ll The Food-Sharing Behaviorof Protohuman Hominids

by Glynn IsaacApril 7978

Excavotions ot two-million-yeor-oid sites in Eost Africoofler new insights info humon evoiutionory progr€ssby showing thot eorly erect-stonding hominids modetools ond coried food to q ftome bose

/a\ver the past decade investigatorsf I ot fossil man have discovered\-z the remains of many ancient

protohumans in East Africa. Findingsat Olduvai. Laetolil. Koobi Fora. theOmo Valley and Hadar, to name someprominent locations, make it clear thatbetween two and three million yearsago a number of two-legged hominids, es-sentially human in form, inhabiled lhispart of Africa. The paleontologists whohave unearthed the fossils report thatthey differ from modern mankind pn-marily in being small. in having rela-tively large jaws and teeth and in hav-ing brains that, although they are largerthan those of apes of comparable bodysize, are rarely more than half the sizeof modern man s.

The African discoveries have manyimplications for the student of humanevolution. For example, one wonders towhat extent the advanced hominids oftwo mill ion years ago were human intheir behavior. Which of modern man sspecial capabil it ies did they share?what pressures of natural selection, inthe time since they lived. led to the evo-lutionary elaboration of mans mindand culture? These are questions thatpaleontologists find dimcult to answerbecause the evidence that bears on themis not anatomical. Archaeologists, byvirtue of their experience in studyingprehistoric behavior patterns in general,can help to supply the answers.

these observations can now be corn-pared with quantitative data from an-other new area ofstudy, namely the cultural ecology of human societies thatsupport themselves without raisingplants or animals: the few survivinghunter-gatherers of loday. Another im-portant new movement has involved thedirect study of lhe ecological circum-stances surrounding human evolution-ary developments. Investigations ol rhiskind have become possible because thestratified sedimentary rocks of East Af'rica preserve. in addition to fos:i l hominid remains, an invaluable store ofdata:a coherent, ordered record of the envi-ronments inhabited by these protohu-mans.

The work of the archaeologist rndrawing inferences from such data rsmade possible by the fact that at a cer-tain stage in evolution the ancestors ofmodern man became makers and usersof equipment. Among other things. theyshaped, used and discarded numerousstone tools. These virtually indestruc-tible artifacts form a kind of fossil rec-ord of aspects of behavior. a recordthat is complementary to the anatomr'cal record provided by the fossil bonesof the toolmakers themselves. Studentsof the Old StoDe Age once concentrat-ed almost exclusively on what could belearned from the form of such tools. To-day the emphasis in archaeology is in-creasingly on the context of the arti-

lacts: for example the distribution pat-tern of the discarded tools in differentsettings and the association of tools withvarious kinds of food refuse. A study ofthe contexts of the early African arti-facts yields unique clues both to the eco-logical circumstances of the protohu-man toolmakers and to aspects of thersocioeconomic organization.

Comparing Men and Apes

What are the patterrs of behavior thatset the species Hono sapiens aparl fromits closest l iving primate relatives? Il isnot hard to draw up a list of such differ-ences by comparing human and ape be-havior and focusing attention not on themany features the two have in commonbut on the contrasting features. In thelist that follows I have drawn on recentfield studies of the great apes (particu-larly the chimpanzee, Pan troglodytes)and on similar studies of the organiza-tion of living hunter-gatherer societies.The list tends to emphasize the contrastsrelating to the primary subsistence ad-aptation, that is, the quest for food.

First. Hotno sapiens 1s a twoleggedprimate who in moving from place toplace habitually carries tools, food andother possessions either with his arms orin containers. This is not true of thegreat apes with regard to either postureor possessions.

Second. members of Hono sapiens so-

sIiIL ,

!

It has long been realized that the hu-man species is set apart from its closestIiving primate relatives far more by dif- pAsr AND PRESENT LANDscApES in rh€ Rift valtey region of East Africa, shown scbc-ferences in behavior than by differen- maticdty on the opposite page, summari?€ th€ geological ;cti;ity rhat 61gt pr€serveit anit tatelces in anatomy. Paradoxically, however, exposed evidence oi protohurnan tife. Two mi ion ycars ago (trl) the bonei of hominids (1-.1,the study of human evolution has tra- crlrr) and other animals (,rJ, rrlor) were distributed across hills snd a floodplain (loregmunoditionally been dominated by work on rdiac€nt to a Rift vallcy laka Also lying on th€ surface w€r€ stonc tools (r/ark do.r) msd€'the skeletal and comparative anatomy uscd .nd discarded by th€ protohumens, Lay€rs of sedimcnts then covered tb€ bones lnd tools

of fossil primates. Seviral new researci lying on-_rhc flood_plain; burial pres€rv€d them, wheieas thc boncs and tools in th€ hills wd€

mouements in recent years. to*eu"r. ."""nlu1lll :1:l"9"1yilll'1i1fto4,,,). afrer s fault has raised a block or sediments, elosion

is exposinq som€ of lhc lone-buried bones and cluners of lools. including the lhree types ofsilenave oegun to oroaoen rne scope oI . loJnonitr".u*u""inthe-lopblockdiagram{,4-c},si tesofTypeAconlainclustersofstonedirect evolutionary inquiry. One suctr *1.1.r"1"f;tii ,h" ;i.;; .i;;; cor€s that provid€d ihe law marerial ror rhe toots andmovement involves investigations of the waste f;kcs from rhe roolmaking process, but tittfi or no bone is present. sites of TypG B con-behavior and ecology of living primates tain simitar clustcrs of tools in asiociation with the bones of a singie large animal. Siies of Typeand of other mammals. The results of C aho coniain similar cluslers of tools. but the bones ar€ from manv difr€rcnt animal sD€cies.

i.

t.l

112 HUMAN ANCESTORS

cieties communicate by means of spo-ken language; such verbal communica-tion serves for the exchange of informa-tion about the past and the future andalso for the regulation of many aspectsof social relations. Apes communicatebut they do not have language.'flwd, n Homo sapr'ens societies theacquisition of food is a corporate re-sponsibility, at least in part. Amongmembers of human social goupings ofvarious sizes the active sharing of foodis a characteristic folm of behavior:most commonly family groups are thecrucial nodes in a network of food ex-change. Food is exchanged betweenadulti, and it is shared between adultsand juveniles. The only similar behaviorobserved arnong the great apes is seenwhen chimpa[zees occasionally feed onmeat. The chimpanzees' behavior, how-eyer, falls far short of active sharing; Isuggest it might bette! be termed tolelat-ed scrounging. Vegetable foods, !r'hichare the great apes' principal diet, are notshared ald are almost invariably con-sumed by each individual oD the spot.

