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Hovers, E., 2009. Learning from mistakes: flaking accidents and knapping skills in the assemblage of A. L. 894 (Hadar, Ethiopia). In: Schick, K., Toth, N. (Eds.), The Cutting Edge: New Approaches to the Archaeology of Human Origins. Stone Age

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Hovers, E., 2009. Learning from mistakes: flaking accidents and knapping skills in the assemblage of A. L. 894 (Hadar, Ethiopia). In: Schick, K., Toth, N. (Eds.), The Cutting Edge: New Approaches to the Archaeology of Human Origins. Stone Age
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  CHAPTER 7 LEARNING FROM MISTAKES: FLAKI NGACCIDENTSAND KNAPPING SKILLS IN THE ASSEMBLAGE OF A.L. 894, (HADAR, ETHIOPIA) ERELLAH OVER S I NT ROD UCT ION Identifying and understanding the skillIc\' els in- \<oll< d in theknapping of theea rl y slOneloolsandthe mental capabilitiesunderly in gthem isa major part of human srcins archaeo l ogy . This is by no means asimple tas k. The actual e~el:ulio n of Sl one knapping im 'olves a multitude of factorsth aI interact in complex ways. Stone knapping isdefined by thephysics of fracture mechan ics and by homininanatom y. R aw materials respond 10 parameterssuchas hammer velocityand fl akinganglcs. whose applicati on 10 theslonedepends in large part on the anatomicalbuild of the t oo l-mak er and hi sdexter ity (c.g., Spelh. 1972.1974. 1975; DibbleandWhittaker.1981: Sullivan and Roze ll .1985: Co tt ere ll andKa mm inga. 1987: Amick andMauldin.1997: Mar.!:ke.1997: Mar l.ke etal..1998:Pelc in ,1997a,1997b,1997c: Toche ri et al . 2008:Tothctal..2006.andreferenccs therein).Differe nt raw materialsrespondvariably10the forces appliedtothemand factor into many of thepat tern sobserved in theearlyassemblages(e.g . Stoutand Sem a w. 2006).Thus stoneknapping involvesdynamic inte ra c ti onsbetweenmultipleelemelltarymovements of the shoulder.amlS.handsand fingers,andIheir cons tantintegration wi thperceptual inf onna tionandsequential planning as the process advances(Biryukova et al.. 2005:Roux andDavid,2005: Stout andChaminade, 2007). These defining components of lithic "designspace" (Moore, 2(05) interact with the goals of any givcn knappingsession.combinedwith individual expertise and idiosyncraticpreferences of the knappcr(whichm ay influence. forexample.thc choice of raw material and of t he type of hammerstonc)and withtechnol ogicaltra ditions (i.e . available technological knowledgeandsocial co nfomlit y. which would dictatethe I'IT/erred manners of geometricallyorganizingcoresurfaccsand ex pl oitingthem:Ilovers.1997. 2(04).The experience andskill of aknapperare expressed in theintegration of pere ep ti onand motorabilities. end go al sand technologicalbackgroundinto a co heren t. dynamic process of decision-making a ll d action.Insuch a complexproccss. fl aking accidents-i.e . uncontrolledremoval offlakes -arcpractically tma\·oidable.While the resultant fl akes (herereferredto as"accidentalflakes") ma ybefunctionallyusefuland can be applied in varioustasks.theystillrepresent ep isodes of (con sc ious or un co nscious)mi sj udgmentonthepart of the knapper.Thus the presence ofacci denlalflakeshasbeen refel'1'l.'d 10 asa proxy of thelevels of inherent andl or ac qu iredski ll s of prehistorichominins (e.g" Kibunjia. 