Relationships between cognitive abilities and prosocial behavior are entirely explained by shared genetic influences: A Nigerian twin study

The relationship between prosocial behavior (PB) and cognitive abilities has been well documented. This study explored genetic and environmental overlaps in the relationship between PB and verbal and non-verbal abilities. Participants included 3179 twins attending public secondary schools in Lagos State in Nigeria (mean age = 14.6 years, SD = 1.7 years). The PB scale of the Strengths and Difficulties Questionnaire was used to measure PB. The set B of the Mill-Hill Vocabulary test (MHV) and Raven's Standard Progressive Matrices Plus (SPM) were used to measure verbal and non-verbal ability, respectively. The MHV-PB and the SPM-PB correlations were 0.29 (95%CI = 0.26, 0.32) and 0.19 (95%CI = 0.15, 0.23), respectively, indicating that PB is more strongly related to verbal than to non-verbal ability at the phenotypic level. Bivariate model-fitting analyses revealed that additive genetic correlations were 0.73 (95%CI = 0.59, 0.92) for MHV-PB and 0.55 (95%CI = 0.40, 0.82) for SPM-PB, respectively. Neither shared nor non-shared environmental correlations were significant. Bivariate heritability was estimated at 1.0 (95%CI = 0.65, 1.00 for MHV- PB and 95%CI = 0.60, 1.00 for SPM-PB), indicating that the relationships between PB and two cognitive measures were mediated entirely by common genes. Multivariate Cholesky model-fitting analysis showed that while MHV explained 10% of additional additive genetic variance of PB above and beyond the common genetic variance, SPM became non-significant after the common genetic variance was controlled. These results suggested that the relationship between cognitive abilities and PB may be largely driven by verbal ability.