Are Complex Behaviors Specified by Dedicated Regulatory Genes? Reasoning from Drosophila

A regulatory gene, fruitless, appears to be specifically responsible for building the potential for male sexual behavior into the CNS of Drosophila. We use these and other findings about genes controlling development in model organisms as a basis for a more general discussion of the possibility that the neural circuits underlying other complex behaviors may also be built by the action of specific, dedicated genetic hierarchies. Do genes control behaviors? This long-standing question at the center of the nature/nurture debate is usually answered by neurobiologists, ethologists, and geneticists by saying: "Well, sort of, but both genes and environment are important in shaping behaviors." Here we argue, from our perspective as geneticists and biologists, that such answers are flawed in three ways: (1) A significant number of behaviors (e.g., certain fixed action patterns and species-specific innate behaviors) are relatively unaffected by environment and thus appear likely to be largely dictated (in some manner) by genes; (2) They fail to distinguish between different levels at which genes might control behavior; and (3) By placing an emphasis on the genetic and environmental components of the differences between individuals in the expression of behavior, such answers may have obfuscated understanding how the basic potentials for particular behaviors are established. Before we expand on these ideas, we need to define what we mean by (1) "behavior" and (2) "the genetic control of behavior," as discussions of this topic have frequently suffered from imprecise or no definitions of these terms.