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Behavioral Ecology and Sociobiology

, Volume 52, Issue 6, pp 435–443 | Cite as

Opposite effects of maternal and paternal grandmothers on infant survival in historical Krummhörn

  • Eckart Voland
  • Jan Beise
Original Article

Abstract.

On the basis of church register entries from the Krummhörn region (Ostfriesland, Germany, 1720–1874) we looked at whether the existence of grandmothers had an impact on the reproductive success of a family. We found that fertility measured by parity progression ratios was influenced by grandmothers, though only in exceptionally large families, while fertility measured by intervals between births was not influenced by grandmothers. However, maternal grandmothers reduced infant mortality when the children were between 6 and 12 months of age. During these 6 months, the relative risk of dying was approximately 1.8 times higher if the maternal grandmother was dead at the time of the child's birth compared to if she was alive. Interestingly, the existence of paternal grandmothers approximately doubled the relative risk of infant mortality during the 1st month of life. We interpret this as being the result of a tense relationship between mother- and daughter-in-laws. We found that Krummhörn grandmothers could be both helpful and a hindrance at the same time. Geographic proximity increased the effects found. If this ambivalent impact of grandmothers on familial reproduction could be generalized beyond the Krummhörn population, the hypothesis that the evolution of the postgenerative life span could be explained by grandmotherly kin-effects would have to be stated more precisely: the costs of social stress in the male descendency would have to be subtracted from the benefits of aid and assistance in the female descendency.

Grandmother hypothesis Krummhörn Human evolutionary reproductive ecology Infant mortality Life history theory In-law conflict 

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Copyright information

© Springer-Verlag 2002

Authors and Affiliations

  • Eckart Voland
    • 1
  • Jan Beise
    • 2
  1. 1.Zentrum für Philosophie und Grundlagen der Wissenschaft, Universität Giessen, Otto-Behaghel-Strasse 10C, 35394 Giessen, Germany
  2. 2.Max-Planck-Institute for Demographic Research, Doberaner Strasse 114, 18057 Rostock, Germany

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