Journal of Evolutionary Psychology, 2011, 1-29 DOI: 10.1556/JEP.9.2011.23.1

“MOST BEAUTIFUL AND MOST WONDERFUL”: THOSE ENDLESS STONE TOOL FORMS STEPHEN J. LYCETT * Department of Anthropology, University of Kent Abstract. In recent years, an increasing range of scientists from the fields of psychology, anthropology and archaeology are recognising the value of utilising Darwinian theory to study cultural transmission and evolution. Such an approach is based on recognition that culture involves a mode of inheritance (social transmission), variation of practice, and the differential representation of particular variants in subsequent generations due to a variety of sorting mechanisms. In other words, culture evolves via a process of “descent with modification”. Two immediate analytical implications arise from this. The first of these is that ‘population thinking’ must be applied to the study of cultural evolution; the second is that understanding the historical process of lineage decent and diversification (i.e. phylogeny) becomes an imperative research goal. Methodologies and principles designed to address these issues in biology can profitably be used to address such questions in cultural data. Here, case studies of Palaeolithic stone tools are used to demonstrate how these principles and methodological approaches may be applied to some of these early artefactual products of the human lineage. Such methods are shedding new light on this “most beautiful and most wonderful” of legacies left to us by our fossil relatives and ancestors. Keywords: cultural evolution, social transmission, Darwin, descent with modification, stone tools, handaxes, Acheulean

1. CULTURE AS A PRODUCT OF “DESCENT WITH MODIFICATION” In The Origin of Species, DARWIN (1859: 459) famously described biological evolution as a process of “descent with modification”. Over the last few years, an increasing number of workers from fields such as archaeology, anthropology, psychology and biology have been arguing that human cultural variation and change may also effectively be characterised as a product of descent with modification (e.g. EERKENS and LIPO 2007; LYCETT 2009a; MESOUDI, WHITEN and LALAND 2004; O’BRIEN and LYMAN 2000; SHENNAN 2000). Indeed, the comparability of biological descent with modification and cultural descent with modification was recognised by Darwin himself, who compared the process of language change to that of change in the natural world when first describing this process (DARWIN 1859: 422). As DARWIN (1859) outlined, and many have commented on since, the process of descent with modification is comprised of three key ingredients (Figure 1). The *

Address for correspondence: STEPHEN J. LYCETT, Department of Anthropology, University of Kent, Canterbury, Kent, CT2 7NR, UK, Tel: +44 (0) 1227 827739; E-mail: [email protected] 1789-2082 © 2011 Akadémiai Kiadó, Budapest

Lycett, S.J. (2011). "Most beautiful and most wonderful": those endless stone tool forms. Journal of Evolutionary Psychology 9 (2): 143-171.

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first essential element is that variation must exist and that new variation may be generated, the second is that such variation has the potential to be inherited by subsequent generations, and the third is that not all variants are inherited uniformly across time. Beyond the simultaneous occurrence of these three elements, there is no stipulation as to exactly how these should occur (e.g. inheritance need not necessarily be limited to genetic inheritance). Yet when all these elements are present, evolution (i.e. ‘descent with modification’) must occur. MESOUDI, WHITEN and LALAND (2004) compellingly laid out the case that human cultures can be seen to possess variation, that many cultural variants are transmitted (i.e. inherited) between individuals via social learning in the form of traditions, and that not all cultural variants are transmitted to an equal extent. MESOUDI et al. (2004), as with several other commentators on cultural evolution, use the term of “selection” to describe the differential representation of cultural variation across time and space. While this term is more in keeping with DARWIN’s (1859) original terminology to describe the process of descent with modification, it may be useful to adopt GOULD’s (2002: 659) term of “sorting”. This is especially the case with regard to cultural evolution, since this is a more inclusive term and emphasises that the differential representation of transmitted elements may occur via a variety of processes such as natural selection, artificial (i.e. human directed) selection, and/or drift (i.e. chance) without assuming the priority of any one mechanism of variant sorting a priori (Figure 1). When described in these terms, the phrase ‘cultural evolution’ does not merely represent an analogy to, or metaphor for, biological descent with modification, but describes a genuine evolutionary process mediated by variation, inheritance and sorting. It is not, however, only humans that possess multiple behavioural variants that are transmitted socially and differ between groups such that they may be subject to sorting through time. Our closest living relatives, the chimpanzees (genus Pan), also display behavioural patterns comprised of tool-use, courtship, grooming and communication behaviours that differ inter-communally (WHITEN et al. 1999; HOHMANN and FRUTH 2003; MCGREW 2004). A growing body of evidence from studies in both the wild and captivity are demonstrating that such cross-community variation is the product of social transmission, just as human cultures are (BIRO 2006; HORNER et al. 2006; LYCETT, COLLARD and MCGREW 2007, 2009; MCGREW 2004; WHITEN et al. 2007). Given this situation, LYCETT (2010) has suggested that ‘culture’ itself, which has often proved to be a difficult phenomenon to define (see e.g. MCGREW 2004 for review), may usefully be characterised as an emergent property of the descent with modification process mediated by the combination of variation, social learning and sorting, in both the case of humans and chimpanzees. Moreover, recognition that our closest living relatives possess a cultural evolutionary system that operates via the same basic mechanisms as our own suggests, on the grounds of parsimony, that our extinct fossil hominin relatives and ancestors also had a cultural evolutionary history that extended back to the divergence of the chimpanzee and human lineages. JEP 9(2011)2

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Cultural evolution – “descent with modification”

• Variation in socially transmitted elements

• Inheritance via social learning

• Sorting of variation in subsequent generations (e.g. due to natural selection, cultural selection and/or drift) Figure 1. Culture is a genuine evolutionary phenomenon (i.e. is a product of ‘descent with modification’) involving the parameters of variation, inheritance and the differential representation of given variants across time

DARWIN’s (1859) characterisation of evolution as ‘descent with modification’ has two immediate analytical outcomes if it is to be used as a framework for understanding cultural evolution. The first of these is that ‘population thinking’ must be applied to the study of cultural phenomena; the second is that understanding the historical process of lineage decent and diversification (i.e. phylogeny) becomes an imperative research goal. Below, I aim to demonstrate how principles and methodologies, developed to address these analytical implications within evolutionary biology, may usefully be applied to the study of Palaeolithic stone tools manufactured by some of our extinct fossil hominin relatives deep in prehistory.

