socialization and behavior, including levels of youthful and young adult drug involvement. Recent observational studies provide suggestions of parental influence on drug involvement under some circumstances, even when affiliation with drug-using peers and variations attributable to different neighborhood environments are taken into account (e.g., see Chilcoat and Anthony, 1996; Brook et al., 2000). Nonetheless, there are contrary observations about the influence of parents (e.g., see Petraitis et al., 1998; Kendler et al., 2000; Collins et al., 2000) and an increased appreciation for the influence of adolescent children on the variations in parenting styles and practices they experience in individual household environments (e.g., see Daniels et al., 1985; Niederhiser et al., 1999). Future research may be expected to yield more integration of the individual-oriented and the environment-oriented models to account for development of drug involvement over the life span, with increasing attention to multilevel or contextual influences of family and neighborhood (e.g., see Kendler et al., 1997; Chilcoat et al., 1996; Duncan et al., 1997; Groenewegen et al., 1999; Petronis and Anthony, 2000).

Research on drug use is especially interesting in relation to these transactions because the pharmacological actions of drugs have been found to be of importance in several different ways. Behavioral science research provides a quite clear view of the reinforcing functions of drug use. From behavioral laboratory evidence on experienced cocaine users, it is clear that many of these users respond to the positively reinforcing functions of cocaine use in a predictable way: they work hard to secure more cocaine. One may infer that outside the laboratory, this behavioral response to the reinforcing functions of cocaine includes a willingness to enter into higher-risk social environments in which there are opportunities to use cocaine. In sequence, facets of the individual’s personality are expressed in the behavior of entering higher-risk social environments in which cocaine is available. Once cocaine use begins, the cocaine-associated reinforcement may help draw the individual back to these environments, and the environmental circumstances again shape the probability and frequency of future return.

A more recent line of evidence from the neuroscience research on postsynaptic signaling mechanisms provides an additional example of the transactions between nature and nurture. As noted earlier, environmental exposure to cocaine actually produces a change in the expression of genes, with presumed impact on future sensitivity to the drug and the development of dependence. Here, there is a clear example of a feature of the environment (i.e., a drug) that does not change the genetic makeup of the individual, but rather alters the expression of the genes within the individual’s genome. This altered gene expression, in turn, has implications for the future behavior of the drug-using individual, whether he or



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