Do a few tools necessarily mean a few people? A techno-morphological approach to the question of group size at Gesher Benot Ya'aqov, Israel

Journal of Human Evolution 128 (2019) 45e58

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Do a few tools necessarily mean a few people? A technomorphological approach to the question of group size at Gesher Benot Ya'aqov, Israel Gadi Herzlinger a, b, *, Naama Goren-Inbar a a b

Institute of Archaeology, The Hebrew University of Jerusalem, Mt. Scopus, Jerusalem 9190501, Israel The Jack, Joseph and Morton Mandel School for Advanced Studies in the Humanities, The Hebrew University of Jerusalem, Israel

a r t i c l e i n f o

a b s t r a c t

Article history: Received 2 May 2018 Accepted 12 November 2018

The question of Paleolithic group size has been addressed by scholars in many disciplines applying different methods. In our study we apply a novel analytical approach in an attempt to assess the group size of hominins that occupied the Acheulian site of Gesher Benot Ya'aqov, Israel (GBY). Within this framework, we subjected the handaxe assemblages from several archaeological horizons at the site to a morpho-technological analysis. The analysis combined high-resolution three-dimensional geometric morphometric analysis with typo-technological attribute analysis to assess the inter- and intraassemblage morpho-technological variability. The analysis was also applied to an experimental handaxe assemblage produced by an expert knapper. The results of the analysis show high morphological homogeneity coupled with high technological variability in each of the archaeological assemblages. This pattern is highly indicative of the work of expert knappers, as is also suggested by the comparison between the archaeological and experimental assemblages. The high density of archaeological remains in some of the GBY occupations and their pristine taphonomic condition provide additional support for the involvement of large groups of hominins, although some horizons are far poorer in archaeological remains and hence do not allow such an interpretation. Nevertheless, the fact that in all assemblages the handaxes show the same techno-morphological pattern indicates that they were all produced by expert knappers. As shown by numerous models and ethnographic data, the presence of experts can be viewed as an indication of large and socially complex societies. Thus, although some of the GBY occupations were not formed by large groups, the smaller groups whose activities are recorded were very likely to be part of larger, socially complex cultural groups. This variability in occupational intensity is interpreted as representing an aggregation-dispersal mechanism, similar to those documented in many huntergatherer societies. © 2018 Elsevier Ltd. All rights reserved.

Keywords: Handaxe Acheulian Geometric morphometric analyses Technology Expertise Social complexity

1. Introduction Estimates of prehistoric population size, and particularly of group size, have been topics of interest and debate in numerous studies pertaining to diverse disciplines. The issue of prehistoric hominin group size has significant implications for many and varied aspects of human evolution and behavior, and for the understanding of mechanisms such as cultural transmission. However, estimating group size in prehistoric times is a difficult task, since the term is in itself highly ambiguous owing to the organization of

* Corresponding author. E-mail address: [email protected] (G. Herzlinger). https://doi.org/10.1016/j.jhevol.2018.11.008 0047-2484/© 2018 Elsevier Ltd. All rights reserved.

groups of humans in hierarchically structured and nested social units (Zhou et al., 2005; Hamilton et al., 2007). Thus, group size may refer to inherently different social units or group levels, such as the intimate, effective, extended and global spheres, each having a different order of magnitude in terms of the number of individuals they include (Gamble, 1998). Furthermore, substantial variability in estimations of prehistoric group size is due not only to the ambiguity of the term but also to the diverse disciplines that provide them. Among these are biology, cognitive science, ethnography and archaeology, each employing different methodological frameworks. Biological studies, based on methods drawn from the field of population genetics and not necessarily referring specifically to human populations, often provide estimations of the minimal size

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of a viable group (e.g. Frankham, 1995 and references therein). However, such estimations of mating population networks do not necessarily correspond to the social units that are relevant to archaeological and anthropological interests. A different, and highly influential, approach rooted in the field of cognitive sciences is the social brain hypothesis. This hypothesis, which originally addressed primates in general, correlates the neocortex to brain capacity ratio with the size of the social group (Dunbar, 1992). This hypothesis has since been applied to various species of extinct hominins (Aiello and Dunbar, 1993) and further developed to address additional aspects of past social and cognitive capacities (Dunbar, 2003, 2009; Voland, 2007). Ethnographic and ethnoarchaeological studies have provided ample data on the group sizes of extant hunter-gatherer societies through direct observations (Yellen, 1976; Lee, 1979; Binford, 1980; Kelly, 2013). These accounts have been especially valuable in describing the many factors that govern the highly dynamic processes related to the changing sizes and variable material signatures of such groups. Size estimates of past groups in different regions and chronologies usually build on one or more of the above-mentioned approaches, while also incorporating formal models that at times integrate different types of archaeological data (Wobst, 1974, 1976; Reich and Goldstein, 1998; Moore, 2001; White, 2017). In many cases, archaeologically based estimates are founded on the numbers and sizes of archaeological sites in a defined region and chronological unit (Bocquet-Appel et al., 2005; Grove, 2008, 2010) or on excavations of extensive surfaces and reconstructions of paleo-landscapes (Ohel, 1986; Martin et al., 2010; Maher et al., nchez, 2017). However, 2012; Domínguez-Rodrigo and Cobo-Sa when the archaeological resolution does not provide such data, for instance in cases of regionally, chronologically or culturally isolated sites, estimation of the size of the group that produced them becomes more problematic. African archaeological surveys and excavations have yielded large collections of Acheulian remains. Within the material culture record, bifaces (both cleavers and handaxes) form the hallmark of this culture, which has a temporal duration of ~1.5 Ma (Sharon, 2007). These tools are made of different raw materials and portray different technologies and styles, and at times were found in association with skeletal remains of Homo erectus sensu lato. One of the most striking traits of the African Acheulian is the immense quantities of bifaces, which occur in large numbers both in excavated sites and as surface scatters (e.g. Olorgesailie [Isaac and Isaac, 1977], Isimila [Cole and Kleindienst, 1974], Kalambo Falls [Clark, 2001], Melka Kunture [Chavaillon and Piperno, 2004], Olduvai Gorge [Leakey and Roe, 1994] and Gadeb [Clark and Kurashina, 1976], to mention but a few). In some parts of eastern Africa, the surface density of stone tools is so impressive that when describing his field work in Ethiopia (where his team drove over 20 km and saw tens of thousands of bifaces) the paleontologist Jon Kalb (2001: 167) referred to it as a “reg” (desert pavement). This example illustrates the richness of the biface component of the Acheulian assemblages. Two different research trajectories have provided means of understanding the presence of such concentrations of numerous bifaces. These developments are: 1) the interpretation of high surface densities of bifaces as resulting from postdepositional processes (Isaac, 1967); 2) the realization, based on experimental archaeology, that the production of bifaces is a relatively rapid procedure once the knapper is an expert, and hence an abundance of bifaces could have been produced by a single knapper (e.g. Jones, 1994). These developments, particularly the influence of the first, led many prehistorians to consider the large quantities of bifaces as representing taphonomic processes, a time-averaged product rather than a single short episode resulting from the activities of a

