Phenotypic plasticity integrates the insights of ecological genetics, developmental biology, and evolutionary theory. Plasticity research asks foundational questions about how living organisms are capable of variation in their genetic makeup and in their responses to environmental factors. For instance, how do novel adaptive phenotypes originate? How do organisms detect and respond to stressful environments? What is the balance between genetic or natural constraints (such as gravity) and natural selection? The author begins by defining phenotypic plasticity and detailing its history, including (...) important experiments and methods of statistical and graphical analysis. He then provides extended examples of the molecular basis of plasticity, the plasticity of development, the ecology of plastic responses, and the role of costs and constraints in the evolution of plasticity. A brief epilogue looks at how plasticity studies shed light on the nature/nurture debate in the popular media. (shrink)

In the six decades since the publication of Julian Huxley's Evolution: The Modern Synthesis, spectacular empirical advances in the biological sciences have been accompanied by equally significant developments within the core theoretical framework of the discipline. As a result, evolutionary theory today includes concepts and even entire new fields that were not part of the foundational structure of the Modern Synthesis. In this volume, sixteen leading evolutionary biologists and philosophers of science survey the conceptual changes that have emerged since Huxley's (...) landmark publication, not only in such traditional domains of evolutionary biology as quantitative genetics and paleontology but also in such new fields of research as genomics and EvoDevo. Most of the contributors to Evolution—The Extended Synthesis accept many of the tenets of the classical framework but want to relax some of its assumptions and introduce significant conceptual augmentations of the basic Modern Synthesis structure—just as the architects of the Modern Synthesis themselves expanded and modulated previous versions of Darwinism. This continuing revision of a theoretical edifice the foundations of which were laid in the middle of the nineteenth century—the reexamination of old ideas, proposals of new ones, and the synthesis of the most suitable—shows us how science works, and how scientists have painstakingly built a solid set of explanations for what Darwin called the "grandeur" of life. (shrink)

The question “What is an organism?”, formerly considered as essential in biology, has now been increasingly replaced by a larger question, “What is a biological individual?”. On the grounds that i) individuation is theory-dependent, and ii) physiology does not offer a theory, biologists and philosophers of biology have claimed that it is the theory of evolution by natural selection which tells us what counts as a biological individual. Here I show that one physiological field, immunology, offers a theory, which makes (...) possible a biological individuation based on physiological grounds. I give a new answer to the question of the individuation of an organism by linking together the evolutionary and the immunological approaches to biological individuation. (shrink)

1 The Zero-Force Evolutionary Law 2 Randomness, Hierarchy, and Constraint 3 Diversity 4 Complexity 5 Evidence, Predictions, and Tests 6 Philosophical Foundations 7 Implications.

Colonial ascidians offer opportunities to investigate how developmental events are integrated to generate the animal form, since they can develop similar individuals (oozooids from eggs, blastozooids from pluripotent somatic cells) through very different reproductive processes, i.e. embryogenesis and blastogenesis. Moreover, thanks to their key phylogenetic position, they can help in the understanding of the molecular mechanisms of morphogenesis and their evolution in chordates. We review organogenesis of the ascidian neural complex comparing embryos and buds in terms of topology, developmental mechanisms (...) and terminology. We propose a new interpretation of bud territories, and reconsider nervous system development based on recent results suggesting that ascidians have vertebrate placodal and neural‐crest‐like cells. Comparing embryonic and blastogenic development in Botryllus schlosseri, we propose that the bud has territories with a placodal potentiality, suggesting that chordate ancestors possessed neurogenic placodes, and that the genetic pathways regulating neurogenic placode formation were co‐opted for new developmental processes, such as blastogenesis. BioEssays 28: 902–912, 2006. © 2006 Wiley periodicals, Inc. (shrink)

This collection broadens the scientific discussion of modularity by bringing together experts from a variety of disciplines, including artificial life, ...

In describing the flawless regularity of developmental processes and the correlation between changes at certain genetic loci and changes in morphology, biologists frequently employ two metaphors: that genes ‘control’ development, and that genomes embody ‘programs’ for development. Although these metaphors have an admirable sharpness and punch, they lead, when taken literally, to highly distorted pictures of developmental processes. A more balanced, and useful, view of the role of genes in development is that they act as suppliers of the material needs (...) of development and, in some instances, as context‐dependent catalysts of cellular changes, rather than as ‘controllers’ of developmental progress and direction. The consequences of adopting this alternative view of development are discussed. (shrink)

The somatic mutation theory has been the prevailing paradigm in cancer research for the last 50 years. Its premises are: (1) cancer is derived from a single somatic cell that has accumulated multiple DNA mutations, (2) the default state of cell proliferation in metazoa is quiescence, and (3) cancer is a disease of cell proliferation caused by mutations in genes that control proliferation and the cell cycle. From this compelling simplicity, an increasingly complicated picture has emerged as more than 100 (...) oncogenes and 30 tumor suppressor genes have been identified. To accommodate this complexity, additional ad hoc explanations have been postulated. After a critical review of the data gathered from this perspective, an alternative research program has been proposed. It is based on the tissue organization field theory, the premises of which are that carcinogenesis represents a problem of tissue organization, comparable to organogenesis, and that proliferation is the default state of all cells. The merits of these competing theories are evaluated herein. BioEssays 26:1097–1107, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

