Is it possible to explain and predict the development of living things? What is development? Articulate answers to these seemingly innocuous questions are far from straightforward. To date, no systematic, targeted effort has been made to construct a unifying theory of development. This novel work offers a unique exploration of the foundations of ontogeny by asking how the development of living things should be understood. It explores the key concepts of developmental biology, asks whether general principles of development can be (...) discovered, and examines the role of models and theories.The two editors have assembled a team of leading contributors who are representative of the scientific and philosophical community within which a diversity of thoughts are growing, and out of which a theory of development may eventually emerge. They analyse a wealth of approaches to concepts, models and theories of development, such as gene regulatory networks, accounts based on systems biology and on physics of soft matter, the different articulations of evolution and development, symbiont-induced development, as well as the widely discussed concepts of positional information and morphogenetic field, the idea of a. (shrink)

This chapter contains sections titled: Introduction The Evolving Evolutionary Synthesis Population Genetics vs. Developmental Genetics Evo‐Devo's Central Target: The Study of Evolvability Origins? Conclusion Postscript: Counterpoint Acknowledgments References.

No comprehensive theory of development is available yet. Traditionally, we regard the development of animals as a sequence of changes through which an adult multicellular animal is produced, starting from a single cell which is usually a fertilized egg, through increasingly complex stages. However, many phenomena that would not qualify as developmental according to these criteria would nevertheless qualify as developmental in that they imply nontrivial (e.g., non degenerative) changes of form, and/or substantial changes in gene expression. A broad, comparative (...) approach is badly needed. In the Cnidaria, for example, even the boundary between generations is problematic. Describing their life cycle in terms of metagenesis (alternation between polyp generation and medusa generation) or in terms of metamorphosis (polyp as larva or juvenile) are matters of semantics more than biology. The life cycle of other metazoans, described in textbooks in terms of larva-to-adult metamorphosis, is hardly different from a typical metagenetic life cycle of cnidarians. This applies to holometabolous insects and to marine invertebrates like sea urchins, where most of the larval cells are discarded at metamorphosis. The uncertain temporal and spatial boundaries of individual development are also shown by the widespread lack of a strict correspondence between adult and mature. A comprehensive theory of development should start with a zero principle of “developmental inertia,” corresponding to an indeterminate local self-perpetuation of cell-level dynamics. Indeterminate growth, scale-invariance, segmentation, and regeneration provide examples of developmental dynamics close to that. (shrink)

Contrary to the traditional claim that needs for unambiguous communication about animal and plant species are best served by a single set of names ruled by international Codes, I suggest that a more diversified system is required, especially to cope with problems emerging from aggregation of biodiversity data in large databases. Departures from Linnaean nomenclature are sometimes intentional, but there are also other, less obvious but widespread forms of not Code-compliant grey nomenclature. A first problem is due to the circumstance (...) that the Codes are intended to rule over the way names are applied to species and other taxonomic units, whereas users of taxonomy need names to be applied to specimens. For different reasons, it is often impossible to refer a specimen with certainty to a named species, and in those cases an open nomenclature is employed. Second, molecular taxonomy leads to the discovery of clusters of gene sequence diversity not necessarily equivalent to the species recognized and named by taxonomists. Those clusters are mostly indicated with informal names or formulas that challenge comparison between different publications or databases. In several instances, it is not even clear if a formula refers to an individual voucher specimen, or is a provisional species name. The use of non-Linnaean names and formulas must be revised and strengthened by fixing standard formats for the different kinds of objects or hypotheses and providing permanent association of ‘grey names’ with standardized source information such as author and year. In the context of a broad-scope revisitation of aims and scope of scientific nomenclature, it may be worth rethinking if natural objects like plant galls and lichens, although other than the ‘single-entity’ objects traditionally covered by biological classifications, may nevertheless deserve taxonomic names. (shrink)

Evolutionary developmental biology is a rapidly growing discipline whose ambition is to address questions that are of relevance to both evolutionary biology and developmental biology. This field has been increasingly progressing as a new and independent comparative science. However, we argue that evo-devo’s comparative approach is challenged by several metaphysical, methodological and socio-disciplinary issues related to the foundation of heuristic functions of model organisms and the possible criteria to be adopted for their selection. In addition, new tools have to be (...) developed to deal with newly chosen model organisms. Therefore, we present a modelling framework suitable to integrate data on individual variation into evo-devo studies on new model organisms and thus to compensate for current idealization practices deliberately suppressing variation. (shrink)

