Number of Close Kin but Not Gendered Fitness Interests Shapes Sex Role Attitudes

Objective Gendered Fitness Interests (GFI) Theory posits that the sex of one’s close kin is a source of variation in socio-political attitudes, especially those concerning sex roles. Drawing on the evolutionary theory of inclusive fitness gained through relatives, it suggests that individuals with greater expected future fitness returns from females will hold more liberal attitudes than those expecting greater future fitness returns from males. Methods We examine the effects of various GFI metrics on 11 sex role attitudes across respondents from 42 countries. GFI metrics were the number of kin of each sex, with these same effects discounted by relatedness, residual reproductive value, and both relatedness and residual reproductive value combined. We also examine differences in attitude prediction when examining effects among descendant-only versus all kin, and accounting for emotional closeness and proximity between kin. Results Accounting for relatedness and residual reproductive value improved attitude prediction more so than just number of kin. In direct contrast to previous work, individuals with female-biased future fitness interests demonstrated more conservative sex role attitudes. Attitudes did not correlate with an individual’s relative balance of fitness interests from males versus females. Effects were stronger when limiting kin to descendants only (but still not supportive of GFI Theory). Discounting by emotional closeness and proximity did not substantially alter the results, and there was little evidence of effect variation among world regions. Conclusion Overall, GFI Theory did not receive convincing support from our findings. We recommend more extensive modelling and empirical testing of GFI theory in order to understand the disparities in support for GFI between studies.