Fou h, in human social groupingsthere exists at any given time what canbe called a focus in space, or "homebase," such that individuals can moveindependently over the sunoundiog ter-rain and yet join up again. No such

home base is evident in the social ar-rangements of the great apes.

Fifth, human hunter'gatherers tend todevote more l ime than other l iving pri-mates to the acquisition of high-protemfoodstutrs by hunting or frshing for am-mal prey. It should be noted that thedistinction is one not of kind but of de-gree. Mountirg evidence of predatorybehavior among great apes and mon-keys suggests that the principal contrastbetween human beings and other livingprimates with respect ro predarion isthat only human beings habitually feedon prey weighing more than about 15kilogams.

The gathering activities of humanhunter-gatherers include the collectionof edible plants and small items of anl-mal food (for example lizards. turtles,frogs, nestling btds and eggs). Charac-teristically a proportion of these food-stuffs is not consumed until the returnto the home base. This behavior is rnmarked contrast to what is observedamong foraging great apes, which al-most invariably feed at the spot wherethe food is acquired.

Still another conrast with great-apefeeding behavior is human hunter-gath-erels'practice of subiecting many food-stuffs to preparation for consumption,by crushing, grinding, cutting and heat-

ing. Such practices are not observedamong the great apes.

Human hunter-gatherers also makeuse of various kinds of equipmeot in th€quest for food. The human society withpelhaps the simplest equipment ever ob-served was the aboriginal society ofTas-mania, a population of hunter-gatherersthat was exterminated io the 19th centu-ry. The inventory of the Tasmanian$'equipment included wood clubs, spearsand digging sticks, cutting tools made ofchipped stone that were used to shapethe wood objects, and a variety of con-tainers: trays, baskets and bags. TheTasmanians also had 6re. Althoughsuch equipment is simple by our stan-dards, it is fa! more complex than thekind of rudimentary tools that we nowknow living chimpanzees may collectand use in the wild, for example twigsano grass srems.

ln addition to this lengthy list of sub-sistence-related behavioral contrasts be-tween human hunter-gatherers and liv-ing primates there is an entire realm ofother contrasts with respect to social or-ganization. Although these impoltantadditional features fall largely outsidethe range of evidence to be consideredhere, they are vital in defining humanpatterns of behavior. Among them is thepropellsity for the formation of long-

DESOLITE LANDSCAPE in the alid Koobi Forr district of Kenyab typicrl of thc ktnd ot erod€d t€rrrin where gullying erposes bothboDcs and stonc tools lbrl wer€ buri€d bencatb sedhhents anil volcan-ic ash E|or€ lhao r million ye$s rgo. Excrvrtlon ln progre6s (cater)

16 €xposiDg lh€ bippopotrmus bon€6.rnd clusters of rrtlf.cts th.t hartbeen prrtially bared by rec€nt erosion and were founil by Rich$dLeak€y in 1969, The site ls typlcrl ol the kind thrt lncluil€s the ro.m.ins of a singl€ anim.l rnd m.ny tools mrnuhclured on ihe spot

ISAAC I THE FOOD-SHARING BEHAVIOR OF PROTOHUMAN HOMINIDS

term mating bonds between a male andone or more females. The bonds we call"marriage involve reciprocal econom.ic ties, ioint responsibility for aspectsof child-rearing and restrictions on sex-ual access. Another such social contrastiE evident in the distinctively humanpropensity to categorize fellow mem-bers of a group according to kinshipand metaphors of kinship. Human be-ings regulate many social relations.mating included. according to complexrules involving kinship categories. Per-haps family ties of a kind exist amongapes, but explicit categories and rules donot. These differences are emphasizedby the virtual absence from observedape behavior of those distinctively hu-man activities that are categor ized some-what vaguely as "symbolic and ritual. '

Listing the contrasts between humanand nonhuman subsistence strategies isinevitably an exercise in oversimplifica-tion. As has been shown by contempo-rary field studies of various great apesand of human beings who. like the San(formerly miscalled Bushmen) of theKalahari Desert, still support them-selves without farming, there is a fargreater degree of similarity between thetwo subsistence strategies than had pre-viously been recognized. For example,with regard to the behavioral repertoriesinvolving meafeating and tool-usingthe differences between ape and man aredifferences of degree rather than ofkind. some scholars have even used thedata to deny the existence of any funda-mental differ€nces between the humanstrategies and the nonhuman ones.

It is my view that significanr diFeren-ces remain. Let me cite what seem tome to be the two most important. First,whereas humans may ieed as they for-age just as apes do, apes do not regularlypostpone food-consumption until theyhave returned to a home base. as humanbeings do. Second, human beings ac-tively share some of the food they ac-quire. Apes do not, even though chim-panzees of the Gombe National Park inTanzania have been observed to toleratescrounging when meat is available-

From Hominid to Human

Two complementary puzzles faceanyone who undertakes to examine thequestion of human origins. The fust re-lates to evolutionary divergence. Whendid the primate stock ancestral to theliving apes diverge from the stock an-cestral to man? What were the circum-stances of the divergence? Over whatgeographical range did it take place? Itis not yet established beyond doubtwhether the divergence occurred a merefive to six million years ago. as VincentM. Sarich of the University of Califor-nia at Berkeley and others argue on bio-chemical grounds, or 15 to 20 millionyears ago, as many paleontologists be-lieve on the grounds of fossil evidence.

PROMINENT SITES in East Alricr include (fiorh nortb to south) Hailar, M€lkr Kuntur6 andShungun in Ethiopia, the Koobi Fora ilistrict to tbe €sst of Lrke Turkana in Kenya, Cheso-wanja in K€nya and P€nfui, Olduvri Gorg€ and Laetolil in Tananir, Dates foi clust€rs of 6tonelools, some associated with animrl bon€s, uncover€d rt lh€6e sites rangc from on€ hillion yerlrago (Olduvri Upper Bed lI) to 2.5 nilliotr (Had.r upp€r beds). Some sites mry bc e}.en older.

1.0

1 . 4

1 _ 6

1 . 8

2.O

2.2

2.4

2.6

2.8

3.0

3.2

OLOUVAI KOOBI FORA OMO VALLEY OTHER

UPPER BED II

MIDOLE EED l l

LO$rEn aEO tl

BEO I

KABAFI SITES

KAS, HAS

i

?

