THE ROLE OF VERBAL INTERACTION DURINGEXPERIMENTAL BIFACIAL STONE TOOL MANUFACTURE

SHELBY S. PUTT, ALEXANDER D. WOODS AND ROBERT G. FRANCISCUSThe University of Iowa, USA

Colorado State University, USA

Many researchers have hypothesized an analogous, and possibly evolutionary, relationship between Paleolithicstone tool manufacture and language. This study uses a unique design to investigate how spoken language mayaffect the transmission of learning to make stone tools and comes to surprising results that may have importantimplications for our views of this relationship. We conducted an experiment to test the effect of verbal communi-cation on large core biface manufacture during the earliest stages of learning. Previously untrained flintknapperswere assigned to two different communication conditions, one with and one without spoken language, and wereinstructed to replicate the bifaces produced by the same instructor. The attempted bifaces (total = ) from thetwo groups were compared using an Elliptical Fourier analysis, the Flip Test, and a rating scale by an independentlithicist. We found no significant difference in the overall shape, symmetry, or other measures of skill among the twogroups, using all three of these methods. Analysis of the , debitage elements from the experiment, however,revealed that the two groups set up their striking platforms in fundamentally different ways. The nonverbal groupproduced more efficient flakes than the verbal group, as evidenced by the significantly higher ratios of platformwidth to platform thickness and size to mass of the nonverbal subjects’ flakes. These results indicate that verbalinteraction is not a necessary component of the transmission of the overall shape, form, and symmetry of abiface in modern human novice subjects, and it can hinder the progress of verbal learners because of their tendencyto over-imitate actions of the instructor that exceed their current skill set.

KEYWORDS: experimental archaeology, skill transmission, flintknapping, emulation vs. imitation, language

Human language has many important qualities,such as symbolism and hierarchical organization,which set it apart from non-human communicationsystems (Cheney and Seyfarth ; Hauser et al.). Indeed, language is widely considered tobe fundamental to the human species (Deacon). Despite considerable research in multiplefields (Christiansen and Kirby ; Fitch ,), it is unknown when or how this complexsystem of spoken communication evolved in thehuman lineage because of the lack of direct fossilevidence (Fitch ). Unfortunately, there arefew, if any, reliable skeletal markers that can beused to infer the presence of speech or language(for a review of potential fossil cues to speechand language, see Fitch , ). The archaeo-logical record of the production of early stone tooltechnologies, despite inherent limitations (Buckleyand Steele ), may offer an indirect windowinto the cognitive and linguistic capabilities ofearly humans due to the varying levels of skillrequired to produce different stone tools.

There is accumulating evidence for a praxicexaptation origin for language, meaning that thelanguage neural network may have co-opted thestructures and functions already in place for thedistal manual motor network (Arbib ;Meister et al. ; Pulvermüller and Fadiga; Rizzolatti and Craighero ; Stout andChaminade ; Uomini and Meyer ;Wilkins and Wakefield , ). Hierarchicalactivities involving sequential actions, like tooluse and tool production, may have a developmen-tal and evolutionary foundation in Broca’s regionof the brain (Greenfield ; Steele et al. ),which also participates in speech production.The Technological Hypothesis of LanguageOrigin asserts that the language circuit in Broca’sarea of the brain is an exaptation of the originaltechnological praxis network in that same region(Stout and Chaminade ). Although Broca’sarea traditionally has been thought to be an anato-mically discrete region of the brain functionallyspecialized in the production of language, there is

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now ample evidence for the overlap of distalmanual motor functions in the homologue ofBroca’s area in non-human primates(Hepp-Reymond et al. ; Kurata and Tanji; Rizzolatti et al. , ; Taglialatelaet al. ) and Broca’s area in a broad sense inmodern humans (Heiser et al. ; Higuchiet al. ). Moreover, studies have also shownthat the caudal region of Broca’s area is activatedduring the replicative manufacture of Oldowanand Acheulian tools by modern humans (Stoutand Chaminade ; Stout et al. ), andlanguage and stone toolmaking cause commoncerebral blood flow lateralization signatures(Uomini and Meyer ). Furthermore, it hasbeen found that many aphasic patients also haveimitation deficits and apraxia, which causes aninability to perform purposeful movements, suchas tool use (Heilman and Valenstein ; Iaco-boni and Wilson ; Kertesz and Hooper; but see Papagno et al. ). These studiessubstantiate the idea that language and tool usedepend on similar biological mechanisms for pro-cessing hierarchical information; however, furtherresearch is necessary to understand the potentialfunctional relationship between tool manufactureand language in the brain.If some aspects of language evolved by co-opting

