The traditional practice of establishing morphological types and investigating morphological organization has found new support from evolutionary developmental biology (evo-devo), especially with respect to the notion of body plans. Despite recurring claims that typology is at odds with evolutionary thinking, evo-devo offers mechanistic explanations of the evolutionary origin, transformation, and evolvability of morphological organization. In parallel, philosophers have developed non-essentialist conceptions of natural kinds that permit kinds to exhibit variation and undergo change. This not only facilitates a construal of species (...) and higher taxa as natural kinds, but also broadens our perspective on the diversity of kinds found in biology. There are many different natural kinds relevant to the investigative and explanatory aims of evo-devo, including homologues and developmental modules. (shrink)

The 1981 Dahlem conference was a catalyst for contemporary evolutionary developmental biology (Evo-devo). This introductory chapter rehearses some of the details of the history surrounding the original conference and its associated edited volume, explicates the philosophical problem of conceptual change that provided the rationale for a workshop devoted to evaluating the epistemic revisions and transformations that occurred in the interim, explores conceptual change with respect to the concept of evolutionary novelty, and highlights some of the themes and patterns in the (...) different contributions to the present volume, Conceptual Change in Biology: Scientific and Philosophical Perspectives on Evolution and Development. (shrink)

A central reason that undergirds the significance of evo-devo is the claim that development was left out of the Modern synthesis. This claim turns out to be quite complicated, both in terms of whether development was genuinely excluded and how to understand the different kinds of embryological research that might have contributed. The present paper reevaluates this central claim by focusing on the practice of model organism choice. Through a survey of examples utilized in the literature of the Modern synthesis, (...) I identify a previously overlooked feature: exclusion of research on marine invertebrates. Understanding the import of this pattern requires interpreting it in terms of two epistemic values operating in biological research: theoretical generality and explanatory completeness. In tandem, these values clarify and enhance the significance of this exclusion. The absence of marine invertebrates implied both a lack of generality in the resulting theory and a lack of completeness with respect to particular evolutionary problems, such as evolvability and the origin of novelty. These problems were salient to embryological researchers aware of the variation and diversity of larval forms in marine invertebrates. In closing, I apply this analysis to model organism choice in evo-devo and discuss its relevance for an extended evolutionary synthesis. (shrink)

A flurry of technological advances in molecular, cellular and developmental biology during the past decade has provided a clearer understanding of mechanisms underlying phenotypic diversification. Building upon such momentum, a recent paper tackles one of the foremost topics in evolution, that is the origin of species‐specific beak morphology in Darwin's finches.1 Previous work involving both domesticated and wild birds implicated a well‐known signaling pathway (i.e. bone morphogenetic proteins) and one population of progenitor cells in particular (i.e. cranial neural crest), as (...) primary factors for establishing beak size and shape. But these results were limited in their ability to explain fully the morphogenetic bases of patterned outgrowth. So in a quest to identify novel genes whose expression correlated with differences in beak anatomy among Darwin's finches, a DNA microarray approach was undertaken using tissues harvested from the Galápagos Islands. The results are striking and point to a protein called calmodulin, which is a mediator of cellular calcium signaling, as a key determinant of beak length. BioEssays 29: 1–6, 2007. © 2006 Wiley Periodicals, Inc. (shrink)

Many scientists and philosophers of science are troubled by the relative isolation of developmental from evolutionary biology. Reconciling the science of development with the science of heredity preoccupied a minority of biologists for much of the twentieth century, but these efforts were not corporately successful. Mainly in the past fifteen years, however, these previously dispersed integrating programmes have been themselves synthesized and so reinvigorated. Two of these more recent synthesizing endeavours are evolutionary developmental biology and developmental systems theory. While the (...) former is a bourgeoning and scientifically well-respected biological discipline, the same cannot be said of DST, which is virtually unknown among biologists. In this review, we provide overviews of DST and EDB, summarize their key tenets, examine how they relate to one another and to the study of epigenetics, and survey the impact that DST and EDB have had on biological theory and practice. (shrink)

Evo-Devo exhibits a plurality of scientific “cultures” of practice and theory. When are the cultures acting—individually or collectively—in ways that actually move research forward, empirically, theoretically, and ethically? When do they become imperialistic, in the sense of excluding and subordinating other cultures? This chapter identifies six cultures – three /styles/ (mathematical modeling, mechanism, and history) and three /paradigms/ (adaptationism, structuralism, and cladism). The key assumptions standing behind, under, or within each of these cultures are explored. Characterizing the internal structure of (...) the cultures is necessary for understanding how they collaborate or compete, and how they are fragmented or integrated, in the rich interdisciplinary /trading zone/ (Galison 1997) of Evo-Devo. Evo-Devo is an important example of how science can progress through a radical plurality of perspectives and cultures. (shrink)

