Doctor of Philosophy

dissertationThis dissertation explores biological individuality in fungi and in symbiotic associations composed of fungi and plants. It consists of three main chapters, which are written as standalone journal articles, along with an introduction that defends the method of theoretical individuation, which is employed throughout. The first main chapter establishes a minimum conception of biological individuality and then employs theoretical individuation to reveal multiple overlapping evolutionary and physiological individuals in a patch of mushrooms. The next main chapter explores individuality in mycorrhizal collectives, symbiotic associations composed of plants and fungi, and argues that these collectives are indeed evolutionary individuals according to two prominent models of evolutionary individuality, including Peter Godfrey-Smith model of collective Darwinian individuality. This chapter further offers an amendment to Godfrey-Smith's model, in order to account for gradations of individuality that follow from variability in the probability that a symbiotic collective will reproduce with pseudo-vertical transmission. The third main chapter resolves a puzzle that arises from Godfrey-Smith's model, which holds that Darwinian individuality both follows from being a selectable member of a population and comes in varying degrees. Population membership is a bivalent condition, so how can Darwinian individuality come in degrees? This puzzle is resolved by locating differences in degree of Darwinian individuality at the level of population lineages, some of which are Darwinian to a greater degree than others