2. POPULATION THINKING: OPERATIONAL TAXONOMY, NOT TYPES It is well known that DARWIN (1859: 51) – in contrast to previous generations who had considered the question of biological taxonomic diversity – placed great emphasis on the variation between individuals. In turn, this led to the replacement of JEP 9(2011)2

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what MAYR (1976) called ‘typological thinking’ with ‘population thinking’ within biology. As MAYR (1976) outlined, prior to Darwin the issue of taxonomic diversity was characterized by the concept of Platonian ‘essences’. Hence, taxa were thought to represent discrete ‘types’, whereby individual variation was simply noise around an ‘ideal’ type. Following Darwin, it increasingly came to be realized that individual variation within animate and dynamic populations (as opposed to inanimate and fixed ‘ideal’ types) was actually the very key to understanding the issue of taxonomic diversity via the process of descent with modification. DARWIN (1859: 485) was also clear on the point that within such a dynamic system, taxa of any level “are merely artificial combinations made for convenience”. Under this framework, taxonomic units consist of individuals that exhibit variation in a set of attributes that may ‘peak’ toward certain tendencies (especially phenotypically), giving an artificial impression of absolute discreteness. However, taxa so defined will also frequently exhibit overlap in the form of these attributes with other taxonomic units, which happen to peak toward alternative tendencies when examined multivariately. The extent of such overlap in each attribute shifts through both space and time as a direct outcome of the dynamic process of descent with modification. Within this framework taxa thus become units defined for pragmatic purposes when faced with a particular evolutionary question (ERESHEFSKY 2011). It is due to these factors that in contemporary evolutionary work the concept of ‘Operational Taxonomic Units’ (OTUs) has risen to prominence. The advantage of such a concept is that it minimizes the amount of a priori assumptions that are required and does not presuppose rankings or interrelationships between populations (GROVES 2001: 7). What the forgoing should illustrate is that if the concept of descent with modification is to be fully incorporated into the study of culture patterning and change, then population thinking and its attendant considerations must be fully assimilated. This is no less the case when studying material culture (i.e. artefacts) as it is for any other aspect of cultural evolution (O’BRIEN and LYMAN 2000). Yet, as discussed thoroughly by O’BRIEN and LYMAN (2000) and emphasised again more recently by RIEDE (2010), there is a long history of typological thinking within archaeology, a factor which may be partly responsible for hindering the successful incorporation of evolutionary thinking into the field.

2.1 Population genetic models and Palaeolithic stone tools As a result of the modern synthesis, population thinking eventually gave rise to the field of population genetics – the quantitative and statistical analysis of genetic variation in the light of mutation, selection, drift and migration (HALLIBURTON 2004). Confusion regarding the extent to which processes of cultural transmission and evolution are both similar and different those of biological transmission and evolution has been widespread (MESOUDI 2007). As noted previously, all that is reJEP 9(2011)2

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quired for a system of descent with modification to be operational is variation, inheritance, and sorting. Hence, in the case of cultural evolution, variation need not be the product of genetic mutation but can be the product of factors such as copying errors, deliberate tampering (i.e. innovation), or differing skill levels across individuals (BETTINGER and EERKENS 1999; EERKENS and LIPO 2005; LYCETT 2008; HAMILTON and BUCHANAN 2009; ROUX 2010). Likewise, transmission in cultural evolution will be the product of social interaction involving mechanisms such as imitation, emulation, stimulus-enhancement or direct teaching (see BYRNE 1995 for a review of various learning mechanisms). As such, transmission of cultural variation is not necessarily limited to transmission between parents and offspring, but may in principle take place between people regardless of their biological relationship. This latter distinction has arguably been one of the most confusing factors in understanding both the parallels and distinctions between biological and cultural evolutionary processes (MESOUDI 2007). However, as a result of characterising cultural evolution as a process of descent with modification, there has been increased recognition that at a statistical level, many of the factors known to structure population variation in genetic data (e.g. population size, drift, dispersal, etc.) must also be considered when addressing questions concerning cultural variation (e.g. BENTLEY, HAHN and SHENNAN 2004; LYCETT 2008; MESOUDI and LYCETT 2009; NEIMAN 1995; ROGERS, FELDMAN and EHRLICH 2009; SHENNAN 2000, 2001, 2006). The simplest form of manufactured Palaeolithic stone tools begin to appear in the archaeological record of Africa from at least 2.6 million years ago (SEMAW et al. 2003). Over the course of subsequent human evolution, stone tools appear in every region of the world that hominins are known to have inhabited. The manufacture of Palaeolithic stone tools involves using one stone (a ‘hammerstone’) to knock flakes from another stone (a ‘core’) in a process termed ‘knapping’. Suitable stone for this purpose must possess a combination of being both hard enough to provide functional tools, yet suitably brittle, elastic and homogeneous to allow the outcome of a single instance of flaking to be predictable within certain boundaries (WHITTAKER 1994). Tools produced in this manner may consist of the sharp flakes removed from the core, or alternatively a sharp edge on the ‘core’ (produced though the flaking action) may itself ultimately be used as the tool. Stone knapping patterns obviously vary depending on the artefact that is being manufactured. However, even within a range of artefacts that clearly have elements in common, variation can be seen to exist (e.g. Figure 2). Differences in the physical properties of the quality of stone can certainly account for some of this variation (GOODMAN 1944), as can factors such as the extent to which a tool may have been used and resharpened (MCPHERRON 2003). The making of stone tools, however, is a noisy activity that takes place in situations where it is frequently observed by others such that elements of the manufacturing process can be transmitted socially (STOUT 2005) just as many aspects of chimpanzee tool use appear to be (LYCETT, COLLARD and MCGREW 2010; MCGREW 2010). Hence, another inevitable source

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of variation – both within and between different populations – is differences in the details of manufacture.

