One conception of the propensity interpretation of fitness describes fitness as a probability distribution that encompasses all possible lineages the organism may give rise to, including how the organism’s traits might change and all possible environments the organism might encounter. This long-term definition of fitness is general enough to avoid counterexamples that other mathematical conceptions face. However, there seem to be downsides to 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 are included in the concept, it becomes hard to see how fitness can fulfill this role. We argue that this is a feature of this view of fitness, rather than a bug: long-term fitness accommodates evolvability considerations, which concern the role that variation plays in evolutionary processes and provides a more accurate accounting of long-term evolutionary success. This collaboration emerged from a workshop that I co-organized this summer, “Evolvability: A Bridge Between the Proximate and the Ultimate?”

Several prominent debates in biology, such as those surrounding adaptationism, group selection, and punctuated equilibrium, have focused on disagreements about the relative importance of a cause in producing a phenomenon of interest. Some philosophers, such as John Beatty have expressed skepticism about the scientific value of engaging in these controversies, and Karen Kovaka has suggested that their value might be limited. In this paper, I challenge that skepticism by giving a novel analysis of relative significance controversies, showing that there are three forms they can take. I argue that these controversies can have significant epistemic upshots, in that they help scientists form predictions about new instances of the phenomenon of interest. Finally, using two historical examples, I show how engaging in these controversies can improve our understanding of causal relationships.

In this paper, I argue that another component of relative significance controversies is the choice in reference class. From probability theory, we know that choices in reference class can make a difference in claims about the frequency of events. The frequency of developing lung cancer will be very different when I am looking at a class of people over 45 who smoke cigarettes versus those between the ages of 20 and 35 who don’t. How do we decide which reference class we should use and how do we justify this choice? I argue that the proposed solution to this puzzle from probability theory—that we should use the most specific reference class available—does not always provide good guidance for scientists. There are principled reasons for using different reference classes to study the same phenomenon. However, the conclusions scientists should draw depend on this choice. Using the evolution of senescence literature as a case study, I explore how the choice in reference class can lead to scientists talking past one another, but it can also be a source of progress.

My dissertation motivates the claim that the success of the concept of evolvability in evolutionary biology hinges on the answers to metaphysical and explanatory questions. Inspired by Rachael Brown’s (2014) seminal call for a unified account of evolvability (and in collaboration with her), I have developed several plausible versions of such an account that show how evolvability could be connected up with standard evolutionary theory, but I remain neutral on which view we should adopt in my dissertation. In response to several recent articles criticizing the unification approach, Rachael and I are co-authoring a follow-up paper to her earlier piece that addresses these criticisms and outlines why we should favor a unified account of evolvability.

As the threat of climate change intensifies, questions concerning whether we ought to assist biological populations living in environments that are susceptible to climate change (and, if so, which ones we should prioritize) become more pressing. Conservation biologists and environmental ethicists answer these questions by assessing adaptability, or the extent to which natural and human systems can adjust to climate change and the effects of climate change. However, this notion of adaptability runs together two sets of features that should be kept distinct: (i) how well-adapted organisms are to their current environment and (ii) how well-equipped a population is to respond to environmental changes. In this paper, I argue that evolvability is a promising alternative criterion for making such decisions. In addition to providing conceptual clarity, evolvability can better track the features that conservation biologists think are relevant to determining whether intervention is appropriate. Using two case studies, I show that evolvability can provide insight into when different kinds of intervention strategies should be implemented. Using this criterion, however, we face a dilemma—either (i) we should prioritize highly evolvable populations since they are more likely to survive a changing climate, or (ii) we should prioritize populations with low evolvability, which will probably not survive without our help. I consider the implications of both alternatives.

There are serious concerns about the feasibility of measuring the evolvability of populations. Because evolvability is a disposition, the realized evolutionary pathway of a population is only a small piece of the puzzle. Further, judgments about the evolvability of a population depend on whether evolvability is considered in the long term or short term, the variance and skew of evolvability within the population, and the scope of environments considered. These problems multiply when we try to compare the evolvability of different populations. Unless they are held fixed, reproduction and lifespan timing can swamp evolvability judgments. Further, the accessible parts of trait spaces for each population will be drastically different. I explore the feasibility of using a reductive account of evolvability, which can avoid some of these challenges. The upshot of this account of evolvability is that it provides a path forward for using comparative methods to test evolvability hypotheses. However, evolvability loses considerable explanatory power in this form. In this paper, I analyze both the costs and benefits of this view and consider a pluralist alternative.