1. ¹UMR 5173 MNHN-CNRS-UPMC, Conservation des espèces, restauration et suivi des populations, Muséum National d'Histoire Naturelle, Rue Buffon, Paris, France
2. ²UMR 5145 MNHN-UPD Eco-anthropologie, Muséum National d'Histoire Naturelle, Musée de l'Homme, Paris, France
3. ³Groupe de recherche interdisciplinaire en démographie et épidémiologie génétique, Département des sciences humaines, Université du Québec à Chicoutimi, Chicoutimi, Québec, Canada

Correspondence: Dr A Robert, EGB, Muséum National d'Histoire Naturelle, CRBPO, 55, Rue Buffon, 75005 Paris, France. Tel: +33 140 795 727; Fax: +33 140 793 835; E-mail: arobert@mnhn.fr

Received 24 January 2008; Revised 6 November 2008; Accepted 13 November 2008; Published online 17 December 2008.

Abstract

Little is known about the effects of inbreeding on reproduction in modern human societies. It appears indeed that biological effects are hidden by socioeconomic factors, which are the major determinants of fertility. It has been established, in particular, that socially induced reproductive compensation tends to homogenize the number of offspring per family in a given population. Besides, in the field of evolutionary biology, a number of empirical and theoretical studies have shown that the effects of inbreeding are condition dependent. In particular, theoretical developments on the evolution of senescence predict that the deleterious effects of inbreeding should increase with age. We rely on these developments to examine the effects of inbreeding on fertility in a cohort of Canadian women born in the late 19th century. The analysis does not allow for the detection of any effect of inbreeding on the overall number of offspring of women. However, results indicate that high levels of close father inbreeding are associated with a reduction of the productivity of parents during the second half of their reproductive period, as compared with the first half. We suggest that inbreeding depression affects reproduction in modern societies through an interaction with age.