Cristina Villegas

The new foundation for the propensity interpretation of fitness (PIF), developed by Pence and Ramsey (Br J Philos Sci 64:851–881, 2013), describes fitness as a probability distribution that encompasses all possible daughter populations to which the organism may give rise, including daughter populations in which traits might change and the possible environments that members of the daughter populations might encounter. This long-term definition of fitness is general enough to avoid counterexamples faced by previous mathematical conceptions of PIF. However, there seem to be downsides to its generality: the ecological role of fitness involves describing the degree of adaptedness between an organism and the specific environment it inhabits. When all possible changes in traits and all possible environments that a daughter population may encounter are included in the concept, it becomes difficult to see how fitness can fulfill this role. In this paper, we argue that this is a feature of Pence and Ramsey’s view rather than a bug: long-term fitness accommodates evolvability considerations, which concern the role that variation plays in evolutionary processes. Building on the foundations, we show that Pence and Ramsey’s fitness—_F_—can be partitioned into fourths: adaptedness, robustness of adaptedness, and two facets of evolvability. Conceptualizing these last three components forces us to consider the role played by grains of description of both organisms and the environment when thinking about long-term fitness. They track the possibility that there could be a change in type in a daughter population as a way of responding to environmental challenges, or that the type persists in the face of novel environments. We argue that these components are just as salient as adaptedness for long-term fitness. Together, this decomposition of _F_ provides a more accurate picture of the factors involved in long-term evolutionary success.

The use of dispositions has been put into question many times in the philosophical literature, especially with regards to how dispositional attributions can be justified. Yet, dispositions are an important part not only of our everyday talk but also of our scientific practices. In this paper, we develop an argument that infers the epistemic justification of dispositional talk from itsindispensability for carrying out basic epistemological projects, and we apply it to the use of dispositions in evolutionary biology. For doing this, we first advocate for a function-based strategy for the epistemic justification of dispositional attributions. We next review the functional role of some key dispositional notions in evolutionary biology, such as fitness and evolvability. Then, we show that alternative non-dispositional substitutes of these dispositions fail to fulfill their roles to the same degree. We conclude that the use of dispositions is justified in evolutionary biology.

This paper applies philosophical tools from the causalists/statisticalists debate to the evo-devo idea of variational tendencies as propensities biasing phenotypic change. It contends that variational properties are present in a statistical sense in some population dynamics models, particularly quantitative genetics ones, providing ultimate variational explanations. It further argues that these properties, contrary to some recent views, cannot be subsumed under natural selection. Finally, it advocates for a causalist interpretation of these explanations, where variational statistical properties indirectly refer to evo-devo’s variational propensities.

The developmental properties of organisms play important roles in the generation of variation necessary for evolutionary change. But how can individual development steer the course of evolution? To answer this question, we introduce developmental channeling as a disposition of individual organisms that shapes their possible developmental trajectories and evolutionary dappling as an evolutionary outcome in which the space of possible organismic forms is dappled—it is only partially filled. We then trace out the implications of the channeling-dappling framework for contemporary debates in the philosophy of evolution, including evolvability, reciprocal causation, and the extended evolutionary synthesis.

Evolutionary developmental biology (evo-devo) is often vindicated by theoreticians of the field as a mechanistic science that brings a mechanistic perspective into evolutionary biology. Usually, it is also portrayed as stressing the causal role that development plays in the evolutionary process. However, mechanistic studies in evo-devo typically refer to lineage-specific transformations and lack the generality that evolutionary explanations usually aim for. After reviewing the prospects and limits of a mechanistic view of evo-devo and their studies of homology and novelty, in this chapter I propose a way to combine the mechanistic view of evo-devo with the population-level inclination of more classical approaches to evolution. Such a proposal provides a philosophical framework for understanding the causal role of development in evolution both as mechanistic and as generalizable, population-level.

A number of biologists and philosophers have noted the diversity of interpretations of evolvability in contemporary evolutionary research. Different clusters of research defined by co-citation patterns or shared methodological orientation sometimes concentrate on distinct conceptions of evolvability. We examine five different activities where the notion of evolvability plays conceptual roles in evolutionary biological investigation: setting a research agenda, characterization, explanation, prediction, and control. Our analysis of representative examples demonstrates how different conceptual roles of evolvability are quasi-independent and yet exhibit important relationships across scientific activities. It also provides us with the resources to detail two distinct strategies for how evolvability can help to synthesize disparate areas of research and thereby potentially serve as a unifying concept in evolutionary biology.

A disposition or dispositional property is a capacity, ability, or potential to display or exhibit some outcome. Evolvability refers to a disposition to evolve. This chapter discusses why the dispositional nature of evolvability matters—why philosophical distinctions about dispositions can have scientific implications. To that end, we build a conceptual toolkit with vocabulary from prior philosophical analyses using a different disposition: protein foldability. We then apply this toolkit to address several methodological questions related to evolvability. What entities are the bearers of evolvability? What features causally contribute to the disposition of evolvability? How does evolvability manifest? The various possible answers to these questions available from philosophical distinctions suggest key implications for why the concept of evolvability as a disposition is useful in evolutionary research. These include (1) securing scientific virtues (e.g., explanatory depth and generalization, prediction or retrodiction, and control or manipulation) and (2) fostering interdisciplinary collaboration through the coordination of definitional diversity and different types of inquiry. Together these facilitate concentration on a variety of research questions at different levels of organization and on distinct time scales, all of which should be expected for a complex dispositional property such as evolvability.

While the notion of chance has been central in discussions over the probabilistic nature of natural selection and genetic drift, its role in the production of variants on which populational sampling takes place has received much less philosophical attention. This article discusses the concept of chance in evolution in the light of contemporary work in evo-devo. We distinguish different levels at which randomness and chance can be defined in this context, and argue that recent research on variability and evolvability demands a causal understanding of variational probabilities under which development acquires a creative, rather than a constraining role in evolution. We then provide a propensity interpretation of variational probabilities that solves a conceptual confusion between causal properties, variational probabilities and extant variation present in the literature, and explore some metaphysical consequences that follow from our interpretation, specifically with regards to the nature of developmental types.