Abstract
There are multiple hypotheses for human responses to glacial cycling in the Late Pleistocene, including changes in population size, interconnectedness, and mobility. Lithic technological analysis informs us of human responses to environmental change because lithic assemblage characteristics are a reflection of raw material transport, reduction, and discard behaviors that depend on hunter-gatherer social and economic decisions. Pinnacle Point Site 5–6 (PP5-6), Western Cape, South Africa is an ideal locality for examining the influence of glacial cycling on early modern human behaviors because it preserves a long sequence spanning marine isotope stages (MIS) 5, 4, and 3 and is associated with robust records of paleoenvironmental change. The analysis presented here addresses the question, what, if any, lithic assemblage traits at PP5-6 represent changing behavioral responses to the MIS 5-4-3 interglacial-glacial cycle? It statistically evaluates changes in 93 traits with no a priori assumptions about which traits may significantly associate with MIS. In contrast to other studies that claim that there is little relationship between broad-scale patterns of climate change and lithic technology, we identified the following characteristics that are associated with MIS 4: increased use of quartz, increased evidence for outcrop sources of quartzite and silcrete, increased evidence for earlier stages of reduction in silcrete, evidence for increased flaking efficiency in all raw material types, and changes in tool types and function for silcrete. Based on these results, we suggest that foragers responded to MIS 4 glacial environmental conditions at PP5-6 with increased population or group sizes, ‘place provisioning’, longer and/or more intense site occupations, and decreased residential mobility. Several other traits, including silcrete frequency, do not exhibit an association with MIS. Backed pieces, once they appear in the PP5-6 record during MIS 4, persist through MIS 3. Changing paleoenvironments explain some, but not all temporal technological variability at PP5-6.
Highlights
Humans are unique for their extreme behavioral plasticity and their exaggerated dependence on social learning [1,2,3,4,5,6,7]
It has been argued that humans adapted to climate change by changing their mobility strategies and the degree to which they invested in inter-group trade and exchange [35], and that fluctuating conditions through the Plio-Pleistocene may have selected for human traits that permit flexible behavioral responses to new environments [36]
For the analyses presented here, StratAggs were lumped into marine isotope stages (MIS) stages based on their mean optically stimulated luminescence (OSL) age estimate; StratAggs Yellowish Brown Sand and Roofspall (YBSR) and Light Brown Sand and Roofspall (LBSR) date to MIS 5, Ashy Light Brown Sand (ALBS), Shelly Ashy Dark Brown Sand (SADBS), Orange Brown Sand 1 (OBS1), Shelly Gray Sand (SGS), Orange Brown Sand 2 (OBS2), and Dark Brown Compact Sand (DBCS) date to MIS 4, Black Brown Compact Sand and Roofspall (BBCSR) and Reddish Brown Sand and Roofspall (RBSR) date to MIS 3
Summary
Humans are unique for their extreme behavioral plasticity and their exaggerated dependence on social learning [1,2,3,4,5,6,7]. At Crevice Cave on the South Coast near Pinnacle Point, speleothem isotopes track this shifting rainfall regime, showing relatively more input from the summer rainfall regime during MIS 4 with a lessened summer rain input during MIS 5 [42] This finding is inconsistent with general predictions that glacial phases will normally be characterized by expansions of the winter rainfall regime [69, 70]. For most parts of South Africa, whether glacial conditions were wetter or drier, and whether there was an increase or decrease in seasonal rainfall are not yet resolved, but there is consensus that the large-scale global changes in temperature resulted in differing rainfall conditions during MIS 5, 4, and 3
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