Identification of the factors that determined fedundity in early Afrikaners

Fecundity determines the magnitude and direction of evolutionary change. By analyzing traits correlating to human fecundity we may understand our own evolutionary roots, and the behaviour and choices that define modern reproduction. For this reason, studies that look at historical populations prior to the demographic inversion and the use of contraceptives have become popular. Very good genealogical records exist for the early Afrikaner population (1652-1820), but only a few studies have utilized this wealth of information, primarily because it is not available electronically. My aim was to determine which factors affected fecundity in this historical population. The Afrikaner population had a very high growth rate, presumably because of ameliorated environmental conditions. Under high growth rates we can expect that the determinants of fecundity may differ from those found to be important in European populations. I recorded fecundity and a number of predictor variables for 1138 first generation offspring (referred to here as B generation) of 517 founder individuals (A generation), as well as the B generation spouses. Data was compiled on nationality of origin; number of marriages (when sequential remarriage occurred); dates of birth and dates of various reproductive events (date of first and last child’s birth/christening, wedding dates). I analysed the data with a variety of approaches to estimate the effects of a number of predictor variables known to affect fecundity as well as a couple of new ones we propose. A few of the key findings are: a gender specific role for the effect of multiple marriages; a discrepancy in fecundity for the various nationality groups suggesting cultural inheritance of fecundity; a new fertility measure, the time lapse between marriage and the birth of first child, explained most of the variation in fecundity; and we found very limited evidence to support the idea that fecundity is heritable.