Figure 2. An example of plan form variation in Acheulean handaxes. Variation both within and between sets of artefacts from different sites may be high such that it will overlap in range between different localities, although patterns of variation may still be statistically distinguishable when analysed in a multivariate framework (see e.g. LYCETT and GOWLETT 2008)

The procedure for making stone tools involves multiple steps, and although the average number of steps required varies depending on the particular tool being made, each step has the potential to vary in specifics of form either in subtle or notso-subtle ways. Thus, for example, in one population there may be a tendency for knappers to turn the core in a certain way after a certain number of blows, while in another population this turning may be done in a slightly different manner following a different number of blows. Likewise, the point at which the hammerstone strikes the core may be manipulated in slightly different ways. In many cases steps may be taken to help ensure that a flake is removed with greater likelihood of what the knapper intends, or what PATTEN (2005: 54) refers to as “process controls”. This might involve, for example, abrading the edge of the core with another stone such that when it is struck, the force of the blow is focused more directly through the core rather than energy being lost through crushing of the core’s edge (WHITTAKER 1993: 98–104). Whether an individual knapper is directly cognisant of these variations (and/or all their material outcomes) or not, any such variation introduced into this process may lead to differences ultimately seen in the specific atJEP 9(2011)2

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tributes of stone artefacts. Sometimes these differences may be readily apparent, while at others, any such patterning in the data may only be visible as a result of multivariate statistical analysis of quantitative variables (see e.g. LYCETT and GOWLETT 2008), as can be expected within a population thinking framework. As such, the cultural variants that comprise a cultural evolutionary system need not necessarily be used as ‘cultural’ markers (i.e. signals of group identity) or even in a strict (i.e. direct) sense be ‘transmitted’ from individual to individual. Rather they merely require a proximate basis in the ideas, thoughts, skills, and behavioural practices that are transmitted between individuals within a social context via one or more of the various means of social learning. Population genetic models are one of the earliest examples of contemporary biological methods that were suggested as being suitable for studying artefactual variation and cultural evolution in general (CAVALLI-SFORZA and FELDMAN 1973, 1981; BOYD and RICHERSON 1985). Given the forgoing, it is perhaps unsurprising that in recent years formal population genetic models have also begun to be applied to the study of stone tools. Principles of population genetics have been used to examine issues of drift and selection in the attributes of stone artefacts (e.g. LYCETT 2008; LYMAN, VANPOOL and O’BRIEN 2008) as well as to study the effects of population demography (HAMILTON and BUCHANAN 2009; LYCETT and VON CRAMON-TAUBADEL 2008). One such model is the so-called ‘serial founder effect model’, which may be used to study population dispersal (LYCETT and VON CRAMON-TAUBADEL 2008). The serial founder effect model operates on the logic that as populations disperse over long distances, the effective population size (i.e. the number of reproductive members of a population) will become somewhat reduced in size with each episode of dispersal (Figure 3). Since each dispersal episode effectively constitutes an instance of genetic bottlenecking, the model therefore predicts a sequential (i.e. ‘serial’ or ‘iterative’) reduction of within-population genetic variance (heterozygosity) with increased geographic distance from the original point of origin. Hence, the model may be assumed to be supported if a statistically significant inverse relationship between within-population variance and geographic distance from a hypothesised point of origin is found. Several genetic studies have demonstrated this effect in the case of Late Pleistocene human dispersals from Africa (e.g. LI et al. 2008; MANICA et al. 2007; PRUGNOLLE et al. 2005; RAMACHANDRAN et al. 2005). Importantly, such a relationship has also been shown in patterns of variation in globallydistributed samples of human crania, demonstrating that the effects of dispersal are also detectable at the (ultimate) phenotypic level even if examined in the absence of (proximate) genetic data (MANICA et al. 2007; VON CRAMON-TAUBADEL and LYCETT 2008). It is also instructive to note that the effect of human dispersal from Africa is also detectable in global patterns of genetic variation seen in human stomach bacteria (Helicobacter pylori) (LINZ et al. 2007). This demonstrates that as human populations carried these bacteria out of Africa in their stomachs, they had an effect on the patterns of variation within another descent with modification system, the inJEP 9(2011)2

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Within-population diversity

ternal dynamics of which are somewhat separate from that of their own genetic system.

Increased geographic distance from point of origin Figure 3. The serial (or iterative) founder effect model can be used to detect instances of population dispersal. The model can be seen to be supported if a statistically significant inverse relationship is found between patterns of within-group variance and increased geographic distance from hypothesised origin of dispersal

LYCETT and VON CRAMON-TAUBADEL (2008) used this model to investigate the dispersal of hominins from Africa that made a particular form of stone tool known as ‘Acheulean handaxes’ (Figure 2). Such artefacts come in a variety of shapes and sizes, but are frequently described as being ‘triangular’, teardrop’ or ‘ovate’ in shape. They are formed by a process of bifacial knapping (i.e. flakes are removed from both sides), whereupon flakes are driven invasively into a block of stone consisting of either a large cobble or large flake blank (GOWLETT 2006). This basic knapping procedure tends to result in the final form displaying an element of bilaterality tending toward symmetry, although the extent of this ‘symmetry’ varies widely in space and time (WYNN 2002). The earliest examples of these artefacts are found in eastern and southern regions of Africa and date from ≤ 1.7–1.6 million years (ASFAW et al. 1992). By at least 500 thousand years ago, classic Acheulean handaxe forms occur at sites in Africa, the Near East, the Indian subcontinent, as well as southern and western Europe (KLEIN 2009). As a result of the fact that Acheulean handaxes occur first in Africa, it had long hypothesised that their subsequent appearance in other areas of the Old World JEP 9(2011)2

