A family reconstitution study of the Krummhörn population (Ostfriesland, Germany, 1720–1874) reveals that infant mortality
and children’s probabilities of marrying or emigrating unmarried are affected by the number of living same-sexed sibs in farmers’
families but not in the families of landless laborers. We interpret these results in terms of a “local resource competition”
model in which resource-holding families are obliged to manipulate the reproductive future of their offspring. In contrast,
families that lack resources have no need to manipulate their offspring and are more likely to benefit from allowing their
offspring to capitalize on whatever opportunities to reproduce present themselves.
Key words Parental investment - Local resource competition - Evolutionary demography - Krummhörn (Germany)
This study was undertaken with financial support from the Deutsche Forschungsgemeinschaft (DFG) and the Science Engineering
and Research Council (SERC). Both authors were affiliated with the University College London at the time this article was
written.
Eckart Voland is currently a professor of philosophy at Giessen University, Germany. He is interested in combining historical
demography and behavioral ecology. Robin Dunbar is a professor of psychology at the University of Liverpool, England. In addition
to his interests in human behavioral ecology, his research frames on the evolution of primate social systems.