the praxis network in Broca’s area, which, asalready discussed, is known to be activatedduring the process of Paleolithic stone tool pro-duction, it is probable that language and tool man-ufacture continued to co-evolve, and the increasingcomplexity of language reinforced the increasingcomplexity and diversity of technology and viceversa (Ambrose , ; Stout and Chaminade). We are aware of only one study to date thathas attempted to test the effect of verbal communi-cation on the production of stone tools in modernhumans (Ohnuma et al. ). In this study,Ohnuma et al. () measured the rates andmean times of acquisition of successful Levalloisflake production among a verbal and a nonverbalgroup (each group consisted of universitystudent subjects) over a period of eight hours intwo days. Because these time and rate parametersdid not differ significantly between the twogroups, the authors concluded that spokenlanguage was not necessary for Levallois flakeproduction in earlier species of Homo.While Ohnuma et al. () admit their results

are preliminary, they conclude that earlierhuman species did not need language based onmodern Homo sapiens as a direct proxy for the

behavior and cognition of other species. The val-idity of the analogy between modern humansand earlier hominin species is a long standingdebate within the field. Researchers have differentperspectives on the usefulness of this analogy. Forexample, Davidson and Noble () argue thatchimpanzees are a better analog for pre-linguistichuman ancestors than modern humans. On theother hand, while Toth and Schick () admitthat modern humans are not a perfect analog forearly hominins in the late Pliocene and early Pleis-tocene, they argue that investigations into theirtoolmaking behaviors could prove to be quitevaluable for interpreting the past. They suggestan experiment which involves teaching modernhumans to make stone tools in two differentways, with verbal and nonverbal instruction,which “might prove to be very informative forinferring levels of communicative sophistication”of pre-anatomically modern hominins (Toth andSchick : ). While it is important to notethat modern humans and their lineal ancestorshave been evolving along their own trajectory forhundreds of thousands of years and undoubtedlyadapting to different selective pressures since theearly Pleistocene, the same can be said for modernapes, whose genes and behaviors are likely evenmore far removed from those of pre-sapiens homi-nins. We are more inclined to agree with Toth andSchick that modern humans and non-human apescan be informative for providing inferences aboutpast hominin species; however, we are aware ofthe problems that such analogies present.It is surprising that Ohnuma et al. () report

such rapid rates of acquisition of the Levalloistechnique (verbal mean = minutes, nonverbalmean = minutes) because it has been arguedthat “the connaissance and savoir faire of Levalloisknappers clearly constitutes a stock of knowledgethat one acquires with years of practice” (Wynnand Coolidge : ), which is probably whythere are relatively few novice Levallois replicativestudies. Those that exist report learning periods ofmonths because of the high level of skill involved(Eren et al. a, b). Nonetheless, Moore() argues that the Levallois is a muchsimpler technology than is often assumed. Heargues that simple flake unit chaining can lead toresults that resemble higher-order architectureand predetermination. Clearly, the complexity ofthe Levallois and the length of time it takes toacquire such a technique is an unresolved debate.There is reason to believe that verbal instruction

may play an important role during the

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transmission of knowledge related to the bifacialreduction of stone tools. Stout () points outthat verbal interaction between apprentice andexpert plays a large role in the learning processof modern bifacial adze making in IndonesianIrian Jaya, especially when communicatingcomplex, technological concepts. Arguably, thetransmission of this skill may be extremelydifficult without verbal instruction. Therefore,we posit that the effect of verbal interaction onthe production of stone tools can be tested. Wepropose that the transition from learning simpleflake removal to bifacial flaking offers a morereliable test than the Levallois technique for theeffect of verbal interaction on stone toolmaking.Bifacial reduction is a relatively complex cognitivetask, requiring the coordination of ongoinghierarchically-organized action sequences (Stoutand Chaminade ), but it can be acquiredover a period of days, instead of months, of prac-tice (Shea ). For these reasons, we should beable to see any effect verbal interaction has onthe final products within the early stages of skilltransmission.To test the effect of verbal communication on

the early stages of transmission of bifacial knap-ping in modern humans, we conducted an exper-iment in which participants with no priorflintknapping experience were differentiallytaught to make large bifacial cutting tools. Wedivided the randomly assigned participants intotwo trial groups; one group was taught how toflintknap using spoken language, while the othergroup learned in a nonverbal environment. Wepredicted that we should see no difference in theresultant bifaces and debitage between the twogroups if verbal interaction does not play animportant role in the transmission of thecomplex action sequence of bifacial reduction.