1994:Delagnesand R oc he.2005: Shea, 2 006 ). The question of knapping ski ll sandtheir identification in the ma terialrecordalia in s special interest in the co ntext of studyingOldow:m lilhic s. It pertainstodefining explicitly th edifferencesbetweenhomininand ape SlO netool-making (Toth el al..2006:Mcreadcr et al..2007). assessingthe levels of eXpo.' rti se required topro du ce thevery early(and.accordingtosome.technologi cally simple)lithic artifacts. and10lhe question of thec\'olulion over timeoftechnicalcapabilities in varioushominin genera and withinthe ge nus HOII/O . In the followingdi sc ussionIpresentdataand so meinterpretations of the occurrence of accidentalflakes in thelithicassclll blagcofA .L. 89 4.locatoo in the /. ·lakaam italuBasin ofthe I-I adar ResearchArea (Ethiopia).The site,dated 2 ,) 6 Ma or slightlyold er (Campisano. 2007).isfound in clayey-siltsrepresentingcrevassesplayde posits on the proximalfloodplain of thcpalco-Awash in: Schick, K., Toth, N. (Eds.), 2009. The Cutting Edge:  New Approaches to therchaeology of Human Origins . Stone Age Institute, Gosport, Indiana.  138 The Cutting Edge: NewApproaches to theArchaeology of HumanOrigins river(l'loverset a1.. 2002.2008), The rich lithic assem·blage I1 this locality possibly represents palimpsests of severaloccupations. The presence of numerous refits(DavidzonandHovers,n.d.)suggests.however, that burial occurredrelatively fast and with minimal geologicaldisturbance. Thislargeassemblage provides an op portunity for a detaill'(\ analysis of fl:lking accidcntsandtheir implicationsforunderstandingtheski ll of the toolmakers.The discussion focusesontwocategories of productssrcinating fromflaking accidents. One includes in completeflakes due to breakage.The second consists of hinge/step flakes and of hinge/step flakescarsoncores andonthe dorsal faces of flakes, Bothtypes of accidental flakespertain to "glitches" in the physical aSJlCcts (e.g .hammer mass andvelocit y. whichcan begaugedfrome:<perimemal andactualisticstudies:Tothetal.. 2006. andreferences therein) and/or in perception-motorcontrolduringthe process of knapping(e.g . tilling androtating of thecore tocontrolflaking angles and distri bution of massonthe core's surface.respectively). Yet these two categories of accidentalflakesalso sistentwith hardhammerpercussion (I·lovers.n.d.). Flakeswere furtherdividedinlo whole and broken artifacts(Table I. Fi gure I ). The l oca ti on ofbrcaks wasnoted, so thatbrokenflakes were divided into se\ 'cralcategories:snapped (whcllthe break is more or le ss par- allel to thestriking platformon either the di stalor p r o . ~ i  malpa rt of heflake).lah:rJIbreaks(whenthe break was more or It.'Ss perpendicular 10 the platfoml). und splitflakes(see belOW). Medialsnaps offlakes wereclassifiedas fl akefragments, Additionally.lithicpiecesthatcould not belinked reliably to anthropicflakingwere classified asangular fragments.(Theirlikely srcin from either flakes or blockscould be inferred from their thicknessvalues.)Thefew natural pebbles(in thesizerange oD-5cm) are excluded from thc following analyses. BR OKEN AR TIFACTS: Ft A KING ACC JI) EN TSOR T A I ) ~ I O N O I \ I 1 C EH "ECrS? Regardless ofthcir size group.the majority(73.8% ofN =3973) of detached pieces had been broken by f l e . ~ - differ in significantways.Snapping or split ting of flakes ollen results in regular. feathertenninations.and do not alter the core l' configuration or geometry(Crabtrce.1968 