Journal of Archaeological Science 32 (2005) 273–285

http://www.elsevier.com/locate/jas

Unmodified lithic material at OlduvaiBed I: manuports or ecofacts?

Ignacio de la Torrea,*, Rafael Morab

aDepartamento de Prehistoria, Instituto de Historia, Consejo Superior de Investigaciones Cientıficas, c/Serrano 13, 28001 Madrid, SpainbDivision de Prehistoria, Facultad de Letras, Universidad Autonoma de Barcelona, 08193, Bellaterra, Barcelona, Spain

Received 22 January 2004; received in revised form 15 August 2004

Abstract

The existence of high percentages of so-called manuports in the Olduvai sequence has given way to abundant papers on the

behavioural explanation of such accumulations of raw material. For this paper, we performed a first-hand re-examination of thelithic collections of two of the most relevant sites in Olduvai Bed I (FLK Zinj and FLK North). The analysis has unearthedextremely significant differences between the unmodified lithic material (the so-called manuports) and the other stone collections,

which has demanded the search for alternative hypotheses to explain the presence of the supposed manuports at these sites. Thus, wehave revised the site formation processes and have compared them with other similar sedimentary contexts in Olduvai and in nearbylacustrine basins. On the basis of our findings, we demonstrate the existence of different sized clasts in low energy contexts, andpropose a natural deposition as the answer to the existence of the supposed manuports at Olduvai Bed I. In all, our analysis suggests

that a great part of the unmodified lithic material from the Olduvai sites is not indicative of human action but the product of naturalcauses, thus being ecofacts and not genuine manuports.� 2004 Elsevier Ltd. All rights reserved.

Keywords: Africa; Olduvai; Manuports; Site formation processes; Oldowan; Plio-Pleistocene

1. Introduction: the role of manuports in

the interpretation of Plio-Pleistocene

archaeological sites

One of the first references in African Plio-Pleistocenearchaeology to the term manuport comes from MaryLeakey [25], who proposed the name for those un-modified objects located on living floors which weredevoid of hydraulic disturbance. According to this idea,manuports were to be considered as that ‘‘whichconveys the essential and only common characteristic,i.e. that the stones have been transported by humanagency’’ (Leakey [26]: 422). Along the same line, other

* Corresponding author.

E-mail address: itorre@ih.csic.es (I. de la Torre).

0305-4403/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jas.2004.09.010

definitions consider that manuports ‘‘are exogenouspieces of stone raw material that show no sign ofartificial chipping or use’’ (Potts [31]: 235) or, in a morerestrictive manner, they assume that ‘‘such unmodifiedstones can be recognized as having been objectsintroduced by hominids only if they are found in bedsthat are otherwise devoid of large stones’’ (Isaac et al.[23]: 275). Other definitions grant manuports a function-ality, by proposing that ‘‘they are unaltered examples ofthe kind of lithic material typically used either as toolsor to make tools and are considered to have beentransported by hominids to the site where they werefound’’ (Potts [32]: 158) or, more explicitly, assertingthat manuports ‘‘may represent stones subjected to suchslight utilization that no trace remains, or raw materialintended for manufacture into tools, or they maypossibly be missiles’’ (Leakey [26]: 422). In sum, these

274 I. de la Torre, R. Mora / Journal of Archaeological Science 32 (2005) 273–285

and other definitions coincide in granting the termmanuport a similar meaning: they are to be consideredas lithic objects, unmodified anthropically, but whichwere supposed to be accumulated by hominids giventhat they are located in a stratigraphical deposit thatdiffers from the sedimentary context where they aredeposited naturally.

Potts [31] conceives the Olduvai sites as stone caches,specific locations in the landscape where stones ‘bothmodified and unmodified’ were transported. Theselocations would be visited repeatedly to obtain ormanufacture tools at the same time as hominidsprocessed food obtained from the surroundings of suchspots. Manuports play a crucial role in this behaviouralproposal. Furthermore, this author considers that thetransport of unmodified lithic material in Olduvaidemonstrates a strategy focused on the reoccupation ofthe sites, i.e. the hominids would stockpile raw materialsin advance for a subsequent visit to the area [31]. In boththe stone-cache model [31] and the subsequent reformu-lation of the resource transport hypothesis [32], theaccumulation of unmodified lithic material was anorganised strategy, which was repeated systematically.

Alongside the hypotheses that aim to explain theconcentrations of modified and natural lithic material inspecific areas of the landscape, there are also numerouscontributions regarding the functionality of manuports.The most parsimonious theories assume that the Bed Imanuports in Olduvai are reserves of raw material accu-mulated for their subsequent use as cores and the pro-duction of flakes. Other activities proposed for certainmanuports, such as those linked to food processing (i.e.Ref. [22]), normally leave conspicuous and inconspicu-ous marks on the pieces, and in any case are classifiedunder the ‘utilised materials’ category created by Leakey[27]. Nonetheless, a third explanation has been soughtfor most of the unmodified lithic material, which hasconsidered manuports as missiles. Thus, authors such asB. Isaac [21] or Cannell [14] have used the ethnographicrecord or actualistic parallels as a comparative frame-work to justify the hypothesis that Olduvai manuportsand spheroids could have been missiles, a theory alsoproposed by others such as Calvin [13] or Bingham [6].