It is desirable that the antecedents of existing, highly specialised, evolutionary mechanisms in animals be sought. The study of the lower Metazoa and especially of their simpler reproductive processes suggests that asexual reproduction is the primitive evolutionary mechanism from which the more advanced sexual mechanisms have evolved. A study of the metagenetic cycles of Coelenterata and Platyhelminthes seems to throw much light upon their prophylogeny and indicates that: Such cycles seem to provide the closest possible recapitulatory parallelism between phylogeny and (...) ontogeny. The Hydrozoa are ancestral to the other classes of Coelenterata. The polypoid adult is more primitive than the medusoid adult. The sporocysts, rediae and scolices represent the more primitive types of adults in their respective ontogenies and phylogenies.On avance la théorie qu'il y a eu une évolution des mécanismes évolutionnaires depuis les stades primitifs jusqu'aux stades avancés. D'après cette théorie les premières étapes dans l'évolution des Métazoaires inférieurs se sont effectuées par la reproduction asexuelle avant que les mecanismes sexuels très spécialisés se soient manifestés.Des preuves à l'appui de cette théorie découlent: de la rencontre actuelle d'une reproduction asexuelle chez des animaux, avec l'indication que sa simplicité est, dans la plupart des cas, originelle, et des cycles d'évolution des Coelentérés et Platyhelminthes qui sont métagénésiques. Leurs cycles peuvent s'interpréter comme partant de stades reproductifs asexuels pour évoluer vers des formes se reproduisant sexuellement.On croit que les organismes ne pouvant se reproduire que sexuellement sont plus avancés que ceux qui peuvent se reproduire asexuellement, ou à la fois sexuellement et asexuellement.Cette théorie a d'importantes implications pour l'étude de la métagenèse, de la récapitulation et de la phylogénie chez les Métazoaires inférieurs; elle exemplifie, dans l'étude de ces phénomènes, la nouvelle orientation qu'on a appelée Prophylogénie.In dieser Arbeit wird eine Theorie entwickelt, die besagt, dass eine Fortentwicklung der Evolutionsmechanismen von primitiven zu fortgeschrittenen Stufen besteht. Dieser Theorie nach haben sich die niedrigeren Metazoen ursprünglich nur ungeschlechtlich entwickelt und fortgepflanzt. Erst später haben sich die höchst spezialisierten geschlechtlichen Mechanismen entwickelt.Belege für diese Theorie sind: Noch heute kommt die geschlechtslose Fortpflanzung in Tieren vor, was dafür spricht, dass ihre Einfachheit in den meisten Fällen ursprünglich ist. Die Lebenskreisläufe der Metagenetischen Coelenteraten und Platyhelminthen lassen sich interpretieren als bestehend aus ursprünglich ungeschlechtlichen Fortpflanzungsstufen, die jedoch später in Formen mit geschlechtlicher Fortpflanzung übergehen.Es wird behauptet, dass Organismen mit nur geschlechtlicher Fortpflanzung weiter fortgeschritten sind als solche mit nur ungeschlechtlicher oder mit sowohl ungeschlechtlicher als auch geschlechtlicher Fortpflanzung.Diese Theorie ist wichtig für das Studium der Metagenese, Rekapitulation und Phylogenie in den niedrigen Metazoen und veranschaulicht die Prophylogenie, d.h. die neue Methode im Studium dieser Erscheinungen. (shrink)

Regeneration capabilities are found in most or all animals. Whether regeneration is part of the development of an animal or a distinct phenomenon independent of development is a debatable question. If we consider regeneration as a process belonging to development, similarly to embryogenesis or metamorphosis, the existence of regenerative capabilities in adults can be seen as an argument in favor of the theory that development continues throughout the life of animals. Here I perform a comparative analysis of regeneration versus “classical” (...) developmental processes in animals in order to determine to what extent these processes are inclusive or distinct. I identify the existence of regeneration-specific processes, i.e., processes that occur during the regeneration, but not the initial development, of a given structure. In addition, I find that seemingly similar processes acting during development and regeneration may have differential molecular and cellular bases. I thus conclude that there are significant differences between regeneration processes in adult animals and developmental processes occurring during earlier phases of the life cycle. The existence of regenerative capabilities in adult animals can therefore not be used as an argument in favor of the idea that development spans the whole life. (shrink)

In the maximal form of indirect development found in many taxa of marine invertebrates, embryonic cell lineages of fixed fate and limited division capacity give rise to the larval structures. The adult arises from set‐aside cells in the larva that are held out from the early embryonic specification processes, and that retain extensive proliferative capacity. We review the locations and fates of set‐aside cells in two protostomes, a lophophorate and a deuterostome. The distinct adult body plans of many phyla develop (...) from homologous set‐aside cells within homologous larvae. We argue that the stocks from which these phyla arose utilized these respective larvae, and the diversity of their adult body plans reflects diverse pattern formation processes executed in their set‐aside cell populations. Chordates and arthropods develop directly, but share adult characters with indirectly developing phyla. Thus the deuterostome and protostome stocks that were ancestral to chordates and arthropods, respectively, also utilized maximal indirect development. (shrink)

In Darwinism's Struggle for Survival Jean Gayon offers a philosophical interpretation of the history of theoretical Darwinism. He begins by examining the different forms taken by the hypothesis of natural selection in the nineteenth century and the major difficulties which it encountered, particularly with regard to its compatibility with the theory of heredity. He then shows how these difficulties were overcome during the seventy years which followed the publication of Darwin's Origin of Species, and he concludes by analysing the major (...) features of the genetic theory of natural selection, as it developed from 1920 to 1960. This rich and wide-ranging study will appeal to philosophers and historians of science and to evolutionary biologists. (shrink)