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The result is that the successes of the sciences become mysterious when viewed from the vantage point of its participants. Epistemic transparency demands a descriptive correspondence between philosophical accounts of science and scientific practice. This does not mean that every claim made by any scientist should be taken with the same credence. The ruling concern is pervasive features of practice.
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The problem with assuming laws are required for explanation is their relative absence from a variety of successful sciences routinely offering explanations, not that no scientist ever appeals to laws as explanatory. Pervasive features of scientific practice should be prominent in philosophical accounts of sciences. But the fact that these calls are rare means we should not assume theories are actually needed to govern and organize inquiry within the domain. It was once thought that each science must have laws in order to offer explanations see the entry on scientific explanations , but now this is seen as unnecessary Giere ; Woodward The expectation that a science have a theory to accomplish the task of organizing and guiding inquiry is of similar vintage.
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It derives from an intuitive expectation of what counts as a mature science in the first place. Even if we find empirically successful and coherent traditions of research without a systematic theoretical framework providing guidance, then the science cannot be mature. One might shrug off these quasi-positivist appeals to maturity by invoking more flexible conceptions of theory and theory structure.
But why retain the expectation that theories should accomplish the same epistemic tasks? It is a preconception about knowledge structure that is not plausible in light of the diversity of research practices found across the sciences. The few scientists who favor this philosophical response have different motivations. Instead of maturity, other reasons are salient, such as guidance in the face of a welter of biochemical detail and the need to forge a synthesis between evolution and development.
While something must provide organization and guidance to developmental biology, it need not be theories that accomplish the task. But this line of argument relies on the degree to which evolutionary theory exhibits the supposed structure to which developmental biologists should aspire.
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The actual practice associated with evolutionary theory indicates a more flexible framework with chameleon qualities that is responsively adjusted to the diverse investigative aims of evolutionary researchers Love b, Therefore, it is not clear that evolutionary theory is a valid template. A productive way forward is to relinquish the prior expectation that sciences must have theories of a certain kind to govern and guide their activity. The criterion of epistemic transparency Section 2.
Developmental biology is organized primarily by stable, broad domains of problems that correspond to abstract representations of major ontogenetic processes differentiation, pattern formation, growth, and morphogenesis; Section 1. One way is to distinguish between theory-informed science—using theoretical knowledge—and theory-directed science—having a theory that directs inquiry and organizes knowledge Waters b ; developmental biology is theory-informed but not theory-directed.
Theories need not be wholly absent from developmental biology but—when present—they play roles very different from standard philosophical expectations. Developmental biology uses theoretical knowledge from biochemistry when appealing to morphogen gradients to explain how segments are established or chemical thermodynamics when invoking reaction—diffusion mechanisms to explain pigmentation patterns.
It also uses theoretical knowledge derived from within developmental biology, such as positional information models. Different kinds of theory inform developmental biology, but these do not organize research—they are not necessary to structure the knowledge and direct investigative activities.
Developmental biologists are not focused on confirming and extending the theory of reaction—diffusion mechanisms, nor are they organizing their research around positional information. All sciences may use theoretical knowledge, but this is not the same as all sciences having a theory providing direction and organization.
Why think that problems provide organizational architecture for the epistemology of developmental biology? They are a pervasive feature of its reasoning practices, illustrated in textbooks that capture substantial community consensus about standards of explanation, experimental methods, essential concepts, and empirical content. Unlike evolutionary biology textbooks that discuss the theory of natural selection or economics textbooks that talk about microeconomic theory, an examination of several editions of major textbooks indicate that developmental biology does not have similar kinds of theories.
These broad clusters are then fleshed out along a standard timeline of early development, highlighting gametogenesis, fertilization, cleavage, gastrulation, and axis specification see Section 1. Different experimental approaches cell and molecular biology, developmental genetics, and experimental embryology are utilized in a specific set of model organisms see below, Section 4 to dissect the workings of these developmental phenomena.
Subsequent chapters cover later aspects of development e.
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Throughout this presentation, no specific theory, set of hypotheses, or dominant model is invoked to organize these different domains of investigation. Instead, broad clusters of questions that reflect generally delineated processes differentiation, specification, morphogenesis, and growth set the agenda of research.
And how does that adult body produce yet another body? These questions can be parsed more analytically in terms of five variables: abstraction, variety, connectivity, temporality, and spatial composition. The values given to these variables structure the constellation of research questions within the broad problem agendas corresponding to generally delineated processes.
For example, research questions oriented around events in zebrafish gastrulation are structured in a way that differs from the research questions oriented around vertebrate neural crest cell migration because they involve different values for the five variables: abstraction zebrafish vs. These configurations can be adjusted readily in response to shifts in the values for different variables Love This anatomy of problems, with explicit epistemological structure derived from different values for these variables, operates to organize the science of development.
Investigators from different disciplines can be working on the same problem but asking different questions that require distinct but complementary methodological resources. Knowledge and inquiry in developmental biology are intricately organized, just not by a central theory or group of models, and this erotetic organization is epistemologically accessible to the participating scientists.
