The sophistry of the "Nature versus Nurture" formulation is becoming ever more apparent as a consequence of the rapid advances in understanding of the basic mechanisms of heredity and in the application of this knowledge to a wide spectrum of issues of human health and welfare. It is clear that a more accurate formulation would emphasize the interaction and coaction of genetic and environmental factors in their influence on complex phenotypes. Furthermore, the potential dependence of the influence of a particular gene on other genes in the system is increasingly realized. This paper documents these perspectives by examples of gene-environment interaction and gene-gene interaction both from animal model and from human research that reveal both the potential power and subtlety of these interactive effects. Copyright 2004 Wiley-Liss, Inc.