inCotterelland Kamminga, 1987:7(0). WhileIheknllpper may perceive of th eproductsthemselves asu se le ssforfuturetasks. de tachment ofsuchflakesoftendoes notentail s~ial treatment tosalvagethecore. Tothe contmry.the removal of accidental flakesthat distortthe core'ssurl ace geometryrequires thata knapper respondstoa newsituation.He needs to first evaluate thesituation andmakea decision whether knappingcan go onunhindered. whether the coreisbeyond sa lvation.orwhether it shouldand can be R'etificd. If the latter decisionismade.theknapperap plieshis skills inorder tocontrolthe damage andenablethecontinuation of the knapping proces.~. I-lin gdslcp nllkt.·s. :lJJd Ih.'ir IJCg;l- tiveonflakes andcore surfaces.ure in teresting becausethey allow a beller undcrstanding of problem-solvingcapaci ti esand adynamic process oflcchno logicaldecision-nlltking. Tabla 1, The composition of the AL. 894 assemblage. TH E; SA MI 'L E; Theassemblage consists of flakedanddetached pieces (following the terminology of IsaacundHarris.1978. rciteratt'd and e.1-p3nded byIsaac and1 lanis. 1997).Theart i- facls are made on voleanicrocks, primarilyrhyolite,basalt and trachyte.all of which hadbeen se lectedfrom the nearbyconglome r- ales in the Makaamitalu basin (Goldmanand Ho\ ·ers. in pROSS). Strikingplatfonn and bulbeharncteristics of the detacheditemsarecon- Ca t egory J)etae hed Elements Flakes(whole) Flakes(broken) Smallflakes (whole)· Smallflakes (broken)ToolsCores-on-flakes TotalFla ked El ements Cores broken reseedcobbles T0I31 Ilebris An,gul:lT IhlJ,;r1lL'rUS pillfibb JiVNI /kd~.I" from cores TotalAsserubl:lge TotBI I I"B lur al Pehbles N .. , 1802387 1121 II (7) 2 (1) 3973(1043) 20 26 4 50 752 53 805482854 .j. in Ca te tor y0.3 0.1 100 .0 16 .31 45.369. 74 28.22(0.67)(0. 1) (100.0) 40 . 00 52.00 8.00100.0 91 A2 6.58 100,0 • Small flakes <20 mm III maKlmum dimenSIOn. .j. o rT otal Asse l l l b l a~e 13.4237.328.0223.22 OJ 0,1)4 82.32 0. 41 0.540.08 1 .034 15.58 1.10 16.68 100 .00 •• Numberin parenlhesas is ofwhole artifaers out of rhe lolal for the type. ••• including one artifact classifiableas polyhedron. a unifacialehopper and a bifaeialehopper.  ion. (The elevatedfrequencies of broken artifacts in the tOlal assemblage aredueto the inelusion of angularfragments.)Frequencies of breaks among large nakes arc not relatedtoraw material properties (X l- S.72.p:.0572. DF =2).Whenallflakesizes andangular fragments are e:tamined,the differences in breakage frequencies arestatistically significant (r. - 11 .53 .p "' .OO36. DF=2). suggestingthat basalt (78.9% incomple te items)shaneredintosmallerpiecesmore onen than rhyolite (74.9"10 incomplcteitems) and especially compared to trachyte (65.4% items) (see also Goldman andH o\ers. in prcss). Thrtt dilTerelltscenarios canaccount forIhefonna lion of ncxion breaks. I) Flakesbreak during 1001 /I/()(lijicmi(JII. This happens whcn retouch thins theflakesuchthatitcannot sustainfunher application of force or pressu re .Thisis a highly unlikcly c.~planat ion in the case of A.L. 894. given thaInone of the broken artif:lcts in theasscmblagebear remnants of retouchscars.Additionally. thelow fre qucncy of retouched items inIh eassemblage(Table I) indiCiltes thm modification of lithicblanks inlo lools wasrarely practiced at thisparticularlocalilY (although it is possible Ih:11 sOllle suchartifactswcre transportedaway from thesite).2)Flakes may break during kllfll'l'illg when hammer force and \'elocityorimpact angles are miscalcu lated in relationtoraw material characteristics and/orcore geomet ry. As a mle. lithic analysts percei\·ehigher ratios of completeto broken artifactsas an expressionofbettercontrolover hammer andrawmaterial proper- 35.25 Hovers. 