My research focuses on the dynamics of multilevel selection, or systems in which natural selection acts simultaneously at more than one level in a biological hierarchy. Life is hierarchically organized, and most reproducing entities contain populations of smaller reproducing entities. Examples include genes, chromosomes, organelles, cells, organisms, colonies, and mixed-species assemblages. Any population evolves if variation in heritable traits affects the reproductive success of its members. This is equally true whether the population consists of organisms or any other reproducing entity. As a result, selection can act at multiple levels of organization. Although each level of selection can be conceptualized as a separate process, they often interact in complex ways that can dramatically affect evolutionary outcomes.

Multilevel selection theory can be a useful tool for studying the evolution of any trait involving cooperation or conflict. Specific examples include problems in: intragenomic conflict, ontogeny, cancer, senescence, sexual reproduction, pathogen virulence, resource exploitation, interference competition, mutualism, social cooperation, and transitions in individuality. I typically study multilevel selection using agent-based computer models to generate the dynamics of interest, and the mathematical models to analyze and interpret those dynamics. In addition to refining multilevel selection theory, I am also working on applying it to several specific problems: What are the evolutionary dynamics of cancer? How do genetic systems evolve to become more evolvable?
How can cooperation evolve among unrelated organisms? What drives transitions in individuality?
How do allometric scaling laws affect the structure and function of ant colonies?