As a conclusion, since the original publication of theOlduvai Bed I and Bed II record [27], many papers haveincorporated themanuport category into the behaviouralinterpretations of the sites [8], and in fact in models suchas Potts’ [31,32], these objects compose one of the basicpillars of the line of argument that supports thishypothesis. Furthering this proposal, in recent yearsPotts ([33]; Potts et al. [34]) has used the Olduvaimanuports as a genuine cultural feature that differentiatesthis region from others with a similar chronology.

However, in this article we present an alternativeproposal. We assert that the Olduvai Bed I manuportscannot be used to elaborate hypotheses on hominid

settlement strategies, nor is it viable to discuss theirfunctionality. To do so, we set forth a basic explanation:we consider that most of the unmodified lithic objectsfrom the Olduvai Bed I sites are not manuports butinstead natural ecofacts. This revision, performed byresearching the original materials deposited in theNational Museum of Kenya in Nairobi, is a means tohighlight the contradictory nature of a great part of thesupposed manuports and the rest of the archaeologicalcollection. In order to present explanatory alternativesthat justify the association of materials to differentsedimentary sources, we will subsequently includecontextual arguments related to the formation processesspecific to the Olduvai sites. Furthermore, the paper willsearch for contemporary analogues that reproduce theproposed sedimentary scenarios. On the basis of allthese arguments, we suggest that most of the so-calledmanuports from Olduvai Bed I are merely clasts thatwere deposited naturally and associated fortuitouslywith the archaeological assemblages.

2. Assessment of the lithic collections of Olduvai Bed I

From the base to the top of Olduvai Bed I, thearchaeological ocurrences described by Leakey [27] aresuccessively FLK NN Level 4, DK, FLK NN Levels 3, 2and 1, FLK Zinj, FLK Upper Levels and FLK NorthLevels 6–1. The original description referred to theshortage of lithic resources in all strata of FLK NN(Leakey [27]: 40–47), as well as in FLK Levels 21–7(Leakey [27]: 58–60), therefore these assemblages werediscarded during our analysis. The same decision wastaken for the DK site, although for different reasons.Leakey herself ([27]: 39) stated that, given the strati-graphical position of this site, located immediately overthe basalts that configure the base of the Upper Memberof Bed I, it was impossible to determine whichunmodified lava fragments had been transported byhominids and which corresponded to natural sedimen-tation. Thus, Leakey refused to use the term manuportwhen describing the DK site and reserved the term forsites in fine-grained sedimentary contexts which, inprinciple, one would not naturally find large clasts.

In Bed I there are only two collections with sufficientrelevance to explore the nature of the so-calledmanuports and their relationship with the rest of thearchaeological collections. These are level 22 of FLK 1(regularly know as FLK Zinj or Zinjanthropus Floor)and the FLK North site, located topographically closetogether and presenting a similar stratigraphical posi-tion (middle part of the Upper Member of Bed I forFLK Zinj and upper part of the Upper Member of BedI for FLK North) and a parallel paleo-geographiclocation, in the eastern margin of the Olduvaipaleolake.

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2.1. The FLK Zinj lithic collections

Although the manuports from FLK Zinj are widelyquoted in the bibliography, only Potts [31] entaileda first-hand systematic re-examination of these objects.However, his analysis of the artefacts (Potts [31]: 377,table D.10) was very similar to the one Leakey ([27]: 58)proposed originally, since ‘although certain percentagesvaried’ the formal classification of the pieces coincided.Turning to more technological criteria for the classifi-cation of Oldowan artefacts (i.e. Refs. [23,36]), weobtain more general categories (Table 1) than the typelist proposed originally for Olduvai.

Leakey ([27]: 58) already observed a large frequencyof manuports (n ¼ 96), which Potts ([31]: 377) increasedslightly (n ¼ 99). We have observed that some of theartefacts previously classified as ‘utilised materials’ donot present any visible anthropic traces, thus thecategory of unmodified material increases once again(n ¼ 107). This collection already supposes a relevantpercentage (4.0%) of the whole, especially if compared toother categories which are in principle more importantsuch as the cores (1.8%) or the flakes themselves (4.8%),which are in fact the basic indicators of the knappingactivities at the site (Table 1A). Moreover, the percent-age of manuports becomes even more relevant if weremove small fragments and chips from the sample(Table 1B), with which unmodified objects double theirrelative frequency (8%). In itself, the representation ofthe categories obtained from the total collection starts topose some interesting questions, since it seems difficult tobelieve that so-called manuports (i.e. the potential coresor the supposed reserves of raw material transported tothe site) constitute a superior percentage to that formedjointly by the cores and the test cores.

Furthermore, if the so-called manuports were un-modified raw materials accumulated as stock for theirsubsequent reduction, it would be logical to think thatthe average size of the manuports, i.e. nodules that havenot yet been exploited, should be larger than that of the

Table 1

Categories represented at FLK Zinj according to our technological

classification

Categories N A (%) B (%)

Cores 49 1.8 3.6

Test cores 19 0.7 1.4

Hammerstones & anvils 21 0.8 1.6

Flakes 129 4.8 9.6

Retouched pieces 15 0.5 1.1

Flake fragments 861 32.3 64.1

Chips 1320 49.5 –

Angular fragments 131 4.9 9.7

Battered fragments 11 0.4 0.8

Non-modified stones 107 4.0 8.0

Total 2663 100 100

A: Chips included. B: Chips removed.

cores, which would be merely the same natural blockssubject to a process of anthropic reduction. Since theknapping process basically involves a loss of core mass,the critical variable to be analysed in this case is theweight of the objects. In line with this reasoning, theweight of the manuports should be greater than that ofthe exploited cores. The Kolmogorov–Smirnov testcorroborated the normality of the distribution of theweights of both the cores and of the supposedmanuports, and a T-test was performed subsequentlyto compare both categories. The results show bothsamples have a similar average weight in essence (seeTable 2), and therefore do not support the aforemen-tioned hypothesis that allow us to consider manuportsas potential cores.