139 ties, i.e.a reflL'Ction of higherskilllevcJs. In thccontcxt of Old ow an lithic production. Tothct al. (2006) argu\:dfor theoppos it e i nt erpretation, suggesting that the efficient reduction ofa core'smass (a highnuke:core ratio)necessitaled higher hammer\clocities. Ilhich could be achieved through higher degTl.'Cs of expertiseyet wouldstill have ledto elc\ated levels of shattering of bolhflakr ~ - nd delached pieces._,Broken nakesare taphonomicphenomenathat occurredp05l-dcpositionally due 10 thepressure in verticsoilsand/ort ru mplin g. Suchprocl.'Ssesevidentlyoper ated at A.L. 894 ( Ho vers, 2003). In this assemblage incompleteflakes that fOrtlled Ihrough unsuccessful flaking or due totaphonomic breakage eannm be distinguishedmorphologicallyfromoneanother (with the exception of splitflakes,secbelow). C O n t c . ~tua[ evidcnce sometime helps in making this distinction. Wherecrackedflakeswcre found undisturbed(Ho .. ers. 2003: figs. 1-2) thetaphonomic n~ture of theirbreakage was easily recognizable.However, if the broken parts of a nake Iwd beenspatiallydissociated from one another. thc agent of fragmentationcouldnot be identified.: lIld such pi eceswere idcntified as either ··broken nake··oras"'angular fraJ;ments"'(accordingtothecriteriamentioned above). The only broken nakes in the A.L H94 assemblagethat can beassigncd with certaintyto accidental flaking arcsplit ("'Sire(')flakes(Siret, 1933) (sec example in Figure 2). In thesecasesthebreak occursalong the flakingaxis(i.e .more or less perpendicular to thestrikingplatfonn)and hahes the bulb ofpcrcussion (i.e . all 23 .1624.22 Whole assemblage (4716) Large flakes (2461)Small nakes(1503) •complete ~ transversal break o longitudinal break o olher breaks Figure 1. The distribution of breakage types. ·Other breaks" isa catch·all category thatincludes combinations of breaktypes as well as angularfra9ments.the srcins of which cannot be traced reliably /0 knappingactivities.  140 ~ The Cu tt ingEdge:N ew Approaches to the Archaeology of HumanOrigins Sirelbreaksare also laterally-brokenflakes.bulnot th eother way around ). Thistype of fl akingaccidcntis specifically associllled with hardhammerpercussion (Inizan ct al .. 1992). Only 142 suchitems (3.6% ofthedetached pieces) werc found in the A.L.894assemblage.Theratio of split towholeflakes (0.14) in A.L. 984 isintermediate between comparableratios in a Bonobo assemblageand the Gona assemblage (0.09 and 0.33. respectively)and is muehl ower thant ha trecorded formodemhumans (0.64) in the comparnti\'estudy ofToth et al.(2006:169). In r.,et the ratio at theHadarsite is closer to Ih at of theBonobo assemblage than 10 any of thehomininsamples discussed by these authors. Figure 2. A core and e refitted Siretflake. Bar = 1 em. Within the interpret:ltiveframework suggestcdbyTo th ct al. (2006), one would expect fromthe ratio of sp lit to whole flakes th atfrequencies of wholeflakes in theassemblage orA L. 894 be higherthan in any of theGona andmodemsample s. due to inferredlowerhammervelocities leadingto le ss sh aner during corereduc tion. Yet