DP13539 | Twins Support Absence of Parity-Dependent Fertility Control in Pre-Transition Western European Populations

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Using evidence from the accident of twin births we show that for three Western European pre-industrial population samples -- England 1730-1879, France 1670-1788 and Quebec, 1621-1835 -- there is no evidence for parity-dependent control of fertility within marriage. If a twin was born to a family in any of these populations, average family size increased by 1 compared to families with a singleton birth at the same parity and mother age, with no reduction of subsequent fertility. Twin births also show no differential effect on fertility when they occurred at high, as opposed to low, parities. This is in contrast to populations where fertility is known to have been controlled by at least some families, such as England, 1900-49. There a twin birth increased average births per family by significantly less than 1.