On the Influence of the Ages of the Parents at the time of Marriage on the Sex of Children, and on the Prolificness of Marriages

Extract

In the course of the inquiries which led to the paper, read before the Institute of Actuaries, and published in the last number of the Assurance Magazine, on “the Uniform Action of the Human Will,” which was principally illustrated by the regularity in the proportion of marriages between different classes and at different ages, I was very much struck by the law which appears to regulate the relative proportion of the sexes at birth. It has long been observed that, in all countries in which the law of population is not unusually disturbed, more males are born than females. This is the result, not of a few isolated observations, but of more than seventy millions of facts, collected from authentic sources in different kingdoms, and for many succeeding years. The proportion varies from nearly 109 males to 100 females in Russia, down to 104·62 males to 100 females in Sweden; Great Britain occupying the last place but one, about 104·75 to 100. The average births for all Europe may be taken as 106 males to 100 females.