The Gwembe Study was launched in 1956 to monitor the responses of 57,000 Tonga-speakers from the Middle Zambezi Valley to involuntary relocation. Since then, periodic censuses and frequent field visits have generated a wide variety of information. This article examines the demography of four Gwembe Tonga villages from 1956 to 1991, a period characterized first by relocation, then prosperity, and finally by economic hardship. White nuptiality does not respond significantly to socio-economic trends, marital fertility falls sharply during relocation, rebounds with the onset of prosperity, and decreases slowly during the most recent decade of economic hardship. Mortality of the very young and old is also sensitive to such changes. There is striking excess male mortality in all periods, especially among male infants and in particular male twins. The sex ratio at 'birth' is 92. This abnormal sex ratio at birth may be the result of conscious sex preference favouring females.