MATERIALS AND METHODS

EXPERIMENTAL DESIGN AND PROCEDURE

The participants were divided based on sche-dule availability into verbal (seven females andsix males) and nonverbal (seven females and fourmales) groups in order to learn how to producebifaces similar to those produced by an instructor.None of the participants had any prior flintknap-ping experience. The participants ranged from to years old, except for one outlier who was years old. This study was approved by the Insti-tutional Review Boards and Human SubjectsOffice at the University of Iowa (IRB ID#

). All subjects gave written informedconsent prior to the experiment. Participantswere not compensated.One of the authors (Woods), who has conducted

replicative flintknapping for more than a decade,was the instructor for both groups. Both groupsmet with the instructor separately to practiceflintknapping for one hour, once a week, for fiveweeks. Each session was video recorded and con-sisted of a quick demonstration, after which theinstructor would circle the room assisting the par-ticipants. Each week, both groups had identicallearning goals to meet, which progressed in orderof difficulty from recognizing ideal angles andmaking flakes, to producing alternate, bifacialflaking, to shaping completed bifaces. In theverbal group, the goals to achieve each sessionand all attendant advice and information wereconveyed via spoken communication, and byexample. Participants in the nonverbal groupreceived no spoken instructions at all; they hadto infer the goals for each session based on observ-ing and mimicking the instructor. All assistance tothe nonverbal group was provided in the form ofhandling rocks, pointing, and knapping demon-stration. Each participant’s flaking debris waskept separate, and at the end of each session,each participant’s cores and bifaces were collectedalong with his/her debitage. The debitage was thengently screened through a ¼ inch mesh, and allpieces which passed through the screen were dis-carded prior to labeling and analysis.

MATERIALS

Participants flaked two different raw materialsdepending on the week of the study. During thefirst four weeks, the participants were allowedunrestricted access to large plastic bins of heat-treated Burlington chert, a fine- to medium-grained stone that is easy to flake (Hoard andAnglen ). These rocks were provided to theparticipants largely without cortex in the form oflarge to medium chunks and pre-made spalls.During the final week, participants were eachallowed to choose one piece from a selection ofPedernales flint from Texas. This flint was ofhigher quality than the Burlington chert, meaningthere were fewer faults within the rock, but it wasnot heated and required more force to fracture.

BIFACE ASSESSMENT

All attempted bifaces (total n = ) produced bythe verbal and nonverbal groups were evaluated

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and scored by an independent assessor, Dr. JohnWhittaker (Grinnell College, IA), who rankedthem in terms of overall quality and the requisiteskill attendant with production. Whittaker is anexperienced lithic specialist with technical exper-tise in prehistoric technologies, flintknapping,and stone tool analysis (e.g., Whittaker ;Whittaker and Kaldahl ; Whittaker andMcCall ). By design, he had no prior knowl-edge about the experiment, and all labels indicat-ing that he was evaluating material from twodifferent groups were masked. He ranked allcores produced from the experiment on a scaleof to , with being representative of verypoor quality and not even formally qualifying asa biface, and being representative of the bestbifaces within the sample.Key qualities Whittaker used to categorize the

bifaces included overall degree of shape symmetry,the degree to which the knapper made the edgebifacial, and the extent of corpus thickness. Thesemeasures reflect standardization of productionbecause of their conformance to the bifaces pro-duced by the instructor during demonstrations(Figure ). Plan-view symmetry, regularity ofform, and corpus thinness are regularly citedcharacteristics of stone tools that indicate highlevels of skill (e.g., Bamforth and Finlay ;Root ; Whittaker ). The highest rankingbifaces were thus combinatorially thin, symmetri-cal, and bifacially worked. Whittaker also factoredin an assessment of the number of edge flakesremoved and the length of the bifacial edge forhis final ranked scores. The higher ranked bifaceshad long, straight bifacial edges and a relativelyhigh number of successful edge flakes removed,while the lower ranked attempted bifaces reflectedthe original shape of the rawmaterial with evidencefor unsuccessful attempts to take off flakes andlittle to no bifacial edge (Figures and ). Whit-taker was also asked to rank only the finalsession bifaces (n = ) on a scale of to , witha score of representative of a core that does noteven qualify as a biface and a score of that isrepresentative of skilled craftsmanship.Because of the subjective characteristic of Whit-

taker’s analysis of overall quality and attendantskill manifested by bifaces, we found it prudentto also conduct quantitative analyses on symmetryand plan-view shape to confirm some of Whit-taker’s measures. Symmetry in the archaeologicalrecord is associated with skilled craftsmanshipand has also been linked with evolving cognition(Wynn ). The Flip Test was used to provide

a numerical measure of asymmetry for eachbiface produced from the last two sessions in theexperiment (Hardaker and Dunn ). The FlipTest is an analytical method that flips the toolover its vertical axis and assesses the amount ofdeviation from perfect symmetry. Mathematically,this calculation is expressed as (A)/(H +W),where A is the number of asymmetrical pixels, His the maximum height, and W is the maximumwidth of the tool. We excluded cores from priorsessions because the participants were not consist-ently producing bifaces until the fourth session;therefore, any measure of asymmetry would bemeaningless.The overall shape of the biface plan-views from

the final two sessions was compared between thetwo groups by performing an Elliptical FourierAnalysis (EFA). EFA is a method used to describethe outline of a two-dimensional closed or opencurve by fitting elliptic Fourier harmonics to anoutline (Kuhl and Giardina ; Lestrel ).Each harmonic is described by four coefficients,which are derived from the x and y coordinatesof a particular shape outline. The outline can bedescribed in more detail with each additional har-monic. While EFA is able to describe complexshapes, it is also useful for identifying subtle differ-ences among similar oval shapes (e.g., Seiffert and

FIGURE . An example of one of the bifaces produced by theinstructor during the experiment which the participants wereto try to imitate. This biface has an index of asymmetry scoreof ..

