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  • Developmental Psychology1993. Vol. 29, No. 1,96-109

    Copyright 1993 by ihe American Psychological Association, Inc.0012-1649/93/S3.00

    Personality Stability and Change in Early Adulthood:A Behavioral Genetic Analysis

    Matt McGue, Steven Bacon, and David T. Lykken

    Seventy-nine monozygotic and 48 same-sex dizygotic twin pairs completed the MultidimensionalPersonality Questionnaire twice, averaging 20 years of age at first and 30 years at second testing.There were significant mean decreases in measures of Negative Emotionality (NE), increases inmeasures of Constraint (CO), but no significant mean changes for measures of Positive Emotional-ity (PE). Variance decreased for measures of NE but remained stable for measures of PE and CO.Biometrical analyses revealed that (a) NE variance reduction was due to diminishing genetic influ-ences, (b) personality stability was due largely to genetic factors, and (c) although some evidence forgenetic influence on personality change was observed, change was determined largely by environ-mental factors. It is concluded that the stable core of personality is strongly associated with geneticfactors but that personality change largely reflects environmental factors.

    There is a growing consensus among personality psycholo-gists that personality stabilizes in adulthood (e.g., McCrae &Costa, 1990). Nonetheless, adolescence, the period leading upto adulthood, has long been recognized as a psychologicallyturbulent age (Hall, 1904; Rutter, Graham, Chadwick, & Uhle,1976). Thus, for example, the rates of violent behavior (Daly &Wilson, 1988), criminal activity (Gottfredson & Hirschi, 1990),alcohol and drug abuse (Johnston, O'Malley, & Bachman,1985), as well as other antisocial behavior all peak before age 25years. Yet, the majority of troubled youths do not go on to haveserious problems in adulthood (e.g., Robins, 1966). The attain-ment of physical maturity is accompanied by significant psy-chological change (Siegel, 1982) and increasing levels of psycho-logical adjustment (Hathaway & Monachesi, 1953). The precisemechanisms that underlie these psychological changes, how-ever, remain to be fully determined.

    Only a few longitudinal studies have investigated personalitychanges during the transition from late adolescence to earlyadulthood, yielding a limited and at times inconsistent set offindings. For example, Stevens and Truss (1985) administeredthe Edwards Personal Preference Survey (EPPS) to two samplesof college alumni, one 12 years and the other 20 years afterinitial completion of the inventory while in college. Stevens andTruss reported mean increasesconsistent across the two sam-plesfor Achievement, Autonomy, and Dominance; consis-tent mean decreases in Abasement and Affiliation; but no con-sistent changes in Aggression or the other EPPS scales. Block

    Matt McGue, Steven Bacon, and David T. Lykken, Department ofPsychology, University of Minnesota. Steven Bacon is now at the Vet-erans Administration Medical Center, San Diego, California.

    This research is supported in part by U.S. Public Health ServiceGrants AG06886, MH73860, and DA05147. We acknowledge thehelpful comments of Thomas J. Bouchard, Jr., Crista Carmichael,Auke Tellegen, and four anonymous reviewers of an earlier version ofthis article.

    Correspondence concerning this article should be addressed to MattMcGue, Department of Psychology, N218 Elliott Hall, 75 East RiverRoad, University of Minnesota, Minneapolis, Minnesota 55455.

    (1971), in the Berkeley longitudinal studies, concluded that, formale subjects, interviewer-rated expressed hostility increasedwhile rebelliousness decreased as the sample aged from seniorhigh school to early adulthood. Stein, Newcomb, and Bentler(1986) reported significant mean increases in Law Abidance,Congeniality, Diligence, Generosity, and Leadership from theearly teen years to the early twenties in a large and broadlyrepresentative school-based sample.

