10-20 percent (Rich, 1998). Finally, the expression of Type 1 diabetes among those with genetic susceptibility (major histocompatibility complex on chromosome 6p21 and 17 and a 14/15 base pair oligonucleotide on chromosome 11p15) is very sensitive to diet, infections, and a range of external environmental triggers (Todd, 1999).
All of the above examples underscore the importance of understanding disease resistance or delay of onset in the face of high risk. Given the dominant focus on predicting disease incidence, rather than avoidance, such inquiry represents largely uncharted scientific territory. It is nonetheless essential for mapping the causal processes involved in disease resistance, particularly in the face of known risk. Behavioral and psychosocial factors (e.g., exercise, nutrition, coping strategies, optimism, social supports) are not necessarily implicated in all such instances. Other genetic factors, for example, may account for aspects of disease resistance, but even these routes need to be explicated, particularly with regard to the nature of environmentally induced gene expression.
Even the most powerful environmental risk factors do not produce uniform outcomes. In studies of children growing up under adverse environmental conditions (e.g., parental psychopathology, parental alcoholism, extreme poverty), some children exhibit remarkable resilience, as evidenced by profiles of healthy development and avoidance of the disorders that characterize their parents (Garmezy, 1991; Glanz and Johnson, 1999; Rutter, 1990; Werner and Smith, 1992). These individuals have “defied others' expectations and survived or surmounted daunting and seemingly overwhelming dangers, obstacles and problems” (Leshner, 1999). Numerous protective factors have been suggested to explain such resilience (e.g., having bonds with at least one nurturing and supportive parent, receiving support from the external community, having an affectionate and outgoing temperament). Intervention studies conducted with children of poverty or those with developmental disabilities also show that significant improvements in cognitive, academic, and social outcomes can be promoted among those lacking early resources or abilities (Ramey and Ramey, 1998).
A further realm for illustrating resilience pertains to the growing interest in social inequalities and health (Adler et al., 1999). A recent transinstitute initiative seeks to advance knowledge of how these effects occur by explicating the intervening behavioral, psychosocial, and neurobiological processes. Existing research shows that lower socioeconomic status (SES) increases risk for ill health, but there is extensive variability within SES groups. Not all individuals with limited life resources and opportunities have poor health; in fact, some show optimal physical and mental health. Greater scientific investment is needed to explain the behavioral, psychosocial, and biological protective factors that underlie class-related health resilience. For example, individuals with cumulative economic adversity are