Male strategies and Plio-Pleistocene archaeology.

Archaeological data are frequently cited in support of the idea that big game hunting drove the evolution of early Homo, mainly through its role in offspring provisioning. This argument has been disputed on two grounds: (1) ethnographic observations on modern foragers show that although hunting may contribute a large fraction of the overall diet, it is an unreliable day-to-day food source, pursued more for status than subsistence; (2) archaeological evidence from the Plio-Pleistocene, coincident with the emergence of Homo can be read to reflect low-yield scavenging, not hunting. Our review of the archaeology yields results consistent with these critiques: (1) early humans acquired large-bodied ungulates primarily by aggressive scavenging, not hunting; (2) meat was consumed at or near the point of acquisition, not at home bases, as the hunting hypothesis requires; (3) carcasses were taken at highly variable rates and in varying degrees of completeness, making meat from big game an even less reliable food source than it is among modern foragers. Collectively, Plio-Pleistocene site location and assemblage composition are consistent with the hypothesis that large carcasses were taken not for purposes of provisioning, but in the context of competitive male displays. Even if meat were acquired more reliably than the archaeology indicates, its consumption cannot account for the significant changes in life history now seen to distinguish early humans from ancestral australopiths. The coincidence between the earliest dates for Homo ergaster and an increase in the archaeological visibility of meat eating that many find so provocative instead reflects: (1) changes in the structure of the environment that concentrated scavenging opportunities in space, making evidence of their pursuit more obvious to archaeologists; (2) H. ergaster's larger body size (itself a consequence of other factors), which improved its ability at interference competition.

Hadza meat sharing.

In most human foraging societies, the meat of large animals is widely shared. Many assume that people follow this practice because it helps to reduce the risk inherent in big game hunting. In principle, a hunter can offset the chance of many hungry days by exchanging some of the meat earned from a successful strike for shares in future kills made by other hunters. If hunting and its associated risks of failure have great antiquity, then meat sharing might have been the evolutionary foundation for many other distinctively human patterns of social exchange. Here we use previously unpublished data from the Tanzanian Hadza to test hypotheses drawn from a simple version of this argument. Results indicate that Hadza meat sharing does not fit the expectations of risk-reduction reciprocity. We comment on some variations of the "sharing as exchange" argument; then elaborate an alternative based partly on the observation that a successful hunter does not control the distribution of his kill. Instead of family provisioning, his goal may be to enhance his status as a desirable neighbor. If correct, this alternative argument has implications for the evolution of men's work.

Grandmothering and the evolution of homo erectus.

Despite recent, compelling challenge, the evolution of Homo erectus is still commonly attributed to big game hunting and/or scavenging and family provisioning by men. Here we use a version of the "grandmother" hypothesis to develop an alternative scenario, that climate-driven adjustments in female foraging and food sharing practices, possibly involving tubers, favored significant changes in ancestral life history, morphology, and ecology leading to the appearance, spread and persistence of H. erectus. Available paleoclimatic, environmental, fossil and archaeological data are consistent with this proposition; avenues for further critical research are readily identified. This argument has important implications for widely-held ideas about the recent evolution of long human lifespans, the prevalence of male philopatry among ancestral hominids, and the catalytic role of big game hunting and scavenging in early human evolution.

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

This is a report on the demography of the Hadza, a population of East African hunter-gatherers. In it, we describe the results of a census, and our estimation of age structure, survivorship, mean age of women at childbearing, number of live children, total population size and density, and rate of change since 1967. We show that relevant measures fit closely the stable population model North 6 chosen by Dyson to represent Hadza demography in the 1960s. We compare aspects of Hadza demography with surrounding non-Hadza and with the !Kung. Among other things, we find that the Hadza have a higher population density, higher fertility, and a faster population growth rate than do the !Kung. These demographic differences are consistent with our expectations, which were based on differences in the costs and benefits of foraging in the two regions. We also show that Hadza demographic parameters display remarkable consistency over the past 20 years. Since neighboring populations have been encroaching on the area used by the Hadza, and Hadza foragers have been subject to interludes of externally imposed settlement, this consistency is surprising. We discuss some of the implications.

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.