Anthropology Discussion 4

Article11 DimForest, BrightChimps Inthe rain forest ofIvory Coast, chimpanzees meet the challenge oflife byhunting cooperatively and using crude tools Christophe Boeschand Hedwige Boesch-Achermann TalNational Park,Ivory Coast, De- cember 3,1985. Drumming, barking, and screaming, chimpsrushthrough the undergrowth, littlemore thanblack shadows. Theirgoalistojoin agroup of other chimps noisilyclustering around Brutus, thedominant maleof this seventy-member chimpanzeecom- munity. Forafew moments, Brutus, proud andself-confident, standsfairly still, holding ashocked, barelymoving red colobus monkey inhis hand. Then he begins tomove through thegroup, followed closelybyhis favorite females and most ofthe adult males. Heseems to savor thismoment ofuncontested su- periority, theculmination ofahunt high up inthe canopy. Butthevictory isnot his alone. Cooperation isessential to captUring oneofthese monkeys, and Brutus willbreak apartandshare this highly prizeddelicacy withmost ofthe main participants ofthe hunt andwith the females. Recipients oflarge portions will, inturn, share more orless gener- ously withtheiroffspring, relatives,and friends.

In 1979, webegan along-term study of the previously unknownchimpanzees of Tal National Park,1,600square miles of tropical rainforest inthe Republic of the Ivory Coast (Coted'Ivoire). Earlyon, wewere most interested inthe chimps' useofnatural hammers- branches andstones-to crackopenthe five species ofhard-shelled nutsthatare abundant here.Asea otter lying onits back, cracking anabalone shellwitha rock, isafamiliar picture,butnopri- mate hadever before beenobserved in the. wild using stones ashammers. East Africa's savannachimps, studiedforde- cades byJane Goodall inGombe, Tanza- nia, usetwigs toextract antsandtermites from theirnests orhoney fromabees' nest, butthey have never beenseenusing hammerstones.

As our work progressed, wewere surprised bythe many waysinwhich the life ofthe Talforest chimpanzees differs fromthatoftheir savanna coun- terparts, andasevidence accumulated, differences. inhow thetwo populations hunt proved themost intriguing. Jane Goodall hadfound thatchimpanzees hunt monkeys, antelope,and:wildpigs, findings confirmed byJapanese biolo- gist Toshida Nishida, whoconducted a long-term study120miles southofGom- be, inthe Mahale Mountains. Sowe were not surprised todiscover thattheTal chimps eatmeat. What intrigued uswas the degree towhich theyhunt coopera- tively. In1953 Raymond Dartproposed that group hunting andcooperation were key ingredients inthe evolution of Homo sapiens. Theargument hasbeen modified considerably sinceDartfirst put itforward, andgroup hunting has also been observed insome social car- nivores (lionsandAfrican wilddogs, for instance), andeven some birdsofprey.

Nevertheless, manyanthropologists still hold thathunting cooperatively and sharing foodplayed acentral roleinthe drama thatenabled earlyhominids, some 1.8million yearsago,todevelop the social systems thataresotypically human.

We hoped thatwhat welearned about thebehavior offorest chimpan- zees would shednewlight onprevailing theories ofhuman evolution. Beforewe could evenbegin, however; wehad to habituate acommunity ofchimps toour.

presence. Fivelongyears passed before we were abletomove withth'em on their daily tripsthrough theforest, of which "our"group appeared toclaim some twelve squaremiles.Chimpanzees are alert andshyanimals, andthelim- ited field ofview inthe rain forest- . about sixty-five feetatbest-made finding themmore difficult. Wehad to rely onsound, mostly theirvocalizations and drumming ontrees. Males often Reprinted withpermission fromNatural History,September 1991,pp.50, 52-56. «J1991 bythe American Museum of Natural History. 63 2.:. PRIMATES drum regularly whilemoving through the forest: pant-hooting, theydraw near a big buttress tree;then, atfull speed they flyover thebuttress, hittingitre- peatedly withtheir hands andfeet.

Such drumming mayresound morethan half amile inthe forest. Inthe begin- ning, ourignorance abouthowthey moved andwho wasdrumming ledto failure moreoftenthannot,buteventu- ally welearned thatthedominant males drummed duringtheday tolet other group members knowthedirection of travel. Onsome days,however: intermit- tent drumming aboutdawnwastheonly signal forthewhole day.Ifwe were out of earshot atthe time, wewere often reduced toguessing.

