Abstract
We conducted a meta-analysis of 17 studies that tested for an association between grandparental survival and grandchild survival in patrilineal populations. Using two different methodologies, we found that the survival of the maternal grandmother and grandfather, but not the paternal grandmother and grandfather, was associated with decreased grandoffspring mortality. These results are consistent with the findings of psychological studies in developed countries (Coall and Hertwig Behavioral and Brain Sciences 33:1-59, 2010). When tested against the predictions of five hypotheses (confidence of paternity; grandmothering, kin proximity, grandparental senescence, and local resource competition), our meta-analysis results are most in line with the local resource competition hypothesis. In patrilineal and predominantly patrilocal societies, the grandparents who are most likely to live with the grandchildren have a less beneficial association than those who do not. We consider the extent to which these results may be influenced by the methodological limitations of the source studies, including the use of retrospective designs and inadequate controls for confounding variables such as wealth.
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Notes
Coall and Hertwig (2010:49) questioned why we scored a particular result in Gibson and Mace (2005:475) as nonsignificant when the 95% confidence interval was 0.51–0.99. In clarification, the reported P-value was 0.06 and exceeded the cutoff of 0.05 (Strassmann and Kurapati 2010). Coall and Hertwig also questioned our scoring of the data in Beise (2005), yet the finding in question (maternal grandmothers) had a P-value > 0.1, which we scored as nonsignficant.
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Acknowledgements
We thank Mary K. Shenk and Siobhan M. Mattison for inviting us to contribute to the special issue on quantitative kinship. We gratefully acknowledge the suggestions of three anonymous reviewers and the statistical advice of Kathy Welch. We thank Nikhil Kurapati, Hawah Freeman, and Erin E. Gager for help in identifying source studies and in preparing the figures and tables. We are grateful to Conrad Kottak for bringing the theory of complementary filiation to our attention. Several authors graciously sent us statistical data through email (Monique Borgerhoff Mulder, Jan Beise, Renzo Derosas, and Rebecca Sear). BIS thanks the Dogon of Mali for their generous participation in her research and for the insights into grandparental investment gained from their friendship. The Dogon research has been supported by the LSB Leakey Foundation, the National Science Foundation (BNS-8612291, SBR-9727229, BCS-0509019, BCS-1029056), the National Institutes of Health (NIH HD 07480–02, NIH 09-PAF00653), and the American Philosophical Society.
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Strassmann, B.I., Garrard, W.M. Alternatives to the Grandmother Hypothesis. Hum Nat 22, 201–222 (2011). https://doi.org/10.1007/s12110-011-9114-8
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DOI: https://doi.org/10.1007/s12110-011-9114-8