large group of individuals (Isaac and Isaac, 1977; Schick, 1986, 2001). This view has been so influential that it has overshadowed other potential explanations for these large concentrations of bifaces. In the light of the different estimations of group size and interpretations from various disciplines, the null hypothesis of a group of “regular” size occupying a campsite (i.e. a band) has been established as 25e50 individuals (Gamble, 1998). This estimation is based on common models and ethnographic analogies. In this article we present evidence derived from observations of the Acheulian material excavated at the site of Gesher Benot Ya'aqov (GBY), Israel, a unique site with regard to its region, chronology and material culture. The first, and most substantial, observation is related to the large quantities and density of anthropogenic remains, especially the biface component, in some of the archaeological horizons. In contrast to many African occurrences, these accumulations cannot be explained as resulting from postdepositional processes (see below). Secondly, based on the significant investment of effort in their production, reflected by their ratoire (Madsen and Goren-Inbar, long and complex chaîne ope 2004; Goren-Inbar et al., 2018), the bifaces are considered formal tool types of great importance. These tools were most probably in use for a long time and were not discarded after the completion of a particular task. This notion is supported by ethnographic analogies confirming that similar tools, which require high expertise, are in fact regarded as prestigious personal property of high value and trequin and serve individuals for a significant amount of time (cf. Pe trequin, 1993). We use the archaeological and ethnographic evPe idence outlined above to challenge the null hypothesis and suggest that some of the archaeological assemblages at GBY were produced by larger groups of individuals that exceeded the numbers given above. However, it should be noted that providing numerical estimations of the sizes of these groups is beyond the scope of this article. Our argument is based on a detailed morpho-technological analysis of several handaxe assemblages from the Acheulian site of GBY. The results of this analysis are then used to assess the level of expertise of the GBY knappers. Subsequently, these insights are used to discuss the size of the social group to which these knappers belonged. 2. Materials and methods 2.1. Materials Prior to the morpho-technological analysis, and in the light of the common archaeological approach that interprets accumulations of bifacial tools as resulting from postdepositional processes, the taphonomic integrity of the materials must be established. We have previously shown that all the archaeological horizons at GBY are thin anthropogenic horizons with a thickness of a single artifact, characterized by rapid sealing (Feibel, 2001, 2004; Goren-Inbar et al., 2018). The archaeological remains that form these entities include lithic artifacts and faunal and floral remains. Analyses of these components have produced results that are relevant for the taphonomic assessments. Previous sedimentological and stratigraphic studies have shown that the history of sedimentation at GBY is varied and that the cultural remains were deposited on storm-generated beaches, on interfaces between fine-grained offshore muds and coquinas, and on offshore muds (Feibel, 2001, 2004). The lithic assemblages indicate that no substantial fluvial processes were involved in their deposition. The preservation condition of the vast majority of the artifacts is either fresh or slightly abraded and there are only minimal occurrences of double patinated items (Goren-Inbar et al., 2018). Additionally, the breakage pattern recorded in the lithic

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assemblages should be associated with the knapping process rather than with high-energy fluvial transport (Herzlinger et al., 2015). The study of the individual archaeological horizons has yielded ample evidence for minimal loss due to postdepositional processes. An important aspect supporting the minimal influence of taphonomic processes is the spatial clustering of lithic microartifacts, whether flint, limestone or basalt. In addition, burned flint microartifacts were found clustered, marking the location of (phantom) hearths (Alperson-Afil et al., 2009; Alperson-Afil and Goren-Inbar, 2010). Such undisturbed clusters of small-sized clasts in lake margin environments, displaying no evidence of winnowing, could have been preserved only by rapid sealing of the discarded artifacts without the involvement of wave action or slow water flow. Irrespective of the nature of the depositional context, all these occupations include organic materials, the preservation of which is excellent due to the waterlogged nature of the site. The organic remains comprise a rich assemblage of wood, bark, climbers, bushes, fruits, nuts, seeds, vegetables and plants producing underground storage organs. These macrobotanical assemblages testify to rapid sealing of the archaeological horizons, as prolonged exposure to atmospheric conditions would have eradicated these plentiful remains (e.g. over 100,000 macrobotanical remains; Goren-Inbar et al., 2002a, 2002b; Melamed et al., 2016). Paleontological indications of a minimal taphonomic modification are supplied by refitting of mammal and bird bones. Elephant skull bones found at a very small distance from the skull were refitted (GorenInbar et al., 1994), and in other occupations fallow deer long bones were refitted (Rabinovich et al., 2012). Fragile broken bird bones were found in anatomical position (Goren-Inbar et al., 2018). In the gastropod assemblage, individual specimens were found to include several embryos each, indicating superb preservation (Ashkenazi et al., 2010). Additionally, the spatially undisturbed configuration of finds (such as anvils, waste products of biface manufacture, tools of various types, and a piece of charcoal) made around the phantom hearths provide supplementary corroboration of the undisturbed original location of the finds (Alperson-Afil et al., 2009). It is clear that multiple lines of evidence support the assumption that the lithic material used in this analysis was deposited in situ and that the accumulations did not result from fluvial transport, winnowing or re-working. Furthermore, each of the assemblages appears to have been deposited during a short period of occupation, which was followed by rapid, almost immediate, sealing by the overlying sediments. In addition, the layers were preserved in a continuously waterlogged, anaerobic environment, which contributed to the excellent preservation of all the anthropogenic materials. Hence, the lithic materials, including the bifaces, can safely be used in assessment of the expertise level of the GBY knappers and discussion of their social group size. The current study addresses the analyses of nine handaxe assemblages. Eight of the assemblages originate in the excavations of the Acheulian site of GBY (Goren-Inbar et al., 2018), while the ninth is an experimental assemblage. The latter was produced by a single expert knapper as part of a systematic experimental project ratoire used for producing aimed at reconstructing the chaîne ope the handaxes (Madsen and Groen-Inbar, 2004; Herzlinger, 2014; Herzlinger et al., 2017a) (Table 1). The experimental knapping constituted selection and procurement of similar raw material to that used at GBY, i.e. large slabs of dense Alkali-Olivine basalt. These were shaped into giant cores using hard and soft hammers of organic and inorganic materials using several core methods. Large flake blanks were detached from the cores and shaped into finished tools with the explicit goal of producing artifacts morphologically similar to those excavated at the site. Each of the GBY handaxe assemblages represents a different archaeological horizon in the depositional/cultural complex of Layer II-6. All these