The concept of developmental constraint was at the heart of developmental approaches to evolution of the 1980s. While this idea was widely used to criticize neo-Darwinian evolutionary theory, critique does not yield an alternative framework that offers evolutionary explanations. In current Evo-devo the concept of constraint is of minor importance, whereas notions as evolvability are at the center of attention. The latter clearly defines an explanatory agenda for evolutionary research, so that one could view the historical shift from ‘developmental constraint’ (...) towards ‘evolvability’ as the move from a concept that is a mere tool of criticism to a concept that establishes a positive explanatory project. However, by taking a look at how the concept of constraint was employed in the 1980s, I argue that developmental constraint was not just seen as restricting possibilities (‘constraining’), but also as facilitating morphological change in several ways. Accounting for macroevolutionary transformation and the origin of novel form was an aim of these developmental approaches to evolution. Thus, the concept of developmental constraint was part of a positive explanatory agenda long before the advent of Evo-devo as a genuine scientific discipline. In the 1980s, despite the lack of a clear disciplinary identity, this concept coordinated research among paleontologists, morphologists, and developmentally inclined evolutionary biologists. I discuss the different functions that scientific concepts can have, highlighting that instead of classifying or explaining natural phenomena, concepts such as ‘developmental constraint’ and ‘evolvability’ are more important in setting explanatory agendas so as to provide intellectual coherence to scientific approaches. The essay concludes with a puzzle about how to conceptually distinguish evolvability and selection. (shrink)

Advances in developmental genetics and evo-devo in the last several decades have enabled the growth of novel developmental approaches to the classic theme of homology. These approaches depart from the more standard phylogenetic view by contending that homology between morphological characters depends on developmental-genetic individuation and explanation. This article provides a systematic re-examination of the relationship between developmental and phylogenetic homology in light of current evidence from developmental and evolutionary genetics and genomics. I present a qualitative model of the processes (...) that cause de-coupling of morphological and molecular evolution by developmental system drift (DSD), and hypothesize that DSD is a widespread and regular stochastic process that is predictable from parameters such as population size, pleiotropy, and regulatory redundancy. These theoretical findings support an integrative approach in which models of DSD aid in determining when developmental-genetic explanations of homology apply and when other explanations such as stabilizing selection are needed. I argue that a phylogenetic monism about the definition and criteria of homology supports the integration of different explanations into a theory of homology better than pluralism does. (shrink)

The theory of concepts advanced in the dissertation aims at accounting for a) how a concept makes successful practice possible, and b) how a scientific concept can be subject to rational change in the course of history. Traditional accounts in the philosophy of science have usually studied concepts in terms only of their reference; their concern is to establish a stability of reference in order to address the incommensurability problem. My discussion, in contrast, suggests that each scientific concept consists of (...) three components of content: 1) reference, 2) inferential role, and 3) the epistemic goal pursued with the concept's use. I argue that in the course of history a concept can change in any of these three components, and that change in one component—including change of reference—can be accounted for as being rational relative to other components, in particular a concept's epistemic goal.This semantic framework is applied to two cases from the history of biology: the homology concept as used in 19th and 20th century biology, and the gene concept as used in different parts of the 20th century. The homology case study argues that the advent of Darwinian evolutionary theory, despite introducing a new definition of homology, did not bring about a new homology concept (distinct from the pre-Darwinian concept) in the 19th century. Nowadays, however, distinct homology concepts are used in systematics/evolutionary biology, in evolutionary developmental biology, and in molecular biology. The emergence of these different homology concepts is explained as occurring in a rational fashion. The gene case study argues that conceptual progress occurred with the transition from the classical to the molecular gene concept, despite a change in reference. In the last two decades, change occurred internal to the molecular gene concept, so that nowadays this concept's usage and reference varies from context to context. I argue that this situation emerged rationally and that the current variation in usage and reference is conducive to biological practice.The dissertation uses ideas and methodological tools from the philosophy of mind and language, the philosophy of science, the history of science, and the psychology of concepts. (shrink)