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was the result of dispersal by hominin populations of African origin (BAR YOSEF and BELFER-COHEN 2001; GOREN-INBAR et al. 2000; KLEIN 2005). While this hypothesis is broadly congruent with the available dating evidence, it had, until recently, not been subject to independent testing. As LYCETT and VON CRAMONTAUBADEL (2008) outlined, within a population and cultural transmission framework for Acheulean handaxes, the serial founder effect model would predict a statistically significant inverse relationship between within-assemblage variance and increased geographic distance from Africa. In order to test this prediction they utilised samples of handaxes (n = 255) taken from 10 Acheulean sites in East Africa, the Near East, northern Europe and the Indian subcontinent. Mean withinassemblage variance was computed from 48 size-adjusted plan-form (shape) measurements taken on each handaxe. Two sets of geographic distances were used in their analyses. The first set of distances simply comprised ‘as-the-crow-flies’ distances between the East African Acheulean locality of Olduvai Gorge (Tanzania) and each of the other Acheulean localities in their sample. This set of distances thus provides only a rather crude estimate of the geographic distances covered in any hypothetical long-term dispersal of African populations, since it does not take into account the unrealistic crossing of large oceans as might be implied by such distances. Hence, a second set of distances was calculated using a minimum-spanning network linking all Acheulean localities and two additional ‘waypoints’ (Cairo, Egypt and Istanbul, Turkey), which effectively ‘tethered’ the projected distances to estimates that might more reasonably be expected under the parameters of a landbased scenario of population dispersal(s) from Africa. As such, it might be predicted that these latter geographic distances show a stronger relationship with mean assemblage variances than do the crude ‘as-the-crow-flies’ distances. These predictions were tested using ordinary least-squares regression (α ≤ 0.05), whereupon in each case the independent variable of mean within-assemblage variance was regressed on the dependent variable of geographic distance from East Africa. Using this approach, LYCETT and VON CRAMON-TAUBADEL (2008) found statistically significant support for the African origin and dispersal of Acheulean populations. Consistent with the predictions derived from the serial founder effect model, a significant (p = 0.033) inverse relationship between the as-the-crow-flies geographic distances and mean within-assemblage handaxe shape variance was shown, with around 45% of such variability explicable by geographic distance (r2 = 0.452). Importantly, the results based on the minimum-spanning network were also significant (p = 0.023) with around 50% of variance being explained by geographic distance from East Africa (r2 = 0.50). Hence, the reasonably more realistic estimates for geographic distances involved in dispersal(s) from Africa showed an increase in fit to the model, as might be expected if the general assumptions underlying the model are to be supported. An alternative set of analyses undertaken by these authors using non-African start points failed to produce statistically significant correlations, either positive or negative. These latter analyses are important since they suggest the results of their initial tests are the product of genuine geographic paJEP 9(2011)2

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rameters (i.e. an African origin). Likewise, they also discussed how raw material factors would not seem to explain clearly the patterns of within-assemblage variance observed, and demonstrated that there was no statistical relationship between sample size and within-assemblage variance. Hence, their analyses provided strong support for the African Acheulean dispersal hypothesis. It should be noted that building a firm understanding of the pattern of hominin dispersals is not a trivial issue. Indeed, reconstruction of hominin movements is a crucial part in helping to understand the general pattern of human evolution and for assessing particular evolutionary scenarios (e.g. FINLAYSON 2005; HUBLIN 2009). As such, the use of population genetic models in this manner is not simply a means of studying stone tools for their own sake, but helps contribute to the wider study of human evolution in a more comprehensive manner.

3. THE PHYLOGENETICS OF PALAEOLITHIC STONE TOOLS Although many of Darwin’s written works were extensively illustrated (see e.g. DARWIN 1868, 1871), the 490 pages of Origin contained just a single illustration, and that diagram was a tree (Figure 4). In chapter 13 of Origin, Darwin outlined how a clear understanding of taxonomic diversity would no longer be achieved merely through the description and classification of evolving entities into groups, but rather needed to take into account the history of lineage descent and divergence of those groups and their characteristics, as caused by descent with modification. In IX VIII VII VI V IV III II I

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Figure 4. Darwin’s Origin of Species contained just a single diagram. The diagram illustrated the process of lineage formation and taxonomic divergence produced by descent with modification of characteristics exhibited by populations (Redrawn and modified from DARWIN 1859)