the frequency of whole fl akes in the A. L. 894ass.:mblage (26.2%) is lowerthan in theBonobo.Gona and modemhumansamp le s(54.9%.37.7%.39.7%.re· spec ti vely)discussedbyTothet at (2006: 168). Of the sc\ 'era[ potential explanations for th e appar·ent discrepancy bcm' . cn the ratio ofsplit to who[eflakes andassemblage composition.two are most peninentto thecurrentdiscussion. Refittingst ud ies of the A.L 894assemblage (Davidzon and1lovers,n.d.)indicate that partly-reducedcoreswereexportedoutofthe local ity.and itispossible that usable.large flakeswere also removedfromthesite,thus inflatingt he proportion of brokento who[e flakes. Secondly, thisdiscrepancymay underline therole of taphonomicprocesses in elevatingthe proportion of incompleteflakes intheassemblage, Thisanalysis is helpful in demonstratingthat. con trary to an implicit assumption of manyworkers. pro portions of brokenitems in anassemblagearefar fr om being astraightforwardreflection of t he sk ill s of t heir authors. Thisprobablypertains to li thic assemblages ofall periods: because ofthespecial in terest of rescarcitm in the knappingskills of Oldowanstone tool makers.t his caveat is especially meaningful in the context of Old owanstudie s. STUPE!> ANO HI NCE D FLAKES AN]) KNAI'I'INC SK ILLS A bricf ovcrview of thefrllcttlre mechanics of hinged andstepped Ullkes Wh cn a strikingforce is applied to acore.a fracture beginsto propagatc from the striking platfonlltownrds th c di s tal e nd oflhecore. FlakeICnllinationssometimesdcvi ate fromasmooth.grad ual propagation fracture separating aflake froma coresurface(ending in feathertemlina ti on),and stepand hinged flakesare fonned.Thisoccurs whenpropaga· tionforeedropsbelow a critical \·alue. Thi svalue issetanew with eachblowby the mass. shapeand rawmaterialtypeofboth the core and th chammer, aswellastheforce with whichimpactisapplied. Sfep flakes happeneither when tht-re isinsufficientenergytocompletea fracture (i.e .. almost immediately when thepropa· ga ti ngforce dropsbelow a critical value) or whenthe propagationer . ckintersccts with aflaw in the rawmaterial Ihat cfkcti\ ' dy blunts it ( Coo kand Gordon, 1964; Cottere ll and K am minga,1987).Bending th cn dive rt sthe forceto the face of t he core. causinga slcp termination.i.e. a 90-degree break of th eflakc'sdistnlendthat is mirrored by a "step" onthe ncgativeonthecorc's surface. A hinge tcrminat ion occurs whenflakes are fornII'd ncar thesurface of the COTC. It is re latively frequent in coreswith fl anish s urf aces. wherethe width of the prop agatingflake increasesasit is spalling o lr t he core.Iftheenergyrequiredtokecpc ra ckpropagation is unavailable. theveloc it yofpropagationdecreascs. immediatdy followed by atumofthe cracktowards thecorc surface. Ahinge tenninationisfomled. andt he detached flake exhibitsatypicalblunt tip and amore-or-Iessrounded cross-section (Collerell andKamminga. 19 79. 1986. 1987). DI.--crease in prop.1gationvelocityfollowed by hinge format ion mayoccurdueto thecurvature of the eore'ssurface (sce abo\ 'c): miscalculated positioning of hammerandcore in re lat ion to oneanother, leading  to high exterior platfon11 anglesand higherfrequencies of hinge or plunging(overshot) temlinat io ns (Dibble and Whiuaker. 1981): an underestimateof th eforce that needs to be applied in o rd cr to rcmovca flake: or a wrong choice of hammcrstone (Callahan. 19 79: 5011-berger. 