Personality resemblance in adoptive families: A 10-year follow-up.

Abstract

Children from 181 of the 300 families of the Texas Adoption Project were recontacted after a 10year interval, at an average age of 17. They completed two standard personality tests, the Minnesota Multiphasic Personality Inventory (MMPI) and the Sixteen Personality Factor Questionnaire (16PF), plus a life events questionnaire and were rated by a parent on 24 bipolar trait scales. MMPI and 16PF scores were available from the earlier study for the adoptive parents, and MMPIs were available from the agency files for many of the adopted children's birth mothers. Parent-child correlations and regressions, sibling correlations, and comparison of the means of adopted and biological children were interpreted as indicating a modest genetic influence on personality traits (narrowsense heritability, uncorrected, of about .25), a near-zero influence of shared family environmental factors, and a substantial contribution of idiosyncratic environment. The relative emotional and social adjustment of the biological and the adopted children had shifted since the time of the first study, to the detriment of the adopted children, but most still fell in the normal range. Studying adoptive families is one way of assessing the extent to which personality differences reflect genetic differences among individuals rather than differences in their family environments. Moreover, if parents who adopt children have one or more biological children of their own, one can compare the resemblance of genetically related and genetically unrelated pairs. If information about the personality of one or both of the birth parents of an adopted child is also available, one can see what the resemblance of parent and child might be in the absence of any explicity shared experiences or interactions between them. If this resemblance is appreciable for some traits, it provides direct evidence for the influence of the genes in accounting for variation on these traits. If some of this information is available on two or more occasions, developmental questions can also be addressed. For example, do the genes play an increasing or a decreasing role in accounting for individual variation in a trait as children grow older? The Texas Adoption Project (Horn, Loehlin, & Willerman, 1979) studied 300 Texas families who had adopted one or more children through a church-related home for unwed mothers. Parents and children in these adoptive families were given various IQ and personality tests. IQ and personality test scores were also available from the agency files for many of the adopted children's birth mothers, from tests taken during their residence at the home some 3 to 14 years earlier. In this article we will report the results of a 10-year follow-up of many of the children in the