The effect of spatial clustering on stone raw material procurement

Brantingham proposes a neutral model to explain observed data on stone tool raw material procurement. Here we provide the results of investigating how real source locations, and their spatial clustering affect the raw material pattern outcome of the neutral model. Our initial findings are that spatial distributions mimicking empirical data challenge the validity of the neutral model. More specifically, increasing the source clustering increases the amount of time where the forager is without raw materials. In terms of foraging behavior, it is not realistic to expect that foragers go extended periods of time without raw materials to create and repair tools

Lithic technological responses to Late Pleistocene glacial cycling at Pinnacle Point Site 5-6, South Africa

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.Social Science and Humanities Research Council of Canada; NORAM; American-Scandinavian Foundation; Fundacao para a Ciencia e Tecnologia [SFRH/BPD/73598/2010]; IGERT [DGE 0801634]; Hyde Family Foundations; Institute of Human Origins; National Science Foundation [BCS-9912465, BCS-0130713, BCS-0524087, BCS-1138073]; John Templeton Foundation to the Institute of Human Origins at Arizona State Universit

The effect of spatial clustering on stone raw material procurement

Brantingham proposes a neutral model to explain observed data on stone tool raw material procurement. Here we provide the results of investigating how real source locations, and their spatial clustering affect the raw material pattern outcome of the neutral model. Our initial findings are that spatial distributions mimicking empirical data challenge the validity of the neutral model. More specifically, increasing the source clustering increases the amount of time where the forager is without raw materials. In terms of foraging behavior, it is not realistic to expect that foragers go extended periods of time without raw materials to create and repair tools

The performance of heat-treated silcrete backed pieces in actualistic and controlled complex projectile experiments

The origins of complex projectile weaponry provides insight into cultural and biological changes associated with the origins and spread of modern human populations. Middle Stone Age backed pieces are often thought to be components of such armaments, however our limited understanding of their functional characteristics as projectiles precludes understanding the adaptive problems they may have solved. Despite acknowledgment of raw material differences and intra-assemblage variability, whether variability in backed piece form reflects functional, economic, or stylistic variation has a paucity of empirical support. Here, the functional differences in backed piece form (size and shape) while hafted transversely and obliquely as high-velocity complex projectile armatures are examined. If there are performance tradeoffs simply in how backed pieces are arranged at the end of armaments that can influence effectiveness, then identifying the archaeological arrangement can provide insight into what variables were being prioritized in prehistoric technological systems. How variation in backed piece size, elongation, and hafting arrangement influences complex projectile performance is tested using experimental and actualistic projectile replications with a calibrated crossbow against animal and ballistics gelatin targets. The results of this study show that, within the size and shape variation of silcrete backed pieces examined, tool form plays a relatively limited role in their performance as projectile armatures. However, hafting orientation has very different performance characteristics for complex projectiles shot at ballistics gelatin compared to animal targets. We demonstrate that transversely hafted tools have more lethal internal wounds, but obliquely hafted backed pieces have greater puncture reliability. These functional differences represent different technological design emphasis: transversely hafted tools create large, deep wounds, while obliquely hafted arrows and darts create a puncture more reliably. Although obliquely hafted armaments cause less internal trauma, they are more likely to penetrate the hide of ungulate prey. Variability in MSA hunting tactics may have played a role in the design of weapon systems to optimize these performance tradeoffs. Despite similarities in shape with ethno-historic technologies, based on these results, MSA-sized backed pieces hafted as projectile armatures were unlikely to have been used with small, low-powered bows - but would have been lethal with a high-velocity delivery system

Summary of analyzed sample from PP5-6.

<p>Summary of analyzed sample from PP5-6.</p

Summary of results.

<p>Summary of results.</p

Correspondence plot of raw material types by temporal trend.

<p>c1 explains 78% of variation. c2 explains 27% of variation. Pearson Chi² = 51.5, p = <0.0001.</p

List of traits by raw material type that associate with MIS and exhibit a pattern consistent with glacial cycling for each raw material type.

<p>Traits that do not show a significant association for any raw material type are excluded from this table. Definitions are provided in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174051#pone.0174051.s001" target="_blank">S1 File</a>.</p

Simplified model of raw material availabilities based on current outcrop locations and mean modelled coastline distance for each MIS [43, 44].

<p>The dispersed distribution of quartz is represented by the light green shade in the background. Each grid square is 5 km x 5 km. The uppermost row of stacked bar graphs present the relative frequencies of each raw material type within each MIS. The lower rows of stacked bar graphs present the relative frequency of cobble and outcrop cortex for each raw material type. Only quartzite and silcrete showed a significant association between cortex type and MIS (Table E in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174051#pone.0174051.s004" target="_blank">S1 Dataset</a>).</p

Summary of minimum distances to different raw material types in each MIS.

<p>Secondary sources (cobbles) depend on modeled sea levels [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174051#pone.0174051.ref043" target="_blank">43</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0174051#pone.0174051.ref044" target="_blank">44</a>]. The distance for primary sources (outcrops) is presented under the assumption that lowered sea levels did not expose good quality outcrops.</p