1994: Pclcin. 1997a. I 997b).Often asuccessionofhingeflakes is I0n11Cd on a corc. Thi shappens becausc when a flakcisremoved from a hinge scar-bearing su rface. it s thi cknessmust increase suddenlywhcn the crack tip in tersectswith the edge oflhe scar and it slorce deceleratessuddenly. Be cause incl\'asing the crackvelocity can only be done by manipulating the hammerstone location on the striking platfoml, it isimpossible to changethisvelocityinstan taneousl y. the result being that propagationvelocityde creases and asecondhinge islikely to foml(Cotterell and Kamminga.1987). Th e fonnation of hinge andstepflakesaffects tile core so that the knapper needs to make a purpose ful deci sio n about hiscoursc of action if thetechnological probl em is \0 be solved and knapping continued.Indeed. Ihe presence of hinge andstepscars on core surfacesisoftcn cited as a cause of discard (e .g.,Ludwig.1999:Sarkai Hovers ~ 141 el al..2005;Delagncs andRochc.2005 ).Yet how hinge!slepfonnation influences th eprocessoflithicproduction beforccorediscard ha srarelybeenexamined.The fol lowing analysis dealswiththe hinge flakes themselves aswell as with thcir marks on coresand on the flakesIhal wereremovedsubsequent to the formation of hing cJ stcp tcmlination s. Hingeandstep fl aking ac ci de n ts in the A. L. 894assemblage There are only 172 large hinge flakes in theassemblage. Theseconstilute7.6% of the detached items(N=]97]) and ].6% orthe total assemblagc (No=4828). (Stepflakcs arc more difficult to identify bccausc theyarcsimilar to sn appedflakes: their presence in the assemblageswas not quantified ). The frequencics of rawmateria! types within thisgroup(71%arc madeon rhyolite.24%on basalt. and ]% on trachyte)arc practicallyidentical to the frequencies of raw material types anlong all the detached pieces.Eighty(46.5%) of Ihehingc flakes also bear accidcntal flakescarson thcir dors al faces,representingsequcntial(albeit not necessarily consecutivc) episodes of accidental removals. Whole Table 2. Frequencies and statistics of accidental scars on cores and flakes F ri.'qucrH:y of itemswith accidell1al scarsF rt" qucncy of items wlo a ccide ntal Sl'ars ~ l ean N of accidentalscar s+Co res 22 (75.86%) 7(2 4.14%) 1.6 5± 1. 73 (N =22) ~Iean N oface idcntal SC' l rs· N/A ~Iean rati o of hinged to s ti.'ppcd scar s+ /l lean ratio of hinged to s tepped ,;cars· N/ A** N/ A** /l lean ratio of all 3("c id crl1alto0.22 :1: 20 regular scars+(N=22) /llean mtio or allaccidental to N/A regu lar scars· + on flakes bearing accidental scars • whole flakes with accidental scars •• only slepped scarswereobserved on cores All Hakes 1066( 28 .56%)2 666( 7 1.44 %) 1.4 2±0.83 (N "' 1059) 1.64 ± I.D4 (N=383)0.IO±0.32 (N=889) 0.16±0.38 (N =327)0.42±0.17 (N = 105 8)0.40±0.17 (N -383) L ar 'e Il akes Sma ll fl akes844(36.73%) 1454 (63.27%) 1189(84.81) X ~ " ' I97.88.p <0 .0 001. 01'=11.49±0.90(N=838)1.14±0.44iN=213) ANOVA F-I aim. 'J 1.39.p =< 0.0001. DF =1 1.74 :1: 1.09 (N =318) 1.19±0.56 (N=64) ANOVAF -\ 'alul'15.39.W O.OOOI. DF =]0.12±0.35 (N =709)0.04±O.22 (N =174) ANOVA F-value 7. 08. po=O.007 9. DF =] O.19 ±0.4I (N :273)0 .0 4±0. 16 ( N ~ 53) A NOVA !'-value 7. 1 3. p=0 .0 080. DF =I 0.41 ±0.17 (N =838)0.45±0.19 (N =21 2) ANOVA!'- va lLl e9.02.W'0.0027.01'=1 0.40±0.16 (N =3 18 )0.43±0.18 iN= 64 ) ANOVA F-value 1.34.1'=0.24 79 . DF =I
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