In the genes vs. environment debate, it is widely accepted that what we do, who we are, and what mental illnesses we are at risk for result from a complex combination of both factors. Just how complex is revealed in Behaving: What’s Genetic, What’s Not, and Why Should We Care? (Oxford University Press, 2016), Kenneth Schaffner’s assessment of the impact of recent biological research on the genetic contribution to behavior. Among the developments he considers are the sequencing of the human genome and the development of a model organism, the nematode C. Elegans, for exploring the relationship between genes, neural function, and development. Schaffner, who is Distinguished University Professor in the Department of History and Philosophy of Science at the University of Pittsburgh, discusses the methodologies for determining genetic influence and the challenges by developmentalists and others of gene-focused research. He also defends a “creeping” form of reduction in which multilevel mechanistic explanations are possible in local, specific areas of biology.