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other words, Darwin realised that as a direct consequence of the process he termed ‘descent with modification’, an understanding of the relationships of evolving entities would become an important research objective for anyone involved in their study. Referring to his own diagram, DARWIN (1859: 431) wrote: “As it is difficult to show the blood relationship between the numerous kindred of any ancient and noble family, even with the aid of a genealogical tree, and almost impossible to do this without this aid, we can understand the extraordinary difficulty which naturalists have experienced in describing, without the aid of a diagram, the various affinities which they perceive between the many living and extinct members of the same great natural class.” Of course, today the study of ‘phylogeny’ is an essential part of evolutionary biology (RIDLEY 2004). Coinciding with the ‘cladistic revolution’ that occurred within evolutionary biology during the latter decades of the 20th century (GEE 2000), suggestions began to be aired that modern phylogenetic concepts might also have something to offer the study of human cultural phenomena (e.g. FOLEY 1987; PLATNICK and CAMERON 1977). However, due to a growing recognition that culture can be characterised as a product of descent with modification mediated by social transmission, and following a seminal paper by O’BRIEN, LYMAN and DARWENT (2001), there has over the last decade been an appreciable rise in the application of formal biological methods to address comparable phylogenetic problems in the study of material culture (e.g. BUCHANAN and COLLARD 2007, 2008; COLLARD, SHENNAN and TEHRANI 2006; GREENHILL, CURRIE and GRAY 2009; HARMON et al. 2006; JORDAN and SHENNAN 2003; LYCETT 2007, 2009a; LYCETT, COLLARD and MCGREW 2010; ROGERS 2009; TEHRANI and COLLARD 2002, 2009). Within evolutionary biology, cladistics is a commonly used method of phylogenetic reconstruction typically applied to genetic and phenotypic data in order to determine the evolutionary relationships of living and fossil taxa (e.g. ARGUE et al. 2009; GILBERT and ROSSIE 2007; LIU, RUBIDGE and LI 2010; SPERLING et al. 2009; TODD 2010). Subsequently, cladistics has also become a tool within archaeology to investigate the historical dimensions of descent with modification in artefactual data (O’BRIEN and LYMAN 2003). Cladistic analysis is based on the parsimonious null model of taxonomic bifurcation and character evolution. Hence, BROWER (2000: 13) succinctly describes it as a “method of grouping by parsimonious patterns of shared character state change”. The method is, however, notorious for its association with abstruse terminology, which is particularly unfortunate when wishing to apply the method outside of its more typical arena of usage (see Table 1 for definitions of key terms). Fortunately, in recent years, several accessible introductions to the principles and terminology of cladistics have become available (e.g. KITCHING et al. 1998; MCLENNAN and BROOKS 2001), including some written specifically for disciplines outside the more typical sphere of application (e.g. O’BRIEN and LYMAN 2003). It has also been noted that despite the use of rather complex computer algoJEP 9(2011)2

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rithms to determine the most parsimonious cladograms, the method can be broken down into a small series of fundamental methodological steps (MCLENNAN and BROOKS 2001). The first step in any cladistic analysis is to delineate the Operational Taxonomic Units (OTUs) (i.e. identify those units that one wishes to understand the structure of relationships between). As noted earlier, this is a question-driven process. The second stage is to generate a character state matrix describing the character states for each OTU. Next, the direction of evolutionary change (‘character polarity’ in cladistic terminology) is determined, most commonly via comparison with an ‘outgroup’ (Table 1). Thereafter, a branching diagram or tree (i.e. cladogram) is constructed that describes the relationships between OTUs for each character. Finally, in accordance with the principle of parsimony, an ensemble cladogram is constructed that is consistent with the largest number of character trees and also, therefore, requires the least number of ad hoc (non-parsimonious) character state changes in order to explain the phylogenetic relationships between the various OTUs. It is due to this application of parsimonious reasoning that cladograms are frequently referred to as Maximum Parsimony (MP) trees. Table 1. Cladistic terminology – Key definitions Cladistic Term

Definition

1. Operational Taxonomic Units (OTUs)

The basic taxonomic units used in the analysis (i.e. the units for which an understanding of relationship is required). Characters are attributes that describe specific properties or ‘features’ of the OTUs. These are sometimes qualitative in form (e.g., a particular feature may be ‘present’ or ‘absent’) or they may be comprised of quantitative (e.g. morphometric) data. A ‘character state’ is the particular form of character possessed by an individual OTU (e.g. the feature is either ‘absent’ or ‘present’ in that particular OTU). Character states may also describe particular shape forms in OTUs such as whether a particular feature is ‘flat’, ‘concave’, ‘convex’, etc. An outgroup is a taxon known to be closely related to the other taxa in the analysis (the ‘ingroup’), but one that can confidently be assumed to have diverged from those taxa at an earlier phylogenetic point than the ingroup taxa diverged from each other. The outgroup is used for comparative purposes in order to determine the direction of evolutionary (character state) changes in a tree. A group of taxonomic units comprising their common ancestor and all of its descendents. Such groups are said to be ‘monophyletic’. Nodes are the junctions (joints) of branches in a tree diagram (or ‘cladogram’) drawn to represent the hypothesized evolutionary relationships of taxonomic units.

2. Character

3. Character state

4. Outgroup

5. Clade

6. Node

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Cladistic Term

Definition

7. Synapomorphies

Synapomorphies are character states that are uniquely shared between two or more closely related species comprising a clade. They are said to be ‘derived’ (or ‘shared-derived’) relative to plesiomorphies. The presence of synapomorphies is particularly important in determining which taxonomic units are most closely related (i.e. deciding which units should be linked together to form a clade).

8. Plesiomorphies

Plesiomorphies are the particular character state(s) that are seen in the taxonomic units that form the lowest branches of a cladogram (tree) closer to the outgroup. Crudely, plesiomorphies are sometimes referred to as ‘primitive’ character states, but it should be emphasized that no specific judgmental connotations in terms of ‘quality’ or ‘value’ necessarily accompany this term.

9. Symplesiomorphies

Symplesiomorphies are ‘primitive’ character states (see Plesiomorphies) shared by two or more taxonomic units.

10. Autapomorphic

An autapomorphic feature is a character state uniquely possessed by only one taxonomic unit. In being ‘unique’ in this sense, autapomorphic features are not useful in determining evolutionary relationships.

11. Homologous

An homologous feature refers to a character state shared between two or more taxonomic units as a result of descent from a common ancestor (compare with homoplasy).

12. Homoplasy (pl. Homoplasies)

Homoplasy is the presence of the same character state in two or more taxa that are not closely related. Instances of homoplasy may occur by processes of convergent or parallel evolution, or by character state reversal.

13. Tree length (TL)

The number of evolutionary changes (or steps) required by the tree to explain the distribution of character states among the taxa.

