Twin study of genetic relatedness and bereavement related measures: Updated analyses and the mediating role of grief

Abstract

A Twin Loss Survey was completed by MZ and same-sex DZ twins following loss of a cotwin and nontwin relatives. Twin survivors (N = 612; MZ = 506; DZ, n = 106) included twins whose age at loss was 15 years or older. Participation age was M = 47.66 years (SD = 15.31). Hamilton's inclusive fitness theory generated two hypotheses: (1) MZ twins will recall greater grief intensity at loss than DZ twins; (2) loss of a twin will receive greater grief intensity ratings than loss of nontwin relatives. We expected females to grieve more intensely for deceased cotwins than males. Males cannot be certain a child conceived by their partner is theirs (paternity uncertainty). As such, grief for the loss of a twin brother (whose child would indirectly transmit common genes) should be reduced by surviving male twins, relative to surviving female twins. Part I: Hypotheses regarding grief intensity were supported. Part II: A structural equation model was estimated; grief significantly mediated relationships between exogenous and endogenous predictors and grief predicted greater preoccupation and less effective coping. MZ twins and females expressed greater grief intensity than DZ twins and males. Associations between genetic relatedness and grief, consistent with evolutionary-based predictions, are highlighted.