Ian is broadly interested in the evolutionary and ecological processes that shape host-pathogen interactions. His aim is to develop theoretical models that incorporate the complexity and heterogeneity found in natural systems, to test the predictions of these models empirically, and to apply his findings to problems related to public health. Big questions that currently interest him include: How does host heterogeneity affect epidemic processes and the evolution of virulence? What are the patterns of variation in the efficacy of the immune system within and between populations? What trade-offs or biotic interactions limit virulence?