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Diachronic Change within the Still Bay at Blombos Cave, South Africa.

Archer W, Gunz P, van Niekerk KL, Henshilwood CS, McPherron SP - PLoS ONE (2015)

Bottom Line: Here we develop a protocol to extract and analyse high resolution 3-dimensional geometric morphometric information about Still Bay point morphology.We demonstrate that at a single, stratified Still Bay site points undergo significant modal changes in tool morphology and standardization.Our results caution against (1) treatment of the Still Bay as a static technological entity and (2) drawing demographic inferences stemming from grouping Still Bay point collections within the same cultural label.

View Article: PubMed Central - PubMed

Affiliation: Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany.

ABSTRACT
Characteristically shaped bifacial points are stone artefacts with which the Middle Stone Age Still Bay techno-complex in Southern Africa is identified. Traditional approaches such as chaîne opératoire and two-dimensional metrics in combination with attribute analyses have been used to analyse variability within Still Bay point assemblages. Here we develop a protocol to extract and analyse high resolution 3-dimensional geometric morphometric information about Still Bay point morphology. We also investigate ways in which the independent variables of time, raw-material and tool size may be driving patterns of shape variation in the Blombos Cave point assemblage. We demonstrate that at a single, stratified Still Bay site points undergo significant modal changes in tool morphology and standardization. Our results caution against (1) treatment of the Still Bay as a static technological entity and (2) drawing demographic inferences stemming from grouping Still Bay point collections within the same cultural label.

No MeSH data available.


Related in: MedlinePlus

Plot showing the interaction between bifacial point stratigraphic layer and bifacial point centroid size, as well as their combined effect on PC1 shape change.Importantly, the “stratigraphic layer” variable has been specifically transformed for usage in the plot: the individual cells along this axis cannot be equated with individual layers, however, the axis represents the spectrum of variation in the stratigraphic layer variable. In the older layers there is little to no relationship between bifacial point size and shape change along PC1. However, in the younger layers point elongation and refinement are correlated with overall point size. Data points on the plot reflect the average response per cell and are scaled according to their size in accordance with the number of data per cell. Data points are depicted as filled when their average is above the fitted model and empty if they fall below.
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pone.0132428.g011: Plot showing the interaction between bifacial point stratigraphic layer and bifacial point centroid size, as well as their combined effect on PC1 shape change.Importantly, the “stratigraphic layer” variable has been specifically transformed for usage in the plot: the individual cells along this axis cannot be equated with individual layers, however, the axis represents the spectrum of variation in the stratigraphic layer variable. In the older layers there is little to no relationship between bifacial point size and shape change along PC1. However, in the younger layers point elongation and refinement are correlated with overall point size. Data points on the plot reflect the average response per cell and are scaled according to their size in accordance with the number of data per cell. Data points are depicted as filled when their average is above the fitted model and empty if they fall below.

Mentions: In the multiple regression investigating the interaction between size and stratigraphic layer, the full-reduced model comparison indicated that the interaction was very close to being significant (F = 3.578, P = 0.06) (Table 4). For many statisticians, a “marginally non-significant p-value” indicates some evidence against the -hypothesis [93,110]. Therefore, size had some influence on the tendency for points to be elongated and refined within the Blombos collection. However, the effect of decreases in point size on decreases in elongation and refinement was not the same for all stratigraphic layers (interaction: estimate+SE = -0.01+-0.005, t = -1.89, P = 0.06). This suggests that the way the interaction operates should be investigated through plotting the relationship between the variables of shape, size and stratigraphic level (Fig 11).


Diachronic Change within the Still Bay at Blombos Cave, South Africa.

Archer W, Gunz P, van Niekerk KL, Henshilwood CS, McPherron SP - PLoS ONE (2015)

Plot showing the interaction between bifacial point stratigraphic layer and bifacial point centroid size, as well as their combined effect on PC1 shape change.Importantly, the “stratigraphic layer” variable has been specifically transformed for usage in the plot: the individual cells along this axis cannot be equated with individual layers, however, the axis represents the spectrum of variation in the stratigraphic layer variable. In the older layers there is little to no relationship between bifacial point size and shape change along PC1. However, in the younger layers point elongation and refinement are correlated with overall point size. Data points on the plot reflect the average response per cell and are scaled according to their size in accordance with the number of data per cell. Data points are depicted as filled when their average is above the fitted model and empty if they fall below.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4489860&req=5

pone.0132428.g011: Plot showing the interaction between bifacial point stratigraphic layer and bifacial point centroid size, as well as their combined effect on PC1 shape change.Importantly, the “stratigraphic layer” variable has been specifically transformed for usage in the plot: the individual cells along this axis cannot be equated with individual layers, however, the axis represents the spectrum of variation in the stratigraphic layer variable. In the older layers there is little to no relationship between bifacial point size and shape change along PC1. However, in the younger layers point elongation and refinement are correlated with overall point size. Data points on the plot reflect the average response per cell and are scaled according to their size in accordance with the number of data per cell. Data points are depicted as filled when their average is above the fitted model and empty if they fall below.
Mentions: In the multiple regression investigating the interaction between size and stratigraphic layer, the full-reduced model comparison indicated that the interaction was very close to being significant (F = 3.578, P = 0.06) (Table 4). For many statisticians, a “marginally non-significant p-value” indicates some evidence against the -hypothesis [93,110]. Therefore, size had some influence on the tendency for points to be elongated and refined within the Blombos collection. However, the effect of decreases in point size on decreases in elongation and refinement was not the same for all stratigraphic layers (interaction: estimate+SE = -0.01+-0.005, t = -1.89, P = 0.06). This suggests that the way the interaction operates should be investigated through plotting the relationship between the variables of shape, size and stratigraphic level (Fig 11).

Bottom Line: Here we develop a protocol to extract and analyse high resolution 3-dimensional geometric morphometric information about Still Bay point morphology.We demonstrate that at a single, stratified Still Bay site points undergo significant modal changes in tool morphology and standardization.Our results caution against (1) treatment of the Still Bay as a static technological entity and (2) drawing demographic inferences stemming from grouping Still Bay point collections within the same cultural label.

View Article: PubMed Central - PubMed

Affiliation: Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany.

ABSTRACT
Characteristically shaped bifacial points are stone artefacts with which the Middle Stone Age Still Bay techno-complex in Southern Africa is identified. Traditional approaches such as chaîne opératoire and two-dimensional metrics in combination with attribute analyses have been used to analyse variability within Still Bay point assemblages. Here we develop a protocol to extract and analyse high resolution 3-dimensional geometric morphometric information about Still Bay point morphology. We also investigate ways in which the independent variables of time, raw-material and tool size may be driving patterns of shape variation in the Blombos Cave point assemblage. We demonstrate that at a single, stratified Still Bay site points undergo significant modal changes in tool morphology and standardization. Our results caution against (1) treatment of the Still Bay as a static technological entity and (2) drawing demographic inferences stemming from grouping Still Bay point collections within the same cultural label.

No MeSH data available.


Related in: MedlinePlus