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Table 1 Sample sizes of the assemblages used in the analysis. Assemblage Experimental II-6/L1 II-6/L2 II-6/L3 II-6/L4 II-6/Lb4 II-6/L5 II-6/L6 II-6/L7 Total

Number of handaxes 21 35 16 7 96 35 5 13 15 243

assemblages reflect the same large flake Acheulian technological tradition and were produced using the same general chaîne ratoire, which includes at least five different methods of giant ope core reduction (Madsen and Goren-Inbar, 2004; Goren-Inbar, 2011; Goren-Inbar et al., 2018). Although there are some differences in specific production procedures between the assemblages, all the procedures are consistently present throughout the cultural sequence. Thus, all the handaxe assemblages are assigned to the same cultural and technological tradition. In addition, although handaxes at GBY were produced on three different raw materials (basalt, flint and limestone), the basalt component is markedly dominant, consisting of more than 90% of the handaxes, and therefore only basalt handaxes were included in the present analysis. Last, as our methodology consists of a highly sensitive three-dimensional (3D) geometric morphometric shape analysis, only complete handaxes or those with slightly broken tips were included in the analysis. 2.2. Methods Morphological analysis A 3D geometric morphometric shape analysis was performed for quantitative measurement of shape variability within and between the different assemblages. Each handaxe was scanned using a structured light camera and a turntable (produced by Polymeric™) (Grosman et al., 2008) to produce a high-resolution 3D digital model of the tool. Following this, the 3D model of each handaxe was subjected to an automated orientation and landmark positioning procedure using Artifact GeoMorph Toolbox 3D software pack (AGMT3-D) (Herzlinger et al., 2017a; Herzlinger and Grosman, 2018). Each model was automatically oriented to the standard positioning, with each of its two faces being parallel to the XY plane and its approximate axis of symmetry being parallel to the Y axis. Along and perpendicular to this axis, which served as the prime meridian, 50 equidistant latitudes were deployed. On each of these latitudes, 50 equidistant homologous 3D semi-landmarks were placed on each of the two faces and their coordinates recorded. Thus, for each handaxe, 5000 homologous 3D semi-landmarks were collected using AGMT3-D, providing a comparable highresolution point cloud representing the volumetric configuration of the artifact. Following the data acquisition stage, the morphological data were subjected to a set of multivariate statistical procedures and analyses to detect, and quantitatively describe, shape differences within and between assemblages. The analysis included a generalized Procrustes analysis and a principal component analysis (PCA) (Dryden and Mardia, 1998; Lycett et al., 2006). The analytical procedures were conducted on a dataset consisting of all tools from all assemblages. This allowed the subsequent comparison of various aspects, trends and patterns in the tools' shapes and their variability. The analytical stage was performed using the AGMT3-D software (Herzlinger and Grosman, 2018).

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The generalized Procrustes analysis serves here as a superimposition procedure, removing non-shape related variability stemming from differences in location, orientation in space and scale. When this procedure is followed, differences in landmark coordinates can be exclusively attributed to shape differences between the different tools (Dryden and Mardia, 1998). The PCA is the main analytical procedure in the shape analysis; it is used to reduce data dimensionality and detect the main axes of variability in the sample (Dryden and Mardia, 1998). Thus, it provides a number of components (i.e. variables or axes) equal to the number of items in the sample minus one, sorted in descending order according to the proportion of variability that they explain. Each principal component (PC) reflects a specific shape trend, a mutual change in the values of a number of homologous landmarks. Each analyzed tool receives a value for each PC, which is based on the values of its relevant coordinates in relation to the shape trend described by that particular PC. Hence, each tool is defined by a series of PC scores that describe its position relative to the other items in the sample for each specific trend. These multidimensional vectors allow us to determine the mean shape for each assemblage and use these means to calculate the intra- and inter-assemblage shape variability. Intra-assemblage shape variability is expressed here as the mean multidimensional Euclidean distance of all items in a given group from its group centroid. In addition, the results can be used to describe graphically and quantitatively the essence of shape differences in and between the assemblages. Differences in intraassemblage shape variabilities and assemblage mean shapes are tested for statistical significance by applying the non-parametric Wilcoxon rank-sum tests to different datasets of inter point distances. All statistical procedures and analyses were conducted using the AGMT3-D software package (Herzlinger and Grosman, 2018). Technological analysis A detailed techno-typological attribute analysis was conducted to provide a description of the technological procedures used in the production of handaxes (Bar-Yosef and Goren-Inbar, 1993; Goren-Inbar et al., 2018). Among the many attributes that were recorded, we focused on those that are most informative and indicative of the production technology. These include the direction of blow of the blank removal, the type of striking platform and the type of retouch applied to the blank following its removal. The nature of each attribute, along with their different attributes state (i.e. categories) and the criteria used for classification are explained in detail in Goren-Inbar et al. (2018). The direction of blow is a highly informative attribute, as it sheds light on the geometry of the core from which the blank was struck. Three states are assigned to this attribute: end-struck, sidestruck and special side-struck flakes (Isaac and Keller, 1968; GorenInbar et al., 2018). End-struck refers to flake blanks that were removed using a blow which was struck parallel to the length axis of the artifact. Side-struck refers to banks that their length axis is perpendicular to the axis of removal. Flakes removed using this method are characterized by a width dimension larger than their length dimension. Last, special side-struck refers to blanks in which the axis of removal deviates from the length axis by about 45
. Although this is not definitive, some directions of blow are more strongly associated with specific core types e for example, sideand special side-struck flakes are more commonly removed from Levallois and bifacial cores, while end-struck flakes are more often associated with along axis or “slicing” cores (Madsen and GorenInbar, 2004). The type of striking platform describes the surface to which the blow was delivered for its removal and can be assigned three different states, plain, dihedral and removed. Plain refers to artifacts with an unmodified flat striking platform. Dihedral refers to

