Achievements and challenges in the biology of environmental effects.

The starting point for the study of adverse experiences is that some have enduring consequences that continue after the period of exposure to the adversity. That raises four basic issues: whether social adversities can be considered homogeneous, whether the crucial effect lies in the "objective" or subjectively perceived "effective" environment, whether the effects are environmentally mediated, and whether the form of biological embedding involves psychological or health consequences. The findings in the literature are discussed in relation to the biological effects of supposedly positive or normal experiences, the use of natural experiments to determine the causal effects of early experience, the heterogeneity of social adversity, the possible mediators of the biological embedding, gene-environment interdependence, and remaining challenges.