How Do We Understand Natural Selection?

Humans have long sought to understand the forces that shape the diversity of living creatures on our planet. This work is primarily concerned with examining one such force---the historical action of natural selection---from practical, philosophical, and pedagogical perspectives. The first half is concerned with a suite of genetic mechanisms in flowering plants---adaptations collectively known as self-incompatibility or SI---that allow an otherwise fertile hermaphroditic plant to recognize and reject its own pollen. The number and phylogenetic distribution of SI systems is not currently known, and a lack of organized data hampers our ability to answer enduring questions related to the evolution and maintenance of SI systems over large timescales. Gathering data on SI is challenging as this trait has no immediately obvious characteristic morphology. First, I examine more than a thousand published reports to create curated datasets on the phylogenetic distribution and frequency of SI across two of the largest flowering plant families---Fabaceae and Orchidaceae. I summarize what is currently known about the nature of SI and its distribution in these families, and provide insights for future study. The second half is concerned with the pedagogy of natural selection. Despite the centrality of the theory of evolution by natural selection to our understanding of biological sciences, natural selection itself remains one of the most poorly understood mechanisms of evolutionary change among the general public. Few empirical studies examine the basic structure of student explanations related to adaptation. For instance, do students more commonly provide descriptions of observed patterns or provide explanations that cite causal mechanisms? Are answers focused at the level of the organism or at the level of the species? Here I develop a novel framework and associated questionnaire that allows for systematic analysis of student responses. I administer this framework to approximately 600 student participants over two semesters, across all levels of biological study. I find that students overwhelmingly prefer pattern-based descriptions to causal explanations, and that their justifications are frequently teleological. I demonstrate methods of formal instruction that may aid students in creating coherent and robust explanatory frameworks.