The impact of kin proximity on net marital fertility and maternal survival in Sweden 1900-1910-Evidence for cooperative breeding in a societal context of nuclear families, or just contextual correlations?

Objective We investigate the association between the geographic proximity of the grandparents on net marital fertility and maternal survival in Sweden, 1900-1910, within the framework of the cooperative-breeding-hypothesis. Methods Data were derived from Swedish full-count censuses (1880-1910) and the Swedish Death Index. Married couples were linked to their parental households. Poisson and logistic regression analyses were used to investigate the association between the geographical proximity of the grandparents on net marital fertility, which we measured as the number of surviving children born between 1900 and 1910, and the mother's survival. Models were fitted with and without fixed effects to assess the effects of unobserved characteristics shared at the parish and the family level. Results The results indicate that net fertility and maternal survival increased with the husband's parents' geographic proximity. In contrast, we found no evidence that the geographic proximity of the wife's parents was associated with increased fertility or maternal survival. Rather, the presence of the mother's parents in the household lowered net fertility and reduced maternal survival. Conclusions This study provides evidence that kin proximity was associated with fertility and mortality of married women, and that the associations differed for paternal and maternal kin in the societal context of Swedish nuclear families (1900-1910). However, the patterns of kin proximity that we identified were correlated with characteristics such as socioeconomic status, occupation, and wealth, which also exhibited strong correlations with fertility and survival. Future research assessing the effects of kinship on demographic developments must therefore carefully consider the socio-environmental context.