lems, and hospital admissions. Second, it is essential to learn about continuities and discontinuities in development and about normal variation so that researchers can begin to clarify when preventive interventions are not warranted as well as when they are. Third, there is much more to understand about indirect causal chain processes, mechanisms, and biological and environmental interactions. Finally, there is a need to assess risk factors and the effects of intervention across multiple age periods in each individual and across generations, such as both mothers and their infants.
There is an increasing tendency within the biological and behavioral sciences to appreciate the complexity and interplay of genetic and environmental interactions. There has been some movement away from the traditional nature-nurture dichotomy toward a recognition that genetic inheritance (the genotype) provides a reaction range within which the environment can have some impact on the characteristic that is expressed (the phenotype).
An understanding of etiology can contribute to the conceptualization and implementation of rational preventive interventions. Research in the core sciences to uncover the wide range of biopsychosocial etiological factors in mental illness is therefore critical to the long-term success of the prevention research initiative. Such basic scientific research endeavors have been the building blocks for the knowledge base on which prevention research has developed.
Many of the interdisciplinary areas of investigation with relevance to prevention research have independently recognized the utility of a developmental focus. These areas include neuroscience, genetics, epidemiology, and developmental psychopathology. From this developmental focus has arisen the concept of sensitive periods.
Eventually, it may become possible to determine the precise mechanisms by which environmental risk factors operate. In attempting to ascertain the relative contributions of the biological and environmental influences on expressed behavior or attributes, a number of paradigms have been useful, including twin, adoption, and experimental studies. In the absence of sound knowledge on risk mechanisms, there is some danger that prevention measures may be either wrongly targeted or so diffuse that they do not bring the expected benefits.
There is considerable evidence that people act in ways that influence the level of risk in the environments they experience. What is less certain is the genetic influence in this process. Genetic influences on behavior