Alongside these metric comparisons, it is also per-tinent to check the representation of each category interms of the raw material located at the site. As shownin Fig. 1, quartz predominates as the main raw materialin the site as a whole, with 69.4% of the cores, 79.8% ofthe flakes and 95.9% of the flake fragments made fromthis raw material. In contrast, the unmodified objects arefundamentally lavas (99.1%) and appear alien to regularknapping activities at the site. A chi-square test wasperformed to compare the distribution of raw materialsbetween the cores and the unmodified lithic materials. Ifthe latter were really raw material reserves, it would belogical to consider that the representation of thedifferent types (lava and quartz) would be similar inboth categories. Once again, the test presented negativeresults, rejecting the hypothesis that both samples werefrom the same assemblage (Table 3). Therefore, thismakes it difficult to consider the proposition stating thatthe supposed manuports were in the site as functionalraw material reserves.

In all, the different comparisons between the modifiedlithic material (cores, flakes, hammerstones, etc.) and theunmodified material, the supposed manuports, displaymajor differences between both samples. These differ-ences are not conspicuous merely via statistical tests, butalso by means of analysing more specific aspects such as

Table 2

T-test comparing the weight variable in both core and unmodified

stones populations in FLK Zinj

Group statistics

N Mean

(grs.)

Std.

deviation

Std.

error mean

Non-modified stones 107 287.11 200.111 19.345

Cores 49 261.86 229.511 32.787

T-Test for equality of means

T df Sig.

(2-tailed)

Mean

difference

Equal variances assumed 0.698 154 0.486 25.26

Equal variances assumed (Levene’s Test: F=1.762. Sig. 0.186).

276 I. de la Torre, R. Mora / Journal of Archaeological Science 32 (2005) 273–285

the quality of the material. Most of the so-calledmanuports are of very poor quality and are covered byvacuoles which make them unsuitable for knapping, andmany of them present extremely irregular forms whichrender them inappropriate for other activities suchas percussion or throwing. As shown in Fig. 1, thehammerstones and anvils present similar percentages tothe supposed manuports in the representation of thelavas. However, in this case, the qualitative criterion isessential: whilst most of the unmodified objects areweathered and irregular lavas, among the hammerstonesthe pattern is the opposite. Numerous examples of veryfine-grained lavas can be identified which must have beenhighly suitable for percussion activities.

On the basis of the analytical study of unmodifiedmaterial and its comparison to the rest of the collection,we find very serious conflicts that question the relation-ship between both assemblages. One last reflection couldbe of help in this sense. In total, we estimate that in FLKZinj there is slightly over 74 kg of lithic material. Of thisamount, 30.72 kg are unmodified objects. Thus, would itbe logical to consider that the hominids transportedalmost half of the lithic material to the site and then didnot modify it in any manner? We think not, as we haveattempted to demonstrate in this analysis of thearchaeological collection per se, and will subsequentlysupport with our contextual model.

Fig. 1. Distribution of raw materials in the categories of FLK Zinj.

Table 3

Chi-square test comparing raw materials from the cores and un-

modified objects from FLK Zinj

Value df Asymp. Sig. (2-sided)

Pearson chi-square 92.608* 1 0.000

Likelihood ratio 96.304 1 0.000

N of valid cases 155

* 0 cells (.0%) have expected count less than 5. The minimum expected

count is 10.84.

2.2. The FLK North lithic collections

The FLK North site, located less than 200 metresaway from FLK Zinj, is a stratigraphical assemblagewith different archaeological levels both in Bed I (Levels6–1) and in Bed II (FLK North with root casts, FLKNorth Deinotherium Level and FLK North SandyConglomerate). The upper part of the sequence in Bed Iwas composed by archaeological Levels 1, 2 and 3,which formed a single 60–90 cm horizon, with a grey-brown silty clay matrix. Given the lithologic uniformityof the level, Leakey [27] subdivided the depositarbitrarily, separating levels 1–2 on the one hand, whichcannot be distinguished, and underlying level 3 on theother. Archaeological Level 4 was located underneath,composed by dark chocolate-brown silty clays, andbeneath that Archaeological Level 5, lithologicallycharacterised by greenish-yellow clays with ferroginousbands and tuff laminations in the lower area. The baseof FLK North is composed by Level 6, where lithicartefacts and fauna are located in a deposit composed bygreyish-brown silty clays with white streaks.