14. Monophyletic

A monophyletic group (or ‘clade’) is a group of taxa, closely related by means of descent from a common ancestor.

Recently, LYCETT (2009b) applied the cladistic methodology to Acheulean handaxes in order to provide a further test of the African Acheulean dispersal hypothesis. It was noted that phylogenetic studies of human genetic data, not only show a strong fit to the serial founder effect model, but also display a phylogeographic pattern, with African populations falling close to the root and nonAfrican populations being further from the root as might be expected given the African ancestry of all non-African populations (e.g. LI et al. 2008). As such, an additional prediction of the African Acheulean dispersal hypothesis is that we might JEP 9(2011)2

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African Handaxes

Eurasian Handaxes

Figure 5. Cladogram produced by cladistic analysis of Acheulean handaxes. The OTUs from different regions form a phylogeographic pattern consistent with a pattern of dispersals from Africa of handaxe producing populations

reasonably expect a strong African versus non-African phylogeographic pattern in Acheulean handaxe datasets. Using standard cladistic procedures, LYCETT (2009b) did indeed find such a phylogeographic pattern to African and non-African handaxe datasets (Figure 5). The tree was also shown to be statistically different from a tree linking the same OTUs based on their raw material properties. As such, the cladistic analysis was consistent with the hypothesis that the appearance of such technologies in areas such as India and Europe was the result of dispersal by populations of African origin.

3.1 Convergence in cultural technologies: a case study using stone artefacts DARWIN (1859) was well aware of the problems involved in correctly reconstructing the phylogenetic relationships of evolving units due to the occurrence of misleading similarities brought about by the process of convergence. For example, in Origin he wrote: “two most distinct lines of descent, may readily become adapted to JEP 9(2011)2

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similar conditions, and thus assume a close external resemblance; but such resemblances will not reveal – will rather tend to conceal their blood-relationship to their proper lines of descent” (DARWIN 1859: 427). Interestingly, in order to illustrate the principle of convergence via descent with modification, Darwin also drew on the example of convergence within the realm of human technology. He thus wrote that: “in nearly the same way as two men have sometimes independently hit on the very same invention, so natural selection … has sometimes modified in very nearly the same manner two parts in two organic beings, which owe but little of their structure in common to inheritance from the same ancestor” (1859: 193–194). What is ironic here, is that while Darwin readily drew on an example of convergence in human culture in order to illustrate this general biological principle to his Victorian audience, drawing such comparison in reverse today sometimes meets with great resistance (e.g. INGOLD 2007). Indeed, within archaeology itself, recognition that artefactual products can be subject to convergence has sometimes been seen as a valid reason to reject phylogenetic principles and cladistic methods (see O’BRIEN and LYMAN 2003 for a review) rather than to justify their application. The lesson from Origin, therefore, is that if we are to understand correctly the relationships between cultural entities (and to distinguish correctly between similarities brought about by both convergence and descent) then we must embrace phylogenetic principles, not reject them. A recent case study applied to stone tools (LYCETT 2009a) illustrates how particular questions relating to the issue of technological convergence might usefully be addressed via the application of modern phylogenetic methods borrowed from evolutionary biology. Around 300–250 thousand years ago a new set of stone artefacts begins to appear more regularly in the archaeological record (DEINO and MCBREARTY 2002; TRYON 2006). These artefacts are termed ‘Levallois’ and consist of cores and flakes, the latter of which appear to be somewhat ‘predetermined’ in terms of their overall size and shape by preceding stages of flaking (Figure 6). In terms of general sequence, replication and refitting studies have shown that the initial stage of Levallois core and flake production consists of removing a series of flakes from around the edge of the core, followed by the removal of flakes from the core’s upper surface, which imposes both a distal and lateral convexity on that surface (BOËDA 1995; EREN and BRADLEY 2009; VAN PEER 1992). Thereafter, the end of the core is struck removing flakes that partly reflect the dimensions and shape of the ‘prepared’ flaking surface from which they are removed (Figure 6). Since their initial discovery in a suburb of Paris (Levallois-Perret) during the late 19th century, the origins of Levallois cores and the significance of their appearance has traditionally been a subject of major debate within Palaeolithic archaeology (see e.g. DIBBLE and BAR-YOSEF 1995 and papers therein). Their appearance is often seen as a mark of the transition from the Lower Palaeolithic to the Middle Palaeolithic (Middle Stone Age), although at least in Africa, the appearance of Levallois appears to overlap with the production of Lower Palaeolithic artefacts such as handaxes (TRYON and MCBREARTY 2002). JEP 9(2011)2

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Early in the 20th century, a series of cores close to the town of Victoria West in South Africa (Karoo region) were discovered by the then local magistrate F.J. Jansen who later wrote a short paper reporting their discovery (JANSEN 1926). Subsequently, the term ‘Victoria West’ has been applied to similar cores from sites in central South Africa, especially along the Vaal River (CLARK 2001; GOODWIN 1934; ROLLAND 1995; SHARON and BEAUMONT 2006). Given that these appeared to have been used to manufacture flake blanks for handaxe and cleaver production alongside which they have been discovered, these cores were – and still are – assigned to the Lower Palaeolithic, even though the dates of assemblages described as ‘Victoria West’ are still imprecise (GOODWIN 1934; LEAKEY 1936; KUMAN 2001; MCNABB 2001; SHARON 2007; VAN RIET LOWE 1945). From their initial discovery, similarities between ‘Victoria West’ cores and Middle Palaeolithic/MSA Levallois cores (Figure 7) were the subject of attention (CLARK 1959: 125; GOODWIN 1934; VAN RIET LOWE 1929). As GOODWIN (1934: 120) put it, Victoria West cores appear to show the “preparation of upper-face and the removal of a large flake from the upper surface”. The comparability with Levallois was perhaps put most candidly by VAN RIET LOWE (1929: 389) who suggested that in the Victoria West “we have revealed to us a technique not unlike a magnified and slightly distorted Levallois of Europe”. Similarities with Levallois were not, however, the only comparisons made, and general similarities with Acheulean handaxe forms were also noted. For instance, CLARK (1959: 125) described how the production of Victoria West cores appeared to proceed “by roughing out from a small boulder what at first sight appears to be a crude handaxe with one face much flatter than the other side”. Likewise, LEAKEY (1936: 85) suggested that unstruck Victoria West cores in particular had “more than a resemblance” to large handaxes.