artifacts with a striking platform characterized by facets separated by a ridge. Removed refers to artifacts that do not retain the original striking platform as it was eliminated by a series of flake removals. This is an important attribute, as it provides information on core preparation procedures, such as the dihedral platform. In the case of GBY, however, this attribute is a better indicator of a postdetachment modification consisting of the removal of the striking platform. This very common procedure is well known at the site and was applied to remove thick areas of the blank and hence provide a uniform distribution of thickness (Goren-Inbar et al., 2018). Last, the attribute of type of retouch describes the type of secondary flaking applied to the removed blank in order to shape it into the finished tool. This attribute can be given four attribute states including flat and limited, thinning, bifacial, and thinning and bifacial. Flat and limited refers to artifacts that show very thin (and hence flat) flake removals, usually occurring on the elevated topography associated with the bulb of percussion. Thinning refers to artifacts on which only a few scars are observed, restricted to the edges and do not extensively cover the surfaces of the biface. This attribute state is also usually associated with the thinning of the bulb of percussion and the removal of the striking platform. Despite its name, bifacial refers to an intensive retouch that may appear on one or both faces of the tool and covers more substantial surface area of the biface. Thinning and bifacial is a combination of the last two attribute states so that a single type is observed on each of the faces (Goren-Inbar et al., 2018). Thus, this attribute expresses the knapper's preferences with regard to the post-removal modification of the blank and design of the tool. The direction of blow, striking platform and type of retouch technological attributes provide an informative description of various aspects of the handaxe production technology and procedures used by the GBY hominins. 3. Results and preliminary discussion 3.1. Morphometric results The results of the handaxe geometric morphometric analyses of the experimental assemblage and archaeological horizons at GBY are presented in Table 2. It shows the extent of the intra-group shape variability of each of the assemblages and that of the experimental assemblage. The intra-group variability is expressed here as the mean multidimensional Euclidean distance of all items in a given group from its group centroid. This value reflects the morphological dispersity of all tools in the group and hence corresponds to its morphological variability; the smaller the value, the more homogeneous the shapes of the bifaces in the group. In general, the samples are fairly similar to one another. The assemblage of Layer II-6 Level 3, with the highest variability, is some 18% more variable than that of Level 5, the most homogeneous assemblage. The value of the experimental assemblage falls

Table 2 Intra-assemblage shape variability (shape variability measured as the mean multidimensional Euclidean distance of all artifacts in an assemblage from its centroid). Assemblage Experimental II-6/L1 II-6/L2 II-6/L3 II-6/L4 II-6/Lb4 II-6/L5 II-6/L6 II-6/L7

n

Shape variability

21 35 16 7 96 35 5 13 15

277.86 293.77 276.06 314.48 302.66 271.61 267.51 299.17 300.31

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within the range of the archaeological ones, but at the lower end. The largest assemblage (Level 4) falls in the middle of the variability range. The results of Wilcoxon rank-sum tests conducted on the inter-point distances between each two group means and the items in their respective groups show that the shape variability value of none the assemblages is significantly different at the 0.05 level than that of any other group, including the experimental assemblage. In addition to the values representing the morphological variability of each assemblage, another important aspect is the spatial distribution of the intra-assemblage morphological variability. The spatial aspect refers to the proportion of variability of homologous landmark coordinates across all landmarks in each assemblage. These correspond to the areas of the tool that differ most among all the handaxes in each assemblage. Figure 1 illustrates the relative variability of each homologous landmark for each assemblage on its respective mean shape. The mean shape of each assemblage is shown in two views (Faces 1 and 2; for terminology see GorenInbar and Saragusti, 1996) using conventional presentation. The variability of each landmark is color-coded, from lowest (blue) to highest (red). This illustration highlights those areas of the handaxes that are the most variable. In addition to the illustration, 3D models of the mean shape of each assemblage are also provided with similar color coding in Supplementary Online Material. Generally, and in all assemblages with the exception of Layer II-6 Level 2, the most variable areas are the edges of the handaxes. In most assemblages, these areas are around the proximal end of the tools, with somewhat less pronounced areas occurring around other parts of the perimeter. However, in Layer II-6 Levels 6 and 7, as well as in the experimental assemblage, the most variable areas are located on the lateral or lateral-distal edges. Most assemblages also show areas of variability that are more centralized on the tools' surface, on at least one face. However, with the exception of Level 3, these are usually far less pronounced than the peripheral areas of variability. The assemblage of Level 2 also deviates from the common pattern, as it presents a remarkably homogenous spatial distribution of its variability (Supplementary Online Material (SOM)). For full understanding of shape variability, it is important to consider not only its spatial distribution on the tools but also its nature. This refers to the way in which the variable areas differ among the tools in the assemblage. Table 3 presents the distribution of the total standardized PC coefficients across the three spatial dimensions X, Y and Z, corresponding to the relative variability of all landmarks. Differences on these dimensions correspond to differences in relative width, length and thickness respectively. Table 3 shows the dimensions in which the homologous landmarks differ the most. In all the archaeological assemblages, most of the variability corresponds to differences in relative thickness. When considering these results together with the spatial distribution of the variability (focused around the edges; Fig. 1), several interpretations could be proposed. One possibility is that the variability results mainly from differences in regularity of the edges. Another interpretation views the variability as resulting from the thinning of the bulb of percussion and removal of the striking platform, both common technological procedures at GBY. In any case, it is clear that in the archaeological assemblages the distribution of variability across the dimensions is fairly homogeneous. Only a few levels deviate from this pattern. Level 6 presents low values of variability of relative thickness, with higher values of both relative length and width. Level 7 displays a somewhat low variability of relative width, while Level 4 shows a fairly high variability of relative length. Perhaps the most striking observation is related to the experimental assemblage, which displays a markedly different distribution pattern. Its variability of relative thickness is lower, while the variability of both relative width and length are higher than in any of the archaeological

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assemblages. This shows that, in contrast to the archaeological assemblages, the variability in this case stems mainly from differences in planform shape of the items rather than in edge regularity or treatment of the striking platform and/or bulb of percussion. A different morphological aspect is inter-assemblage variability, which measures the extent of mean shape differences between the assemblages. Figure 1 provides a graphic visualization of the mean shape of some of the assemblage (see also Supplementary Online Material (SOM)). It indicates that while some assemblages, such as those of Levels 4 and 4b, show highly similar mean shapes, others, such as Levels 2 and 4, are markedly different. The geometric morphometric shape analysis allows the quantitative expression of these differences using a single value, representing the multidimensional Euclidean distance between each two group means. These, along with the results of Wilcoxon ranksum tests conducted on the inter-point distances between each two group means and the items in the respective and opposite groups, are provided in the distance matrix shown in Table 4. The distance matrix of Table 4 supports the general visual observations regarding the differences between the assemblages' means. The most similar assemblages are Levels 4 and 4b, 1 and 2, and 1 and 6 while the most different ones are Levels 2 and 5, 5 and 7, and 1 and 5. The probabilities that each of the two groups' means are significantly different generally support the Euclidean distance observations. The shapes of the group means that are closest to one another are indeed not significantly different at a 0.05 level, in contrast to those that are farthest away. These results strengthen the distance observations, as in addition to the Euclidean distances the test also takes into consideration the sample sizes and withingroup variability of each of the assemblages. These results also indicate that the differences between the experimental assemblage and each of the archaeological assemblages fall within the range of differences between the archaeological assemblages. The mean shape of the experimental assemblage is closest to that of Level 4 and farthest away from that of Level 7. However, it should be noted that while these values provide a convenient method of comparing the mean shapes, they also mask similarities and differences that exist between more specific shape aspects of the means. This is reflected in the results of the significance test, which indicates that the mean shape of the experimental assemblage is significantly different at a 0.05 level from all archaeological assemblages with the exception of that of Level 1. An additional assessment of similarities and differences can be achieved using individual PC scores of the assemblage means. Figure 2 displays a bivariate plot of the first two PCs, which account for some 33% of the entire shape variability in the sample, with the 95% confidence ellipses and centroids (corresponding to the mean shapes) of all assemblages. While the mean score of the experimental assemblage on PC1 falls in the middle of the archaeological assemblages' range, on PC2 it has a substantially lower score than any of the archaeological assemblages. This score corresponds morphologically to the lower thickness on the central surface of the handaxe in relation to the higher thickness of the peripheral areas as well as to a right skew in symmetry. Thus, despite the general similarity between the experimental and archaeological assemblages in terms of their mean shape values, some of the latter's specific morphological aspects are markedly different in the former. 3.2. Technological results The analyzed archaeological and experimental assemblages were all produced on large basalt flakes struck off giant cores. This, however, does not imply a finer technological homogeneity within the different assemblages. In order to examine the technological variability, we analyzed three selected technological attributes that