Leakey [27] identified a large number of unmodifiedobjects in most of the levels, proposing the existence of 7of these specimens in Level 6, 29 manuports in Level 5,17 in Level 4, up to 39 unmodified objects in Level 3 anda total of 123 supposed manuports in Levels 1–2. Ourrevision of these collections has identified a largernumber of unmodified objects in most of the levels(Table 4). As occurred in the neighbouring site of FLKZinj, it is also surprising to find that in FLK North thesupposed raw material reserves double (Level 5) andeven triple (Levels 4, 3 and 1–2) the percentage of cores.The same occurs when comparing the frequency ofunmodified objects with categories such as chips orflakes, usually the dominant types in paleolithic sites,and which in Levels 5–1 have less representation thanthe supposed raw material reserves. Once again, it seemshard to present a behavioural explanation statinghominids accumulated more unaltered lithic materialthan they genuinely modified and used.

Given the low density of archaeological remains inmost of the FLK North levels, it would not beappropriate to apply inferential tests to all collections,thus they were limited to Level 1–2, with a sample ofalmost 1500 lithic pieces (Table 4). Referring to theearlier hypothesis that the weight of the supposedmanuports should be greater than that of the cores ifthey were genuinely raw material reserves, a T-Test wasperformed to compare both populations. As the datawas not homoscedastic, it was necessary to transformthe weight variable by Naperian logarithm, and thenverify the normal distribution implementing theKolmogorov–Smirnov test (Fig. 2). However, the sub-sequent T-test assumed the equivalence of the averagesin both samples; that is to say, both the unmodified

277I. de la Torre, R. Mora / Journal of Archaeological Science 32 (2005) 273–285

Table 4

Categories represented in the 5 archaeological levels of FLK North in Bed I according to our classification

Level 6 Level 5 Level 4 Level 3 Level 1–2 Total

N % N % N % N % N % N %

Cores 4 3.1 15 9.2 8 9.6 11 5.1 84 5.8 122 6.0

Test cores – – 1 0.6 – – 5 2.3 16 1.1 22 1.1

Hammerstones & anvils 21 16.3 29 17.8 14 16.9 35 16.4 99 6.8 198 9.7

Flakes 9 7.0 5 3.1 4 4.8 16 7.5 85 5.8 119 5.8

Retouched pieces 1 0.8 1 0.6 – – 3 1.4 8 0.5 13 0.6

Flake fragments 18 13.9 48 29.5 10 12.0 58 27.1 542 37.3 676 33.0

Chips 35 27.1 4 2.5 5 6.0 18 8.4 222 15.2 284 13.9

Angular fragments 9 7.0 23 14.1 14 16.9 20 9.3 117 8.0 183 8.9

Battered fragments 30 23.3 4 2.5 – – 4 1.9 37 2.5 75 3.6

Non-modified stones 2 1.6 33 20.2 28 33.7 44 20.6 246 16.9 353 17.2

Total 129 100 163 100 83 100 214 100 1456 100 2045 100

objects and the cores have a similar weight, withoutvisible substantial differences in size of the supposedmanuports that would lead us to assume their sub-sequent reduction as cores (Table 5).

The distribution of raw materials in terms of eachcategory of artefacts can also help in the discriminationof both populations. In Table 6 we can observe that,except for Level 4, quartz predominates as the main rawmaterial in all levels. Nonetheless, when we break downthe raw materials in terms of technological categories,as in Fig. 3 for Level 1–2, it can be observed thatunmodified objects do not follow this general trend. Inthis level the great majority (86.2%) of the supposedmanuports are basalt items, whilst amongst the coresthis percentage drops to 50% and there is only 26.1%basalts in the whole collection. The same trend is visiblein the other levels, despite the shortage of the sample.Thus, in level 3, 93% of the unmodified objects arebasalt items compared to 54.5% of the cores and 34.1%of the total, with a similar trend in Level 4 (85.7% of theunmodified objects are basalt whilst only 49.4% of theknapped pieces in that level are) and level 5 (87.5% ofthe supposed manuports are basalt items in the

Fig. 2. Normal distribution of Naperian logarithms of the weight of

cores and unmodified objects at FLK North Level 1–2. (A) Normal

curve of the cores. Std. Deviation=0.54. Mean=5.67. N ¼ 84. Level

of significance in the Kolmogorov–Smirnov test=0.120. (B) Normal

curve of the unmodified lithic objects. Std. Deviation=0.64.

Mean=5.52. N ¼ 245. Level of significance in the Kolmogorov–

Smirnov test=0.220.

collection in which these types of lavas only compose35.6% of the total).

A chi-square test was carried out in order to verify ifthe distribution of raw materials is similar in unmodifiedobjects and in the cores. This time, phonolites were alsoincluded in the comparison of quartzes and basalts, andthe analysis was limited to Level 1–2, the collectioncontaining the greatest amount of elements. The results(Table 7) are similar to those obtained for FLK Zinj,rejecting the option that both samples (cores andunmodified objects) come from the same population.That is to say, the raw material that predominates in themanuports does not coincide with the distribution of thecores, thus it seems difficult to sustain that the latterwere selected from the unmodified lithic material.

On the basis of the analytical comparisons per-formed, we consider we have effectively justified thehypothesis asserting that most of the unmodified objectsare not related to the activities of lithic artefactproduction and use in the different levels of FLKNorth. However, even though the visual analysis of thesupposed manuports in FLK Zinj have already shedsome light on the origin of these materials, given the badquality of almost all of them, the pattern is not asevident in FLK North. In the different levels of FLKNorth some high quality river cobbles very similar to theblanks which were used as hammerstones can beidentified, although they do not present traces ofutilisation. Therefore, we cannot exclude the possibilitythat some of these unmodified river cobbles weresupplied anthropically. Nonetheless, alongside these

Table 5

T-Test for the similarity of the means of the logarithms of the weight

variable in the cores and unmodified objects at FLK North Level 1–2

(see significance tests in Fig. 2)

T df Sig.