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Kappelman ). EFA is a common technique inbiology and paleontology (e.g., Lestrel ;Renaud et al. ) and has recently beenapplied to lithic artifacts in the archaeologicalrecord (e.g., Iovita ; Iovita and McPherron; Saragusti et al. ).Measurements were derived from digital photo-

graphs of each biface, which were taken in plan-view at a ° angle. EFA requires every object tobe oriented in the same direction in the photo-graph, and as others have noted, this is a very

difficult task (Iovita and McPherron ;McPherron and Dibble ), especially whendealing with the products of novice flintknappers.All bifaces were oriented with the tip facing the leftside of the picture. For those products that lackeda tip, the tool was oriented with the widest portiontowards the right side of the picture. The shapeoutline was placed on a Cartesian grid, andpoints along the outline were given x and y coordi-nates (Hammer and Harper ). Using SHAPEsoftware (Iwata and Ukai ), we extracted

FIGURE . Examples of relatively low-quality bifaces with ranked scores falling between – shown in facial view (a), and inside view (b).

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the x and y coordinates by first using ChainCoderto record the contour of the objects as a chain-code(Freeman ) and then ChcNef to calculate thenormalized elliptic Fourier descriptors from thechain-code. Finally, to describe the morphologicalfeatures of the tools, we performed a PrincipalComponent Analysis (PCA) of the normalizedelliptic fourier descriptors.

DEBITAGE ANALYSIS

Following screening, all collected debitageelements (total count = , pieces) werelabeled and analyzed. Each piece was weighed tothe nearest tenth of a gram, measured formaximum thickness to the nearest millimeter,and allocated to a metric size category continuum

FIGURE . Examples of relatively high-quality bifaces with ranked scores falling between – shown in facial view (a), and inside view (b).

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as defined by the smallest of a series of nestedsquares on centimeter graph paper into whichthe piece would completely fit (i.e., , , cm…,etc.). To discern any differences in skill at rawmaterial selection between the groups, both rawmaterial quality and the presence of faults wererecorded for each debitage piece. As raw materialquality can be very difficult and time consuming toquantify (Woods ), the quality of each debit-age piece of material was simply coded either as“high”, “low”, or “mixed” (for analytic purposes“mixed” quality was considered “low”). The pres-ence of faults as evidenced by cracks or surficialmineral staining on flat interior surfaces wasnoted. Each piece was coded as a flake (eitherproximal or distal), or nonflake debitage shatter(Andrefsky ). Proximal flakes were deter-mined by the presence of an intact striking plat-form and a bulb of percussion, while distal flakeswere determined by the presence of recognizableventral and dorsal surfaces. We classified anyangular pieces with no clear ventral or dorsal sur-faces as nonflake debitage shatter. The maximumlength and width of striking platforms were alsocollected. These measures provided a means toexamine several aspects of flake and shatterdimensions, material quality, and platform setupas key factors in this analysis. All statistical ana-lyses were performed using SPSS (IBM Corp.,) and NCSS (Hintze ).

RESULTS

While the use of two different rawmaterials was notideal, it was, in the end, necessary. The novicesproduced kg of debitage over five weeks, notincluding the cores. By the final week, theyexhausted the originally large stock of Burlingtonchert, and Pedernales flint had to be substitutedfrom the instructor’s personal supply. No significantdifference could be found between the volume of theflint nodules provided to both groups during thefinal week (t-test, t = −., p = .). Becauseboth groups always had the same quantity andquality of stone at the same points in learning, andit has been argued that knapper skill may havemore to do with successes and failures than stonequality (Eren et al., b; Sharon ; but seeClark ), it is our interpretation that this shiftin raw material had little effect on the results.

BIFACE ASSESSMENT

Analysis of the attempted bifaces produced in thecourse of this experiment reveals that access to

verbal instruction does not have a significanteffect on the overall quality of the biface, includingsymmetry and shape. We evaluated the bifacerankings from all sessions combined (total n =), as well as those from only the final flintknap-ping session (total n = ) in order to assess bifacequality in both trial groups throughout the exper-iment (aggregate), as well as for only those bifacesmanufactured with the highest level of experience(final flintknapping session only). In terms of theaggregate sample comparisons, the total range ofbiface quality scores was similar for both groups,ranging from to in the nonverbal group and to in the verbal group. The nonverbal grouphad slightly higher mean and median qualityscores (. and . respectively) than the verbalgroup (. and . respectively). In terms of thefinal flintknapping session sample comparisons,the total range of biface quality scores wasreduced slightly from to in both groups, andthe nonverbal group again had slightly highermean and median quality scores (. and .respectively) than the verbal group (. and .respectively). Nonetheless, and most importantly,in both cases (the combined aggregate across allsessions, and the final session biface end-products), the verbal and nonverbal groups werenot statistically significantly different from eachother in their assessed biface quality scores(Table and Figure ).The results of the Flip Test exhibit a similar

