Demography of the Hadza, an increasing and high density population of Savanna foragers.

ABSTRACT

PIP: The research objective was to obtain demographic information of the Hadza, hunter-gatherers from the Eastern Rift Valley, southeast of Lake Eyasi in eastern Africa, in 1985. The aim was to gain insight into their reproductive strategies and how local ecology affects the population. Fertility is assumed to increase where it is more difficult to feed offspring. Comparisons are made to the ]Kung reproductive model. Demographic data were obtained in a 1985 census among 36 camps plus 2 villages in eastern-Hadza-occupied territory in the Eastern Rift Valley. Previous demographic surveys in 1966-67 and 1977 and the Tanzanian Census of 1978 for neighboring populations were important as independent checks on the accuracy of family compositions and age structure. Null hypotheses were tested: that the 1985 data fit the model chosen by Dyson in 1967, or that the data fit the model chosen by Howell for the ]Kung. Data were collected on 1) the age structure of the population, 2) survivorship of people counted in the 1967 census, 3) the mean age of childbearing for mothers of small babies in 1985 and previous censuses, 4) the number of live children/women by age, and 5) calculation of the total population in 1967. 719 eastern Hadza were recorded for 1985 and density was calculated as .30/km squared of .74/sq mile. Density varies locally and with the seasons. With villagers excluded, the density is .24/km squared or .61/sq mile. The methods for constructing the age structure involved fitting a 3-term polynomial regression of individuals of known age against the distribution of all individuals by age rank, and estimating ages of reach rank with a regression equation. The results were not different from the 1967 data; age structure does vary with location. Mortality was closer to Dyson's North 6 stable population model, but very close to Howell's estimates for the ]Kung. The mean age of childbearing was 30.9 years which is later than the ]Kung. The findings support Dyson's conclusions, and reflect higher density, higher fertility (6.15 vs. 4.7), and higher rates of growth than the ]Kung. Bush-living Hadza were even more different from the bush-living ]Kung. A number of explanations for the differences are explored.