This paper examines the biophilia hypothesis put forth by E. O. Wilson, which asserts the existence of a fundamental, genetically-based human need and propensity to affiliate with other living organisms and lifelike processes. It reviews research by Wilson and others that supports the biophilia hypothesis, and examines some of the issues and concerns that are at the forefront of the debate over the validity of the biophilia hypothesis. The paper then draws on structural-developmental psychological theory to expand Wilson's hypothesis in order to address perceived flaws in Wilson's original hypothesis. Finally, the paper discusses three studies conducted in the United States and the Brazilian Amazon on children's moral and ecological conceptions of the natural environment. The studies were found to support a structural-developmental account of biophilia. (Contains 65 references.) (MDM)