SHUNGURA ET'BEA F

SHUI{GURA MEMBER E

feenruI ELXA KUNTURE

LCHESOWAITJA

HADAB UPPER BEDS

HADAB LOWEF BEDS

LAEfOLIL

RELATM ANTIQUITY of selected sites in Eest AIiic! is indiceted in this table. OlduvaiGorge b€ds I anrt ll range fron l.E to 1.0 nillion years in agc. Tbe Sbungura sites in tbe OmoVdl€y are more thrn two million yeals old. Two Koobi Fora locsles, tbe hippopotamus/arti-f.ct site (HAS) and th€ Kay Behrensm€ycr site (KBS), are at least 1.6 hillioo yeais old, Initialgeologicd s,tudie6 of th€ Koobi Forr sites suggest€d thrt tbey mi8ht be 2.5 million years olrt(colored line\, Only hominid fossils have b€en found ir the lower b€ds at Hadr.nd ai Laetolil.

zI

>-t-z

e(D

ut

F T H I ' P A

iurixl xururunE t -

SHUNGURA

71,4 HUMAN ANCESTORS

At least one fact is clear. The divergencetook place long before the period whenthe oldest archaeological remains thusfar discovered first appear. Archaeolo-gy, at least for the present, can make nocontribution toward solviog the puzzleof the split between ancestral ape andancestral man.

As for the second puzzle, fossil evi-dence from East Africa shows that thedivergence, regardless of when it tookplace, had givenrise two to three millionyears ago to populations ol smallishtwolegged hominids. The puzzle is howto identify the patterns of natulal selec-tion that transformed these protohu-mans into humans. Archaeology has amajor contriburion to make in elucidat-ing the second puzzle. Excavation ofthese protohuman sites has revealed evi-dence suggesting that two million yearsago some elements that now distinguishman from apes were already part of anovel adaptive strategy. The indicationsare that a particularly important part ofthat strategy was food-sharing.

The archaeological research that hasinspired the formulation of new hypoth-eses concerning human evolution begannearly 20 years ago when Mary Leakeyand her husband Louis discovered thefossil skull he named "zinjanthropus" atOlduvai Gorge in Tanzania. The exca-vations the Leakeys undertook at thesite showed not only that stone toolswere present in the same strata that heldthis fossil and other hominid fossils butalso that the discarded artifacts were as-sociated with numerous broken.up ani-mal bones. The Leakeys termed theseconcentrations of tools and bones 'liv-

ing sites." The work has continued atOlduvai under Mary Leakey's direction,and in 1971 a major monograph waspublished that has made the Olduvai re-sults available for comparative studies.

Other important opportunities for ar-chaeological research of this kind havecome to light in the Gregory RiftValley,at places such as the Koobi Fora (for-merly East Rudolf) region of northemKenya, at Shungara in the Omo Valley

of southwestern Ethiopia and in the Ha-dar region of eastern Ethiopia. Currentestimates ofthe age ofthese sites cover aspan of time from about 3.2 millionyears ago to about 1.2 million.

Since 1970 I have been co-leader withRichard Leakey (the son of Mary andLouis Leakey) of a team working atKoobi Fora. a district that includes thenortheastern shore of Lake Turkana(the former Lake Rudo10. Our researchon the geology, paleontology and pa-leoaothropology of the district involvesthe collaboration of colleagues from theNational Museum of Ke[ya and frommany other parts of the world. Workbegannin 1968 and has had the help andencouragement of the Covemment oiKenya, the National Science Founda-tion and the National Ceographic Socie-ty. Our investigations have yielded ar-chaeological evidence that corroboratesand complements the earlier evidencefrom Olduvai Gorge. The combineddata make it possible to s€e iust howhelpful archaeology can be in answering

,$

KOOBI FORA ARTIFACTS includ€foulfrom the HAS assemblage(lel0 a four frorn the KBS ess€hblege (riano. AII are shown actualsiz€; the slone is besalt Tbe HAS cor€ (d) shows what is ldt of a pieceof stone alter a number of fak€5 have been struck ftom it by p€rcus-sion. Ibc jrg8ed edges produced by fake iehoval give the cor€ po.

tential usefulness as a tool. The frkes were iletrched frorr the coreby blows with a brmmelstone like tbe one shown here (c). The sharyedges of tbe flakes,sucb as lbe example illustrated (r), allow tbeir usess cutting tools. The tiny flake (d) is probably an accidentrl proaluctof lhe percussion proc€ss; the pres€nce of many stonc splinters such

ISAAC THE FOOD.SHARING BEHAVIOR OF PROTOHUMAN HOMINIDS

dv'\-,

questions concerning human evolution.At Koobi Fora. as at all the other East

African sites, deposits of layered sedi,ments, which accumulared long ago inthe basins of Rift Valley lakes. are nowbeing eroded by desert rainstorms andtraDsient streams. As the sedimentarybeds erode, a sample of the ancient arti,facts and fossil bones they contain is ex-posed at the surface. For a while theexposed material l ies on the ground.Eventually, however, the fossil bonesare destroyed by weathering or a stormwashes away stone and bone alike.

All field reconnaissance in East A1n-ca progresses along essentially similarlines. The field teams search througheroded terrain looking for exposed fos-sils and artifacts. In places where con-centrations of fossil bone or promisingarchaeological indications appear on thesurface the next step is excavation. Thedigging is done in part to ulcoverYur-ther specimens that are still in place rnthe layers of sediments and in part toSalher exact informalion abour rhe orig-

inal stratigraphic location of the surfacematerial. Most important of all, excava-lion allows the investigalors to plot indetail the relative locations of the mate-rial that is unearthed. For example, ifthere are associations among boDes andbetween bones and stones. excavationwill reveal these characteristics of theslte.

The Types of Sites

The archaeological traces of protohu-man life uncovered in this way may ex-hibit several different configurations. Insome ancieDt layers we have found scat-terings of sharp-edged broken stoneseven rhough lhere are no other stones inthe sediments. The broken stones comein a range of forms but all are olthe kindproduced by deliberate percussion, sothat we can classify them as undoubt,ed artifacts. Such scatterings of artifactsare often found without bone being pres-ent in signincant amouots. These I pro-pose to designate sites of Type A.

ln some instances a layer of sedimentmay include both artifacts and animalbones. Such bone-and-artifact occurren-ces fall into lwo categories. I he first con-sists of artifacts associated with bonesthat represent the carcass of a singlelarge animal: these sites are designat-ed Type B. The second consists of ar-tifacts associated with bones represent-ing the remains of several different ani-mal species; these sites are designatedType C.

