Historically, explanations for the origins of behavior have vacillated be­ tween nurturist and nativist camps. Nurturists emphasize environmental determinants of development, whereas nativists emphasize biological de­ terminants. Contemporary develop mentalists reject such dichotomies on the assumption that the organization of behavior is driven by interac­ tions between environmental and biological regulators. For example, Sameroff (1989; Sameroff & Fiese, 1989) reminds us that throughout the life span, development of the biological organism has meaning only when considered in relation to its contextual environment because it is the events in the environment that trigger expression of the genotype or, at minimum, work in transactional relationship with biological reg­ ulators. Put another way, the expression (phenotype) of the organism''s biological makeup (genotype) will always be affected by the environ­ ments in which the organism develops. Sameroff argues that the search for biological regulators of develop­ ment led investigators to downplay the importance of environmental regulators. He proposes that the "environ type" should have equal status with the phenotype and genotype as a developmental regulatory system. Environtype refers to the environmental context(s) within which orga­ nisms develop-the environmental events that trigger expression of the genotype. And, for Sameroff, social organization is accorded special status because it influences the individual''s adaptation to society.