Abstract
Traditional, quantitative behavioral geneticists and developmental psychobiologists such as Gilbert Gottlieb have long debated what it would take to create a truly developmental behavioral genetics. These disputes have proven so intractable that disputants have repeatedly suggested that the problem rests on their opponents' conceptual confusion; whilst others have argued that the intractability results from the non-scientific, political motivations of their opponents. The authors provide a different explanation of the intractability of these debates. They show that the disputants have competing interpretations of the concepts of reaction norm, genotype-environment interaction, and gene. The common thread that underlies each of these disagreements, the authors argue, is the relevance of potential variation that is not manifest in any actual population to the understanding of development.