The discovery of sites with these var-ied configurations in the sediments atKoobi Fora and Olduvai provides evr-dence lhat when the sediments contain-ing them were being deposited some 2.5to 1.5 mill ion years ago, there was atleast one kind of hominid in East Africathat habitually carried objects such asstones from ooe place to another andmade sharp-edged tools by deliberatelyfracturing the stones it carried with it.How does this archaeological evidencematch up with the hominid fossil rec-ord? The fossil evidence indicates that

J ,-<:J!/:

'a-{

as this on€ in rh€ HAS tool clust€ls indicates thatthe stone tools w€.emade on th€ spot At the same timc the absenc€ of tocat unworkcdstone as potential raw mateiial for tools suggests that the cores werecanied to tb€ site by the toolmakers. The artifacts from the secondassemblage also include a core (€) that bas had many flakes removed

by percussion and anothersmall splinter of stone (t). The edges of th€two flakes (l a)are sharp cnougb lo cut m€al, hide, sinew or wood. Asal the hippopotamus/artifact site, tte absence of local raw materi.lfor stone tools at tb€ Kay Behrensh€yer sit€ suggests tbat suitabl€lumps ot lava must hsve b€en transport€d there by the toolmak€N,

HUMAN ANCESTORS

KOOBI FORA LANDSCAPE in ihc vicinity of the hippopotaDus/rrtitact site consisted of rlevel foodpkin n€gr tbe mergin of a leke (ro? s?.tior). Protobumrn foragers rpparently foutrdtbe c$cass of. hippopotamus lying in a strerm-bed bollorv and made tools on tbe spot in od€rto butcher ihe carcass. Their rctions left a scatter of stone tools among the bones .nd on ih€ground neerby, The floodplain w.s bu €d ulder layers of silt end ash and was sub6€quentlycrodeil lbotton yction), exposing som€ bones and tools. Tb€ir discovery led to excsvation.

two and perhaps three species of bipedal man were making the stone tools. Thesehominids inhabited the area at this time, are the fossil forms, of early Pleistoceneso that the question arises: Can the spe- age, classified by most paleontologistscies responsible for the archaeological as an early species of the Eenus Homo.evidence be identified? The question of whether or not contem-

For the moment the best working hy- poraneous hominid species of the genuspothesis seems to be that those hominids Australopithecus also made tools must bethat were directly ancestral to modern set aside as a challenge to the ingenuity

IIAMMERSTONE un€artbed at the bippopot mus/artifact site is . six.centirnet€r basrlt peb-bl€; it is shown her€ being lilted from its position on lh€ sncient ground surface sdi.c€nt to thehippopotrmus bones. Worn srnooth by r.l.r .ction before it caught ihe eye of . toolmskcrsoln€ 1.7 orillion yerrs .go, the pebble is bltter.d .t bolb ends ss a result of use as a hrrnrn€r.

of future investigators. Here I shall sim-ply discuss what we can discover aboutlhe activit ies of early toolmaking homi-nids without artempting to identify theirtaxonomic position (or positions).

Reading the Evidence

As examples oi the archaeological ev-idence indicative of early hominid pafterns of subsistence and behavior, con-sider our findings at two Koobi Foraexcavations. The fust is a locality cata-logued as the hippopotamus/artifactsite (HAS) because of the presence offossilized hippopotamus bon€s andstone tools.

The site is 15 miles east of Lake Tur-kana. There in 1969 Richard Leakeydiscovered an erosion gully cutting intoan ancient layer of volcanic ash knownas the KBS tuff. (KBS stands for KayBehrensmeyer site: she, the geologist-paleoecologist of our Koobi Fora re-search team, first identified the ash layerat a nearby outcrop.) The ash layer lsthe uppermost part of a sedimentary de-posit known to geologists as the LowerMember ol the Koobi Fora Formation;here the ash had filled in one of the manydry channels ofan ancient delta. Leakeyfound many bones of a single hippopot-amus calcass weathering out of theeroded ash surface, and stone artifactslay among the bones.

J. w. K- Harris, J. Onyango-Abujeand I supervised an excavation that cutinto an outcrop where the adtacent deltasediments had not yet b€en disturbed byerosion. Our digging revealed that thehippopotamus carcass had originallylain in a depressior or puddle within anancient deita channel. Among the hip-popotamus bones and ir the adjacentsteam bank v/e recovered 119 chippedstones: most of them were small sharpflakes that, when they are held betweenthe thumb and the frngers, make effec-tive cuiting implements. We also r€cov-ered chunks of stone n ith scars showiogthat flakes had been struck from themby percussion. In Paleolitiic tool classi-fication these larger stones fall into thecategory of core tool or chopper. In ad-dition our digging exposed a roundedriver pebble that was battered at bothends: evidently it had been used as ahammer to strike flakes from the stonecores.

The sediments where we found theseartifacts contain no stones larger than apea. Thus it seems clear that the makersof the tools had carried the stones hereirom somewhere el$e. The associationbetween th€ patch of artifacts and thehippopotamus bones further suggeststhat toolmakers came to the site carry-ing stones and hammered off the smallsharp-edged ffakes on the spot in orderto cut meat from the hippopotamus car-cass. We have no way of telling at pres-ent whether the toolmakers themselveskilled the animal or only came on it

ISAAC THE FOOD-SHARING BEHAVIOR OF PROTOHUMAN HOMINIDS

dead. Given the low level of stone tech-nology in evidence, I am inclined to sus-pect scavenging rather than hunting

The HAS deposit was formed at least1.6 million years ago. The archaeologl-cal evidence demoDstrates that the behavior of some hominids at that timediffered from the behavior of modern

great apes in lhaL these prolohumansnot only made cutt ing lools but also atemeal from the carcasses of large animals. The hippopotamus/art i fact si tethus provides cortoboration for evt-dence of similar behavior just as longago obtained from Mary Leakey's exca-vations at Olduvai Gorge.

This finding does not answer all ourquestions. Were these protohumansroaming the landscape, foraging andhunting. in the way that a troop of ba-boons does today? Were they insteadhunting like a pride of lions? Or didsome other behavioral pattern prevail?Excavation of another bone-and-arti-

',r11.

,''ii:"{-.

,ffiFINDINGS at the hipFoPot.mus/artifactsite are shown schematical-

ly in this block diagram; squ.res are one m€ter io a side. ln the fore-

;rountl sre lbe obiects lhar had bcen exPosed bv weathering: bippo-

ootsmu! limb bones (a-d) and reerh t'mall oper rif.lr\). man) frrg-

ments of bonc (sror"/ ddtrss) and a few stone artitaets (colorcd dots)

Trenching (dasn.d ti e, color' ^.rlt billside excavation over a wid€

a.ea exposed an ancient soil surface (drlor) overlying a deposit of sil-

tr iufi, Lvine on lbe ancicnl surface $ere slone cores loper (ircler'

i"tort t,i^ "t'icl

strarp'edgea flakes had be€n \trucl' mor€ then

100 other stone arlifacts and more than 60 additional fragm€nts of

te€th and boncs. The scatter of tools 5nd broken bones suggests the

hypothesis thal the toolmakeN fed on meat from the hippoPotamus'

118 HUMAN ANCESTORS

fact association, only a kilometer awayfrom the h ippopotam us/arl ifact site.has allowed us to cary our inquiriesfurther.