While theoretical knowledge, especially that drawn from molecular biological mechanisms see the entry on molecular biology and mathematical models e. Further analysis of this problem anatomy is possible, including how it is displayed in regular research articles and not just textbooks, as well as other areas of biology Brigandt and Love ; Love a, Explanations in developmental biology are usually causal, though unlike standard mechanistic explanation there is a constant acquisition of new causal capacities in terms of constituent entities, activities, and their organization through development Parkkinen Although much work remains in characterizing different aspects of explanation in developmental biology, there is no doubt that a difference making or manipulability conception of causation see the entry on causation and manipulability provides a core element of the reasoning Woodward ; Strevens ; Waters a.
Genetic explanations of development Section 3. More recently, there has been growing interest in physical explanations of development Section 3. Researchers agree on the phenomena that need to be explained Section 1. Many philosophers have turned to explanations of development over the past two decades in an effort to esteem or deflate claims about the causal power of genes Keller ; Neumann-Held and Rehmann-Sutter ; Rosenberg ; Robert ; Waters a.
Developmental biology … deals with the process by which the genes in the fertilized egg control cell behavior in the embryo and so determine its pattern, its form, and much of its behavior … differential gene activity controls development. Wolpert et al. These types of statements are amplified in appeals to a genetic program for development. Whether or not these statements can be substantiated has been the subject of intense debate.
Longman Illustrated Animal Encyclopedia
But this leaves intact the difference-making principle of genetic explanation exhibited in molecular genetics Waters a , which yields more narrow and surgical causal claims under controlled experimental conditions, and is applicable to diverse molecular entities that play causal roles during development, such as regulatory RNAs, proteins, and environmental signals. We can observe this by reconsidering the example of vertebrate cardiogenesis Section 1.
Are there problems with claiming that genes contain all of the information see the entry on biological information to form vertebrate hearts?
Is there a genetic program in the DNA controlling heart development? Are genes the primary supplier and organizer of material resources for heart development, largely determining the phenotypic outcome? Existing studies of heart development have identified a role for fluid forces in specifying the internal form of the heart Hove et al.
Biochemical gradients of extracellular calcium are responsible for activating the asymmetric expression of the regulatory gene Nodal Raya et al. A number of genes are clearly difference makers in these processes Srivastava ; Brand ; Olson , but the conclusion that genes carry all the information needed to generate form features of the heart is unnecessary and unwarranted. While it may be warranted empirically in some cases to privilege DNA sequence differences as causal factors in specific processes of ontogeny Waters a , such as hierarchically organized networks of genetic difference makers explaining tissue specification Peter and Davidson , the diversity of entities appealed to in molecular genetics and the extent of their individual and joint roles in specifying developmental outcomes means that debates about the meaning, scope, and power of genetic explanations will continue Griffiths and Stotz But a shift away from genetic programs and genetic determinism to DNA, RNA, and proteins as difference makers that operate conjointly suggests that we conceptualize other causal factors in a similar way.
Fluid flow, as a physical force, is also a difference maker during the development of the heart, and ontogeny more generally, and developmental biologists appeal to physical difference makers, which are understood as factors in producing the morphological properties of developmental phenomena Forgacs and Newman This occurred in the milieu of increasing attention to the chromosomal theory of inheritance and attempts to explore developmental phenomena via classical genetic methods Morgan , , Thompson appealed to differential rates of growth and the constraints of geometrical relationships to explain how organismal morphology originates.
Visual representations of abiotic, mechanical analogues provided the plausibility, such as the shape of liquid splashes or hanging drops for the cup and bell configurations of the free-swimming sexual stage of jellyfish.
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If physical forces generated specific morphologies in viscoelastic materials, then analogous morphologies in living species should be explained in terms of physical forces operating on the viscoelastic materials of the developing embryo. But morphogenetic processes that produce the shape and structure of morphology have been seen primarily, if not exclusively, in terms of genetics for the last half-century.
Physical approaches faded from view as molecular genetics approaches went from strength to strength Fraser and Harland The molecularization of experimental embryology is one of the most striking success stories of contemporary biology as genes and genetic interactions e. Genetic approaches predominate in contemporary developmental biology; physical modes of causation are typically neglected, if not negligible. The frustration among researchers interested in physical causation during embryogenesis has been palpable.
To the molecular types, a cause is a molecule or a gene. To explain a phenomenon is to identify genes and characterize proteins without which the phenomenon will fail or be abnormal. Despite this predominance of genetic explanatory approaches and the frustration among researchers utilizing other approaches, a groundswell of interest has been building around physical explanations of development, especially in terms of their integration with genetic explanations Miller and Davidson Thompson held that physical forces were explanatory but inadequate in isolation to account for the developmental origin of morphology; heredity genetics was also a necessary causal factor.
Thompson : Despite this latter form of exaggeration manifesting itself through much of the 20 th century, an agenda to combine or integrate the two approaches is now explicit. There is no controversy about whether genetic and physical modes of causation are at work simultaneously:.
Von Dassow et al. They are not competing causal explanations of the same phenomenon. Explanations should capture how their productive interactions yield developmental outcomes:. Genetic causes can lead to physical causation and vice versa. Physical causation brings about genetic causation through mechanotransduction. Stretching, contraction, compression, fluid shear stress, and other physical dynamics are sensed by different molecular components inside and outside of cells that translate these environmental changes into biochemical signals Hoffman et al.
Genetic causation brings about physical causation by creating different physical properties of cells and tissues through the presence, absence, or change in frequency of particular proteins. For example, different patterns of expression for cell adhesion molecules e. If these modes of causation are not competing, then how might one combine genetic and physical difference makers into an integrated causal explanation?