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Figure 1. Spatial distribution of the intra-assemblage morphological variability of selected assemblages. Colors correspond to the proportion of variability of homologous landmark coordinates for all landmarks in four handaxe assemblages (blue ¼ low; red ¼ high). Axes are in scaled centroid size unit. The distribution is presented on the mean shape of the assemblages. (a) Layer II-6 Levels 3 and 4; (b) Experimental and Layer II-6 Level 1.

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Figure 1. (continued).

show a degree of variability indicating that the specific technological procedures applied to the production of handaxes were varied (Goren-Inbar et al., 2018). It should be noted that due to the weathered and “difficult-to-read” condition of the basalt tools,

many observations fall within the indeterminate category. Within the archaeological assemblages, this category includes 43% of the items (n ¼ 104) in the striking platform attribute, 56% of the items (n ¼ 135) in the direction of blow attribute and 20% (n ¼ 49) of the

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Table 3 Distribution of relative shape variability across dimensions (calculated as the proportion of variability in each homologous landmark coordinate for each specific dimension). Assemblage Experimental II-6/L1 II-6/L2 II-6/L3 II-6/L4 II-6/L4b II-6/L5 II-6/L6 II-6/L7

X variability (%)

Y variability (%)

Z variability (%)

47.94 41.24 41.32 43.72 40.10 42.13 41.47 45.94 38.30

9.74 6.09 2.41 6.10 6.62 3.60 6.00 8.03 4.51

42.32 52.67 56.28 50.18 53.28 54.27 52.53 46.03 57.19

type of retouch attribute. In the following description, the indeterminate category was excluded from the calculations. Although no detailed technological analysis of the experimental assemblage was carried out, its production involved large basalt flakes that were obtained by a smaller number of giant core reduction methods than those observed for the archaeological assemblages (Madsen and Goren-Inbar, 2004; Goren-Inbar et al., 2018). Thus, one would assume that the technological variability of the experimental assemblage is lower than that of the archaeological assemblages. The frequencies of the technological attributes are presented in Tables 5e7. The technological variability is expressed, among other attributes, by the different directions of blow (Table 5). Only three assemblages have more than 10 observations in total, and these comprise all three types of directions of blow in the manufacture of the large flakes. The majority of tools were produced on blanks that are special-side struck (Isaac and Keller, 1968) and side-struck, with the former usually being the most frequent category. These frequencies indicate that varied detachment modes for flakes to be used as blanks for handaxes were employed in all assemblages with sufficient sample sizes. Most assemblages consist of tools with both plain and removed striking platforms (Table 6). The removed striking platform category is more abundant in almost all assemblages. While this pattern highlights the importance of this technological procedure in the technological tradition of GBY, it should be noted that a significant portion of the tools retain their original plain striking platform. The lowest frequency is that of dihedral striking platform, which is represented in each assemblage by only one or two observations.

The pattern resulting from the analysis of the type of retouch attribute (Table 7) displays higher complexity. The most common type is that of bifacial retouch, which appears in all assemblages and ranges between 60% and more than 80%, a somewhat trivial observation as it is typical of the modification of a handaxe. The least frequent type is the flat and limited category, which appears in only four of the assemblages. The categories of thinning (a process associated with attempts to remove high topography in the area of the bulb of percussion [Goren-Inbar et al., 2018]) and thinning and bifacial are somewhat more abundant, although still in rather small proportions. Thus, although some variability is encountered, the attribute is generally dominated by the bifacial retouch type. Though limited by the small sample sizes, these results provide additional insight into the overall nature of technological variability of the assemblages. The technological analyses show that all the archaeological assemblages include several different ways of producing and modifying handaxes. Furthermore, it appears that the distribution of each attribute state is fairly similar in all assemblages. These two observations suggest that each of the archaeological assemblages shows internal technological variability while in diachronic terms there is a general technological homogeneity across the different assemblages. 4. Discussion and conclusions The following sections discuss the results obtained from the analyses of the GBY handaxes from the perspective of knapping expertise and its implications for the size of the social group. 4.1. Knapping expertise at GBY The variability of bifaces, particularly Acheulian handaxes, is clearly a central issue in the multitude of attempts to understand these long-lasting tools and their tradition of manufacture as expressed by their technology and style. Views of the factors affecting the observed variability and its meaning include raw material availability and cultural tradition, to mention but a few (Wynn and Tierson, 1990; Mithen, 1994; White, 1998; Lycett and Gowlett, 2008; Sharon, 2008). In this study we apply methods that enable quantitative examination and comparison of the intraand inter-assemblage variability of handaxes. The results of the morpho-technological analysis indicate that, in general, the GBY assemblages display relatively high morphological homogeneity alongside high technological variability.

Table 4 Distance and significance test results matrix between each of the assemblages (distance calculated as the multidimensional Euclidean distance between each two assemblages' mean shapes; p values of Wilcoxon rank-sum test on inter-point distance between the means of each two groups and their items are also given).