The second site had been located byBehrensmeyer in 1969. Erosion was un-covering artifacts, together with piecesof broken-up bone, at another outcropof the same volcanic ash layer that con-tained the HAS artifacts and bones.With the assistance of John Barthelmeof the University ofCalifornia at Berke-ley and others I began to excavate thesite. The work soon revealed a scatterof several hundred stone tools in anarea 16 meters in diameter. They restedon an ancient ground surface that hadbeen covered by layers of sand and silt.The conceltration of artifacts exactlycoincided with a scatter of fragmentedbones. Enough of them, teeth in particu-lar, were identifiable to demonstratethat parts of the remains of several ani-mal species were present. John M. Harris of the Louis Leakey Memorial Insti-tute in Nairobi recognized, among other

species, hippopotamus, giraffe, pig. por-cupine and such bovids as waterbuck,gazelle and what may be either harte-beest or wildebeest. It was this site thatwas designated KBS. The site obvious-ly represented the second category ofbone-and-artifacl associationsr rools inassociation with the remains of manydifferent animal species.

Geological evidence collected by A.K. Behrensmeyer of Yale Universityand others shows that the KBS deposithad accumula ted on the sandy bed o f astream that formed part of a small delta.At the time when the toolmakers usedthe stream bed, water had largely ceasedto Row. Such a site was probably fa-vored as a focus of hominid activity fora number of reasons. First, as everybeachgoer knows. sand is comfortableto sit and l ie on. Second, by scooping ahole of Do great depth in the sand of astream bed one can usually find water.Third, the growth of trees and bushesin the sun-parched floodplains of EastAfrica is often densest along watercour-

ses, so that shade and plant foods areavailable in these locations. It may alsobe that the protohuman toolmakers wholeft their discards here took shelter frompredators by climbing trees and alsospent their nights protected in this way.

Much of this is speculative, of course,but we have positive evidence that theobjects at the KBS site did accumulatein the shade. The sandy silts that came tocover the discarded implements andfractured bones were deposited so gent-ly that chips of stone small enough to beblown away by lhe wind were nol dis-turbed. In the same silts are the impres-sions of many tree leaves. The species oftree has not yet been formally identifled,but Jan Gilette of the Kenya NationalHerbarium notes that the impressionsclosely resemble the leaves of Africanwild fig trees.

Carrying Stones and Meat

As at the hippopotamus/artifact site,we have established the fact that stones

i .. -'

BONES AND STONE TOOLS were also found in abundance at theKay Bebrensmey€rsita As th€ plot of bonedisbibution (a) shows,tbeanimal iemains represent many difieient species. Thes€ are identificdby capitsl lctters; if the nnd was a tooth the letter is circled. Most

arc small to medium-sized boyids, such as gazelle, waterbuck andhartebee$(A). The remains of crocodile (C),girafie(G), hippopotamus(H), porcupine (P) and extinctspecies of pig (J) wer€ also present. Dotsand dashes locate unidentified teeth and bone fragmenti respectively.

/ ,I /i .

Th

her

ISAAC I THE FOOD.SHARING BEHAVIOR OF PROTOHUMAN HOMINIDS 119

larger than the size of a pea do not occurnaturally closer to the Kay Behrensmey-er site than a distance of three kilome-ters. Thus we know that the stones wefound at the site must have been carriedat least that far. With the help of FrankFitch and Ron Watkins of the Universi-ty of London we are searching for thespecific sources.

It does not seem likely that all the ani-mals of the different species representedamong the KBS bones could have beenkil led in a short interval of t ime at rhisone place. Both considerations encour-age the advancement of a tentative hy-pothesis: Like the stones, the bones werecarried in, presumably while there wasstill meat on them.

If this hypothesis can be accept€d, theKay Behrensmeyer site provides veryearly evidence for the transport of foodas a protohuman attribute. Today thecarrying of food strikes us as being com-monplace, but as Sherwood Washburnof the University of California at Berke-ley observed some years ago such an

action would strike a living ape as beingnovel and peculiar behavior indeed, Inshort, if the hypothesis can be accepted,it suggests that by the time the KBS de-posit was laid down various fundamen-tal shifts had begun to lake place inhominid social and ecological arrange-ments.

It should be noted that other earlysites in this category are known in EastAfrica. so that the Kay Behrensmeyersite is by no means unique. A number ofsuch sites have been excavated at Oldu-vai Gorge and reported by Mary Lea-key. Of these the best preserved is the"Zinjanthropus" site of Olduvai Bed I,which is about 1.7 million years old.Here too a dense patch of discarded artifacts coincides with a concentration ofbroken-up bones.

There is an even larger number ofType A sites (where concentrations ofartifacts are found but bones are virtual-ly or entirely absent). Some are at KoobiFora: others are in the Omo Valley,where Harry V. Merrick of Yale Uni-

versity and Jean Chavaillon of theFrench National Center for ScientificResearch (CNRS) have recently uncov-ered sites of this kind in members E andF of the Shungura Formation. The Omosites represent the oldest securely datedartifact concentations so far reportedanywhere in the world; the tools weredeposited some two million years ago.

One ofthe Olduvai sites in this catego-ry seems to have been a "factory": aquaffy where chert, an excellent toolmaterial, was readily available lor flak-ing. The other tool concentrations, withvery few associated bones or none at all,may conceivably be interpreted as fociof hominid activity where lor one rea-son or another large quantities of meatwere not carried in. Until it is possible todistinguish between sites where bonewas never present and sites where thebones have simply vanished because ofsuch factors as decay, however, thesedeposits wil l remain diff icult to inter-pret in terms of subsistence ecology.

lvhat, in summary, do these East Af-

b

I

, I

r t l

a

,o

, . \

1 '?IIIIIII

I6 \

II

2

Tbe plot of rnifrct dishibution (r) shows tbat three of fom stonecorfs (open circlesr, most wasle stone (stlares) and flak€s and freg-m€nts of flak€s (dots) were found in 12 adjacent squsres. AIso foundhere wrs an unworked stone (,{) tbag Iike thc cores, must bsve been

canied to th€ site from r distrnc€, Plotting of all tools and bon€s un-carthed at the site wrs not .tternpt€d. Numbers in grid squares (c)show how many flakes and bits of was(e stone (.r/or) and fragmentsof bone (r/dck) werc recolded witbout exact plotting in €-rch square.

