Marry In or Die Out

Optimal Inbreeding and the Meaning of Mediogamy

Authored by: Robin Fox

Handbook on Evolution and Society

Print publication date:  January  2015
Online publication date:  November  2015

Print ISBN: 9781612058146
eBook ISBN: 9781315634203
Adobe ISBN: 9781317258339


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This chapter is a rethinking of the analysis of exogamy and endogamy with a new approach to the adaptive benefits of the latter. Bateson's principle of optimal inbreeding in plants and animals leads to the definition of mediogamy (close-cousin marriage) as the human equivalent. Incest avoidance is examined as the driver of human exogamy and as a form of dispersion subject to general laws of fragmentation and dispersion. The basic forms of exogamic marriage, the human phenomenon of endogamy through parallel cousin marriage, and dispersion in animals and humans and its relationship to the preservation of the optimal number (after Malthus) are examined. The possibility that a mechanism other than resource optimization is responsible for population segmentation and dispersion across species, namely, optimization of fertility by consanguineous mating, is examined. Data from four taxa (mammals, birds, fish, and insects) and from human birth records suggest that the same underlying mechanisms are present from single-celled organisms to humans governing population fluctuations and fragmentation that has to do with preserving levels of fertility through optimal inbreeding and losing them through dilution of consanguinity. This challenges the Malthusian resource-based paradigm and makes mediogamy the optimal strategy in human mating systems. The consequences of its decline for fertility levels in current populations are examined.

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