Experimental II-6/L1 II-6/L2 II-6/L3 II-6/L4 II-6/L4b II-6/L5 II-6/L6 II-6/L7

Experimental

II-6/L1

II-6/L2

II-6/L3

II-6/L4

II-6/L4b

II-6/L5

II-6/L6

II-6/L7

0

145.96 0.1 0

192.05 <0.01 100.38 0.16 0

164.40 0.01 132.77 0.07 174.78 0.01 0

133.21 0.01 143.91 <0.01 184.88 <0.01 129.24 <0.01 0

132.15 <0.01 172.62 <0.01 220.40 <0.01 166.99 <0.01 68.71 0.62 0

196.11 <0.01 247.42 <0.01 288.91 <0.01 230.21 0.03 139.09 0.03 128.22 0.05 0

157.45 0.01 101.14 0.18 128.48 0.11 142.71 0.13 124.27 <0.01 147.06 <0.01 230.57 <0.01 0

197.72 <0.01 101.37 0.08 143.51 0.03 136.25 0.07 161.38 <0.01 194.04 <0.01 268.56 <0.01 106.48 0.16 0

G. Herzlinger, N. Goren-Inbar / Journal of Human Evolution 128 (2019) 45e58

53

Figure 2. Bivariate plot of the items' scores on principal component (PC) 1 against PC 2. The two first PCs explain some 33% of the morphological across all assemblages. Plus signs (þ) indicate the score of each assemblage's mean shape. Ellipses correspond to 95% confidence interval. Colors denote different assemblages.

Table 5 Frequencies of the directions of blow for blank removals in each assemblage. Layer

II-6/L1 II-6/L2 II-6/L3 II-6/L4 II-6/L4b II-6/L5 II-6/L6 II-6/L7 Total

Direction of Blow

Layer

End-Struck

Side-Struck

Special SideStruck

n

%

n

%

n

%

n

%

1 1 1 15 4 e 1 e 23

9.09 33.33 20.00 23.44 30.77 e 14.29 e 21.30

5 2 1 22 3 1 4 2 40

45.45 66.67 20.00 34.38 23.08 50.00 57.14 66.67 37.04

5 e 3 27 6 1 2 1 45

45.45 e 60.00 42.19 46.15 50.00 28.57 33.33 41.67

11 3 5 64 13 2 7 3 108

100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

Total

Striking Platform Plain

II-6/L1 II-6/L2 II-6/L3 II-6/L4 II-6/L4b II-6/L5 II-6/L6 II-6/L7 Total

Dihedral

Removed

Type of Retouch Flat and Limited

Table 6 Frequencies of striking platform types in each assemblage. Assemblage

Table 7 Frequencies of types of retouch in each assemblage.

Total

n

%

n

%

n

%

n

%

4 1 2 34 6 1 4 e 52

30.77 14.29 50.00 47.89 24.00 25.00 36.36 e 37.41

e 1 e 2 1 e 1 e 5

e 14.29 e 2.82 4.00 e 9.09 e 3.60

9 5 2 35 18 3 6 4 82

69.23 71.43 50.00 49.30 72.00 75.00 54.55 100.00 58.99

13 7 4 71 25 4 11 4 139

100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

II-6/L1 II-6/L2 II-6/L3 II-6/L4 II-6/L4b II-6/L5 II-6/L6 II-6/L7 Total

Thinning

Bifacial

Total

Thinning and Bifacial

n

%

n

%

n

%

n

%

n

%

1 e e 2 2 e 1 e 6

3.03 e e 2.47 6.67 e 8.33 e 3.09

e 3 e 3 3 1 1 2 13

e 18.75 e 3.70 10.00 20.00 8.33 18.18 6.70

27 13 5 58 22 4 8 7 144

81.82 81.25 83.33 71.60 73.33 80.00 66.67 63.64 74.23

5 e 1 18 3 e 2 2 31

15.15 e 16.67 22.22 10.00 e 16.67 18.18 15.98

33 16 6 81 30 5 12 11 194

100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

The morphological homogeneity of handaxes is apparent when the intra- and inter-assemblage variabilities of the GBY assemblages are examined. This trend can be attributed to a constant mental template (Chase, 2008) possessed by the knappers in each of the archaeological levels. Moreover, the inter-assemblage homogeneity indicates that this mental template remained quite similar through generations during the significant time span represented by the complex of Layer II-6. This observation is further highlighted by the close morphological proximity expressed by the mean shapes of bifaces from superimposed levels. An additional indication of the tools' morphological homogeneity comes from the spatial distribution of the variability within the assemblages. As indicated in Figure 1 and in the Supplementary Online Material (SOM), it is apparent that in most levels of the Layer II-6 complex

54

G. Herzlinger, N. Goren-Inbar / Journal of Human Evolution 128 (2019) 45e58

this distribution is fairly similar and that variability is seen mainly around the proximal edges of the tools. While some assemblages, such as Levels 3 and 6, diverge from this pattern, the deviation could be attributed to their very small sample sizes. This pattern suggests a general similarity in planform shape and relative thickness of the tools within and between assemblages, while differences stem mainly from the design of the edges. Such a configuration can be attributed to a general morphological similarity in the selected blanks, while the differences in edge design reflect individual preferences on the part of the knappers in their post-detachment modifications. In contrast, the results of the technological analysis clearly indicate a high degree of within-assemblage variability in the production process of the tools. Although all the GBY assemblages are attributed to the large flake Acheulian technological tradition, it should be noted that even within the tradition's relatively welldefined and strict reduction sequence there is substantial flexibility in specific reduction and modification procedures. These are seen in the different technological attribute states synchronously used in each of the assemblages. In contrast, a substantial technological homogeneity can be observed between the different assemblages, indicating a conservative technological tradition used over-time. Differences in directions of blow, striking platforms and types of retouch suggest that there were several different ways of detaching and modifying blanks into finished tools. Furthermore, even though the sample sizes are very small as a result of the strict selection criteria imposed for the morphometric analysis, the high technological variability is supported by a more comprehensive analysis performed on larger samples from the site and published elsewhere (Madsen and Goren-Inbar, 2004; Goren-Inbar, 2011; Goren-Inbar et al., 2018). This pattern of morpho-technological variability can be used as the basis for discussion of the skill level of the knappers who produced the handaxes. Assuming a constant mental template, the ability to maintain low morphological variability in a tool assemblage is clearly an attribute of expert knappers (Winton, 2005; Nonaka et al., 2010; Herzlinger, 2014). This ability requires both good knowledge of fracture mechanics and familiarity with the reduction sequence. Moreover, it necessitates a high level of technical knowhow, expressed in the motor skills used during the knapping process (Bamforth and Finley, 2008; Bril et al., 2010; Rein et al., 2013). This requirement is even more critical when the endproduct is produced on a challenging type of raw material such as alkali-olivine basalt and in the framework of a highly complex reduction sequence such as that used at GBY (Madsen and GorenInbar, 2004; Goren-Inbar, 2011; Goren-Inbar et al., 2018). Furthermore, this assertion is supported by the technological diversity of the GBY assemblages. The ability to use different production procedures in order to reach morphologically similar end-products can also be viewed as a characteristic of expert knappers, since it can signify procedural flexibility, foresight and planning used in response to unexpected circumstances in the knapping process. Additionally, the technological diversity of another bifacial tool, the cleaver at GBY has demonstrated that their production was governed by “expert cognition” (Herzlinger et al., 2017b). This term refers to a set of cognitive capacities forming the type of thinking that characterizes modern specialists in their various fields of expertise. This cognitive observation further supports the notion ratoire of that the knappers who produced the general chaîne ope bifaces were indeed experts. A high morphological homogeneity is clearly seen in the analyzed experimental assemblage, which was produced by a skilled modern knapper. However, despite the declared intention to mimic the morphology and production technology of the GBY tools and the knapper's great skill, the mean shape of the experimental

