The consequences of sibling formation on survival and reproductive success across different ecological contexts: a comparison of the historical Krummhörn and Quebec populations

Abstract

This article investigates the relationship between additional siblings and the probability of offspring survival, marriage, and fertility across the historical populations of the St Lawrence Valley in Quebec (1670–1799) and the Krummhörn region in Germany (1720–1874). Both populations existed in agriculturally based economies, but differ in important ways. The Krummhörn population faced a fixed supply of land, which was concentrated amongst a small number of farmers. Most individuals were landless agricultural workers who formed a relatively competitive labor supply for the large farmers. In contrast, individuals in Quebec had access to a large supply of land, but with far fewer available agricultural workers, and had to rely on their family to develop and farm that land. Results indicate that more siblings of the same gender were generally associated with increases in mortality during infancy and childhood, later ages of first marriage, and fewer numbers of children ever born. For mortality and age at first marriage, the effects of sibling formation appear strongest in the Krummhörn region. Notwithstanding these observed differences, the general consistency and robustness of the sibship effect across the different ecological and economic contexts is our most interesting result. In addition, through side-by-side comparison of across-family and within-family analyses, we argue that sibling competition – or sacrifice – is manifested as an internal familial dynamic, but is obscured in non-fixed effects models by a broader trend of family cooperation. Through this comparison we are able to reconcile family solidarity and sibling competition/sacrifice as coexisting phenomena. Results are robust to inclusion of covariate interactions with time, inclusion of indicators for high levels of extrinsic risk, estimation of shared frailty models, alternative methods of dealing with ties in the dataset, including recomposed families in the dataset, excluding individuals whose death dates are ‘heaped’, and excluding individuals born to large families.