    The evidence concerning the stability of individual differ-ences in personality from late adolescence to early adulthood issimilarly inconsistent. Thus, for example, Stein et al. (1986)reported 4-year stability coefficients from the late teens to earlytwenties that generally fell in the range of .5 to .6, leading themto conclude that individual differences crystallize with advanc-ing age. Stevens and Truss (1985), however, reported 12- and20-year stability coefficients for the EPPS that generally fell inthe .2 to .4 range, suggesting only modest stability of individualdifferences. The apparently inconsistent pattern of resultscould be caused by different sampling strategies (college stu-dents vs. representative samples), different assessment proce-dures (e.g., self-ratings vs. ratings by others), and very probablyalso the use of different measuring devices. In the present study,a community-based sample completed an omnibus self-reportpersonality inventorythe Multidimensional Personality Ques-tionnaire (MPQ; Tellegen, 1982)first in late adolescence(average age of 20 years) and then again 10 years later when inearly adulthood. The MPQ has excellent psychometric proper-ties and includes validity scales to screen out likely invalid pro-files. Of particular significance to the present study is theMPQ's hierarchical factor structure, which provides a basis forassessing consistency of results within the study.

    The psychological changes that accompany the transitionfrom late adolescence to early adulthood have typically beenattributed to environmental factors; for example, to "culture"(e.g., Stein et al., 1986), to societal expectations (e.g., Dubow,Huesman, & Eron, 1987), and so on. An alternative, but lessfrequently considered, possibility is that biological factors con-tribute to personality changes. The field of developmental be-

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  • PERSONALITY STABILITY AND CHANGE 97

    havioral genetics seeks to identify and characterize genetic andenvironmental influences on behavioral stability and change(Plomin, 1986). The present study uses a standard yet powerfulbehavioral genetic design, a longitudinal twin study, to investi-gate genetic and environmental influences on personality sta-bility and change in the transition from late adolescence toearly adulthood.

    Loehlin (1992) reviews longitudinal behavioral genetic stud-ies of normal between-person variation in personality and con-cludes that although there are significant genetic contributionsto personality change in childhood, personality change in lateadolescence and early adulthood appears to be due largely toenvironmental factors. In an earlier review of behavioral ge-netic research on temperament, Goldsmith (1983) came to es-sentially the same conclusion. This pattern is not altogetherunexpected. The normative changes of childhood are moreconsistent with a genetic influence, common across individ-uals, than are the individuated changes of later adulthood.Some traits change developmentally in the same direction formost people but to varying degrees; other traits change both indirection and in magnitude. The extent of the first type ofnormative change might owe more to genetic factors, whereasthe (nonnormative) change of the second type of trait might owemore to environmental determinants (cf. Wilson, 1983).

    Identifying the basis of behavioral continuity is as central toan understanding of personality development as is identifyingthe basis for behavioral change. Several lines of behavioral ge-netic research converge in suggesting that environmental influ-ences may not endure unless exposure is persistently and con-sistently experienced. Thus, for example, a recent meta-analysisof similarity among preadult twins ended with the conclusionthat the effects of common rearing wane once the twins haveleft their rearing home (McCartney, Harris, & Bernieri, 1990).Similarly, Kaprio, Koskenvuo, and Rose (1990) reported thatthe greater behavioral similarity observed among living-to-gether adult twins disappears once they separate. One mighttherefore expect that the continuity of individual differences inpersonality from late adolescence to early adulthood is duelargely to the influence of genetic rather than environmentalfactors.

    The present investigation is a longitudinal study of personal-ity similarity among monozygotic (MZ) and same-sex dizy-gotic (DZ) twins aimed at determining the extent to which per-sonality stability and change in early adulthood is associatedwith genetic or environmental factors or both. It is expectedthat individual differences in personality change will be causedlargely by environmental factors, with genetic contributions tochange being largest for personality dimensions undergoingnormative rather than individual change. In contrast, the conti-nuity of individual differences in personality is expected to becaused largely by enduring genetic influences.

    Method

    SampleThe sample consisted of 127 pairs of same-sex reared-together twins

    originally recruited and tested in the early 1970s (Lykken, 1982). Thestudy began before the establishment of population-based U.S. twin

    registries, so that twin pairs were recruited from a variety of sources.Most were identified from rosters of students who were seniors inMinneapolis or St. Paul high schools during the preceding year. Pairsof individuals from the same high school with identical surnames,birthdates, and mailing addresses were contacted and recruited to par-ticipate in a study on twins. A few additional pairs, then current orformer undergraduate students at the University of Minnesota, wereidentified as twins from the records of the University Health Service.As is usual in such studies of volunteer twin samples (Lykken, McGue,& Tellegen 1988), about two thirds of the individuals were female twinsand two thirds of the pairs were MZ pairs. Participation involved ahalf-day vis