This dissertation advances the new mechanistic philosophy of science by developing novel accounts of activities and good parts. In the first chapter, I develop a Hybrid Account of activities that integrates production and difference-making approaches to causation, enabling the identification and individuation of causally productive activities. In the second chapter, my account of good parthood grounds being a good part in the role parts play in mechanisms as activity-enablers as well as their inclusion in what I call the explanatory mosaic of science. This account is robust enough to characterize parts of mechanisms throughout the life sciences. In the third chapter, I apply the account I develop to the case of the use of race in epidemiology and biomedicine. I show how the mechanism discovery approach, and the accounts I develop in earlier chapters, offer a normatively and explanatorily attractive methodology to researching, diagnosing, and treating complex trait disorders. The dissertation applies these accounts to case studies from the life sciences to show how they solve outstanding problems in philosophy and biology.