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Figure 6. Levallois production. Distal and lateral convexities (A and B) allow some predetermination of flake form. A strong blow to one end of the core (C) results in the removal of a flake or flakes predetermined by the patterning of flake scars on the core’s upper surface (D and E) (Redrawn and modified after BORDES [1968] and SCHLANGER [1994])

Following a visit to South Africa, the distinguished French prehistorian Abbé Breuil proposed that because Victoria West cores were generally associated with Acheulean material, they should be considered the morphological and technological ancestor of later Levallois core forms (BREUIL 1930: 215). Subsequently the term JEP 9(2011)2

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‘proto-Levallois’ was adopted by several prominent archaeologists to refer to Victoria West cores (e.g. CLARK 1959: 126; OAKLEY 1958: 51; VAN RIET LOWE 1945). This scenario was developed most elaborately by VAN RIET LOWE (1945: 57–58), who outlined explicitly a unilinear scheme going from Victoria West ‘protoLevallois’ cores, up through African examples of Levallois, up to “comparable European forms”.

Figure 7. Upper (left) and lower (right) views of the surfaces of Victoria West cores (Redrawn and modified after GOODWIN [1929])

Despite all this, an early word of caution came from LEAKEY (1936: 85) who noted that: “Where the ‘Victoria West’ technique was employed to obtain the flakes which were made into hand-axes and cleavers, there was definitely a resemJEP 9(2011)2

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blance to the Levalloisian technique. That is to say, a core was very carefully prepared before the required flake was detached, and the flake shows a prepared or facetted platform. The question is whether this was a case of parallel evolution or whether the techniques are more closely related.” In other words, LEAKEY (1936) highlighted exactly the same general nature of problem that DARWIN (1959) had earlier drawn attention to: similarity is undoubtedly evident, but is the similarity due to a direct ancestor–descendant relationship or is convergence at work? In modern terminology, the question might be rephrased as whether is it more parsimonious to assume that the similarities are ‘homologous’ or ‘homoplastic’ (Table 1). It is exactly this question that cladistic procedure, via the application of parsimony, is designed to address (MCLENNAN and BROOKS 2001; RICHTER 2005). To this end, LYCETT (2009a) employed a cladistic approach to test directly whether similarities in Levallois cores and Victoria West cores are – most parsimoniously – the result of ancestor–descendant relationship versus convergence. A total of 441 artefacts were included in the analysis divided into a total of 20 OTUs. In addition to an OTU comprised of 34 Victoria West cores, a series of Levallois OTUs from localities in Africa, the Near East, India and Europe were included in the analysis. Given the role that handaxes have played in this debate in terms of their noted similarity to Victoria West cores, a series of Acheulean handaxe OTUs with an equivalent geographic distribution to the Levallois samples was also included. From a phylogenetic standpoint, clear predictions can be made as to where the Victoria West OTU should fall in a cladistic analysis if the results are to be consistent with the ‘proto-Levallois’ hypothesis. Figure 8A shows the Victoria West OTU positioned at the base of a clade containing the Levallois OTUs. Should such a cladogram be returned by the analysis, this would be consistent with the suggestion that the morphological similarities between Victoria West cores and Levallois cores are, most parsimoniously, phylogenetically homologous and thus be consistent with the ancestor–descendant scenario of the ‘proto-Levallois’ hypothesis. Conversely, Figure 8B depicts a situation where the Victoria West OTU is not positioned at the base of a clade containing Levallois cores in a manner inconsistent with the ‘protoLevallois’ hypothesis. Moreover, via a tracking of the evolution of individual characters within the tree, it would be possible to determine potential instances of convergent similarities in the Victoria West and Levallois OTUs. Hence, should the analysis return results of this nature, this would provide strong evidence that the Victoria West cores are not – most parsimoniously – a ‘proto-Levallois’ core form, but rather represent an instance of convergent technological evolution. In order to implement the analysis, quantitative data for a total of 72 characters for each artefact were recorded. These characters described specific aspects of artefact shape (in plan and section), with additional attributes describing such information as consistency in the length and width of complete flake scars, flake scar morJEP 9(2011)2

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A

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Figure 8 A&B. An hypothetical example (A) of a cladogram consistent with the predictions of the Victoria West ‘proto-Levallois’ hypothesis, and (B) an hypothetical example of a cladogram inconsistent with the ‘proto-Levallois’ hypothesis

artefact (see LYCETT 2009a for full details and description). Metric data were size adjusted in order that they reflect differences in the shape characteristics of the artefacts rather than merely reflecting overall size differences. A confounding factor in cladistic analyses is the inter-correlation of different characters, thus adding redundant information (FARRIS 1983). Hence a statistical screening procedure was undertaken in order to search for examples of character inter-correlation across all OTUs (NADEL-ROBERTS and COLLARD 2005). Following this stage, six characters were removed from the character matrix leaving a total of 66 characters for the analyses. In order to convert the data into discrete character states required by cladistic analysis, a statistical procedure termed divergence coding was implemented (THORPE 1984). Statistical procedures for the coding of characters in this manner are desirable since they do not depend upon arbitrary decisions or untested assumptions regarding character similarity or difference to be made (RAE 1998). An OTU comprised of handaxes from Olduvai Gorge (Bed II), Tanzania was used as an outgroup, since being in the region of 1.4–1.2 million years old, they are among some of the oldest known examples of Acheulean technology (ASFAW et al. 1992; HAY 1990) and are therefore most likely to be informative regarding plesiomorphic character states (SMITH 1994: 58–59). The commonly used cladistic program PAUP*4.0 (SWOFFORD 1998) was used to undertake the analysis in conjunction with MacClade 4.02 (MADDISON and MADDISON 2001). Figure 9 shows the maximum parsimony tree returned by the cladistic analysis. In a manner inconsistent with the predictions of the ‘proto-Levallois’ hypothesis, the Victoria West cores are not positioned as the basal ‘sister-taxon’ of an exclusively Levallois clade (Figure 9). Rather, the Victoria West cores are situated between the African and non-African handaxe OTUs. The analysis therefore contradicts the main prediction of the ‘proto-Levallois’ hypothesis. Moreover, subseJEP 9(2011)2

