The question of the influence of genes on behavior raises difficult philosophical and social issues. In this paper I delineate what I call the Developmentalist Challenge (DC) to assertions of genetic influence on behavior, and then examine the DC through an indepth analysis of the behavioral genetics of the nematode, C. elegans, with some briefer references to work on Drosophila. I argue that eight "rules" relating genes and behavior through environmentally-influenced and tangled neural nets capture the results of developmental and (...) behavioral studies on the nematode. Some elements of the DC are found to be sound and others are criticized. The essay concludes by examining the relations of this study to Kitcher's antireductionist arguments and Bechtel and Richardson's decomposition and localization heuristics. Some implications for human behavioral genetics are also briefly considered. (shrink)