There Are No Intermediate Stages: An Organizational View on Development (original) (raw)
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The Organism in Developmental Systems Theory
Biological Theory 5(3): 216-222, 2010
In this paper, I address the question of what the Developmental Systems Theory (DST) aims at explaining. I distinguish two lines of thought in DST, one which deals specifically with development, and tries to explain the development of the individual organism, and the other which presents itself as a reconceptualization of evolution, and tries to explain the evolution of populations of developmental systems (organism-environment units). I emphasize that, despite the claiming of the contrary by DST proponents, there are two very different definitions of the ‘developmental system’, and therefore DST is not a unified theory of evolution and development. I show that the DST loses the most interesting aspects of its reconceptualization of development when it tries to reconceptualize evolutionary theory. I suggest that DST is about development per se, and that it fails at offering a new view on evolution.
Animal Development, an Open-Ended Segment of Life
Biological Theory, 2011
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. Keywords Adult Á Adultocentrism Á Larva Á Metagenesis Á Metamorphosis Á Theory of development Á Zero model of development
An Interpretation of Biological Development
2020
The research programs and practices used to address biological problems are often grounded in the way one interprets biological organisms. There is a practical motive to explain organismic development in terms of genes and the environments in which genes are expressed. This interpretation presupposes that organisms are simply gene environments. In this way, genes either control the outcome of development or contain information that specifies particular outcomes. In either case, development is basically a problem to be resolved through an increased understanding of genes and the ways genes are expressed. This interpretation fails to adequately explain the process by which complex form is generated. Therefore, there are grounds for rejecting it. An approach centred around the whole organism directs attention towards its many constituents and requires that one take seriously the role of multiple organismic elements in order to adequately explain development.
Developmental Dynamics: Past, Present, and Future
Human Development
At the end of the 20th century, as new tools and techniques from the interdisciplinary field of nonlinear dynamics began enjoying increased application to the study of development, interest in dynamics flourished in the developmental sciences. In the eyes of many prominent dynamics thinkers of the time, these new dynamics approaches-by virtue of their grounding in time and variability-not only established a thoroughgoing process orientation to development but also stood in marked opposition to the structural, or organizational, focus that had marked classic organicist and systems treatments of development from earlier in the century. Treatments of developmental dynamics today, however, are embarking on exciting new ways to integrate the organizational focus of classic systems accounts with modern principles of nonlinear dynamics. As a consequence, today's dynamics orientations are taking seriously the explanatory significance of phenomena like purposiveness, end-directedness, normativity, and subjectivity that characterize organisms as unique levels of process organization. Many challenges lie ahead for fully realizing such an integration, and we highlight two noteworthy conceptual issues that today's treatments need to confront: (1) the notion of abilities or powers as potentials for action and what it means for "potential" to explain action; and (2) the notions of real time change, developmental time change, and what it means for these different timescales to interrelate.
An Organizational Account of Biological Functions
The British Journal for the …, 2009
In this paper, we develop an organizational account that defines biological functions as causal relations subject to closure in living systems, interpreted as the most typical example of organizationally closed and differentiated self-maintaining systems. We argue that this account adequately grounds the teleological and normative dimensions of functions in the current organization of a system, insofar as it provides an explanation for the existence of the function bearer and, at the same time, identifies in a non-arbitrary way the norms that functions are supposed to obey. Accordingly, we suggest that the organizational account combines the etiological and dispositional perspectives in an integrated theoretical framework.
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(s) can be considered as the most satisfactory.
Managing variation in the investigation of organismal development: problems and opportunities
This paper aims to clarify the consequences of new scientific and philosophical approaches for the practical-theoretical framework of modern developmental biology. I highlight normal development, and the instructive-permissive distinction, as key parts of this framework which shape how variation is conceptualised and managed. Furthermore, I establish the different dimensions of biological variation: the units, temporality and mode of variation. Using the analytical frame established by this, I interpret a selection of examples as challenges to the instructive-permissive distinction. These examples include the phenomena of developmental plasticity and transdifferentiation, the role of the microbiome in development, and new methodological approaches to standardisation and the assessment of causes. Furthermore, I argue that investigations into organismal development should investigate the effects of a wider range of kinds of variation including variation in the units, modes and temporalities of development. I close by examining various possible opportunities for producing and using normal development free of the assumptions of the instructive-permissive distinction. These opportunities are afforded by recent developments, which include new ways of producing standards incorporating more natural variation and being based on function rather than structure, and the ability to produce, store, and process large quantities of data.
“Organization” as Setting Boundaries of Individual Development
Biological Theory, 2011
''Development'' suggests that there is something that is developing, or changing over time. We can ask about temporal boundaries of that developmental process, asking when development begins or ends and whether it has defined stages along the way, for example. We can ask about spatial boundaries as well: where does the developing object start and end? For this article, I ask about the boundary definition of the developing organism in particular. What is an individual organism, and what defines it as the same organism as it changes over time? In particular, how has this been answered historically: how have researchers described and explained what an individual developing organism is? This article explores ideas and approaches especially starting in the late 19th century, and in particular looks at the role of ''organization.''