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quent tracking of the evolution of individual characteristics within the most parsimonious cladogram, demonstrated that several specific characteristics relating to

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Figure 9. Maximum parsimony tree based on cladistic analysis of 66 characters. The tree is inconsistent with the main phylogenetic prediction of the ‘proto-Levallois’ hypothesis, and examination of character evolution within the tree demonstrates that several similarities shared by Levallois cores and Victoria West cores are, on the grounds of parsimony, the product of convergence

the upper surface morphology of Victoria West cores and Levallois cores, as well as the area of the largest flake removed from these various core forms, were – most parsimoniously – the product of convergent technological evolution (LYCETT 2009a). Further post hoc analyses also determined that factors such as raw material factors could not account for the structure of the cladogram, and the results were also shown to be strongly supported in bootstrapping and resampling tests. Hence, in combination, the phylogenetic analyses provided robust evidence that Victoria West cores cannot appropriately be regarded as ‘proto-Levallois’, just as LEAKEY (1936) had warned over seventy years earlier might be the case. Given these factors, LYCETT et al. (2010) suggested that Victoria West cores should more appropriately JEP 9(2011)2

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be referred to by BORDES’ (1961: 16) term of ‘para-Levallois’; a label which recognises their evident similarities to Levallois in specific characteristics, yet which also conveys the point that such similarities are not the result of a direct ancestordescendant relationship. More generally, of course, these analyses also demonstrate that even deep in prehistory, the evolution of culture was generating instances of convergence which, as Darwin observed, are a likely outcome in any phenomena produced via a process of descent with modification.

4. CONCLUSION: “from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” DARWIN (1859: 490) When DARWIN (1859: 490) wrote of “simple beginnings” giving rise to “endless forms” he was indubitably thinking of somatic life. However, as the preceding discussion has demonstrated, Darwin was also clearly aware of the similarities between biological and cultural evolution via the general process of descent with modification. The sheer abundance and non-perishability of stone artefacts ensures that they present our best available source of data for studying cultural evolution into the deeper parts of human prehistory. MESOUDI, WHITEN and LALAND (2006) have argued that an evolutionary approach to human culture may be able to integrate separate disciplines within the social sciences. However, despite the validity and desirability of this agenda, the cultural evolutionary analysis of hominin behaviour in the recesses of prehistory is of specific importance in regard to a wider synthesis of human evolutionary studies in general. Two points in particular stand out in this regard. The first of these is the contribution that a cultural evolutionary analysis of stone artefacts can make in terms of linking, more directly, the study of social transmission and cultural evolution in extant primates to the evolutionary analysis of culture in humans (Figure 10). The potential for such integration has perhaps never been greater, with attempts to apply the techniques of one field to the questions of another increasing in frequency (e.g. CARVALHO et al. 2008; GOWLETT 2009; LYCETT et al. 2009; MESOUDI and WHITEN 2008). Fully developed, each branch of cultural evolutionary research could provide a source of data and a source of questions for the other. A second important point is the role it has to play in linking the fields of cognitive evolution and physical anthropology (i.e. study of the evolution of the human phenotype). Humans are cultural animals, and the potential for culture to act as a selective environment for genes – and equally for the cognitive and phenotypic manifestations of proximate genetic factors to act as a selective environment for culture – has been recognised for some time and is beginning to grow as a research agenda (DURHAM JEP 9(2011)2

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1992; RICHERSON and BOYD 2005; LALAND, ODLING-SMEE and MYLES 2010; LY2010; WHITEN 2005). As such, the study of human cultural evolution in the deeper past has a crucial role to play in negotiating between areas of work involving our closest living primate relatives, human fossils, and living humans when it comes to questions of evolution in terms of genetic patterns, phenotypic patterns, and the human mind.

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Figure 10. From a phylogenetic perspective, the cultural evolutionary analysis of hominin behaviour is situated between the cultural evolutionary research of humans and our closest primate relatives. As such, it provides a crucial link between work ongoing in these extant species. For examples of phylogenetic analyses using the types of material culture illustrated here see, LYCETT et al. 2010 (chimpanzee tools), LYCETT 2007, 2009 (Palaeolithic stone tools), TEHRANI and COLLARD 2002 (carpet designs), JORDAN and SHENNAN 2003 (basketry weaving)

Over 150 years ago, DARWIN’s (1859) insight provided us with a means of beginning to work toward understanding diversity as seen in the biological world. Today, the principles of inheritance, transmission and the differential preservation of ideas and knowledge in subsequent generations are proving to be useful in understanding cultural evolution in human groups as well as in our closest primate relatives. The application of these same ideas to the study of stone artefacts may have yet more to offer both of these endeavours, as well as improving our understanding of the factors mediating cultural evolution in our fossil hominin relatives and ancestors.

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ACKNOWLEDGEMENTS I am grateful to Metin Eren, Noreen von Cramon-Taubadel and the anonymous reviewers for helpful comments on an earlier version of this paper.

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