Changing Patterns of Mobility as a Response to Climatic Deterioration and Aridification in the Middle Holocene Southern Sahara Christopher M. Stojanowski* and Kelly J. Knudson Center for Bioarchaeological Research, School of Human Evolution and Social Change, PO Box 872402, Arizona State University, Tempe, AZ 85287 KEY WORDS bioarchaeology; radiogenic strontium isotope analysis; North Africa; Saharan prehistory; paleomobility ABSTRACT The African Humid Period witnessed a rapid human re-occupation of the Sahara as numerous lakes formed during the Holocene climatic optimum circa 10-5 kya. Permanent waters attracted a variety of aquatic and terrestrial fauna allowing for long-term occupation of specific paleolake basins. The Gobero pale- olake in central Niger was one such location that pre- serves a unique mortuary record from the southern Sahara. Here, we use radiogenic strontium isotope anal- ysis to investigate how human communities adapted to aridification throughout the Holocene. In particular, we examine the effects of increasing climate instability on patterns of human mobility. Results of radiogenic stron- tium isotope analysis of enamel and bone samples from Middle Holocene burials (7.2–4.9 kya) indicate predom- inantly local values with no evidence for sex-based vari- ation. Comparisons of radiogenic strontium isotope data with previously published (Stojanowski and Knudson: Am J Phys Anthropol 146 (2011) 49–61) Early Holocene burials (9.7–8.3 kya) indicate significant differences in both enamel and bone values. Middle Holocene individu- als demonstrate a predominantly non-local signature for enamel values and a predominantly local signature for bone values. Those individuals with non-local bone val- ues always demonstrated non-local enamel values; how- ever, the opposite was not the case. This suggests a divergence of mobility strategies during the Middle Hol- ocene with a minority of individuals maintaining a more mobile existence throughout their life and others main- taining a similar strategy as Early Holocene hunter– gatherers that was tied to the paleolake basin. The more mobile individuals likely lived during the terminal phase of the lake’s occupation. One response to aridifica- tion by Saharan peoples, then, was increasing mobility. Am J Phys Anthropol 154:79–93, 2014. V C 2014 Wiley Peri- odicals, Inc. Climate change is one of the most important external stimuli affecting levels of population stress and overall well-being. Adaptable and resilient populations are able to buffer periodic climate stress through diverse strat- egies, the result of which is improved health and overall quality of life. We argue that inferring adaptive approaches from past populations informs modern strat- egies of resilience in regions with marginal, sub-optimal climates, or during short-term periods of stress affecting subsistence practices and water security. This dynamic relationship between climate, aridity, and human adapt- ability is perhaps no more evident than in the Sahara where, for much of the Holocene, human communities adapted to climate degradation that reduced surface waters and modified ecosystems. Throughout the Holo- cene, Saharan populations witnessed the transformation from hunting–gathering–fishing economies to pastoral and eventually agricultural economies, demonstrating diverse solutions to the problem of aridity and food inse- curity. Importantly, a community’s subsistence adapta- tion impacts group structure and composition, which in turn determine patterns of mobility across the human lifespan. Mobility is a key aspect of a population’s rela- tionship with the landscape, and the ability to move and the strategies involved in spatially organizing people are important buffers to short and long term changes in cli- mate. One of the most visible approaches for inferring paleomobility is through radiogenic strontium isotope ratios (see Bentley, 2006), which can be used to deter- mine life course changes in residence and extra-local in- migration, both of which determine group composition and affect biocultural adaptations and patterns of genetic variability. Previous studies of paleomobility in North Africa have focused on the following three contexts: the New King- dom of the Nile Valley (Buzon et al., 2007; Buzon and Simonetti, 2013), the Early and Middle Holocene sequence from the Libyan Fezzan (Tafuri et al., 2006; di Lernia and Tafuri, 2013; di Lernia et al., 2013), and the Gobero region of central Niger (Sereno et al., 2008; Grant sponsor: National Science Foundation; Grant numbers: BCS-0636066, BCS-0820805; Grant sponsor: Wenner-Gren Founda- tion; Grant number: GR-7747; Grant sponsors: Arizona State University Institute for Social Science Research Catalyst Grant, and Arizona State University School of Human Evolution and Social Change. *Correspondence to: C.M. Stojanowski, Center for Bioarchaeologi- cal Research, School of Human Evolution and Social Change, PO Box 872402, Arizona State University, Tempe, AZ 85287. E-mail: christopher.stojanowski@asu.edu Received 26 September 2013; accepted 7 January 2014 DOI: 10.1002/ajpa.22474 Published online 22 January 2014 in Wiley Online Library (wileyonlinelibrary.com). Ó 2014 WILEY PERIODICALS, INC. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 154:79–93 (2014)