Abstract

Much of biology, especially evolutionary theory, makes assumptions about the individuality of living things. A population, for example, is made up of individuals. Those individuals sometimes reproduce, creating new individuals. The very use of these concepts requires that living individuals can be distinguished both synchronically and diachronically. There are many examples in nature, however, in which a living system is present, but it is not clear how to understand that system's individuality. Plants, fungi, colonial marine invertebrates, insect colonies, and symbiosis are all classic cases that have puzzled biologists interested in understanding their population structure and evolution. Scientific exploration of these issues has connections with traditional philosophical terrain, particularly the ontology of persistence and the nature of individuality broadly construed. A biologically informed philosophical literature has arisen in recent years, aimed at understanding the nature of biological individuality and its role in biological theorizing. My dissertation makes two kinds of contributions to this current literature. One contribution is theoretical, reframing our thinking about biological individuality. I distinguish between two categories of individuality and argue that they play different roles in theorizing about nature. One important kind of individual is that of the organism, understood as an entity that persists through space and time, takes in and processes resources from the environment, and maintains physiological autonomy. Another important kind of individual is that of the evolutionary individual, understood as an entity that has the capacity to participate in processes of natural selection. Distinguishing between these two types of individuality has theoretical utility, keeping clear the distinctive kinds of biological processes that individuals engage in. The other contribution of my dissertation involves detailed natural historical analysis of three kinds of problem cases. Using the framework articulated earlier in the dissertation, I assess the individuality of symbioses between larger organisms and their microbial associates, mushroom-producing fungi, and the classic case of ant colonies. The combined result of the assessments is a hierarchical pluralism about biological individuality.