A un secolo e mezzo dalla pubblicazione dell'Origine delle specie, la nozione di omologia di Owen, che implica che due organi o due funzioni a confronto possono essere riconosciuti come “la stessa cosa” continua a dominare gli attuali approcci al problema dell’omologia. L'idea che i caratteri possano “rimanere se stessi” attraverso un numero indefinito (anche se finito) di stati alternativi che si susseguono nel corso dell'evoluzione è probabilmente basato su un'interpretazione idealistica di come gli organismi si evolvono. Se si dà (...) per scontata l'esistenza di caratteristiche del corpo che conservano la loro identità nel cambiamento, l'esistenza di omologhi può essere spiegata (i) in termini di leggi universali della forma, magari nella forma moderna dello strutturalismo di processo, o (ii) come il prodotto di discendenza comune, o (iii) in termini di cause prossime responsabili della comparsa di moduli di sviluppo conservati. Tuttavia, leggendo la storia della vita attraverso la lente dell’evoluzione, appare molto problematico descrivere un organismo come una somma di caratteri che, una volta apparsi come novità evolutive, rimangono poi come unità costruttive essenzialmente immutabili tra le quali possiamo predicare (o negare) omologia. Tutti i tratti sono meglio interpretati come incroci complessi e mutevoli di un numero indeterminato di elementi e dei processi che li modellano nel corso dell’ontogenesi e della filogenesi. Di conseguenza, appare raccomandabile un approccio fattoriale, o combinatorio, all’omologia. (shrink)

Is it possible, and in the first place is it even desirable, to define what "development" means and to determine the scope of the field called "developmental biology"? Though these questions appeared crucial for the founders of "developmental biology" in the 1950s, there seems to be no consensus today about the need to address them. Here, in a combined biological, philosophical, and historical approach, we ask whether it is possible and useful to define biological development, and, if such a definition (...) is indeed possible and useful, which definition can be considered as the most satisfactory. (shrink)

This study analyzes shells of marine gastropods of a zoological museum and the Latin epithets expressing perceptual and connotative attributes that they have received in the standard, Linnaean nomenclature. Making use of the Osgood semantic differential, we presented the subjects with digital 3-D reproductions of the shell specimens to be subjectively evaluated according to 17 pairs of attributes. The results show that, overall, the subjective evaluations given by the subjects are consistent, which suggests that an intersubjective characterization of the shells (...) as wholes according to their qualitative and morphological traits is possible and scientifically explicable. This may apply to other biological items as well. The results also show that the epithets given to the shells by taxonomists do not always reflect the perceptual evaluation of the general population, being a product of the well-known ambiguity in taxonomic categorization and naming. (shrink)

This study analyzes shells of marine gastropods of a zoological museum and the Latin epithets expressing perceptual and connotative attributes that they have received in the standard, Linnaean nomenclature. Making use of the Osgood semantic differential, we presented the subjects with digital 3-D reproductions of the shell specimens to be subjectively evaluated according to 17 pairs of attributes. The results show that, overall, the subjective evaluations given by the subjects are consistent, which suggests that an intersubjective characterization of the shells (...) as wholes according to their qualitative and morphological traits is possible and scientifically explicable. This may apply to other biological items as well. The results also show that the epithets given to the shells by taxonomists do not always reflect the perceptual evaluation of the general population, being a product of the well-known ambiguity in taxonomic categorization and naming. (shrink)

According to the evolutionary theory, biodiversity is the product of change. However, biodiversity exists also because there are rules against an uncontrolled mixing of individuals or species that would create monsters such as the mythical chimera or the hybrids between lion and tiger. Unease in front of them is not necessarily proportional to the extent of the mixing. We fear most that the consequences of the breakup of a natural boundary may become lasting and uncontrollable. Boundaries, however, work also in (...) different way. First, you should not eat another member of your species. Second, individuality should not been breached by grafting together two individuals of the same species. Third, your enemy should not cross your skin unseen, to feed on you from inside. All these rules, however, are widely breached in nature. Humans have added to this catalogue, challenging borders by a diversity of practices that do not respect the boundaries within and between the species. All these practices are the ultimate treat – material and cultural alike – to the survival of biodiversity. (shrink)

Because of the steady involvement of organisms in evolutionary dynamics, of the frequent occurrence of uniparental reproduction and of the diverse outcome of hybridisation events, the species category does not easily apply to a sizeable part of the living world. Problematic is also often the use of the category of the individual, especially in the case of polyembryony, and the distinction between metamorphosis of the individual and metagenesis (alternation of generations) is also often uncertain. More generally, fixing origins is commonly (...) arbitrary, in respect to phylogeny (‘origin’ of species) and ontogeny (‘origin’ of individual) alike. (shrink)

What is a larva, if it is not what survives of an ancestor's adult, compressed into a transient pre‐reproductive phase, as suggested by Haeckel's largely disreputed model of evolution by recapitulation? A recently published article hypothesizes that larva and adult of holometabolous insects are developmental expressions of two different genomes coexisting in the same animal as a result of an ancient hybridization event between an onychophoran and a primitive insect with eventless post‐embryonic development. More likely, however, larvae originated from late (...) embryonic or early post‐embryonic stages of ancestors with direct development. Evolutionary novelties would thus be intercalary rather than terminal, with respect to the ancestor's ontogenetic schedule. This scenario, supported by current research on holometabolous insects and marine invertebrates with complex life cycles, offers a serious alternative to the traditional scenario (‘what is early in ontogeny is also early in phylogeny’) underlying the current perception of the evolution of genetic regulatory networks. (shrink)