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Data on the natural fertility (complete absence of birth control) of 13 populations are examined with the study restricted to legitimate birthrates and those of unmarried women in a stable union. Very different fertility levels were found among these populations despite a similar pattern of fertility as it varies from 1 age group to another. Where the fertility rates for European populations are greater than for the non-European differences can be attributed to variation in birth spacing. It is hypothesized that differences in fertility level are either the result of variations in behavior related to resumption of sexual relations and the duration of lactation or to the differences of a physiological nature related to frequency and duration of anovulation during lactation.
Louis Henry (Thu,) studied this question.
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