1.2O HUMAN ANCESTORS

rican archaeological studies teach usabout the evolution of human behav-ior? For one thing they provide unam-biguous evidence that two million yearsago some hominids in this part of Afn-ca were carrying things around, for ex-ample stones. The same hominids werealso mating simple but effective cuttingtoolsofstone and were at t imes active inthe vicinity of large altimal carcasses,presumably in order to get meat. Thestudies strongly suggest that the homi-nids carried animal bones (and meat)around and concentrated this Dortablefood supply at certain places.

Mod€l Strategies

These archaeological facts and indi-cations allow the conshuction of a theo-retical model that shows how at leastsome aspects of early hominid social ex-istence may have been organized. Crit-ical to the validity of the model is theinference that the various clusters of re-

mains we have uncovered reflect socialand economic nodes in the lives of thetoolmakers who left behind these an-cient patches of litter. Because of theevidence suggestive of the transport offood to certain focal points, the f,rstquestion that the model must confront iswhy early hominid social goups depart-ed from the norm among living subhu-man primates, whose social groups feedas they range. To put it alother way,what ecological and evolutionary ad-vantages are there in postponing somefood consumption and transporting theiood?

Several possible answers to this ques-tioo have been advanced. For example,Adrierure Zihlman and Nancy Tanner ofthe University of Califomia at SantaCruz suggest that when the protohu-mans acquired edible plants out on theopen grasslands, away from the shelterof trees, it would have been advanta-geous for them to seize the plant prod-ucts quickly and withdraw toplaces shel-

tered from menacing predators. Othershave proposed thatwhen the early hom-inids foraged, they left their young be-hind at "nest" or "den" sites (in the man-ner of birds, wild dogs and hyenas) andreturned to these locales at intervals,bringing food with them to help feedand wean the young.

If we look to the recorded data con-cerning primitive human societies, athird possibility arises. Among extantand recently extinct primitive humansocieties the transport of food is asso-ciated with a division of labor. The soci-ety is divided by age and sex into clas-ses that charactelistically make differentcontlibutions to the total food supply.One significant result of such a divisionis an increase in the variety of foodstuffsconsumed by the group. To generalizeon the basis of many different ethlo-graphic reports, the adult females of thesociety contribute the majority of the"gathered" foods; such foods are mainlyplant products but may include shell-fish, amphibians and small reptiles,eggs, insects and the like. The adultmales usually, although not invariably,contribute most of the "hunted" food-stufs: the flesh of mammals, fishes,bilds and so forth. Characteristically themales and females range in separategroups and each sex eventually bringsback to a home base at least the surplusol its foraging.

Could this simple mechanism, a divi-sion of the subsistence effort, have ini-tiated food-carying by early hominids?One cannot dismiss out of hand themodels that suggest safety ftom com-petitors or the leeding of nesting youngas the initiating mechanisms for food-carrying. Nevertheless, neither modelseems to me as plausible as one that hasdivision of labor as the primary initiat-ing mechanism. Even if no other argu-ment favored the model, we know for afact that somewhere along the line in theevolution of human behavior two pat-terns became established: food-sharingand a division of labor. If we includeboth patterns in our model of earlyhominid society, we will at least be par-slmonl0us.

Other arguments can be advanced infavor of an early development of a divi-sion of labor. For example, the East Af-rican evidence shows that the plotohu-man toolmakers consumed meat froma far greater range of species and sizesof animals than are eaten by such liv-ing primates as the chimpanzee and thebaboon. Amoog recent human hunter-gatherers the existence of a division oflabor seems clearly related to the fe-males being encumbered with children,a handicap that bars them from huntingor scavenging. activit ies lhat requLespeed afoot or long-range mobility. Forthe protohumans too the incorporationof meat in the diet in signifcant quanti-t ies may well have been a key factor inthe development not only of a division

CLUSTERED MIXTURE of artifacis anil animal bones rt the Kay Behremmeyer site is evident when the stone (rrlor) and bone (r/dcf) plots ar€ superposed. Combinetions of this kindare som€timcs produc€d by str€am actiotr, but sucb is not likely to be the case her€, rs is att€stedby tbe pr€servatio[ of l€af ihpr€ssions anil olher r€sdily wash€d-sway debris such a! fftr€splint€rs of slone. It apperrs inst€ad that the prolobumrnE who made and discailed their tootsh€re rveie rlso r€sponsible for the bon€ rccumulation becauae thcy met h€Ie to shar€ their food,

7.;ri\0' I ,@

'^o )fa

h.: a

ISAAC I THE FOOD,SHARING BEHAVIOR OF PROTOHUMAN HOMINIDS

of labor but also oi the organization ofmovements around a home base and thetransport and sharing of food.

The model I propose for testing visu-alizes food-sharing as the behavior cen-tral to a novel complex of adaptationsthat included as critical componentshunting and/or scavenging. gatheringand carrying. Speaking metaphorically,food-sharing provides the model witha kind of central platform. The adap-tive system I visualize, however, couldonly haye functioned through the use oftools and other equipment. For exam-ple, without the aid of a carrying deviceprimates such as ourselves or our ances-tors could not have transported fromthe field to the home base a suflicientamount of plant food to be worth shar-ing. An object as uncomplicated as abark tray would have seryed the pur-pose, but some such item of equipmentwould have been mandatory. In fact,Richard Borshay Lee of the Universr-ty ofToronto has suggested that a carry-ing device was the basic invention thatmade human evolution possible.

What about stone tools? Our ances-tors, like ourselves. could probablybreak up the body of a small animal, aschimpanzees do. with nothing but theirhands and teeth. It is hald to visualizethem or us, however. eating the meat ofan elephant, a hippopotamus or someother large mammal withoutthe aid ofacutting implement. As the archaeologi-cal evidence demonstrates abundantlv.

the protohumans of East Africa notonly knew how to produce such stoneflakes by percussion but also foundthem so useful that they carried the rawmatelials needed to make the imple-ments with them from place to place.Thus whercas the existence of a carryingdevice requted by the model remainshypothetical as far as archaeological ev-idence is concerned. the fact that toolswere used and carried about is amplyattested to.

In this connection itshould be stressedthat the archaeological evidence is alsosilent with regard to protohuman con-sumption of plant foods. Both the mor-phology and the patterns of wear ob-servable on hominid teeth suggest sucha plant component in the diet, and sodoes the weight of comparative data onsubsistence patterns among living non-human primates and among nonfarm-ing human societies. Nevertheless, ifpositive evidence is to be found, we shallhave to sharpen our ingenuity, perhapsby turning to organic geochemical anal-yses. It is clear that as long as we do notcorrect for the imbalance created by thedurability of bone as compared withthat of plant residues, studies of humanevoluiion will tend to have a male bias!