pattern to the qualitative ranking analysis in thatthe nonverbal group produced lower meanscores of asymmetry (i.e., more symmetricalbifaces) than the verbal group. We found no sig-nificant difference in symmetry between the twodistributions (Table ). Index scores ranged from. to . in the entire sample of bifacesfrom the final two practice sessions (n = ).Hardaker and Dunn () provide a table tohelp interpret the Flip Test scores, with scoresranging from (virtually perfect symmetry) to and above (very low symmetry). Using this tableas a guide, a score of . is considered to be avery high level of symmetry, representing anexceptionally skilled craftsman. Only about percent of the specimens could be consideredaverage to highly skilled work. The rest of thespecimens are interpreted as having low to verylow symmetry. There is a decrease in medianasymmetry scores for both groups from thefourth to the fifth practice session, indicating animprovement in this specific skill over time(Figure ).

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We found no significant differences in outlineshape of the bifaces between the verbal and non-verbal groups for Principal Components – (seeTable for harmonic descriptions). The firstseven elliptic fourier descriptors explain .percent of the total variance of shape. Theseresults are in concordance with Whittaker’s quali-tative analysis and the Flip Test. PC (. percentof total variance), which represents the degree of

base roundedness, was found to be statisticallydifferent between the verbal and nonverbalgroups.

DEBITAGE ANALYSIS

Even though we found no significant difference inquality between the bifaces from the verbal andnonverbal groups, there is striking evidence from

TABLE . SUMMARY OF QUALITY SCORE RANKINGS FOR BIFACIAL CORE PRODUCTS

Verbal Nonverbal

n Mean SD n Mean SD Prob

Aggregate end products . . . . . nsFinal session end products . . . . . nsProbability results for equal means via Mann–WhitneyU tests following non-normal distributions with equal variances. ns, notsignificantly different. One subject assigned to the nonverbal group participated in all flintknapping sessions except the finalsession, and thus did not produce a final handaxe. Also, one subject in the verbal group accidentally snapped the final biface intwo and subsequently bifacially flaked both halves. These two factors account for the slight difference in sample sizes reported forfinal session end products here, with the debitage sample sizes reported in Table .

FIGURE . Boxplot distribution of (a) quality rank scores by group for the total aggregate number of bifaces from all fiveflintknapping sessions (n = ), and (b) the scores for the final session bifaces only (n = ). In both cases, the groups werenot significantly different (see Table ).

TABLE . SUMMARY OF FLIP TEST

Verbal Nonverbal

n Mean SD n Mean SD Prob

Week Bifaces . . . . . nsWeek Bifaces . . . . . nsTotal . . . . . nsProbability results for equal means via Mann–WhitneyU tests following non-normal distributions with equal variances. ns, notsignificantly different.

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the debitage analysis that the verbal environmentaffected the transmission of certain concepts.While both groups produced the same overallratio of shatter to flakes, showed similar skill inselecting raw material as defined by the ratio offlakes to shatter produced on high or low qualitystone, and broke nearly the same overall mass ofrock over the duration of five weeks (verbal =,. g, nonverbal = ,. g), the nonver-bal group produced significantly more lithic debit-age elements (nearly twice as many as the verbalgroup). Moreover, the verbal group set up signifi-cantly larger striking platform areas than the non-verbal group, resulting in significantly larger, more

massive flakes in terms of mass, flake size, andflake thickness (Table and Figure ).Skill was measured by the ratio of platform

width to platform thickness, the ratio of flakesize to flake mass, and by the frequency ofmissed hits, as evidenced by incipient cones andcrushed areas on the flakes and shatter. The non-verbal group’s overall mean ratio for platformwidth to platform thickness was significantlyhigher than that of the verbal group (Table ).As a result, the ratio for flake size to flake masswas also significantly higher in the nonverbalgroup (Figure ). Increased platform width relativeto platform thickness increases the ratio of surfacearea to flake thickness, thus making the flake moreefficient (Dibble ). Learning differences wereapparent between the two groups from the veryfirst week and continued throughout the five ses-sions. This was most obvious in the ratio of flakesize to flake mass. The nonverbal group ratio ofsize to mass was significantly higher (p < .)than the verbal group for all five sessions(Figure ). Moreover, the nonverbal groupshowed significant improvement between someindividual sessions and overall (Games-Howell,p < .), while the verbal group only showedsignificant improvement from Week to Week (Games-Howell, p = .) but displayed no sig-nificant improvement between individual sessions.The overall number of incipient cones and crushedareas on the debitage was significantly higher forthe verbal group than the nonverbal group. Incipi-ent cones are caused by striking a platform with anangle of more than degrees or by misestimatingthe amount of force required to fracture the stone(Whittaker ), and they usually occur at higherfrequencies among less experienced flintknappers(Bamforth and Finlay ; Finlay ).

