This book offers a novel defence of a highly contested philosophical position: biological natural kind essentialism. This theory is routinely and explicitly rejected for its purported inability to be explicated in the context of contemporary biological science, and its supposed incompatibility with the process and progress of evolution by natural selection. Christopher J. Austin challenges these objections, and in conjunction with contemporary scientific advancements within the field of evolutionary-developmental biology, the book utilises a contemporary neo-Aristotelian metaphysics of "dispositional properties", or causal powers, to provide a theory of essentialism centred on the developmental architecture of organisms and its role in the evolutionary process. By defending a novel theory of Aristotelian biological natural kind essentialism, represents the fresh and exciting union of cutting-edge philosophical insight and scientific knowledge.