(2-tailed)

Mean

difference

Equal variances assumed �1.845 327 0.066 �0.1445

Equal variances assumed (Levene’s Test: F=3,434. Sig. 0.065).

278 I. de la Torre, R. Mora / Journal of Archaeological Science 32 (2005) 273–285

Table 6

Distribution of raw materials per level in FLK North

Raw material Level 6 Level 5 Level 4 Level 3 Level 1–2 Total

N % N % N % N % N % N %

Basalt 19 14.7 58 35.6 41 49.4 73 34.1 380 26.1 571 27.9

Quartz 108 83.7 76 46.6 31 37.3 110 51.4 884 60.7 1209 59.1

Phonolite 2 1.6 28 17.2 11 13.3 25 11.7 174 12.0 240 11.7

Others – – 1 0.6 – – 6 2.8 18 1.3 25 1.2

Total 129 100 163 100 83 100 214 100 1456 100 2045 100

items there are numerous lava pieces, some vesicular andof extremely poor quality (see Fig. 4) which, alongsidethe reduced size of some of them (30–40 mm), alsoprovide qualitative information rejecting a humanaccumulation of these pieces.

When analysing FLK North, we have calculated thatthe ensemble of the 5 levels being studied producedslightly over 248 kg of lithic material. Of this amount,101 kg corresponded to unmodified lithic material.Thus, would it make sense that the hominids did notmodify almost half of the lithic material after makingthe effort of concentrating it in this location? In all, weconsider these qualitative features, together with thestatistical descriptions presented above, compose a suf-ficiently sound argument to propose that most of thesupposed manuports located in the analysed sites areunrelated to hominid activities and, instead, theiraccumulation answers to a natural origin.

3. The sedimentary contexts of Olduvai Bed I

In the previous section we have proposed that a greatpart of the unmodified lithic material from FLK Northand FLK Zinj has a natural and not an anthropogenicorigin. It is necessary now to justify the reasons wherebylarge stones were located in sediments deposited in low

Fig. 3. Distribution of raw materials in the categories represented at

FLK North Level 1–2.

energy contexts such as the FLK complex. This line ofargument is especially relevant, since it is precisely themetric conflict between the predominant sedimentarymatrix (clays) and the large associated stones which ledresearchers to propose the impossibility of them beingdeposited in these locations naturally, and led them toturn to the anthropic supply of the rocks, consideringthem genuine manuports.

Referring to the original description (Leakey [27]:49), Zinjanthropus Floor was a paleosol approximately30 cm thick with a sedimentary matrix composedbasically by silty clays, although Leakey also docu-mented many nodular limestones throughout the wholeof the exposed surface. They are lake-margin sediments,and it is estimated that the perennial lake was locatedapproximately 1 km away [18], thus low energysedimentation took place. The original publicationproposed that FLK Zinj was a living floor in pristineconditions in which there had been no kind of post-depositional modification process [27]. This idea hasbeen maintained over the years on the basis of thetaphonomic analyses of the fauna (i.e. Refs. [11,31]) andthe lithic industry [29], as well as the spatial distributionof the remains [24]. Convincing data has been presentedcontradicting a hydraulic alteration of the archaeolog-ical materials, such as the different sized objects, the lackof roundness in the industry and, primarily, thesedimentary context (clays) which indicates a low energydeposition.

Similar findings have been noticed in the five levels ofFLK North in Bed I. Four of them were originallyconsidered living floors and the other a butchering site,all preserved in their original position (Leakey [27]: 61)and in silty clay sedimentary contexts. Once again, thelarge unmodified blocks present a metric conflict with

Table 7

Chi-square test comparing the raw materials of the cores and

unmodified objects in FLK North Level 1–2

Value df Asymp. Sig. (2-sided)

Pearson chi-square 52,500* 2 0.000

Likelihood ratio 47,100 2 0.000

N of valid cases 322

* 1 cell (16.7%) have an expected count of less than 5. The minimum

expected count is 2.29.

279I. de la Torre, R. Mora / Journal of Archaeological Science 32 (2005) 273–285

the clays, the latter typical of low energy sedimentationand with low or zero traction, which made researchers(i.e. Refs. [27,31]) turn to anthropic causes to explain thepresence of these items.

The location of large clasts in clay contexts withoutthe energy capacity to transport them was the onlyargument implemented to consider that they had beenintroduced anthropically. In short, this leads to theassumption that these anomalies in the heterometries ofthe sedimentary matrix cannot be produced naturally. Inthis case, and considering we are referring to intentionalanthropic accumulations, it would be logical to thinkthat we would not encounter this phenomenon beyondthe clusters of archaeological remains formed by thesites, at least in the sedimentary contexts associated withthe lake margin. At these locations, deposition wouldalways be linked to clays and other low energysediments, devoid of large natural clasts.