FIGURE . Median asymmetry index scores for the verbaland nonverbal groups from the fourth practice session (darkgrey) to the fifth session (light grey). Error bars represent percent confidence intervals.

TABLE . SUMMARY OF PCA FROM ELLIPTICAL FOURIER ANALYSIS

Description Proportion of variance (%) T Statistic Prob

PC Elongation . . . nsPC Center width . . . nsPC Tip width . . . nsPC Base width . . . nsPC Degree of Side A center-tip convexity . −. . nsPC Degree of base convexity . . . nsPC Degree of side B center-tip convexity . . . nsPC Degree of base roundedness . . .*Student’s t-test. Significant at *p < .; ns, not significantly different. The t-test is based on comparisons of the means for theindividual PC scores for each component between the two trial groups.

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TABLE . SUMMARY OF AGGREGATE DEBITAGE ANALYSIS

Verbal (n = ) Nonverbal (n = )

Mean S.D. Mean S.D. Prob

Total debitage elements (counts) , – , – <.***Total debitage mass (kg) . – . – . nsMaximum flake thickness (mm) . . . . .**Flake mass (g) . . . . .*Flake size (cm) . . . . .*Platform area (mm) . . . . .*% Shatter . . . . . ns% Flakes . . . . . ns% Flakes on high quality stone . . . . . ns% Shatter on high quality stone . . . . . ns% Flakes on low quality stone . . . . . ns% Shatter on low quality stone . . . . . nsRatio of pWidth to pThickness . . . . <.***Ratio of flake size to flake mass . . . . <.***Missed hits/hammer marks . . . . <.***Probability results for equal means via t-tests in the case of normal distributions and equal variances, the Kolmogorov–Smirnovtest in the case of non-normal distributions and unequal variances, and the Mann–Whitney U test in the case of non-normaldistributions and equal variances. For total debitage counts, the probability result is based on the exact binomial test for equalproportions. Significant at *p < ., **p < ., ***p < .; ns = not significantly different.Trait for which an additional test (F-test on the ratios of the variances of the log-transformed traits between the verbal andnonverbal samples following Lewontin, ) was conducted to test the possibility that inherent skill differences amongindividuals between groups may have influenced these mean values (see discussion section). This procedure, which tests the nullhypothesis of equal coefficients of variation as elaborated by Lewontin () has advantages over the use of the standardcoefficient of variation (SD/Mean). No statistically significant differences were found for the three variables of interest here (allresulting values ranged between p > .–.).

FIGURE . The relationship between the mean mass and mean platform area of flakes produced by participants in the verbal(circles) and nonverbal (triangles) groups. The groups are significantly different in both variables (see Table ) whether or notthe outlier for both variables in the upper right portion of the bivariate plot is retained. There is a significant positive correlationbetween the two variables when all the participants are included (r = .; p < .), as well as when the outlier is removed (r =.; p < .).

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DISCUSSION

The hypothesized prediction that a group ofnovice flintknappers in a spoken language-basedlearning environment will produce significantlydifferent large core bifacial tools from a similargroup deprived of spoken language is not valid.This leads us to the more general conclusion thatthe overall shape and form of the biface, and theconcept of symmetry during stone tool reduction,

can be transmitted via verbal or nonverbal com-munication in modern human novices. This resultsupports other lines of evidence that toolmakingknowledge can be transmitted nonverbally (Cool-idge and Wynn ; Dunbar ; Gardner; Gatewood ; Keller and Keller ).The attributes of biface quality we chose for

comparison of the two groups (plan-view shapeand symmetry, corpus thickness, and bifacialedge length) are often used to describe the stan-dardization, and thus, the attendant skill requiredfor production, of stone tools in the Lower Paleo-lithic archaeological record. It is now generallyagreed upon that Acheulian handaxes increasedin symmetry through time (Saragusti et al. ;Wynn ), and there was selection for increasedsymmetry, likely because it improved the efficiencyand functionality of the tool (Lycett ; Mitch-ell ; but see Machin et al. ). While it isimportant to note how our measurements of skillrelate to the archaeological record, we wish tostress that the participants in this study were notreplicating specimens from the archaeologicalrecord. Instead, they were trying to replicate thelarge core bifaces produced by the instructor,which were consistently symmetrical, thin, andbifacially worked. Furthermore, these attributeswere emphasized by the instructor as goals forthe participants to try to meet, which is whythese are the attributes of biface quality wesought to measure and compare between groups.

FIGURE . A comparison of the mean ratio of flake size toflake mass between the verbal and nonverbal groups, clearlydemonstrating a significant difference between the twogroups (error bars represent percent confidence intervals).A higher ratio of size to mass is the result of a higher ratio ofplatform width to platform thickness.

