How are we to understand the complex forces that shape human behav ior? A variety of diverse perspectives, drawing on studies of human behavioral ontogeny, as well as humanity’s evolutionary heritage, seem to provide the best likelihood of success. It is in an attempt to synthesize such potentially disparate approaches to human development into an integrated whole that we undertake this series on the genesis of beh- ior. In many respects, the incredible burgeoning of research in child development over the last two decades or so seems like a thousand lines of inquiry spreading outward in an incoherent starburst of effort. The need exists to provide, on an ongoing basis, an arena of discourse within which the threads of continuity among those diverse lines of research on human development can be woven into a fabric of meaning and under standing. Scientists, scholars, and those who attempt to translate their efforts into the practical realities of the care and guidance of infants and children are the audience that we seek to reach. Each requires the oppor tunity to see-to the degree that our knowledge in given areas per mits-various aspects of development in a coherent, integrated fashion. It is hoped that this series-which brings together research on infant biology, developing infant capacities, animal models, and impact of so cial, cultural, and familial forces on development, and the distorted products of such forces under certain circumstances-serves these important social and scientific needs.