Project 4

Coastal Foraging Models

Coastal foraging, social behavior, and modern human dispersal
Coast of South Africa

Principal Investigators

Project 4 uses ethnographic and experimental field data wedded to computer simulation to test the hypothesis that the high productivity of coastal habitats was critical to early modern human adaptive success in the southern African later Pleistocene, which will be examined in the field with archaeological data in Project 5.

This project examines the late Pleistocene ecological context for the uniquely human levels of cooperation among non-kin and exceptional reliance on cultural transmission via social learning. The comparison of intertidal foraging and associated social behavior to other sites using computer simulation models explores how coastal adaptations may have facilitated culture, cooperation, and the rapid migration of Homo sapiens to other parts of the globe.

Detailed Project Description

Homo sapiens emerged in the late middle Pleistocene of Africa, spread through the continent for some 100,000 years, and then, by ca. 50 ka, spread out of Africa rapidly to colonize the rest of the world. This expansion included replacement of resident hominin populations with only small amounts of genetic introgression, suggesting that the expanding H. sapiens populations had some type of significant advantage over the pre-existing hominins. It has been hypothesized that this advantage included cognitive advances, language, cooperation, cumulative culture, and associated increases in social network size. The IHO team will explore whether some of these traits emerged in coastal southern Africa due to some exceptional combination of environmental and ecological conditions in the late middle Pleistocene. Of particular interest is the entry into a marine intertidal foraging niche and the accessibility of geophytes in the Cape Floral Region.

To evaluate this hypothesis we must investigate the role of typical terrestrial plant and animal resources in other parts of the world and whether marine resources and geophytes in coastal South Africa have special properties not found in other human foraging sites (denser distributions, rapid regeneration, more predictable or defendable, etc.). We propose to develop agent-based models (see: (link is external)) of the South African coastal foraging niche in order to evaluate hypotheses about the potentially special nature of that cultural/economic niche for within- and between-group cooperation and social learning.

Previous work suggests that coastal foragers show greater sedentism, higher population densities, larger groups, and metaband social organization. In addition, the expansion of modern humans from Africa may have followed coastlines (from southern Asia to Australia, to the Americas), suggesting that coastal adaptations may have played a special role in human dispersal. This might be because coastlines offer linear migration routes with negligible geographic barriers, and similar marine resources requiring related knowledge, technology, and techniques across vast areas. Here we will examine the emergence of cooperation, specialization, stratification, and cultural transmission in marine-resource-dependent communities. Fieldwork will be conducted in coastal communities of Panama, South Africa, and the Philippines, and compared to behavioral ecological data on terrestrial foragers (especially the San, the Hadza, the Ache, and inland foragers of the Philippines).

Foraging experiments

The first step in evaluating this hypothesis is to reconstruct the overall foraging niche of coastal South Africa in the middle to late Pleistocene. We will focus on marine intertidal foraging because it first emerges around the time of early Homo sapiens in this region. Then we will examine social implications of that foraging niche and compare it to marine and terrestrial foraging elsewhere. We will make a detailed map of current coastline intertidal habitats from Cape Agulhas to Mossel Bay (~250 km of coastline) at 100 meter resolution. This map will code six habitat types that we have identified as relevant to marine foraging in the region; these will then be inputted into simulation models. We will conduct foraging experiments using experienced KhoeSan descendant residents in coastal villages to measure the profile of foraging productivity for each of these habitat types. This research was initiated in 2012 with a preliminary sample that included both sexes and a wide age range of foragers. The most notable result thus far is exceptionally high foraging returns (> 5,000 kcal/hr) on spring low-tide days, and a strong effect of the monthly tidal cycle on harvest rates. In addition, preliminary sampling suggests that three of the most productive habitat types make up more than 80 percent of the coastline. These intertidal foraging returns are much higher than our recent observations in southern Mindanao (~ 200-500 Kcal/hr) and most others that have been reported in other coastal studies. Our goal is to produce a complete understanding of Coastal South African foraging returns as a function of tidal cycles, weather conditions, and age and sex. This will allow us to determine exactly how dependent people can be on intertidal marine resources through the month, and which age-sex groups are in a better position to provision themselves or others, when compared to terrestrial foragers. Comparative observations will be collected in southern Mindanao, an area with evidence of shellfish exploitation for ~35,000 years and ongoing inland terrestrial foraging. Another set of observations will be conducted along the pacific coast of Panama where we have also observed extensive intertidal foraging.