assemblage diverges in some aspects from those of the archaeological ones. This is clearly seen in the mean PC2 score of the experimental assemblage (Fig. 2) and in the different spatial distribution of its morphological variability, which is located around the more distal parts of the edges (Fig. 1). While it is true that the experimental assemblage is more homogeneous than most of the GBY assemblages, it should be noted that the former was produced by a single knapper, as opposed to an unknown number of knappers for the latter. This is important, as assemblages produced by a larger number of knappers have been shown to correspond to higher values of morphological variability, at least for limited sample sizes (Herzlinger, 2014). Furthermore, despite the absence of data for the technological variability of the experimental assemblage, personal observations suggest that it was lower (i.e. more homogeneous) than that observed for the GBY assemblage. This fact too may have contributed to the higher morphological homogeneity of the experimental assemblage in relation to the archaeological ones. Additionally, even the least morphologically homogeneous archaeological assemblage (Level 3) is only 13% more variable than the experimental one. Thus, the comparison between the GBY and the experimental assemblages supports the notion that the archaeological assemblages were produced by expert knappers. Last, some ethnographic evidence provides additional support for our interpretation of production by experts. These originate in the seminal ethnographic work concerned with the chaîne ratoire of bifaces (axes and adzes) in the Indonesian Irian Jaya ope trequin and Pe trequin, 1993; Stout et al., 2002). This work de(Pe scribes how the quarrying and roughing-out of basalt (the most difficult of the raw materials used) for the production of prestigious bifaces is conducted by many members of the group, while the transformation of the basalt rough-outs into finished tools is performed only by expert knappers. Despite the many differences between the modern Irian Jaya people and the ancient GBY knappers, such observations may be closely analogous to the production of bifaces at GBY. In conclusion, the morpho-technological patterns of the archaeological assemblages and their comparison with the experimental assemblage and the ethnographic data support the hypothesis that all the GBY assemblages were indeed produced by expert knappers. 4.2. Expert knappers and group size After establishing the presence of expert knappers in each of the archaeological horizons at GBY based on multiple lines of evidence, we can now turn to discussion of the implications of their presence for the social group size. Although the cultural record of the Acheulian Technocomplex has been often considered to present relatively low cultural complexity, persisting for a long period without significant “development” (e.g. Somel et al., 2013), this view has been heavily influenced by both preservation bias and lack of in-depth analyses. The cultural record at GBY provides ample evidence for high cultural complexity, due to the extraordinary preservation and meticulous study of the finds. This complexity is expressed in the varied cultural repertoire reflected in numerous aspects of the archaeological material. Among others, the cultural complexity is reflected in the abundant, varied and systematic exploitation of food resources, both vegetal and faunal, in the systematic and controlled use of fire and in the exploitation of three lithic raw materials in numerous and varied reduction processes for the production of a diversified tool kit (Goren-Inbar et al., 2002a, 2004, 2018; Rabinovich et al., 2008, 2012; Alperson-Afil and Groen-Inbar, 2010; Goren-Inbar, 2011; Melamed et al., 2016). Each of these aspects represents direct evidence for cumulative cultural

G. Herzlinger, N. Goren-Inbar / Journal of Human Evolution 128 (2019) 45e58

traits that were most probably socially learned by the inhabitants of GBY. The existence of expert knappers at GBY contributes an additional tier to the above evidence, providing even stronger support for a high level of cultural complexity. Experts are associated with complex and difficult tasks that cannot be performed by most members of the group. Their expertise, expressed in their products of material culture that are often considered as prestigious objects, contributes additional elements to the cultural repertoire and thus increases the overall cultural complexity of the group (Henrich and Gil-White, 2001; Bell, 2015). Beyond their contribution to cultural complexity, the presence of experts in a group has implications for the group's level of social complexity as well. In comparison with other, non-expert members of the group, the experts possess large amounts of theoretical knowledge and specific motor skills. These in turn are directly dependent on substantial investment of time and energy in learning complex and structured action sequences and gaining experience through practice (Wynn and Coolidge, 2004; Bamforth and Finley, 2008; Mesoudi and O'Brien, 2008; Madsen and Lipo, 2015). These will always occur, at least to some degree, in a social context. Furthermore, the acquisition of a high level of expertise in a complex domain has been suggested to be dependent on the existence of a formal master-apprentice learning context (Stout, 2005; Baforth and Finley, 2008; Olausson, 2008). Such a social context may even point to craft specialization and division of labor, in which an individual dedicates a greater proportion of his time and efforts to his domain of expertise while being at times socially exempt from some of the other tasks performed by different members of the group. Although expertise in a social context is usually associated with later periods of prehistory such as the Upper Paleolithic (Pigeot, 1990; Bleed, 2008), or even the Neolithic (Khalaily et al., 2007), it has been suggested that it could have been established in much earlier times, such as the Lower Paleolithic (Hiscock, 2014; Assaf et al., 2016). Hence, the presence of expert knappers in each of the levels of GBY indicates that they were a part of a culturally and socially complex society. Cultural and social complexity have often been linked to demographic factors such as the size of the social group and the intensity and complexity of the social relationships between its members (Kosse, 1990). These relationships have been described in many theories and models (Carneiro, 1967; Henrich, 2004; Henrich and Boyd, 2008; Pradhan et al., 2012). In general, these theoretical frameworks and models show that in order to maintain high levels of cultural complexity and the social infrastructure to support experts and division of labor, a society must be larger than a critical threshold. When the population size of the social group decreases below the threshold, the intensity and quality of cultural transmission will be negatively affected. This notion is supported by experiments that clearly associate successful performance in complex tasks with a larger number of models from which an individual performer can learn (Derex et al., 2013; Kempe and Mesoudi, 2014; Muthukrishna et al., 2014; for a contradictory view see; Caldwell and Millen, 2010). Reduction in the size of cultural groups, and hence in the number of potential models and teachers, will cause the gradual loss of critical knowledge and skills, which will eventually result in the disappearance of experts. In terms of material culture, such a process will be documented in the disappearance of more elaborate and prestigious objects, those which require high levels of knowledge and skill, and hence in lower cultural complexity. Such reasoning has often been employed in interpretations of various archaeological phenomena (Mithen, 1994; Lycett and von Cramon-Taubadel, 2008).

