a multidisciplinary integration of many relevant disciplines (from paleontology to population genetics). This involved several universities in Paris, as well as the Paris Museum of Natural History. Through extensive meanderings and a not quite predictable evolution, this cursus still frames the education of students in evolutionary biology at the Museum and Paris 6 University (and elsewhere). The 1990s were dominated by the mutual rediscovery of molecules and morphology because the new phylogenetics at last made possible a dialogue between, and even some integration of, molecular and morphological sciences. This was later expanded as the molecular genetics of development opened up new relationships with organismal morphology. In turn, this was further extended with the flood of empirical findings about the molecular evolution of developmental genes, which brought along with it astounding connections between molecules, morphology and systematics. It generated a completely renewed comparative developmental biology. These developments have extensively modified the “classical” Modern Synthesis, which in part metamorphosed into the new “Evo-devo” paradigm, where the organism and its morphology find again, at last, their well-deserved place (de Ricqlès and Padian 2009; de Ricqlès 2010). Perhaps unsurprisingly, the seeds for much of this conceptual development in evolutionary theorizing can be found in Dahlem 1981.

4 The Conceptual Landscape of Evolution and Development Today: The Case of Bone Tissue

Many of the conceptual themes that were present in the context of Dahlem 1981 are manifested in current research by myself and colleagues on bone tissue, including the analysis of complex causality in biology through the integration of historical, functional and structural factors. Bone—as a tissue—is an extraordinarily complex biological system; it exists within highly varied structural patterns, connected to numerous functional processes and physiological demands. Histovariability describes how bone tissue exhibits changes within the individual body depending on the age, sex, specific bone, specific location within a given bone, or given site within a section. Histodiversity describes bone tissue changes that obtain between conspecific individuals within a species, between closely related taxa, between higher-level, supra-specific groups, including within and among higher vertebrate clades.

Traditionally, bone histovariability and histodiversity have been explained within the framework of a single point of view; either historical, or functional, or structural factors are given preeminence. For example, paleontologists readily interpret data by reference to the systematic–phylogenetic situation of the organisms observed. Other biologists interpret data with reference to functional features, such as the ontogenetic circumstances of bone development or the biomechanical functions of mature bone. Nevertheless, a robust comparative histological analysis demonstrates that bone results from a complex set of factors that require biologists to integrate the phylogenetic, structural, and functional inputs (de Ricqlès 1975–78). For some time there were no tools available to pass beyond this qualitative analysis but now the situation has changed. Recently developed statistical methods have been used (Desdevise et al. 2003) to partition the variation so that it becomes possible to assign the outputs and interactions among historical, functional and structural factors of bone tissue variability (Cubo et al. 2008; de Ricqlès and Cubo 2010). This gives a material example of “Seilacher’s triangle” (Gould 2002), which had been more of a heuristic than an operational tool, and provides new ways to elucidate the complex web of causality that is the signature of historical sciences. Evolution is simultaneously a historical (palaetiological) and a non-historical (nomological) science.

5 Concluding Remarks

Thirty years later, the pivotal importance of Dahlem 1981 is more and more apparent. Indeed, there has been a “before” and an “after” for many of the original participants. During the conference they discovered that they were not alone in their reluctance with some (or many) aspects of the Modern Synthesis, even though everyone attending accepted it as the necessary starting point from which more satisfactory intellectual extensions and explorations could take place. Accordingly, subsequent to Dahlem 1981, there was a new spirit of intellectual freedom relative to the orthodoxy of the Modern Synthesis, which has proved fruitful over the intervening decades. This has led to the modification and revision of theoretical outlooks in many research fields. The edited volume deriving from the conference (Bonner 1982) has also proved immensely influential on a whole generation of evolutionary and developmental biologists. It has operated as a catalyst for the emergence of what was to become the “super Evo-devo synthesis” (de Ricqlès and Padian 2009).

From my own philosophical vantage point, Dahlem 1981 initiated a major shift, later immensely developed by molecular genetics, towards a probabilistic rather than deterministic vision of evolutionary mechanisms. This does not underplay the importance of natural selection as a causal mechanism of evolutionary change. Instead, it both relativizes the role of natural selection, by taking into account more fully the historical and structural constraints within which selection can act, and extends it, by taking into account the multiple levels of biological organization where selection operates. This probabilistic view, which emerges from an integrative approach to structural, functional, and historical factors in evolution from both nomological and palaetiological perspectives, is observable in the final views of Stephen Jay Gould (Gould 2002) who, for people like myself, has been and remains the very soul of Dahlem 1981, before and beyond.