However, Leakey herself already contradicted thishypothesis when describing the DK stratigraphy, bystating that ‘‘a characteristic feature of the whole bedwas the presence of small pebbles of lava, quartz andpink feldspar in otherwise fine-grained sediments’’(Leakey [27]: 21). Geological studies on Olduvai alsosupport this proposal; Hay ([18]: 46) referred to theappearance in the eastern lake-margin deposits of theMain Gorge in Olduvai of a large variety of basementand volcanic detritus, some pebble size and some up to64 mm long, made of different raw materials. Theyappeared independently or formed small assemblageslocated in mudflat sediments. The complexity of thepedogenic processes in the Olduvai sequence has beenverified in the latest studies, which show that thepaleosol of the lake-margin of the Lower Bed II wasaffected by multiple pyroclastic episodes, mass move-ment, sheet flow and debris-fan processes (Ashley andDriese [1]: 1077), which could have left considerablevolcanic material in low energy sedimentary contexts.

Fig. 4. Basalt unmodified lithic material at FLK North Level 1–2. See

morphological irregularity of the pieces and their vesicular structure.

In addition to all this evidence, the current archae-ological project in Olduvai has made a series of trenchesin the Lowermost Bed II (i.e. Refs. [7,8]), and thesedimentary analysis of those pits [2] once againprovides significant data. The lithologic analyses (Ash-ley and Hay [2]: 115, Table 1) indicate that the fragmentsof volcanic rocks compose relevant percentages linkedto short events, typical of a medium with a systeminvolving ephemeral, shallow and multichannel flows,always in a lake-margin environment.

4. Contemporary examples of coarse sediment

inputs in lake-margin deposits

As stated above, the offsite analyses of the Olduvaigeology indicate the regular presence of medium-sizedvolcanic clasts in lake-margin sedimentary contexts.However, this is not the only available evidence:Deocampo [15] describes current formation processesof the wetland deposits in sedimentary basins similar toOlduvai, such as lake Eyasi, Ngorongoro and Natron. Inthese contemporary lake-margin wetlands, Deocampo[15] observes coarse-grained deposits from the streamsthat drain the basin. These streams often erode and arewedged in the wetland substrate, transporting coarsesediments from the outcrops that are being eroded andthus are mixed with typical lake-margin sediments.

The analytical framework supplied by Deocampo’swork [2] led us to visit several of the lake-margins hedescribes as well as other nearby margins, in order tosearch for examples similar to the model that appears inOlduvai. All the visited lake basins presented positiveresults. For example, at lake Manyara we observed lake-margin wetland deposits characterised by clay sedi-ments. However, it also presented angular cobbles indifferent sizes (50–200 mm). These cobbles sometimesappeared isolated and others in small patches (seeFig. 5). It is interesting to point out that the examples ofnatural cobbles observed in Lake Manyara are locatedin lake-margin deposits that are very near the perenniallake (approximately 200–300 metres), and thus evencloser than the FLK sites. Therefore, despite observingdeposits that are even more typically lacustrine than theOlduvai deposits, at Manyara we registered a variety ofvolcanic cobbles which in another context would havebeen considered manuports, and are merely the resultof complex natural lake-margin deposit formationprocesses.

These objects were also documented in Eyasi, wherewe located cobbles and pebbles over 100 mm in themudflat on the lake’s eastern margin (see Fig. 6A,B). Inthis case the source area for these materials (theescarpment) was further away than in Lake Manyara.At Ndutu (Fig. 6C,D), cobbles appear in the lake-margin deposits which were originally from a small

280 I. de la Torre, R. Mora / Journal of Archaeological Science 32 (2005) 273–285

Fig. 5. Contemporary examples of lava clasts in the lake-margin at Lake Manyara. (A) Landscape of the shore of Lake Manyara; area where clasts

were documented is marked. (B) and (C): Examples of clasts in the mudflat surface. (D). Buried clasts in mudflat contexts of the lake-margin of Lake

Manyara.

nearby outcrop. At Lake Natron, we also found a varietyof volcanic cobbles in the mudflat deposits of the lake,although given the area of the basin, they were from thefluvial processes described by Deocampo [15] or enteredthe lake sediments directly via gravitational phenomenain the area where the shores of the lake practically reachthe escarpment (Fig. 7).

In short, all our observations at lake margins withsuch different sedimentary supplies as the Manyara,Natron, Eyasi and Ndutu provided identical results:either by sheet flows, interbedding, erosion, gravitation,reworking processes, bioturbation, etc, the sedimentarycontexts of clays typical of lake-margin wetlands presentan array of volcanic clasts of a variety of sizes,morphologies and origins. These occur both isolatedand in small clusters, which in principle do not seem tocorrespond to the sedimentary dynamic where they arelocated, but which have nonetheless been deposited inthese locations naturally, not anthropically.

These clasts are also located in the paleosols of thelacustrine mudflat with lake-margin origin in the Old-uvai deposits. Given the supposed lithological anomalythese large clasts contained in clay deposits such as thosedescribed in Olduvai, Hay himself [18] even explored thepossibility of them being manuports, although heproposed sheet floods and small streams as the mostprobable agents, which could have transported the clasts

to the mudflat paleosols and even to the lake-margins.Since, according to Hay [18], the pebbles and cobbleswere scattered all over the facies of the lake-margin (andnot only in the assemblages clustered in the archaeo-logical sites), it would not be very realistic to considerthat the hominids scattered clasts along the Olduvaibasin, and it is more parsimonious to propose a naturaldeposition. Thus, if we add the contemporary referencespresented in this section to the offsite evidence ofOlduvai, we can evidently conceive the existence ofnatural processes that incorporate large cobbles to lowenergy sediments such as those typical of lake-margindeposits.

