Intervention as Experiment
Steven F. Warren
The University of Kansas
A phenotype is defined as “the manifest characteristics of an organism collectively, including anatomical and psychological traits, that result from both its heredity and its environment” (Neufeldt & Guralnik, 1988, p. 1013). The purpose of this chapter is to demonstrate the potential value of intervention research as a tool for understanding the nature of various behavioral phenotypes that are manifested at least in part by developmental language disorders. Because a phenotype by definition results from the interaction of heredity and environments, the first part of this chapter is devoted to the role of the environment in determining a phenotype and then the role of the phenotype in determining the environment. This discussion sets the stage for an examination of the central question: How can intervention research enhance our knowledge of specific phenotypes?
AFFECT A PHENOTYPE?
The genetic contribution to an individual phenotype is in part a collection of trait propensities. Traits are considered probabilistic in nature, not deterministic. However, the probability of some traits being manifested may be very high (e.g., eye color). Nevertheless, many phenotypic characteristics reflect some degree of gene-environment interaction over time. Consequently, changes in the environment may have an impact on the expression