Yoshinari Yoshida (University of Minnesota), Alan Love (University of Minnesota)
Confirmed empirical generalizations are central to the epistemology of science. Through most of the 20th century, philosophers focused on universal, exceptionless generalizations — laws of nature — and took these as essential to scientific theory structure and explanation. However, over the past two decades, many sought to characterize a broader range of generalizations, which facilitated the elucidation of a more complex space of possibilities and enabled a more fine-grained understanding of how generalizations with different combinations of properties function in scientific inquiry. However, much work remains to characterize the diversity of generalizations within and across the sciences.
Here we concentrate on one area of science — developmental biology — to comprehend the role of two different kinds of scientific generalizations: mechanisms and principles. Mechanism generalizations (MGs) in developmental biology are descriptions of constituent biomolecules organized into causal relationships that operate in specific times and places during ontogeny to produce a characteristic phenomenon that is shared across different biological entities. Principle generalizations (PGs) in developmental biology are abstract descriptions of relations or interactions that occur during ontogeny and are exemplified in a wide variety of different biological entities.
In order to characterize these two kinds of generalizations, we first discuss generalizations and explanatory aims in the context of developmental biology. Developmental biologists seek generalizations that are structured in four different dimensions — across taxa, across component systems, across developmental stages, and across scales — and in terms of two primary conditions: material and conceptual. Within scientific discourse, these generalizations appear in complex combinations with different dimensions or conditions foregrounded (e.g., distributions of developmental phenomena and causal interactions that underlie them in a specific component system at a particular stage under specified material conditions to answer some subset of research questions).
MGs and PGs have distinct bases for their scope of explanation. MGs explain the development of a wide range of biological entities because the described constituent biomolecules and their interactions are conserved through evolutionary history. In contrast, the wide applicability of PGs is based on abstract relationships that are instantiated by various entities (regardless of evolutionary history). Hence, MGs and PGs require different research strategies and are justified differently; specific molecular interactions must be experimentally dissected in concrete model organisms, whereas abstract logical and mathematical properties can be modeled in silico. Our analysis shows why a particular kind of generalization coincides with a specific research practice and thereby illuminates why the practices of inquiry are structured in a particular way.
The distinction between MGs and PGs is applicable to other sciences, such as physiology and ecology. Furthermore, our analysis isolates issues in general philosophical discussions of the properties of generalizations, such as ambiguities in discussions of “scope” (how widely a generalization holds) and a presumption that abstraction is always correlated positively with wide scope. Scope is variable across the four dimensions and MGs have wide scope as a consequence of their reference to concrete molecular entities that are evolutionarily conserved, not because of abstract formulations of causal principles.