FIGURE . A comparison of the mean ratio of flake size to flake mass between the verbal and nonverbal groups from individualpractice sessions.

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Despite similarities in their final bifacial pro-ducts, analysis of the debitage from this exper-iment revealed that the verbal and nonverbalgroups flintknapped in fundamentally differentways. These differences were almost entirely theresult of variation in how the two groups set uptheir striking platforms. The verbal group set upand utilized significantly larger striking platforms,which resulted in the production of significantlylarger, more massive flakes than those producedby the nonverbal group. Platform size has pre-viously been shown to correlate with flake size(Dibble ), which is consistent with ourfindings (Figure ). The nonverbal group flakes,however, had significantly higher ratios of plat-form width to platform thickness and size tomass, which mean the participants in the nonver-bal group produced arguably more efficientflakes in that they were both large and thin(Dibble ). The nonverbal group also showedmarked improvement in flake efficiency week toweek, while the verbal group showed onlygradual improvement and some backsliding(Figure ). While the verbal group producedlarger flakes on average than the nonverbalgroup, they were also much thicker, signifyingthat the verbal flintknappers may have had lesscontrol over platform size. This result is furthersupported by their significantly higher frequencyof incipient cones on the debitage, which meansthey had more failed attempts to remove flakes.On the other hand, the participants in the nonver-bal group produced a much larger frequency ofdebitage than the verbal group, which may bethe result of misjudgment of the amount of forcerequired for flake detachment. This is a character-istic of novices attempting any kind of lithicreduction (Milne ; Shelley ). Participantsin the verbal group were more economic in theircore preparation, meaning they produced fewerflakes to reach the same end goal, which may bea sensitive marker of skill (Eren et al. a).These results indicate that bifacial knapping can

be transmitted quite successfully in a nonverballearning condition. In fact, the presence of verbalinteraction during the transmission of bifacialknapping may actually hinder the novice’s pro-gress toward producing more efficient flakes, atleast in the early phases of learning. It could beargued that the verbal group had less practicethan the nonverbal group because they spentmore time receiving instructions and asking ques-tions and not striking platforms, and this couldexplain our results; however, from our analysis

of videotaped sessions, we found that theamount of time the instructor spent demonstratingand instructing (speaking or gesturing, dependingon the group) did not significantly differ betweenthe verbal and nonverbal groups (t-test, t =., p = .). Thus, there must be anotherexplanation for why novices who learned toflintknap nonverbally produced so many moreflakes and showed more facility in managing plat-form dynamics.The pattern that emerges from these data is the

occurrence of more experimental flake detachmentamong nonverbal flintknapping novices to reachthe goal of a symmetrical, large core biface, andthe setup of more ambitious platforms amongverbal flintknapping novices to reach the samegoal. These results present an interesting parallelwith current comparative and developmental psy-chology literature on the issues of emulation vs.imitative learning and their role in cultural trans-mission among human and non-human apes (seeWhiten et al. for a review). Emulationrefers to a process by which an observer learnsfrom the results of a model’s actions, rather thanthe details of the actions leading up to theseresults (Horner and Whiten ; Tomaselloet al. ). In contrast, imitation is broadlydefined as copying a model’s behavior, both themethods and results (Horner and Whiten ),and when an observer reproduces the actions ofa model with such high fidelity that the efficiencyof the task is reduced, this phenomenon isknown as over-imitation (Lyons et al. ;McGuigan et al. , ). When interpretingthe results of this experiment, it is apparent thatthe verbal participants more faithfully imitatedthe instructor, to the point of over-imitation, bydevoting more time to setting up ambitious plat-forms that, in the end, were too difficult to executeat this early a stage of learning. Thus, their taskefficiency was reduced, as is evidenced by theirhigher frequency of missed hits and thick flakes.Over-imitation was first described in children,

and it was thought that this blanket copyingwould decline with age. Quite surprisingly, itwas discovered that over-imitation increases withage, and adults imitate causally irrelevant aspectsof tool use with higher fidelity than young children(McGuigan et al. , ; Nielsen and Toma-selli ). Our results support this pattern ofover-imitation in adults; however, the fact thatnonverbal instruction among flintknappingadults leads to emulation requires explanation.One possible explanation for the reduced imitative