As far as the model is concerned thekey question is not whether collectablefoods-fruits, nuts, tubers, greens andeyeD insects-were eaten. It is whetherthe$e protohumans carried such foodsabout. Lacking any evidence for the

consumption of plant foods, I shall fallback on the argument that the system Ivisualize would have worked best if themobile hunter-scavenger contributionofmeat to the social group was balancedby the gatheler-carrier collection ofhigh-grade plant foods. lvhat is certainis that at some time during the past sev-eral million years just such a divisionof labor came to be a standard kind ofbehavior among the ancestors of mod-ern man.

A final cautionary word about themodel: The reader may have noted thatI have been carelul about the use of thewords hunter" and 'hunting. This isbecause we cannot judge how much ofthe meat taken by the protohumans ofEast Africa came from opportunisticscavenging and how much was obtainedby hunting. It is reasonable to assumethat the carcasses of animals killed bycarnivores and those of animals that hadotherwise died or been disabled wouldalways have provided active scavengersa certain amount of meat. For the p!es-ent it seems less reasonable to assumethat protohumans, armed primitively ifat all, would be particularly effectivehunters. Attempts are now under way,notably by Elizabeth Vrba of South Af-rica, to distinguish between assemblagesof bones attributable to scavenging andassemblages attributable to hunting, butno indings from East Africa are yetavailable. For the present I am inclinedto acceDt the verdict of J. Desmond

TOLERATEDSCROUNGING

BEIIAVIOR PATTERNS that difter in ilegree of organizatiotr aieconhssted in lhese disgnms Living grelt ape6, €xemplified b€rc byth€ chinpanzee, cxhibit b€hrvior pattems that becsme imporlant inhumsn €volution but tbe prtterG (&l) exist largely as isolated cl€.mcnts. Hunting occurs otr a small scalc but lerds only to "loleratedscrounging" ralb€r than rctive food.sbaringi similarly, fools sre usdbut tool us€ is nol irtegrrted with huntidg or scroutrging. Tbe euthor'smodel (c?x&r) integrates these tbree behavior prtlems rnil othels intor coherenl structur€. Food-shsring is s€en ss a cenhrl sbuctural €l€.

hetrt, incorponting thc provisiotr of both animal and plant fooils, tbeorganization of s home bosc rnd e division of labor. Supportiog tb€int€grrt€d structur€ is . ncc€ssery infnshuclure of tool and equlp-m€nt manufrctur€; for exrmplc, without devices for csrrying food"stufis th€re could not be r divisiotr of labor.ml orgadzed food€hrr-ing.ln hodern buman societies (riArr) the food-sharing shucture hasundergoDe socioecolomic ehboration. Its infr$huctur€ now incor-porates all of tcchnology, and a matcbing superstructure hes aris€nto incorportt€ other €l€mcntr oI whrt i6 collectiv€ly call€d cultur€.

CULTUBE

FOOD€HARING

722 HUMAN ANCESTORS

Clark of the University of Califomia atBerkeley and Lewis R. Binford of theUniversity of New Mexico. In their viewthe earliest meat-eaters might have ob-tained the flesh of animals weighing upto 30 kilograms by deliberate hunting,but the flesh of larger animals was prob-ably available only tfuough scavenging.

Tools as Testimony

Of course, the adaptive model I haveadvanced here reflects only a workinghypothesis and not established lact.Nevertheless, there is sumcient evidencein its favor to justify looking further atits possible implications for the courseof human evolution. For example, themodel clearly implies that early tool-making hominids displayed certain pat-terns of behavior that, among the pat-terns of behavior of all primates.uniquely characterize our own speciesand set it apart from its closest livingrelatives, the great apes. Does this meanthat the toolmaking hominids of 1.5to two million years ago were in fact"human"?

I would surmise that it does not, and Ihave been at pains to characterize theseEast African pioneers as protohumans.In summarizing the contrasts betweenliving men and living apes I put highon the list language and the culturalphenomena that are dependent on it.We have no direct means of learningwhether or not any of these early hom-inids had language. It is my suspicion,however, that the principal evolutionarychange in the hominid line leading tofull humanity over the past two millionyears has been the great expansion oflanguage and communication abilities,together with the cognitive and cultur-al capabilities integrally related to lan-guage. What is the evidence in supportof this surmise?

One humble indicator of expandingmental capacities is the series of changesthat appears in the most durable materi-al record available to us: the $tone tools.The earlier tools from the period underconsideration here seem to me to show asimple and opportunistic range of formsthat reflect no more than an uncompli-cated empirical grasp of one skill: howto fracture stone by percussion in such away as to obtain fragments with sharpedges. At that stage oi toolmaking themaker imposed a minimum of cultural-ly dictated forms on his artifacts. Stonetools as simple as these perform perfect-ly well the basic functions that supportprogress in the direction of becominghuman, for example the shaping of adigging stick, a spear and a bark tray, orthe butchering of an animal carcass.

The fact is that exactly such simplestone tools have been made and usedever since their first invention, rightdown to the present day. Archaeologyalso shows, however. that over the pastseveral hundred thousand years some

assemblages of stone tools began to re-flect a greater cultural complexity on thepart ol their makers. The complexity rsfirst shown in the imposition of morearbitrary tool forms; these changes werefollowed by increases in the number ofsuch forms. There is a marked contrastbetween the pure opportunism apparentin the shapes of the earliest stone toolsand the orderly array of forms that ap-pear later in the Old Stone Age wheneach form is represented by numerousstandardized examples in each assem-blage oftools. The contrast strongly sug-gests that the first toolmakers lacked thehighly developed mental and culturalabilities of more recent humans.

The evidence of the hominid fossilsand the evidence of the artilacts togeth-e! suggest that these early artisans werenoDluman hominids. I imagine that ilwe had a time machine and could visit aplace such as the Kay Behrensmeyer siteat the time of its original occupation, wewould find hominids that were living msocial groups much like those of otherhigher primates. The differences wouldbe apparent only after prolonged obser-vation. Perhaps at the start of each daywe would observe a group splitting up assome of its members went off in onedirection and sorne in another. All thesesubgroups would very probably feed rn-termittently as they moved about andencountered ubiquitous low-grade plantloods such as berries, but we might wellobserve that some of the higher-gradematerials-large tubers or the haunchof a scavenged carcass-were beingreserved for group consumption whenthe foraging parties reconvened at theirstarting point.

