This thesis examines the impact of seasonal and inter-annual variations in rainfall on food supply and disease environment, and hence the biological welfare of savannah populations in southern Zimbabwe. Ecological dynamics are thought to determine the impact of rainfall, and this hypothesis is tested through the comparison of populations either side of a major ecological boundary between heavy clay rich and sandy soils. Due to differences in soil-moisture productivity relations, and the level and form of ecological heterogeneity, the sandveld environment shows much less seasonal and inter-annual variation in agro-ecological productivity than does clayveld, and this is reflected in food supply and consumption. Child anthropometric and birth weight data from several years shows opposite seasonality, and weight-loss in a serious drought was most marked on clay-rich soils as predicted. Differences in soil-moisture relations also influence disease environment dynamics; child morbidity shows the same seasonal and inter-annual contrasts between the zones as found with nutritional status. Furthermore, infant mortality is increased following dry years on clay-rich soils whilst high rainfall leads to increased infant mortality on the sandy soils. These differences in welfare dynamics between sandveld and clayveld appear to typify conditions in other moist and dry savannah areas respectively. Variability in grain production results from unequal access to livestock for ploughing and manure, but urban wage labour derived remittances also affect wealth. The extent and nature of socio-economic differentiation varies between ecological zones for historical reasons, and its impact on welfare (together with that of religion and maternal education) is variable and complex, operating at several levels in household and lineage. Maternal education has a marked impact on child well-being, particularly upon infant mortality. Dramatic improvements in Infant mortality and declines in fertility since Independence (1980) reflect upgrading of medical services and education provision for women, Indicating the limits of ecological welfare determinants.