Why High Birth Rates Are So Low

The highest fertility ever recorded reliably in a society is found among the Hutterites, a religious sect living in small communities near the United States-Canadian border. In 1950 Hutterite women who had reached the end of their reproductive years had given birth to an average of 8.9 children. With mortality near national US levels, this high rate of childbearing has resulted in the unprecedented growth of the Hutterite population, which increased nearly 20-fold between 1870 and 1950. Although Hutterite fertility is very high compared with that of many other human populations, it is surprisingly low from the point of view of biological reproductive efficiency. Clearly, a woman is able to bear more than about nine children during her 30 years or so of reproductive life (ages 15 to 45 approximately), as is evident from the numerous examples of women who have given birth more than 15 times.' A theoretical upper limit would be around 40 births per woman during 30 reproductive years, since an interval between two successive births cannot be shorter than about nine months required for a complete pregnancy. Why then are women in societies such as the Hutterites, where deliberate birth control is absent, reproducing at rates substantially below biological limits? Before discussing the demographic and biological factors responsible for this finding, some aspects of the measurement of fertility and the values of fertility indices in various countries around the world will be presented.