To the observer in the time machinebehavior of this kind, takeD in contextwith the early hominids' practice ofmaking tools and equipment, wouldseem familiarly "human." If, as I sup-pose, the hominids under obseryationcommunicated only as chimpanzees door perhaps by means oivery rudimenta-!y protolinguistic siglals, then the ob-server might feel he was witnessing theactivities oi some kind of fascinating bi-pedal ape. When one is relying on ar-chaeology to reconstruct protohumanlife, one must strongly resist the tempta-tion to protect too much of ourselvesinto the past. As Jane B. Lancaster ofthe University of Oklahomahas pointedout, the hominid life systems of two mil-lion yeals ago have no living counter-parts.

Social Advances

My model of early hominid adapta-tion can do more than indicate that thefirst toolmakers were culturally proto-human. It can also help to explain thedynamics of certain significant advancesin the long course of mankind's develop-ment. For example, one can imaginethat a hominid social organization in-

volving some division of labor and adegree of food-sharing might well havebeen able to function even if it hadcommunicative abilities little more ad-vanced than those of living chimpan-zees. In such a simple subsistence sys-tem, howeYer, any group with membersthat were able not only to exchange foodbut also to exchange information wouldhave gained a critical selective advan-tage over all the rest. Such a group'sgatherers could report on scavengingor hunting opportunities they had ob-served, and its hunters could tell thegatherers about any plant foods theyhad encountered.

By the same token the fin€ adjustmentof social relations, always a matter ofimportance among primates, becomesdoubly impoltant in a social systemthat involves food exchange. Languageserves in modern human $ocieties notonly for the exchange of informationbut also as an instrument for social ad-justment and even for the exchange ofmisinfolmation.

Food-sharhg and tie kinds of behav-ior associated with itprobably played animportant part in the development ofsystems of reciprocal social obligationsthat characterize all human societies weknow about. Anthropological researchshows that each human being in a groupis ordinarily linked to many other mem-bers ol the group by ties that are bothsocial and economic. The French an-thropologist Marcel Mauss. in a classicessay, "The Gift. published in 1925,showed that social ties are usually recip-rocal in the sense that whereas benefitsfrom a relationship may inirially pass inonly one direction, there is an expecta-tion of a future retum of help in timeol need. The formation and manage-ment of such ties calls for an ability tocalculate complex chains of contingen-cies that reach far into the future. Afterfood-sharing had become a part of pro-tohuman behavior the need for such anability to plan and calculate must haveprovided an important part of the bio-logical basis for the evolution of the hu-man intellect.

The model may also help explain thedevelopment of human marriage ar-rangements. It assumes that in earlyprotohuman populations the males andlemales divided subistence labor be-tween them so that each sex was prefer-entially tapping a different kind of foodresource and then sharing within a so-cial group some of what had been ob-tained. In such circumstances a matingsystem that involved al least one male in"family" food procurement on behalfofeach child-rearing female in the groupwould have a clear selective advantageover, for example, the chimpanzees'pattern of opportunistic relations be-tween the sexes.

I have emphasized food-sharing as aprinciple that is central to an under-standing of human evolution over the

ISAAC I THE FOOD.SHARING BEHAVIOR OF PROTOHUMAN HOMINIDS

past two million years or so. I have alsoset forth alchaeological evidence thatfood-sharing was an established kindof behavior among early protohumans.The nolion is far from novel: it is implic"it in many philosophical speculationsand in many writings on paleoanthro-pology. What is novel is that I have un-dertaken to make the hypothesis explicitso that it can be tested and revised.

Accounting for Evolution

Thus the food-sharing hypothesisnow joins other hypotheses that havebeen put iorward to account for thecourse of human evolution. Each olthese hypotheses tends to maintain thatone or another innovation in protohu-man behavior was the critical drivingforce of change. For example, the argu-ment has been advanced that tools werethe "prime movers." Here the underly-

ing implication is that in each successivegeneration the more capable individualsmade better tools and thereby gainedadvantages that favored the transmis-sion of their genes through natural se-lection: it is supposed that these great-er capabilities would later be appliedin aspects of life other than technolo-gy. Another hypothesis regards huntingas being the driving force. Here the ar-gument is that hunting requires intelli-geoce, cuDning, skilled neuromuscularcoordination and. in the case of grouphunting, cooperation. Among other sug-gested prime movers are such practicesas carrying and gathering.

If we compare the food-sharing ex-planation with these alternative expla-nations we see that in fact food-sharingincorporates many aspects of each ofthe others. It will also be seen that in thefood-sharing model the isolated ele-ments are treated as beilg integral partsof a complex, flexible system. The mod-el itself is probably an oversimplified

version of what actually happened, buti l seems sumciently realistic to be wor-thy of testing through further archaeo-logical and paleontological research.

Lastly, th€ food-sharing model can beseen to have interconnections with thephysical implications of fossil hom!-nid anatomy. For example, a prerequi-site offood-sharing is the ability to carrythings. This abil i ly in turn is greally fa-cilitated by a habitual twolegged pos-ture. As Cordon W. Hewes of the Uni-versity of Colorado has pointed out. animportant part of the initial evolution-ary divergence of hominids from theirprimate relatives may have been thepropensity and the ability to caffy thingsabout. To me it seems equally plausiblethat the physical selection pressures thatpromoted an increase in the size of theprotohuman brain, the!€by surely en-hancing the hominid capacity for com-munication. are a consequence of theshift from individual foraging to food-$haring some two million years ago.

Reodings from

SCIDNTIFICAMDRICN

HUMAN ANCESTORS

With on Introduction by

Glynn IsaacUnivercily ol Colif onio, Eerkeley

Richard E. F. LeakeyNotionol Museums of Kenyo

W. H. Freeman and CompanySon Froncisco

All of tle ScrrNrrrrc AMERTcAN aticles in llrmanAncesto6 aie available as separate Offprints. For acomplete list of articles now available as Ofiprints, writeto W. H. Freeman and Company, 660 Market Street, SanFrancisco, California, 94104.

Library of Congress Cataloging in Publication Data

Main entry imder title:

Human ancestors.

Bibliogaphy: p.Includes index.I. Human evolution-Addresses, essays, lectures.

2. Paleolithic period-Addresses, essays, lectures.I. Isaac, Glynn L., 1937- II. Leakey, Richard E,III. Scientiffc American.,I\mencan.cN281.H847 573.2 79-4486ISBN 0-7167-1100-1ISBN 0-7167-1I01-x pbk.

Copyright O 1960, 1962, 1964, 1966, 1967, 1969, 1974,1977,1978, 1979 by Scientiffc Ame can, Inc.

No part of this book may be reproduced by anymechanical, photographic, or electronic process, or in theform of a phonographic recording, nor may it be storedin a retrieval system, transmitted, or otherwise copied forpublic or private use, without wdtten permission ftomthe publisher,

Printed in the United States of America

9 8 7 6 5 4 3 2