Under the mentorship of Richard Lewontin and then Timothy Prout, he used Drosophila to study the forces of cohesion within animal species. As he grew weary of changing flies, he seized an opportunity to reinvent himself as an evolutionary bacteriologist, with the guidance of Conrad Istock, Richard Michod, and John Spizizen. While he first saw bacteria as a convenient system for studying very general questions about evolution that one might rather study in elephants (if one could), he has grown to see bacteria as very interesting creatures in their own right. He is intrigued by what is the same and different about species and speciation across all walks of life, and investigates how the unique combination of enormous population size and rare but promiscuous genetic exchange in bacteria affect bacterial speciation and diversity. As a professor of biology at Wesleyan University, he teaches various courses in evolutionary biology, bioinformatics, and the effects of global change on infectious disease. He is a member of the Connecticut Academy of Science and Engineering.