Effect of infertility on the population structure of the Herero and Mbanderu of southern Africa.

Analysis of the fertility of Herero and Mbanderu pastoralists of the northern Kalahari Desert of Botswana indicates that they have suffered from infertility. The smoothed population pyramid constructed from a recent census shows waves of births occurring about every 22 years. Since generation times in human populations are typically longer, we suggest that infertility is responsible for prematurely terminating the reproductive spans of women, resulting in a reduced generation time. The eigenvalues of a series of Leslie matrices indicate that the periods of oscillation in the population have increased from 22 to 29 years following the recovery from infertility. Increases in fertility since the 1950's have also transformed the Herero from a slowly declining population to one growing at a rate of nearly 3.5 per cent per year.