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learning amongst the nonverbal group is thatambitious platform preparation may not havebeen obvious to them as a goal to attempt tomeet because of the absence of verbal interaction;therefore, they focused more on emulating theprocess to reach the goal of a large core bifaceby detaching small, thin flakes until they weresatisfied that their product resembled those pro-duced by the instructor. Through their experimen-tation, they learned from their mistakes andimproved their flake production each week. AsTomasello et al. (: ) note, sometimes“the most efficient strategy might be to simplyobserve the relation between the tool and thegoal and then experiment with the specifics onone’s own.” Alternatively, Nielsen () foundthat toddlers months of age are more likely toimitate rather than emulate when the model isengaged and social compared to when the modelis aloof. It is possible that the instructor in ourexperiment was perceived by the participants inthe verbal group to be more engaged and socialbecause of his verbal instructions, thus stimulatingmore imitation in the verbal group than the non-verbal group; however, the social account forover-imitation has come under some scrutiny byMcGuigan et al. (), who found that televisedmodels also produced patterns of over-imitationamongst children and adults.Other researchers have also noted the important

relationship between imitation and language. Forexample, Meltzoff () and Tomasello ()have argued that imitation plays a crucial role inlanguage acquisition. Multiple lines of evidencesupport that this link between imitation andlanguage occurs at the neural level, which mayhave evolutionary implications (Heiser et al.; Iacoboni et al. ; Thurm et al. ).While the differences in debitage between the

two groups are quite obvious, there are a fewcaveats to keep in mind. First, because of the con-straints of raw material, the sample size used forthis experiment is not ideal, and therefore, individ-ual idiosyncrasies may have had an effect on theresults. Our study design did not evaluate subjectsfor manual dexterity, and future work involvingnovice flintknappers should include a test ofmanual dexterity during the consideration ofgroup assignment to ensure that one group doesnot consist of more naturally dexterous, orskilled individuals than the other group.However, there is no indication that thewithin-group degree of variation in key variables(e.g., flake size, flake mass, or the ratio of these

two variables) is significantly different betweenthe two groups as would be expected if inherentskill differences existed between the verbal andnonverbal samples (see footnote in Table ). Asecond caveat to note is that the participantswere allowed to flintknap only for a shortamount of time. It is possible that with more prac-tice and time, these differences might disappear;however, we argue that the results of this studynonetheless provide an important contribution tothe understanding of the initial stages of learningand understanding of basic flintknapping conceptsunder varying communicative learning conditions.A final caveat is that we cannot ignore the fact thatthe participants in the nonverbal group are stillinherent symbol-users who have been immersedin language all their lives. It is possible that theirlearning and thoughts were mediated by innerspeech during the experiment (Vygotsky ).

CONCLUSIONS

In sum, we found that large bifacial cutting toolscan be produced by novice flintknappers underverbal or nonverbal linguistic learning conditions.Thus, the presence of verbal interaction during theearly stages of transmission of flintknapping con-cepts has little to no effect on the overall quality,shape, and symmetry of large core bifaces;however, verbal communication does appear tohave a strong effect on debitage output. Weassert that the difference in learning strategies isthe result of emulation amongst the nonverbalnovices and over-imitation amongst the verbalnovices. The nonverbal participants showed themost improvement over time and produced moreefficient flakes, but they generated nearly twice asmany debitage elements as the verbal participantsin the process. Although the results of this studyspeak specifically to the flintknapping learningbehaviors of modern humans under varying lin-guistic conditions, some inferences could bemade about the linguistic behaviors of earlierhominin species.

ACKNOWLEDGEMENTS

We thank the participants for the time they devoted to thestudy. We are grateful to J. Whittaker for his expertise andefforts in ranking the end products. We thank R. Ciochonfor facilitating the production of Figures and . We thankE. Thompson, N. O’Shea, C. Beeler, S. Burnette, andK. Looney for their assistance in the lab. We are grateful toR. Hunt for providing the raw material. Additionally,T. Marks, S. Athreya, and C. Nicholas provided helpful com-ments on early drafts, and we are grateful to the editor, and

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our anonymous reviewers for their many helpful commentsand suggestions that greatly improved the final paper. Thisresearch was funded by the Department of Anthropology atthe University of Iowa.

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NOTES ON CONTRIBUTORS

Shelby S. Putt is a doctoral candidate in Anthropology at the University of Iowa. She has an A.A. in International Language &Culture Studies and a B.A. in Anthropology and English & Linguistics from Indiana University-Fort Wayne and a M.A. inAnthropology from the University of Iowa. Her research focuses on the integration of lithic technology and functional neuroi-maging to explore questions related to the evolution of human language and cognition.

Correspondence to: Shelby S. Putt, Department of Anthropology, University of Iowa, Macbride Hall, Iowa City, IA ,USA. Email: shelby-putt@uiowa.edu

Alexander D. Woods earned his PhD in Anthropology from the University of Iowa in . His research focuses on lithic rawmaterial quality, lithic reduction strategies, and the Early Upper Paleolithic. He is currently managing the Tomah, WisconsinArchaeology Laboratory for Colorado State University’s Center For The Environmental Management of Military Lands.

Center for the Environmental Management of Military Lands, Colorado State University, Fort Collins, CO , USA

Dr. Robert Franciscus earned a Ph.D. degree in Anthropology in from the University of NewMexico. He has held academicpositions at Stanford University, and at the University of Iowa where he is currently Professor of Anthropology. His researchinterests have primarily focused on Neanderthal and early modern human anatomy and behavior.

Department of Anthropology, The University of Iowa, Iowa City, IA , USA

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