O Brother, where art thou? Investment in siblings for inclusive fitness benefits, not father absence, predicts earlier age at menarche

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Abstract

Numerous studies have indicated that father absence is associated with earlier age at menarche, with many evolutionary theories assuming that father absence is a causal factor which accelerates reproductive development. However, an alternative interpretation suggests that offspring may reproduce earlier in the presence of half- or step-siblings as the indirect fitness benefits to investing in them are lower, relative to delaying reproduction and investing in full siblings. From this perspective, father absence may perform no causal role in facilitating the onset of menarche. Using data from the Avon Longitudinal Study of Parents and Children, I find that individuals with only half- or step-siblings reach reproductive age earlier than those with only full siblings, with no independent effect of father absence. These results suggest that inclusive fitness benefits to investing in siblings, rather than father absence, may predict variation in age at menarche. These results provide a greater understanding of the adaptive mechanisms involved in reproductive decision-making, as well as potential implications for human life history evolution and cooperative breeding more broadly.
Original languageEnglish
Article number20170464
Number of pages4
JournalBiology Letters
Volume13
Issue number10
Early online date18 Oct 2017
DOIs
Publication statusPublished - Oct 2017

Keywords

  • Inclusive fitness
  • Siblings
  • Father absence
  • Menarche
  • Life history
  • ALSPAC

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