In the distant past, our ancestors experienced highly variable environmental and climatic conditions. During the Middle Stone Age, a period extending from 250,000 to 30,000 years ago, early humans experienced a series of wet/dry cycles in Africa related to ice age climates in more temperate parts of the world. Although theories of modern human origins and the evolution of human-like culture and behavior are generally based in the Middle Stone Age of Africa, our understanding of what makes the Middle Stone Age so important for these modern human features is limited.
One avenue of research is to investigate the nature of these cycles of glaciation in equatorial and southern African habitats where the earliest evidence for evolution of our species exists. In this project, conducted by Emory University doctoral student Joshua Robinson, under the mentorship of Dr. John Kingston, a series of established Middle Stone Age sites in Kenya, Ethiopia, Zambia, and the Democratic Republic of Congo will be utilized to study the local manifestations of global and regional environmental and climatic events. Through chemical analyses of the teeth of fossil animals from these archaeological sites, the research will reconstruct dietary patterns and climatic conditions. Specifically, carbon and oxygen isotopic analyses will form the basis for reconstructing vegetation, humidity, and rainfall at eight sample sites. These analyses will directly test the hypothesis that regional records fail to document local conditions that might be associated with these evolutionary innovations.
The ultimate goal of the research is to improve our understanding of the development of distinctly modern human behaviors, and the relationship between behavior and climate. This relationship is one of the enduring questions in anthropology, and the data to be collected here will provide new insights into when modern behavior emerged and delineate possible reasons for this emergence. The high-resolution, long-term database of environmental and climatic data generated by the study also will find broader application as an innovative framework for contextualizing and understanding modern climate change.
Characterizing the tempo and mode of Middle and Late Stone Age behavioral change in Africa is integral to understanding the evolution of our species. Environmental change has been implicated in the technological changes, migratory patterns, and subsistence changes that characterize this transition. However, before we can develop links between behavior and ecology we need more complete climatic and environmental data for individual archaeological sites relevant to this interval. This study utilizes the well-established method of stable isotope analysis to: (1) investigate to what extent existing regional climatic proxies calibrate with local records, (2) evaluate the role of shifting environmental patterns in human ecological and behavioral adaptations, and (3) develop a comparative framework for studying the intensification of social networks and resource acquisition across Africa in the late Pleistocene. The research focus is on the period ranging from ~75 thousand years ago through the transition from the Middle to Late Stone Age across the Last Glacial Maximum (~28-14 thousand years ago). Paleoenvironments at six study sites (Figure 1) spanning this time period - Omo-Kibish and Porc Epic, Ethiopia; Lukenya Hill, Kenya; Kalemba and Makwe Caves, Zambia; Sibudu Cave, South Africa - were reconstructed through carbon and oxygen isotopic characterization and zooarchaeological analysis of fossil tooth enamel of faunal communities. Testing the hypothesis that local climatic and environmental records provide a higher-resolution and locally distinct reconstruction than existing regional proxies is a necessary first-step to understanding the complex relationship between environment, behavior, and demography. The main results from the isotopic analysis from these sites suggest that the Last Glacial Maximum was the most significant continent level event in Africa during the late Pleistocene. Oxygen profiles for all taxa at all sites indicate an enrichment in 18O (signaling aridity) in the time period of ~28-14 thousand years ago. Most of the study sites reflect this as a rapid change from the pre-Last Glacial time period. However, Omo-Kibish and Porc Epic appear to have been characterized by highly enriched 18O values throughout the late Pleistocene, and both of these sites may have actually have become slightly less arid during the Last Glacial Maximum. In Zambia, a concurrent transition to C3 grasslands is indicated by carbon isotopic profiles of traditional grazers, particularly equids (zebra). In Africa today, most grasses utilize the C4 photosynthetic pathway, and most trees and bushes the C3 pathway. A similar phytogeographic transition may have happened earlier at Sibudu Cave during a previous glaciation. Such a transition is not interpreted from the data for sites in Kenya or Ethiopia, suggesting that human groups in southern Africa may have experienced more extreme shifts in local climate and environment. High-resolution site-level environmental data allows for a greater appreciation of the microeconomic forces influencing behavior. Aridification of southern Africa during the Last Glacial may have had a major impact on migration and population change altering population distributions and densities. Patchy resource distribution and ecological changes during the late Pleistocene would have had transformative effects on populations and social networks. Ultimately, these climatic events and subsequent behavioral changes could have shaped the origins of agriculture in southern Africa. C3 grasslands have a lower carrying capacity and produce less biomass than ecosystems that support C4 grasses. This phytogeographic event may have had an impact on the delayed origins of agriculture in southern Africa, and may be a lesson for modern times when we consider the greater proportion of C3 grasses appearing in the prairies and farmlands of North America. Ethiopia with its relatively dry, but stable, environment throughout the late Pleistocene may have been a refugia for human groups and a cul-de-sac in terms of migrations out of Africa. These differences in environment also appear to correlate with changes in human behavior, specifically the transition between the Middle and Late Stone Ages characterized by the appearance of microlithic tool technologies. Based on the data collected in this study, microlithic tool technologies are related to deteriorated environmental conditions and greater residential mobility. Isotopic data collected for this research provides the largest single amount of site-level data for the late Pleistocene. The database is being prepared for public dissemination through an online geoinformatics database. Some of these data have already been used to organized a new module for Emory University's Foundations of Sustainability course to provide students with a greater understanding of the climatic history of our planet and how past populations adapted to climatic transitions. The co-PIs believe in making the data available to other researchers and the public through a shared open-source format. It is important to investigate how human culture has been adaptive and resilient to climatic change. Results of this study provide a more complete picture of regional environmental diversity for contextualizing local habitats in which humans evolved across Africa and provide lessons of past human-environment interactions which resonate with our current climate change issues.
