The Royal Commission on Population was appointed in 1944 to investigate the significance of demographic trends in Great Britain which during the 1930 s had caused widespread anxiety. Although the population figures had continued to grow between the two world wars at the rate of about 180,000 per year it was suspected that the birth-rate had fallen below replacement level even to the extent of ‘a substantial margin’ (p. 60).

The main factors influencing the natural increase (excess of births over deaths) of a population are the death-rate and birth-rate. The vast majority of births are to married women and therefore this factor is dependent almost entirely upon the number of marriages and the size of the family. The causes of the changes in the demographic trends in this country over the past seventy years may therefore be sought in four main contributory factors: migration, mortality, marriage and the size of the family.