Changing patterns of mobility as a response to climatic deterioration and aridification in the middle Holocene Southern Sahara.

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 paleolake in central Niger was one such location that preserves a unique mortuary record from the southern Sahara. Here, we use radiogenic strontium isotope analysis 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 strontium isotope analysis of enamel and bone samples from Middle Holocene burials (∼7.2-4.9 kya) indicate predominantly local values with no evidence for sex-based variation. 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 individuals demonstrate a predominantly non-local signature for enamel values and a predominantly local signature for bone values. Those individuals with non-local bone values always demonstrated non-local enamel values; however, the opposite was not the case. This suggests a divergence of mobility strategies during the Middle Holocene with a minority of individuals maintaining a more mobile existence throughout their life and others maintaining 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 aridification by Saharan peoples, then, was increasing mobility.