During thesedifficult earlydays, one feature ofthe chimps' routineprovedto be our salvation: nutcracking isanoisy business. Sonoisy, infact, thatinthe early daysofFrench colonial rule,one officer apparently evenproposed the theory thatsome unknown tribewas forging ironinthe impenetrable and dangerous jungle.

Guided bythe sounds madebythe chimps asthey cracked opennuts, which theyoften didforhours atatime, we were gradually abletoget within sixty feetofthe animals. Westill seldom saw thechimps themselves (theyfledif we came tooclose), buteven so,the evi- dence leftafter asession ofnut cracking taught usagreat dealabout whattypes of nuts theywere eating, whatsortsof hammer andanvil toolstheywere using, and-thanks tothe very distinctive noise a nut makes whenitfinally splits open-how manyhitswere needed to crack anut and how many nutscould be opened perminute.

After somemonths, webegan catch- ing glimpses ofthe chimpanzees before they fled, andafter alittle more time, we were abletodraw close enough to watch thematwork. Thechimps gather nuts from theground. Somenutsare tougher tocrack thanothers. Nutsofthe Panda oleosatreearethemost demand- ing, harder thananyofthe foods pro- cessed bypresent-day hunter-gatherers and breaking openonlywhen aforce of 3,500 pounds isapplied. Thestone ham- mers U!?edbythe Tal chimps rangefrom stones often ounces togranite blocks 64 of four toforty-five pounds.Stonesof any size, however, areararity inthe for- est and areseldom. conveniently placed near anut-bearing tree.Byobserving closely, andinsome casesimitating the way thechimps handlehammerstones, we learned thatthey have animpressive ability tofind justtheright toolforthe job athand. Talchimps couldremember the positions ofmany ofthe stones scat- tered, oftenoutofsight, around apanda tree. Without havingtorun around re- checking thestones, theywould select one ofappropriate sizethatwasclosest to the tree. These mental abilities inspa- tial representation comparewithsome of those ofnine-year-old humans.

To extract thefour kernels fromin- side apanda nut,achimp mustusea hammer withextreme precision. Time and time again, wehave been impressed to see achimpanzee raiseatwenty- pound stoneabove itshead, strikeanut with tenormore powerful blows,and then, using thesame hammer, switchto delicate littletapsfrom aheight ofonly four inches. Tofinish thejob, the chimps oftenbreak offasmall piece of twig anduseitto extract thelast tiny fragments ofkernel fromtheshell. In- triguingly, femalescrackpanda nuts more often thanmales, agender differ- ence intool usethat seems tobe more pronounced inthe forest chimps thanin their savanna counterparts.

After fiveyears offieldwork, we were finally abletofollow thechimpan- zees atclose range, andgradually, we gained insights intotheir wayofhunt- ing. One morning, forexample, wefol- lowed agroup ofsix male chimps ona three-hour patrolthathadtaken them into foreign territory tothe north. (Our study group isone offive chimpanzee groups moreorless evenly distributed in the Talforest.) Asalways duringthese approximately monthlyincursions, which seemtobe for thepurpose ofter- ritorial defense, thechimps weretotally silent, clearly onedge andonthe lookout for trouble. Oncethepatrol wasover, however, andthey were backwithin their own borders, thechimps Shiftedtheirat- tention tohunting. Theywereaftermon- keys, themost abundant mammals inthe forest. Traveling inlarge, multi-species groups, someofthe forest's tenspecies of monkeys aremore aptthan others to wind upasameal forthe chimps. The relatively sluggishand1arge (almost thirty pounds) redcolobus monkeys are the chimps' usualfare.(Antelope also live inthe forest, butinour tenyears at Tal, wehave never seenachimp' catch, or even pursue, one.Incontrast, Gombe chimps attimes docome across fawns, and when theydo,they seize theoppor- tunity-and thefawn.) The sixmales moved onsilently, peering upinto thevegetation andstop- ping from timetotime tolisten forthe sound ofmonkeys. Nonefedor groomed; allfocused onthe hunt. We followed oneoldmale, Falstaff, closely, for hetolerates uscompletely andisone of the keenest andmost experienced hunters. Evenfromtherear, Falstaff set the pace; whenever hestopped, the others paused towait forhim. After thirty minutes, weheard theunmistak- able noises ofmonkeys jumpingfrom branch tobranch. Silently,. thechimps turned inthe direction ofthe sounds, scanning thecanopy. Justthen, adiana monkey spottedthemandgave analarm call. Dianas arevery alertandfast; they are also about halftheweight ofcolobus monkeys. Thechimps quickly gaveup and continued theirsearch foreasier, meatier prey.

