Broad and narrow environmental and genetic sources of personality differences: An extended twin family study

The Assessment and Heritability of a Brief Measure of Agency

The interpersonal circumplex describes two major axes of personality that guide much of social behavior. Agency, one half of the interpersonal circumplex, refers to relatively stable behavioral patterns that center on self-focused dominance and assertiveness assessed in terms of goals, values, or personality traits. However, the psychometric overlap between agency and the most closely linked big five dimension, extraversion, is not well-established, and little behavior genetic work has documented evidence concerning the role of genetic and environmental influences on trait agency. We used the Midlife Development in the United States study to examine agency, big five, and generativity with replication and robustness checks (Nnon-twins = 5,194; Ntwins = 1,914; NMilwaukee = 592). Results indicated that agency was higher in men (d = - 0.24), moderately heritable (44.4%), strongly correlated with extraversion (r =.51), moderately correlated with generativity (r =.36), and approximately 41% of the variance in agency was shared with the big five. The current brief measure of agency across two samples reflected smaller gender differences than historical expectations but supported its distinction from the big five traits at the current levels of analysis.

Personality differences between birth order categories and across sibship sizes

We examined associations of self-reports on the HEXACO Personality Inventory-Revised (HEXACO-PI-R) with birth order category and sibship size, controlling for participant sex and age. In a first sample (N > 700,000 online adults, mainly from English-speaking countries), Honesty-Humility and Agreeableness both showed the highest means for middle-borns, followed in order by last-borns (youngests), firstborns (oldests), and only children, with differences between middles and onlys of d ≥ 0.20. The same result was replicated in a similar but smaller second sample (N > 70,000) in which sibship size was also assessed, thereby allowing birth order differences to be separated from sibship size differences. In that sample, Honesty-Humility and Agreeableness showed higher means with larger sibship sizes, with differences between sibship sizes of 1 and 6+ of d = 0.30 and d = 0.36, respectively. Controls for upbringing religiousness and current religiousness reduced these differences by about 25%. Within sibship sizes, birth order differences in these dimensions were considerably smaller but oldests remained up to d = 0.10 lower than middles and youngests. Openness was d ≈ 0.10 higher for onlys than for non-onlys collectively, and within sibship sizes, Openness was d ≈ 0.10 higher for oldests than for middles and youngests.

Explicating narrow and broad conceptualizations of environmental influences on personality

BACKGROUND

A surge of studies aims to identify environmental factors that explain individual differences, personality stability, and personality development. This special issue builds on this large interest and solicited articles on broad and narrow environmental factors of personality.

OBJECTIVE

We provide an overview of the motivations behind the special issue, review each of the articles, and present data on researchers' perceptions of environmental factors contributing to personality expression and development.

METHOD

We review 16 special issue articles, thematically grouped into seven topics-culture and race, genes and environment, geography and habitat, major/minor life events, social relationships, socioeconomic status and economic inequality, and work. We also present data on researchers' (N = 223) responses and ratings of environmental influences on personality expression and development.

RESULTS

In the open-ended responses, the most important environmental influences were family, culture, peers, relationships, and trauma. Among the least important were weather, birth order, geography, climate, and shared environment. Nearly all the environmental influences featured in this special issue were considered at least somewhat important; however, there was considerable heterogeneity in how important researchers found each topic.

CONCLUSIONS

There is no perfect consensus among researchers as to which environmental factors contribute most to personality expression and development. We hope that there is a larger surge of studies on personality constructs beyond traits, that contextualize concepts within a cultural and historical framework and develop more stringent theories to hypothesize about the environmental influences on personality.

Basic or Adaptation: The Assessment and Heritability of a Brief Measure of Agency

The interpersonal circumplex describes two major axes of personality that guide much of social behavior. Agency, one half of the interpersonal circumplex, refers to relatively stable behavioral patterns that center on self-focused dominance and assertiveness. Past empirical work on agency tends to treat the dimension as a characteristic adaptation, rather than a basic component of personality, in part due to the relatively large gender difference in agency with masculine individuals tending to behave more agentic. However, the psychometric overlap between agency and the most closely linked big five dimension, extraversion, is not well-established, and no behavior genetic work has documented evidence concerning the role of genetic and environmental influences. It is unclear whether agency is more similar to a personality trait, with no evidence of shared environmental influence and moderate heritability, or a characteristic adaptation, with some evidence for shared environmental influence and possibly lower heritability. We used the Midlife Development in the United States study to examine agency, big five, and generativity with replication and robustness check (Nnon-twins = 5,194; Ntwins = 1,914; NMilwaukee = 592). Results indicated that agency was higher in men (d = -.24), moderately heritable (44.4%), strongly correlated with extraversion (r = .51), moderately correlated with generativity (r = .36), and that approximately 40% of the variance in agency was shared with the big five. Agency also changed strongly with extraversion and openness, but less so generativity. Altogether, these results indicate that agency functions similar to other basic personality dimensions but is not clearly a dispositional trait.