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Thursday, July 21, 2022

Testing heritability of moral foundations: Common pathway models support strong heritability for the five moral foundations

Zakharin, M., & Bates, T. C. (2022). 
European Journal of Personality.


Moral Foundations Theory (MFT) predicts that moral behaviour reflects at least five foundational traits, each hypothesised to be heritable. Here, we report two independent twin studies (total n = 2020), using multivariate multi-group common pathway models to test the following three predictions from the MFT: (1) The moral foundations will show significant heritability; (2) The moral foundations will each be genetically distinct and (3) The clustering of moral concerns around individualising and binding domains will show significant heritability. Supporting predictions 1 and 3, Study 1 showed evidence for significant heritability of two broad moral factors corresponding to individualising and binding domains. In Study 2, we added the second dataset, testing replication of the Study 1 model in a joint approach. This further corroborated evidence for heritable influence, showed strong influences on the individualising and binding domains (h2 = 49% and 66%, respectively) and, partially supporting prediction 2, showed foundation-specific, heritable influences on Harm/Care, Fairness/Reciprocity and Purity/Sanctity foundations. A general morality factor was required, also showing substantial genetic effects (40%). These findings indicate that moral foundations have significant genetic bases. These influenced the individual foundations themselves as well as a general concern for the individual, for the group, and overall moral concern.

From the General Discussion

Two of the highly heritable common factors in our model clearly correspond to the binding (Ingroup/ Loyalty, Authority/Respect and Sanctity/Purity) and individualising (Harm/Care and Fairness/Reciprocity) moral domains theorised by Graham et al. (2011), thereby supporting their model. At the same time, three out of five specific genetic effects were non-significant, which was unexpected. This may suggest that differences between individual foundations, for example, distinctions between Authority and Ingroup – are purely learned in origin. At this point, however, an equally plausible hypothesis is that we simply lacked the power to distinguish all the effects in the moral foundations. The sample size, but more particularly the abbreviated measures used in both datasets with reduced ability to detect facet-specific variance mean that this possibility cannot be ruled out. Future studies investigating these issues using larger, extended and even longitudinal twin designs and a wide range of measures would be valuable. In particular, it will be of value to explore whether the five distinct foundations reflect, at a genetic level, different combinations of these two major domains. Another area of interest for future research would be an analysis of distinctions between individualising measures such as Harm/Care and Fairness/Reciprocity and motivations such as compassion in other evolutionary models (e.g. Lin & Bates, 2021; Sznycer et al., 2017).