5. Revision of the FLK sites formation processes

After illustrating the viability of large clasts appear-ing naturally in clay contexts, we will now explore if thiscould be the case for the FLK Zinj and FLK Northsites. We have previously pointed out that the archae-ological record of FLK Zinj was subjected to low orzero hydraulic transport (Refs. [29,31], etc.). Yet, thisdoes not mean that the formation of the archaeologicalsite responds to a single depositional event. On the basisof the bone weathering stages a sedimentation intervalthat ranges between several months (i.e. Refs. [9,11])

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Fig. 6. (A) Lake-margin of the east shoreline of Lake Eyasi. (B) Detail of the clasts located in the surface of the mudflat in Lake Eyasi. See presence of

fish by clasts that indicates the recurrent lacustrine flooding of these deposits. (C). Floodplain of the small Lake Ndutu. (D). Detail of the clasts

located on the shores of Lake Ndutu.

and a few years [30,31] is proposed. Regardless of thereal deposition interval, a weak paleosol was formedand, as verified even for the Olduvai sequence (i.e.Ref. [1]), this supposes the combination of a variety ofbiotic and sedimentary agents in a complex formationsequence.

In this complex site formation process, we must notexclude the possibility of hydraulic supplies of naturalclasts, although as we have stated, even though thearchaeological remains do not present traces of fluvialtraction, the existence of a small channel 35 cm deep and53 cm wide was documented at FLK Zinj [27,31]. Evenif this channel did not have sufficient significance to alterthe original configuration of the archaeological remains,it could have dragged natural clasts from nearby areas.Or perhaps, more probably, the channel eroded andredistributed levels underlying the FLK Zinj site inwhich there were fragments of lava that were therebyincorporated to the FLK Zinj clay paleosol.

In fact, we do not believe that it was mere coincidencethat most of the supposed manuports from Zinj are ofa very irregular vesicular lava which is identical to thebasalt that emerges from the immediate proximities ofthe site (see Fig. 8). Furthermore, the majority of thesupposed manuports that Leakey ([27]: Fig. 24) plots in

the Zinjanthropus Floor plan are located on theperiphery (western and southern area) of the archaeo-logical concentration, which should be linked to thenatural deposition processes of the clasts, and probablyof some of the bones (see also Binford et al. [5]: 131).Despite the silty clays that configure the main body ofthe stratigraphical level, we consider the erosion oflower levels, the redistribution of clasts and other micro-scale processes that take place in the formation of sites,could have led to archaeological remains becomingmixed with totally different lithic materials produced bynatural sedimentation.

The site formation processes that were operative inFLK North must have been even more complex than inFLK Zinj. Although Leakey ([27]: 61) considered thatfunctionally four of the levels (Levels 5–1) of FLKNorth Bed I were living floors and the other wasa butchering site (Level 6), in the same work shespecified that Levels 5–1 were sites with diffusedmaterials, in which the archaeological remains werescattered along a thick stratigraphical sequence (Leakey[27]: 258). FLK North Level 6, the only level whichLeakey [27] considered as belonging to a single archae-ological event but fortuitously linked to a naturalbackground of bones (also Bunn [10]), also seems to

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Fig. 7. (A) Central-western shore of lake Natron beside the escarpment. (B) and (C) Details of the lava clasts in the lake’s clay contexts beside the

escarpment, probably deposited by gravitation processes. (D). Basalt clasts in the lake itself in the northwestern area of Lake Natron.

correspond to a long formation period with differenttempos in the deposition of the carcasses [31]. There-fore, despite once again encountering (as occurred inFLK Zinj) clay contexts linked to low energy sedimen-tation, it is easy to propose processes such as the onesstated by Ashley and Driese [1], Mack et al. [28], etc.,regarding the complexity of the formation of the strataassociated with a lake-margin. It would be perfectlyplausible to consider a natural explanation for a largepart of the unmodified clasts which could have theirorigin in, for example, small hydraulic events like sheetflows.

Another possibility to consider is the vertical mig-ration of lithic objects. FLK North is around 7.2 m indepth (Leakey [27]: 61) therefore, speaking of generallyvery fine sediments such as clays, there could havebeen vertical movements of large elements, a fact thatis very common in archaeological sites (i.e. Refs.[12,17,19,37,38], etc.). Leakey herself [26] observed thatpart of the archaeological remains of FLK North Level1–2 ‘‘appear to have sunk down from the higher level,either when the clay was wet, or else down cracks whichform when it becomes dry’’ (Leakey [26]: 428). Likewise,vertical migration was one of the possibilities Hay [18]

Fig. 8. (A). Current state of the FLK Zinj site. View in the foreground of the close proximity to the site of weathered vesicular lavas from the erosion

of underlying basalts. (B) Detail of the weathered lavas that appear by FLK Zinj.

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considered to explain the presence of pebbles in claydeposits in many of the Olduvai contexts. Accordingto this author, in Olduvai we must contemplate thepossibility whereby pebbles originally deposited in a levelabove the unconsolidated sediments could subsequentlybe scattered vertically via trampling or burrowing byanimals, or by the effect of the roots themselves (Hay[18]: 85). Therefore, it seems justified to assert that thesevertical migration processes could have occurred sys-tematically in FLK North, mixing elements fromdifferent depositional stages and, among them, naturalcobbles which were fortuitously associated with archae-ological remains.

