Evolutionary hypotheses and behavioral genetic methods: Hopes for a union of two disparate disciplines

The interaction between the dopamine receptor D4 (DRD4) variable number tandem repeat polymorphism and perceived peer drinking norms in adolescent alcohol use and misuse

Peer drinking norms are arguably one of the strongest correlates of adolescent drinking. Prospective studies indicate that adolescents tend to select peers based on drinking (peer selection) and their peers' drinking is associated with changes in adolescent drinking over time (peer socialization). The present study investigated whether the peer selection and socialization processes in adolescent drinking differed as a function of the dopamine receptor D4 (DRD4) variable number tandem repeat genotype in two independent prospective data sets. The first sample was 174 high school students drawn from a two-wave 6-month prospective study. The second sample was 237 college students drawn from a three-wave annual prospective study. Multigroup cross-lagged panel analyses of the high school student sample indicated stronger socialization via peer drinking norms among carriers, whereas analyses of the college student sample indicated stronger drinking-based peer selection in the junior year among carriers, compared to noncarriers. Although replication and meta-analytic synthesis are needed, these findings suggest that in part genetically determined peer selection (carriers of the DRD4 seven-repeat allele tend to associate with peers who have more favorable attitudes toward drinking and greater alcohol use) and peer socialization (carriers' subsequent drinking behaviors are more strongly associated with their peer drinking norms) may differ across adolescent developmental stages.

Why are children in the same family so different? Nonshared environment a decade later

OBJECTIVE

To review recent developments in the study of nonshared environment; that is, the environmental influences that make children growing up in the same family different, rather than similar.

METHOD

We review several recent influential books and papers on the subject of nonshared environment from the decade following the 1987 paper that highlighted its importance in psychological development.

RESULTS

Modest progress has been made toward identifying the specific aspects of the environment responsible for nonshared environment. Although parents treat their multiple children differently, such differential treatment accounts for only a small amount of nonshared environmental influence, once genetic factors are controlled. It has been suggested that some degree of nonshared environment may be due to the fact that siblings react differently to ostensibly shared environmental influences. Peer influence and other experiences outside the family may be more important sources of systematic nonshared environment.

CONCLUSIONS

Despite the difficulties encountered in identifying specific sources of nonshared environment, the fact remains that most environmental variance affecting the development of psychological dimensions and psychiatric disorders is not shared by children growing up in the same family. More research and theory are needed to explain why such siblings are so different. Chance, in the sense of idiosyncratic experiences, also needs to be considered.