At the beginning of the twentieth century Haeckel’s biogenetic law was widely questioned. On the one hand, there were those who wanted to dismiss it altogether: ontogeny and phylogeny did not have any systematic or interesting relation. On the other hand, there were those who sought to revise it. They argued that while Haeckel’s recapitulationism might have been erroneous, this should not deter the research over the relation between evolution and development. The British embryologist Walter Garstang was one of the (...) main figures on the “revisionists” side. In this paper, I first situate Garstang’s contribution to embryology and evolution within the extraordinarily creative period of the first three decades of the twentieth century. Then, I review some of Garstang’s specific ideas in detail, especially his most well-known 1922 paper “The Theory of Recapitulation.” Finally, I look at how the demise of the biogenetic law in light of Garstang’s views—as well as from the perspective of contemporary developmental evolution—should be understood. My main concern is not about the dismissal of Haeckel’s law or the sidelining of embryology in the twentieth-century evolutionary biology. I am rather interested in exploring why Garstang’s revised version of biogenetic law—which was entirely consistent with the neo-Darwinian perspective underpinning the Modern synthesis—did not spur a major new agenda in evolutionary biology after the 1930s. (shrink)

It is useful to envision two fundamentally different ways by which the timing of plant development is regulated: developmental stage‐transition mechanisms and time‐to‐flowering mechanisms. The existence of both mechanisms is indicated by the behavior of various mutants. Shoot stage transitions are defined by dominant mutants representing at least four different genes; each mutant retards transitions from juvenile shoot stages to more adult shoot stages. In addition, dominant leaf stage‐transition mutants in at least seven different genes have similar phenotypes, but the (...) leaf rather than the shoot is the. focus (and at least two of these genes encode domain proteins.) One mutant, Hairy sheath frayed 1‐0 (Hsf1‐O) simultaneously affects shoot and leaf; this mutant's behavior initiated our interest in plant heterochronism(1). The second type of timekeeping involves time‐to‐flowering. As with most plant but not animals species, cultivars of the maize species vary greatly for the time‐to‐flowering quantitative trait: between 6 and 14 weeks is common. It is via the 'slipping time frames' interaction that takes place between stage‐transition mutants and time‐to‐flowering genetic back‐grounds that unexpected and radical phenotypes occur. We see a reservoir of previously unsuspected morphological possibilities among the few heterochronic genotypes we have constructed, possibilities that may mimic the sort of variation needed to fuel macroevolution without having to posit (as done by Goldschmidt(2)) any special macromutational mechanisms. (shrink)

Transitional forms of the recent classes of vertebrates are only known in paleontology. The well described examples are:Eusthenopteron foordi,Ichthyostega andAcanthostega between Osteichthyes and Amphibia,Seymouria baylorensis between Amphibia and Reptilia,Archaeopteryx lithographica between Reptilia and Aves, and the mammal-like reptiles Pelycosauria, Therapsida and Cynodontia between Reptilia and Mammalia. The description of their phylogenetical heterochronies in terms of peramorphosis and paedomorphosis shows the progressive role of the motorial, especially the locomotorial organ systems and their functions in comparison with the retarded evolution of the (...) axial system, especially the skull and central nervous system. The evolution of the Hominidae shows the same rule. — The evaluation of these transitional forms in their fossil context reveals them as inhabitants of biotopes situated in the border areas of coastal and shore landscapes of marine, brackish or fresh water. These biotopes have obviously favoured the innovations on the high taxonomic level of macro-evolutionary characteristics. (shrink)

Although the construction of neo-Darwinism grew out of Thomas Hunt Morgan's melding of Darwinism and Mendelism, his evidence did not soley support a model of gradual change. To the contrary, he was confronted with observations that could have led him to a more "evo-devo" understanding of the emergence of novel features. Indeed, since Morgan was an embryologist before he became a fruit-fly geneticist, one would have predicted that the combination of these two lines of research would have resulted in early (...) formulations of concepts relevant to evolutionary developmental biology. It is thus of interest to review Morgan's thought processes and arguments for at first rejecting both Darwinism and Mendelism, and then for later dismissing data that would have yielded a model of rapid morphological change in favor of a model of change based on the accumulation of minor mutations and their morphological consequences. (shrink)

