Lauren Ross (Irvine): Causal concepts in biology: how pathways differ from mechanisms and why it matters

For nearly two decades few topics in philosophy of science have received as much attention as mechanistic explanation. One motivation for these accounts is that scientists frequently use the term “mechanism” in their explanations of biological phenomena (Machamer, Darden, and Craver 2000, 2), (Bechtel and Richardson 2010, xvii) (Wimsatt 1976, 671). Biologists, of course, use a variety of causal concepts in their explanations, including concepts like pathways, cascades, triggers, and processes. Despite this variety, mainstream philosophical views interpret all of these concepts with the notion of a mechanism (Robins and Craver 2009, 42) (Craver 2007, 3). This mechanistic approach faces a significant problem. Although philosophers use the notion of a mechanism interchangeably with other causal concepts, this is not something that scientists always do. Consider the notion of a pathway, which commonly figures in biological explanation. Examples of this concept include gene expression pathways, cell signaling pathways, metabolic pathways, anatomical pathways, developmental pathways, and ecological pathways. Scientists often distinguish pathways from mechanisms. They claim that a single pathway can be instantiated by different mechanisms, that distinct pathways can have similar mechanisms, that pathways are be discovered without any knowledge of the mechanisms underlie them. Furthermore, when introducing scientific material they often promise to discuss both the mechanisms and pathways relevant to the domain of inquiry.

These points raise a number of puzzles for the dominant mechanistic program. If all or most of the causal concepts in biology are well interpreted with the notion of a mechanism, why do scientists often distinguish mechanisms from these other concepts? Why do they use a variety of causal terms if the single notion of mechanism would suffice? Finally, what explains their seemingly consistent use of particular causal concepts in some situations, while not in others? These puzzles suggest that it is worth exploring how scientists distinguish various causal concepts in biology and how these distinctions matter for understanding causal explanation in this domain. This talk examines how the mechanism and pathway concepts are used in the biology and how they figure in biological explanation. I argue that these concepts have distinct features, that they are associated with different strategies of causal investigation, and that they figure in importantly distinct types of explanation.