While it is well-established that education and Right Wing Authoritarianism (RWA) are quite strongly negatively correlated, it is still unclear why this is the case. There could be causal effects between these variables, in one or both directions, which can be either direct or mediated. And there could also be confounding third variables influencing their association. Using a sample of 320 monozygotic- and 312 dizygotic twin pairs, we were able to control for confounding influences from both genes and the family-environment, increasing our ability to infer causal effects. Furthermore, we investigate the roles of perceived Socio-Economic Status (SES) in both childhood and adulthood; SES in childhood could be a confound between education and RWA, and SES in adulthood could be a mediator. We explore these hypotheses with ACE-β models, which extend the logic of discordant twin designs into a structural equation framework. Our results are consistent with a causal effect of education to reduce RWA. SES in adulthood did not mediate this effect. We find that the negative correlation between RWA and education is further amplified by confounding influences, mostly from the family environment, which are partly associated with SES.

Heritability is a concept that is often misunderstood. The term is used somewhat differently by researchers from how it is used in common parlance. This paper is a gentle introduction to the scientific concept of heritability, and to how it can be estimated for psychological traits in humans through analyses of data from monozygotic and dizygotic pairs of twins. The paper then explores some of the assumptions of the classical twin design, and presents calculations of the consequences of breaking these assumptions. Lastly, the paper introduces multivariate twin modeling, with a focus on how heritability of traits can be impacted by causal effects from other traits, and how twin designs can be informative when making causal inferences.

Moral judgments may be driven by both principled and opportunistic motivations. Being morally principled is to consistently adhere to a single set of rules about morality and justice. Opportunistic morality rather involves selectively enforcing rules when they are beneficial to one's interests. These two kinds of motivations sometimes pull in the same direction, other times not. Prior studies on moral motivations have mostly focused on principled morality. Opportunistic morality, along with its phenotypic and genetic correlates, remains largely unexamined. Here, utilizing a sample from the Norwegian Twin Registry, consisting of 312 monozygotic-and 298 dizygotic twin pairs (N = 1220), we measure people's propensity to react to injustice as victims, observers, beneficiaries, and perpetrators of injustice, using the Justice Sensitivity scale. Our genetically informative sample allows a biometric modeling approach that provides increased stringency in inferring latent psychological traits. We find evidence for two substantially heritable traits explaining correlations between Justice Sensitivity facets, which we interpret as a principled justice sensitivity (h 2 = .45) leading to increased sensitivity to injustices of all categories, and an opportunistic justice sensitivity (h 2 = .69) associated with increased victim sensitivity and a decreased propensity to feel guilt from being a perpetrator. These heritable justice traits share a genetic substrate with broad strategies for cooperation (as measured by altruism and trust) and for selectively benefitting oneself over the adaptive interests of others (as measured by social dominance orientation and support for monopolizing territory and resources), and differ genetically and phenotypically from Big Five personality traits.