The orthogenetic development of some characteristic features during the evolution of the Hominidae has been pointed out. Especially brain- and skull development have been dwelt on . A parallel has been drawn with the orthogenetic development of some characteristic features during the evolution of the Equidae. It appears that during human evolution early-ontogenetic features come more and more to the front whereas during the evolution of Horses these characters are more and more pushed back in ontogeny. By this, human evolution, (...) at least as concerns the orthogenetically developing features which happen to be very characteristic of the organisation of Man, shows a generalising developmental tendency whereas that of Horses shows on the whole a specialising tendency.Some modes in which early-ontogenetic characters can be present in the adult stages are dealt with such asBolk's theory of retardation andSchindewolf's theory of proterogenesis which are considered not to differ very much in essentials. Also the principle of development along a roundabout way is mentioned in this connection and some examples are given.A better understanding of orthogenetic evolution and of the differences existing between that of the Hominidae and that of the Equidae is found in the principle of heterochronic development, the change of developmental intensity and the rate of growth of features in the ontogenies of allied forms. This is illustrated by the two diagrams of Fig. 2. Here we also established connection with the science of genetics which can explain experimentally the heterochronous shifting of features in compared ontogenies by difference in rate of action and quantitative action value of genes or sets of genes.Il est démontré que le développement phylogénétique de certains caractères morphologiques chez les Hominides est orthogénétique. Principalement le développement du cerveau et du crâne est discuté dans cette connection. Comparativement le développement orthogénétique de certains caractères pendant la phylogénie des Equides est traité. Il résulte que pendant l'évolution humaine des caractères fetaux se misent progressivement en premier plan dans les ontogénèses pendant que ceux dans la phylogénie des Equides se misent de plus en plus en arrière-plan ontogénétiquement. Dans cette manière l'évolution humaine montre, aux moins relative aux caractères orthogénétiques, qui sont exactement très caractéristiques pour l'organisation de l'Homme, une tendence généralisante de développement, celle des Equides au contraire une tendence spécialisante.Quelques possibilités avec lesquelles des caractères fetaux peuvent paraître dans la phase adulte sont discutées comme la théorie de retardation deBolk et la théorie de développement proterogénétique deSchindewolf. Celles-ci sont regardées comme principalement pas différentes. Aussi le principe de développement selon un détour est nommé dans cette connection et quelques exemples en sont donnés.Le principe du développement hétérochronique, le changement de l'intensité et de la vitesse du développement chez des caractères des formes alliés, nous donne un meilleur notion de l'évolution orthogénétique et de la différence, cité ci-dessus, entre la phylogénie humaine et celle des Equides. Ceci est démontré détaillé avec des exemples à l'aide des deux diagrammes de Fig. 2. Dans, cette façon une connection est mise avec la science génétique, qui peut expliquer expérimentalement le développement hétérochronique des caractères morphologiques dans des ontogénèses comparables par des différences dans la vitesse d'action et dans la réalisation quantitative des gènes.Es wird gezeigt wie die phylogenetische Entwicklung einiger charakteristischen Merkmale bei den Hominiden orthogenetisch verläuft. Vor allem werden Gehirn- und Schädelentwicklung in dieser Weise betrachtet. Vergleichenderweise wird die orthogenetische Entwicklung von einigen charakteristischen Merkmalen während der Phylogenie der Equidae besprochen. Es ergibt sich, dass während der menschlichen Evolution früh-ontogenetische Merkmale immer mehr in den Vordergrund treten während solche in der Phylogenie der Equiden immer mehr zurück treten in der Ontogenie. In dieser Weise zeigt sich die menschliche Evolution, wenigstens was den sich orthogenetisch entwickelnden Merkmalen anbelangt, welche gerade sehr charakteristisch für die Organisation des Menschen sind, eine verallgemeinerende Entwicklungstendenz, die der Equidae dagegen eine spezialisierende.Einige Möglichkeiten durch welche früh-ontogenetische Merkmale im erwachsenen Zustand auftreten können werden besprochen, so die Retardationstheorie vonBolk und die Proterogenesistheorie vonSchindewolf. Diese werden als nicht grundverschieden betrachtet. Auch das Prinzip der umwegigen Entwicklung vonNauck wird in diesem Zusammenhang genannt und einige Beispiele gegeben.Das Prinzip der heterochronischen Entwicklung, die Abänderung der Entwicklungsintensität und der Wachstumsgeschwindigkeit bei Merkmalen von verwandten Formen bietet uns einen besseren Begriff von der orthogenetischen Evolution und von dem oben angeführten Unterschied zwischen der menschlichen Phylogenie und der der Equidae. Dies wird näher ausgeführt und mit Beispielen belegt mit Hilfe der beiden Diagramme von Fig. 2. In dieser Weise wird auch eine Verbindung hergestellt mit der genetischen Wissenschaft, die in experimenteller Weise im Stande ist die heterochrone Verschiebung von Merkmalseigenschaften in vergleichbaren Ontogenesen durch Unterschiede in der Geschwindigkeit der Wirkung und in dem quantitativen Verwirklichungswert der Gene zu erklären. (shrink)