Inbreeding and fertility in a South Indian population.

Among 1913 women in Karnataka State, South India, 37.74% had married a relative (a consanguineous union), 60.79% were non-consanguineously married, and 1.46% did not know whether they had married a relative. Mean number of living offspring for consanguineously married women who had completed their reproduction was 3.89, and for the non-consanguineous 4.07. There is no significant difference in the mean level of fertility for the two groups measured in this way. Pre-natal mortality is lower (but not significantly) among consanguineously married women who have completed their reproduction than among the non-consanguineous group, but post-natal mortality is significantly higher among the conceptuses of the consanguineously married women. Although consanguineously married women conceive more frequently, that is, are more fecund than the non-consanguineous women (mean number of conceptions being 6.61 and 6.28, respectively), the difference is not significant. The differential survival of the offspring results in the consanguineous group having slightly lower net fertility, although the difference is not statistically significant. The lower sterility rates of the consanguineously married women (3.21% of all consanguineously married women show primary sterility compared to 3.47% of the non-consanguineous) may be due to greater compatibility of uniting gametes in the consanguineous marriages. The data reveal that women married to a relative and having completed their reproduction show higher fecundity, lower pre-natal mortality, higher post-natal mortality, lower sterility rates, and thus no significant difference in net fertility to those who had not married a relative.