Following a brief consideration of the nature of "stress" as implied in the articles in this special section, the possible role of biological measurements in the study of behavioral development is examined. (PCB)

This study concerns the onset and early development of wariness in human infants. The data suggest positing a hierarchy of aversive reactions, from distress reactions to acquired fears. (Author/GB)

Longitudinal data concerning fear responses in 30 boys and 30 girls observed from ages one month to 8 1/2 years suggest that in males--but not in females--a predisposition to a particular level of fearfulness is set by events that occurred before 6 months of age. (Author/MG)