R. Cowling (NMMU, South Africa) (link is external), K. Esler (Stellenbosch, South Africa) (link is external), A. Potts (NMMU, South Africa) (link is external), J. Engelbrecht (CSIR Paleoclimate Modeling Group, South Africa) (link is external), M. Bar-Matthews (Geological Survey, Israel) (link is external)
Project 6 uses experimental field observation and computer simulation to develop a paleoscape model that can predict productivity of fynbos and the conditions under which it would be exploited by hominins. The outcome of these projects will be more complete empirical documentation of exactly when and under what conditions steps were made at different stages of the human career toward novel, cognitively complex behaviors tied to technological advances in hominin resource use.
This project is designed to establish the crucial environmental context for Project 5 so that the results from that project can be used to investigate questions of the origins of complex cognition and cooperation.
Detailed Project Description
Human hunter-gatherers take all of their resources from the naturally occurring environment. Accordingly, the distribution of resources has an impact on population distributions and, ultimately, on social organization and cultural transmission in these societies. Integrating environmental research and paleoanthropology requires formal understanding of how climate-driven changes in environment, as reflected in proxies, shape the resources crucial to hunter-gatherer life-ways.
Because hunter-gatherer adaptations are tied to the way that the environment shapes the food and technological resource base, environmental changes must have had significant impacts on human evolution. While there has been significant improvement in the development of high-resolution paleoclimatic and paleoenvironmental sequences and in the relation of these sequences to hominin evolution, there has been a frustrating lack of progress on understanding if and how hominin bio-behavioral evolution responded to environmental change. This lack of progress is likely due to the dearth of well-understood connections between the environment and the abundance and productivity of resources critical to hunter-gatherer life-ways.
We propose to advance the study of the impact of changing climates and environments on human evolution by moving beyond a strictly correlative endeavor to a more theoretically grounded mechanistic approach by constructing a paleoscape model. We propose to construct the first such model for paleoanthropology on the south coast of South Africa, where the richest record of early modern humans exists. This project will begin with models of modern vegetation (the current climate state) linked to the spatial location, abundance, and return rates of the major food and technological resources of hunter-gatherers on the south coast today. These will then be projected at three climate states in the past and tested with long, continuous records from speleothems and short-term records from other sources. We will develop an Agent Based Simulation (ABS) of foragers within the four climate states to develop test implications for the archaeological record. The paleoscape model will be tested with ongoing and new fieldwork (see Project 5: Discovering the evidence for the beginnings of complex cognition).
Defining the Resources and Return Rates in the Different Habitats
Two central premises of our approach are 1) the abundance of most food and organic technology resources is a function of vegetation type and species composition, and 2) vegetation distributions in the Cape Floral Region (CFR) are largely determined by climate, sediment, and slope. Vegetation types (fynbos, renosterveld, etc.) and species distributions can be projected at different climate states, and projections can be tested with field observations. Our model construction begins with an integrated modern GIS of onshore and offshore geology, soils, climate, topography, and modern terrestrial vegetation. We mined South Africa’s mapping of onshore geology, soils, topography, climate and vegetation and built them into our GIS, and conducted original research on the offshore geology (funded by the National Geographic Society). Field surveys of lithic raw material sources are complete and added to the GIS.
The distribution and return of food and water on the paleoscape are the most obvious critical resources for understanding hunter-gatherer adaptations. Our model will focus on three specific food types: plant foods, coastline foods, and terrestrial animal foods. Sources of water are already mapped in terrestrial locations by geophysical survey on the now submerged shelf, and sub-surface springs will be modeled. Our paleoscape model and ABS require realistic estimates of net return rates for the major food items, but indigenous foragers here are no longer extant, though local people do some tasks (shellfish and geophyte collecting) in traditional ways. We have already begun this phase of the study with the now-established tradition of generating experimentally estimated return rates through utilizing traditionally-estimated technologies and techniques.
Projecting Past Habitats During Different Climate States
Prior studies hindcast the paleodistributions of plant species and vegetation using species distribution models, sometimes called “climate envelope models.” These paleodistribution modeling studies typically use the same suit of modern statistical and machine-learning models that are well established in vegetation distribution modeling to associate observations of vegetation type (or species) with environmental predictors (climate, geology, soil, topography) derived from GIS maps. Statistical models based on contemporary distributions can then be applied to predictively map distributions under past or future climate states by substituting the climate maps and assuming other environmental factors are static (or that their distributions can be also be reconstructed, e.g., distance to coast).
We will develop statistical models and rule-based models from expert knowledge for the contemporary distribution of the major vegetation types from geology, soil, slope, aspect, mean annual temperature, presence of frost, mean annual rainfall, and season of rain. These two approaches will then be compared, validating each of them against current vegetation distributions, so that model uncertainty will be better understood. The paleodistributions of vegetation type will then be projected to past climate states using paleoclimatic reconstructions and both types of vegetation model (statistical and expert).
Computer Simulations within the Modeled Environments
By combining models drawn from behavioral ecology with ABS we will generate realistic predictive models of hominin behavior that specify aspects of economic behavior testable against the archeological record. This will enable us to and test the competing hypotheses of mobility systems that are central to ideas about social organization. We will confront the models with a realistic paleoscape of resources (rather than assuming homogenous resource distributions). We will use foraging models drawn from behavioral ecology, which has been extensively employed by anthropologists. The goal of these models is to make predictions about foraging decisions by assuming maximization of specified fitness-related currencies (energy, nutrient utility, reduction of starvation risk, etc.), given a specified option set (resource types available, patches, times to forage, etc.) and constraints describing relationships between decisions and outcomes (density of resources, time required to obtain resources, nutrient value of resources, etc.).
We will test the feasibility of the models on a rich spatial and temporal data set of Ache resource distribution patterns and foraging behavior prior to applying them to the paleoscape. Our publication on the Ache model has been accepted with minor revision in the journal Human Ecology. Using our ABS we will also investigate the conditions under which cooperative groups and territorial behavior emerge. A significant portion of the funds requested here will support a postdoctoral researcher to work to develop the ABS. The Ache data were collected in order to verify that these input data can indeed being used in agent-based modeling to predict foraging outcomes. Our model is designed from basic behavioral ecological principles, and we use the Ache as a test case because they are one of the few extant human groups where we have the type of data needed to test the model’s efficacy. We do not assume that the Ache patterns necessarily match foraging patterns in ancient environments of human origins.
Testing the Predictions With Archaeological and Paleoclimatic Data
The archaeological data needed to test the predictions of the paleoscape model will be produced by the associated Project 5 (Discovering the evidence for the beginnings of complex cognition). We will test the predictions of the climate and vegetation modeling primarily through speleotherm analysis that can produce long continuous records precisely datable by U-Th methods. We initiated such a study at Pinnacle Point where rain is bimodal and the surrounding regions, building sequences, discovering and documenting other sample sites, and building comparative rainfall data for interpreting the sequences. We recently published a high resolution sequence from 90-53 ka from Crevice Cave. We have completed a composite sequence from Pinnacle Point that stretches back to ~350 ka, and have tested the suitability of several other localities. The site locations, most of which have already provided preliminary and proof-of-concept results, include Die Kelders, Robertson, and the Klein Karoo. Die Kelders is in close proximity to several archaeological sites, is coastal, and is in the strongly winter rainfall regime. Robertson is ~100 km nearly directly north of DK. The Klein Karoo sites are 90 km directly north of Pinnacle Point, and thus all four provide coastal and interior samples of strong winter rain and bimodal rain.