As a whole, it is viable to assume the possibleexistence of small hydraulic events, slow sedimentationprocesses, vertical migrations, and a variety of eventsthat mixed a natural background deposit of bones withgenuine archaeological remains (i.e. Refs. [10,22,27]), orat least archaeological pieces from different occupationsof the site [31]. Considering all the above processes, itwould seem appropriate to justify the non-anthropicpresence of unmodified stones in FLK North which wenow know were also scattered naturally around thelandscape of the Olduvai lake-margin.

6. Conclusions

Over the last few decades, the term manuport hascirculated vastly in bibliographies referring to theOldowan in East Africa (i.e. Refs. [22,23,27,31,32],etc.). In fact, the idea of the accumulation of unmodifiedlithic material in specific areas of the landscape has beenused for the preparation of several models on Plio-Pleistocene hominid land-use and organisation (i.e.Refs. [20,22,31,32,34]).

However, it has not always been easy to differentiatewhich unmodified stones had been transportedanthropically to the sites, therefore we have often turnedto arbitrary criteria such as a certain size of the rocks inorder to consider them manuports, and, even then, asregards the Koobi Fora record ‘‘of course, it does notfollow that the large unmodified stones were introducedby hominids; they are listed here simply because theymay have been’’ (Isaac et al. [23]: 275). Along this line ofreasoning, some researchers (i.e. Refs. [23,34]) havereferred to genuine differences between the technologicalstrategies of areas such as Olorgesailie and Koobi Fora,where manuports are very scarce, and Olduvai where ithas been assumed that these items constitute relevantpercentages.

Throughout this article, we have aimed to decon-struct precisely the idea asserting that in Olduvai Bed Ithe genuine manuports compose significant percentages.In order to do so, we started by comparing the itemswith traces of anthropical modification to those that do

not present any traces of human alteration. In this sense,we consider we have provided sufficient arguments todefend the statement that a great part of the unmodifiedobjects cannot be considered potential raw materialreserves, as they do not present the same characteristicsfound among objects that have been subjected toanthropical alteration.

With the sedimentary conflict between large clastsand low energy contexts being the only argument usedto justify the human transportation of these objects, thesubsequent step was to find out if the pattern can appearin natural circumstances. Both the geological researchon Olduvai [1,2,18] and on other lake-margin environ-ments (i.e. Refs. [28,35], etc.) stress the complexity ofmudflat formation processes and the possibility offinding detritic deposits in typical clay sediments.Contextual frameworks such as those presented byDeocampo [15] also allowed us to verify the presence oflarge clasts. We personally visited several lakes in NorthTanzania to find clasts that were present (isolated and insmall patches) similar to the supposed manuports, butwhich had been deposited naturally in low energycontexts.

On the basis of these examples, we have presenteda hypothesis regarding the formation of the FLK Zinjand FLK North sites, in which we put forward a naturalexplanation for many of the so-called manuports.Without doubting the more or less primary nature ofthe archaeological remains, at least as regards FLKZinj, we also assume the dynamic features implicit in theformation processes of any archaeological site. That isto say, we believe in the existence of different agents(biotic and physical) involved in the formation of bothsites, on the basis of the aggregation of natural andarchaeological elements from successive events. Ourproposal to interpret events that took place in FLK Zinjand FLK North can be summarised perfectly in thescenarios described by Foley ([16]: 172, figure 6.12) fora more general sphere: the successive filling and erosionprocesses created cumulative palimpsests giving a multi-causality of events. From this dynamic perspective, andconsidering the existence of large clasts in the lake-margin landscape, it is not hard to image these itemsbeing easily transported to the area where the archae-ological remains were located, and then misinterpretedas manuports.

Researchers have always insisted on the multiplicityof events involved in the formation of the Bed I sites (i.e.Refs. [4,7,24,29,31,33]). Yet the matter of the so-calledOlduvai manuports is still pending, and there is recentresearch (i.e. Refs. [14,34] that continues to use theseobjects to propose behavioural models. Throughout thispaper, we have attempted to show that many of the so-called manuports are actually natural occurrencesunrelated to hominid activities. We are obviously nottrying to deny the concept of ‘‘unmodified object

284 I. de la Torre, R. Mora / Journal of Archaeological Science 32 (2005) 273–285

transported anthropically,’’ and, in fact, some of themprobably were accumulated intentionally, i.e. they aregenuine manuports. However, we consider many ofthem were deposited naturally, and the high percentagesof manuports assumed in Olduvai and implemented topresent different behavioural hypotheses are false. Webelieve it is necessary to recognise that there area number of non-human processes that can createassemblages which may resemble those attributed tohuman activities (i.e. Refs. [3]). This could haveoccurred at Olduvai Bed I, and we may be grantingcultural significance to issues that could be explained vianatural causes and that, in all, the supposed accumu-lations of hominid raw material reserves are merelynatural ecofacts.

Acknowledgements

We would like to thank the Governments of Kenyaand Tanzania for authorising us to research the Olduvaicollections. We are indebted to Jane Hallos for her helpwith the stylistic corrections. We thank to ManuelDomınguez for his courtesy by supplying the photosthat compose parts a, b and c of Fig. 5. This work hasbeen financed by the Estades per a la Recerca a Fora deCatalunya 2001 (BEAI400198) of the Generalitat deCatalunya, and the Projects BHA 2000-0405 and BTE2000-1309.

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