In parallel with the marine foraging experiments, we will conduct experiments on plant foraging and non-food resource procurement in the study zone (firewood, stone sources). Again, all habitat types will be mapped (1 hectare resolution and 20 km inland from Cape Agulhas to Mossel Bay), and experimental foraging observations with local KhoeSan descendent collectors will be employed to determine potential harvest rates, seasonality, age effects, etc., and the association of highly profitable resource types with specific habitats. These parameters will then be input into an agent-based model of forager behavior in the study area that can generate archaeological predictions.

One of the critical questions we wish to answer is whether marine or plant resources experience less depletion through time in this area, due to human harvesting, than is typical for many terrestrial foragers. Modeling shows that low depletion favors larger and more sedentary groups. We are collaborating with colleagues in South Africa who have designed research to harvest protected plots at various levels and then monitor resource density over a three-year period as the experimental plots are repopulated by important prey species. Similar experiments have already been carried out on the west coast of South Africa.

Resource profitability and social value in the Pleistocene

One of the difficulties of developing a realistic foraging model for Pleistocene coastal South Africa is determining the profitability of terrestrial vertebrate hunting. This problem can be partially solved by using extant literature on hunting returns for San and other African foragers who hunt with limited technology and harvest species known to have inhabited the study region during the time periods of interest. But, a more general model of terrestrial vertebrate profitability (return rates upon encounter when pursued by hunters) is desirable. A number of archaeological papers have argued for the use of prey-species attributes as a means of predicting prey ranks from the zooarchaeological record.

We propose to develop a predictive model, using theory and empirical extrapolation, to give reasonable estimates of prey profitability rankings in archaeological contexts. Attributes that have been proposed as indicators of prey ranks will be examined and evaluated on an individual basis (especially size, sociality, and predator avoidance behaviors). Library research on a large body of foraging studies will allow us to examine the statistical relationships between the most promising attributes and prey ranks using previously collected data sets on tribal hunters (that eliminate or control for the use of firearms).

Computer simulations of foraging and implications for social behavior

We have recently demonstrated that agent-based foraging models can accurately predict the observed economic patterns over 20 years with Ache foragers in eastern Paraguay. Importantly we were able to use the models to test the advantages of alternative group sizes and mobility patterns. The model demonstrates that small mobile bands are optimal only when resources are dispersed, and depletion along with predator avoidance prey behavior is common. We will further extend the modeling process in order to assess the implications of density, resource-patch size, resource depletion, and resource defensibility for several key features of foraging societies. These include territoriality, residential endogamy, and tendency for specialized provisioning and cooperative breeding. Based on the Ache modeling, the changing distribution and depletion rates of key resources will radically alter the social patterns that are associated with highest nutrient gain rates. This will allow us to predict social patterns based on marine intertidal foraging and high densities of geophytes that characterize the cape floral region but not the typical mobile-band societies of most recently observed hunter-gatherers.

Hunter-gatherers are cooperative breeders, with “helpers at the nest” making up more than a third of the population. Is there greater reproductive skew with more provisioners among coastal foragers compared to egalitarian terrestrial foraging societies? To examine these questions we will collect life history data for different age and sex classes in our coastal forager study populations.

Network interaction patterns in foragers

Do marine dependent communities have more or less interaction with distant communities and how does this effect opportunities for cultural transmission? Recent work has suggested that hunter-gatherer network size is unique to vertebrates and interconnect foraging bands into large metaband societies where novel ideas can be copied from a thousand or more individuals through direct observation. This exceptional network size is critical to cumulative culture. We hypothesize that these patterns are derived from economic constraints and a pair-bond based, cooperative breeding life history. To measure network size we will conduct structured interviews about behavioral interactions among the Ache of Paraguay, and several inland and coastal villages in Mindanao (Philippines) and Panama. This will be complimented with computer simulations that estimate number of lifetime encounter partners based on yearly rates of interaction. Comparisons among our experimental foraging populations should allow us to determine whether societies dependent on marine resources have different inter-settlement interaction patterns than those dependent on terrestrial resources. These interviews, and ethnographic accounts will allow us to determine how often individuals living in different bands encountered each other, whether there were good opportunities for social learning during those encounters, and whether interband interactions included cooperative behavior at a scale beyond that of kin groups and residential units.