In 1966, a National Survey on Fecundity and Fertility was organized in Belgium. Approximately 3000 married women under 41 years of age and living with their husbands were interviewed and asked about their reproductive histories. The present paper records the sociobiological aims and methods and some preliminary results of this survey. The aims were to:
(1) study the influences of contraception on human needs and qualities, in this case mainly potential fecundity;
(2) study the influence of attempts to increase the potential fecundity level in modern society on fecundity gene frequencies;
(3) study the influences of the overall socio-cultural environment on fecundity and fertility variables with particular reference to differences in social status in Western society;
(4) analyse the role of social assortment of fecundity and fertility variables on the biological structure, and possibly the composition, of modern populations.
A relatively large, but far from complete body of data has been collected on a number of individual fecundity and fertility variables, on the medical processes employed to increase fecundity, on contraception, and on a number of conventional sociological and demographic variables.
The principles underlying the present approach to the study of fecundity are explained, and a few preliminary results for one of the general fecundity classifications are shown.
The information collected on contraception has been qualitatively analysed and a correction and evaluation method is described. Data on the use of the different contraceptive methods show that substantial sections of the Belgian population are limiting their family size in a way which is inefficient, from both sexual and familial standpoints.