Behavior-genetic studies indicate that at least half of the variance in major traits is attributable to the environment, primarily “non-shared” influences operating at the level of the individual rather than the family (Plomin, 2011; Turkheimer et al., 2014). Several research directions help to fill the gaps in understanding of personality development. The idea that the self is socially constructed is familiar to social psychologists. From a personality perspective, individual differences in the acquisition of self-regulative capabilities in childhood influence trait development guided by socially endorsed reference values or norms (Denissen et al., 2013). Over the lifespan, the neo-socioanalytic theory of Roberts and Nickel (2017) emphasizes investing in social institutions as a driving mechanism for personality development, supported by evidence for plasticity of traits in adulthood. The studies cited illustrate how an adequate account of trait development requires specification of how biological and social factors interact dynamically; it is not enough to assume that the genotype feeds forward directly into the individual's trait composition (Matthews, 2016).

A pillar of biological trait theory is the claim that major traits, such as the Big Five are universal across cultures (Costa and McCrae, 1992). However, while dimensions resembling the Big Five are indeed found in most studies, data often fail to meet criteria for true measurement invariance, especially in non-Western and non-industrialized cultures (Church, 2016). Personality research also identifies culture-specific “emic” or indigenous traits. There is a clear opportunity for personality researchers to examine the social processes that shape cultural differences, including the impact of cultural norms for beliefs, values, and interpersonal communication (Lehman et al., 2004). Understanding of group and individual differences in such processes may in turn lead to insights into the role of gene-culture interactions in personality (Church, 2016).

Interactionism has always been central to personality research but traditional biological theories admit only a narrow range of situational factors, such as presence and intensity of positive and negative reinforcers (Boyle et al., 2008). Within trait personality itself, this view is challenged by studies showing that context specific-measures, such as those for work self-efficacy and evaluative anxieties are often more predictive in-context than general measures (Matthews, 2020b). Within social psychology, a major contribution is the identification of “behavioral signatures” as elements of personality consistency (Mischel and Shoda, 1995), i.e., if-then relationships that specify the individual's typical cognitive, affective and behavioral reactions to specific social contexts. Accounts of narrative identity provide another way to understand stability of personality from a social perspective (McAdams and McLean, 2013). Thus, the social-psychological perspective enhances the capacity of trait models to handle situational factors.

Following from the previous point, social-psychological theory enriches understanding of the influence of personality traits on subjective experience and behavior. Social-cognitive theories of self-regulation identify processes, such as self-verification and self-presentation that vary systematically across individuals and can mediate trait effects (Robinson and Sedikides, 2020). Understanding traits for negativity, such as neuroticism and trait anxiety is a case in point. While basic brain mechanisms, such as sensitivity to punishment play a role, individuals high in these traits often display specifically social vulnerabilities and characteristic core self-evaluations (Chang et al., 2012). Process-oriented work on relevant traits, such as rejection sensitivity (Berenson et al., 2009) contributes to understanding the social expression of major traits. More generally, social-cognitive theories provide a wealth of dynamic process models that can be integrated with trait accounts of personality (Cervone, 2005).

Traditionally, social psychologists are skeptical about measurement of broad individual dispositions divorced from social context. Nevertheless, numerous scales have been developed for core social-psychological constructs including values, concerns with social evaluation, intergroup contact, stereotyping, and prejudice, attitudes toward sexual orientation, and others (Boyle et al., 2015). Such scales are validated against the same criteria used for personality and other individual-difference measures. Obviously, measuring prejudice with a self-report scale is insufficient for understanding the construct, but the scale provides a tool for capturing some (explicit) elements of prejudice and investigating how personal dispositions interact with situational factors.

Just as trait psychologists should recognize the importance of social processes, so too should social psychologists recognize systematic, dispositional influences on social behavior. These influences are captured by facet-level traits, such as social anxiety, rejection sensitivity, sociability, self-consciousness, and many others. The interpersonal circumplex provides a broad framework for understanding social traits that can be mapped to trait dimensions (Gurtman, 2009). Traits are important too for understanding personality disorders that negatively impact social functioning. For example, it would be difficult to fully explain criminal and antisocial behavior without reference to the Dark Triad (or Tetrad) (Paulhus, 2014). Some social psychologists may harbor skepticism about the value of trait accounts from a reasonable desire to avoid crude biological reductionism. However, understanding of abnormal social psychology benefits from an integration of perspectives.

The relationship between personality and moral character is a theme going back to antiquity. Various instruments measuring moral dispositions and values (Campbell et al., 2015) can inform relevant social-psychological studies. Similarly, the rise of populism has revived interest in individual differences in political attitudes and their underpinnings including right-wing authoritarianism, nationalism, and ethnocentrism. Evidence linking conservatism to brain systems for threat processing suggests a biological component to individual differences (Pedersen et al., 2018).

The influence of biologically-based temperamental factors on child development (Rothbart et al., 2020) has profound implications for understanding social factors. Environmental and genetic factors may be correlated. Suppose we find that troubled parents tend to have troubled children. Is this because the parents adopt a suboptimal parenting style, or because parents and children share genes for personality? More nuanced accounts of gene-environment correlation and interaction suggest multiple developmental processes (Rutter, 2012; Cicchetti, 2016). The parents' genes shape their behaviors toward the child, and hence the environment in which it grows up. The child's genes influence the environments it selects for itself, and the behaviors it elicits from parents and others (Rutter, 2012). Maladaptive environments interact with genes to affect brain development (Cicchetti, 2016). Such interactions include epigenetic effects, where environment influences gene expression (Rutter, 2012). These complex and subtle effects do not negate the value of social-cognitive perspectives on child development, but they do imply that a full account of individual differences in social learning must accommodate biological factors. The advent of social neuroscience (Cacioppo et al., 2010) provides paths toward mechanistic explanations. As these authors discuss, social behavior may reflect reciprocal interactions between social and biological antecedents.

Multi-leveled organizational theory identifies levels of analysis that characterize groups. Kozlowski and Klein (2000) differentiated three categories of team-level constructs: shared, configurable and global constructs. Shared constructs mirror individual-level ones; for example, team self-efficacy may be a composition of individuals' self-efficacy. Configural constructs, such as team diversity, are emergent from individual characteristics, but are conceptually distinct from them. Global constructs refer to the team as a unit, such as its function at work, with no reference to individuals. Studies addressing configural and, especially, global constructs are unmoored from personality and individual differences. Furthermore, group-level constructs can be defined at different levels themselves, ranging from teams to organizations. In certain contexts, it is thus legitimate for social psychologists to work at the group-level only.

Does genetic modeling of personality variance actually tell us anything about causal processes? Turkheimer et al. (2014) argue that while personality traits universally show heritabilities of ~0.4, such findings tell us little about behavioral expressions of the trait phenotype. Individual genes have vanishingly small effects on personality, and so even molecular genetic studies do not lead to specifications of specific biological mechanisms. Behavior genetics provides insight into correlational data, such as associations between parent and child personalities, but it is irrelevant to causal hypotheses. Not all geneticists would agree, but according to Turkheimer et al. (2014, p. 535), “Personality is heritable, but it has no genetic mechanism.” Similar cautions have been expressed about the inferences to be drawn from genome-wide association studies (GWAS: Feldman and Ramachandran, 2018).