55

4.3. Group size at GBY Several archaeological horizons at GBY provide direct and strong indications of the presence of a large group of hominins. Among these are Levels 4 and 4b of Layer II-6, which display great abundances of bifacial tools. It should be noticed that the numbers of bifacial tools are in fact higher than those presented in Table 1, since only well-preserved handaxes are included in the analysis presented here. The majority of the bifacial tools are in pristine condition, lacking any indications that they were discarded due to wear resulting from use. In fact, many of the tools do not seem to have ever been utilized. Moreover, the quantitative analysis of the waste products associated with these reduction sequences suggests that, although some of the tools were knapped on site, many others were brought to it as finished tools (Madsen and Goren-Inbar, 2004; Goren-Inbar et al., 2018). Similarly, Level 1 also presents a relatively high number of bifacial tools, albeit in somewhat smaller quantities and density. However, in contrast to Levels 4 and 4b, the bifacial tools of this level may have been used, as they were found in direct association with the skull of a large proboscidean (Palaeoloxodon antiquus) (Goren-Inbar et al., 1994). The skull shows clear damage marks resulting from butchery and other processing activities performed by the hominins, who most probably used bifacial tools alongside other implements. Ethnographic analogies have demonstrated that, although large mammals can be hunted by a few individuals, their subsequent butchery and field processing requires the collaboration of a large group (Janmart, 1952; Duffy, 1960, 1984). Thus, in the light of the varied lines of evidence and taphonomic data, we can safely interpret these particular archaeological horizons as resulting from short and intensive occupations of a large group of hominins engaged in various activities. In contrast, in other levels at GBY there is no equivalent evidence for such large groups in terms of the abundance and density of cultural remains. Archaeological horizons such as Levels 3, 5 and 6 of Layer II-6 are relatively scarce in bifacial tools as well as other anthropogenic remains. This situation naturally prevents an interpretation similar to that of Levels 1, 4 and 4b with respect to group size. This brings up the question of archaeological visibility, which was briefly described in the Introduction. Regarding the question of group size, the discipline of archaeology is limited to what is visible at an excavated locality, usually limited in space, duration and chronological resolution. In the specific case of GBY, each of the horizons consists of a central camp site, or central place (sensu Isaac [1983]), a central locality to which and from which hominins introduced and removed materials and performed various activities (Goren-Inbar et al., 2018). However, one cannot simply equate this type of site with a specific group size, as camp sites probably differed greatly in the number of people they contained at any given time. The mechanism that governs group size dynamics is an aggregation-dispersal one (Lee, 1979). Human populations are always organized in several different hierarchically structured and nested social units or group levels (Gamble, 1998; Zhou et al., 2005; Hamilton et al., 2007). These range from small sized nuclear families or daily foraging bands consisting of a few individuals to the higher lingual and cultural spheres that can comprise thousands of individuals. Hunter-gatherer societies, as well as some species of social mammals, often change their group size at a given time and locality (Aureli et al., 2008). These subgroups periodically aggregate for a time and then split again into lower-level subgroups that disperse across the landscape. This phenomenon is well documented ethnographically (Yellen, 1976; Lee, 1979) and has been also used for interpretation of archaeological sites, albeit in later periods than GBY (Ohel, 1986; Wadley, 1987, 1989; Martin et al., 2010). Although similar models have at times referred to

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ecological factors affecting the periods and durations of aggregation occurrences, they are not the only factor, or even the main factor, in effect. While an appropriate environmental setting is a necessity, social factors may be seen as the prime motive for such occasional aggregations (Lee, 1979). This mechanism can be used to explain the differences between the levels at GBY, of which some show direct evidence for large numbers of people while others do not. Levels with an abundance of bifaces can be seen as evidence for aggregation of several subgroups pertaining to the same larger socio-cultural sphere. In contrast, levels with a small number of bifaces can be interpreted as camp sites, or less populated occupations. Nevertheless, the results of the morpho-technological analysis presented here allow us to see beyond the evidence provided by the frequency of cultural remains in a given locality and a time stratigraphic unit. Following the logic that the bifaces at GBY were made by experts, necessarily members of a large social group, we suggest that even where only a small number of bifaces were recorded they were nevertheless products of experts, who were members of a large social group. These archaeologically invisible social groups must have been large enough, and more importantly their social relations and interconnectedness strong enough, to allow the training of the expert knappers who produced the handaxes. This large, archaeologically invisible group is somewhat analogous to the extended network suggested by Gamble (1998), albeit in the case of GBY it appears to have already be in place, even in rudimentary form, by 780 ka. Hence, we may conclude that the techno-cultural tradition observed throughout the occupational sequence at GBY was consistently produced by expert knappers whose presence necessarily indicates they were part of a large, complex and strongly interconnected social group of hominins. This demographic notion must hold true even in these levels that yielded relatively sparse cultural remains. Acknowledgments This research was made possible thanks to the generous scholarship granted to GH by the Israeli Planning and Budgeting Committee (VATAT) in memory of Nathan Rotenstreich, via the Hebrew University’s PhD honors program at The Jack, Joseph and Morton Mandel School for Advanced Studies in the Humanities. The authors thank Noah Lichtinger for the production of Figure 1a,b and the Computerized Archaeology Laboratory at the Hebrew University of Jerusalem for their assistance in scanning the artifacts and processing the digital models. We are grateful to the Institute for Advanced Studies for their hospitality and for providing us with a home for an intellectual and scientific dialogue. We thank Sue Gorodetsky for editing this manuscript and the reviewers for their valuable and helpful comments. Supplementary Online Material Supplementary online material to this article can be found online at https://doi.org/10.1016/j.jhevol.2018.11.008. References Aiello, L.C., Dunbar, R.I., 1993. Neocortex size, group size, and the evolution of language. Current Anthropology 34, 184e193. Alperson-Afil, N., Goren-Inbar, N., 2010. The Acheulian Site of Gesher Benot Ya'aqov Volume II: Ancient Flames and Controlled Use of Fire. Springer, Dordrecht. Alperson-Afil, N., Sharon, G., Kislev, M., Melamed, Y., Zohar, I., Ashkenazi, S., Rabinovich, R., Biton, R., Werker, E., Hartman, G., 2009. Spatial organization of hominin activities at Gesher Benot Ya'aqov, Israel. Science 326, 1677e1680. Ashkenazi, S., Klass, K., Mienis, H.K., Spiro, B., Abel, R., 2010. Fossil embryos and adult Viviparidae from the EarlyeMiddle Pleistocene of Gesher Benot Ya'aqov, Israel: ecology, longevity and fecundity. Lethaia 43, 116e127.

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