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.
This is a preview of subscription content, log in to check access.
Buy single article
Instant access to the full article PDF.
Price includes VAT for USA
Subscribe to journal
Immediate online access to all issues from 2019. Subscription will auto renew annually.
This is the net price. Taxes to be calculated in checkout.
About this article
Cite this article
Voland, E., Beise, J. Opposite effects of maternal and paternal grandmothers on infant survival in historical Krummhörn. Behav Ecol Sociobiol 52, 435–443 (2002). https://doi.org/10.1007/s00265-002-0539-2
- Grandmother hypothesis Krummhörn Human evolutionary reproductive ecology Infant mortality Life history theory In-law conflict