Shortly after,weheard thecharac- teristic coughofared colobus monkey.

Suddenly RousseauandMacho, two twenty-year-olds, burstintoaction, run- ning toward thecough. Falstaff seemed surprised bytheir precipitousness, but after amoment's hesitation, healso ran.

Now thehunting barksofthe chimps mixed withthesharp alarm callsofthe monkeys. HurryingbehindFalstaff, we saw himclimb upaconveniently situ- ated tree. Hisposition, combined with those ofSchubert andUlysse, twoma- ture chimps intheir prime, effectively blocked offthree ofthe monkeys' pos- sible escape routes.Butin,another tree, nowhere nearanyescape routeandthus useless, waitedthelast ofthe hunters, Kendo, eighteen yearsoldand theleast experienced ofthe group. Themonkeys, taking advantage ofFalstaff's delayand Kendo's error,escaped.

The sixmales moved onand within five minutes pickedupthe sounds ofan- ~ othergroup ofred colobus. Thistime, the chimps approached cautiously,no- body hurrying. Theyscreened thecan- opy intently tolocate themonkeys, which werestillunaware ofthe ap- proaching danger.MachoandSchubert chose twoadjacent trees,bothfullof monkeys, andstarted climbing veryqui- etly, taking carenottomove any branches. Meanwhile, theother four chimps blocked offanticipated escape routes. WhenSchubert washalfway up, the monkeys finallydetected thetwo chimps. Aswe watched the:colobus monkeys takeoffinliteral panic, theap- propriateness ofthe chimpanzees' sci- entific name-Pan cametomind: with a certain stretchofthe imagination, the fleeing monkeys couldbeshep- herds andshepherdesses frightenedat the sudden appearance ofPan, thewild Greek godofthe woods, shepherds, and their flocks.

Taking offinthe expected direction, the monkeys weretrailed byMacho and Schubert. Thechimps letgowith loud hunting barks.Trying toescape, two colobus monkeys jumpedintosmaller trees lower inthe canopy. Withthis, Rousseau andKendo, whohadbeen watching fromtheground, spedupinto the trees andtried tograb them. Onlya third ofthe weight ofthe chimps, how- ever, themonkeys managed tomake it to the next treealong branches toosmall for their pursuers. ButFalstaff hadan- ticipated thismove andwas waiting for them. Inthe following confusion, Fal- staff seized ajuvenile andkilled itwith a bite tothe neck. Asthe chimps metin a rush onthe ground, Falstaffbeganto eat, sharing withSchubert andRous- seau. Ajuvenile colobusdoesnotpro- vide much meat,however, andthistime, not allthe chimps gotashare. Frustrated individuals soonstarted offonanother hunt, andrelative calmreturned fairly quickly: thissortofhunt, byasmall band ofchimps actingontheir ownat the edge oftheir territory, doesnotgen- erate thekind ofhigh excitement that prevails whenmoremembers ofthe community areinvolved.

So far we have observed some200 monkey huntsandhave concluded that success requires aminimum ofthree motivated huntersactingcooperatively. Alone orinpairs, chimps succeed less than 15percent ofthe time, butwhen .three orfour actasagroup, morethan half thehunts result inakill. The chimps. seemwellaware ofthe odds; 92 percent ofall the hunts weobserved were group affairs.

Gombe chimpsalsohunt redcolobus monkeys, butthepercentage ofgroup hunts ismuch lower: only36percent.

In addition, welearned fromJaneGoo- dall thateven when Gombe chimps'do hunt ingroups, theirstrategies aredif- ferent. WhenTalchimps aniveunder-a group ofmonkeys, thehunters scatter, often silently, usuallyoutofsight ofone another buteach aware ofthe others' po- sitions. Asthe hunt progresses, they gradually closein,encircling thequarry.

Such movements requirethateach chimp coordinate hismovements with those ofthe other hunters, aswell .as with those ofthe prey, atall times.

Coordinated huntsaccount for63 percent ofall those observed atTal but only 7percent ofthose atGombe. Jane Goodall says.thatinaGombe group hunt, thechimpanzees typicallytravel together untiltheyanive atatree with monkeys. Then,asthe chimps begin climbing nearbytrees,theyscatter as each pursues adifferent target.Goodall gained theimpression thatGombe chimps boosttheirsuccess byhunting independently butsimultaneously, thereby disorganizing theirprey; ourimpression is that theTal chimps owetheir success to being organized themselves.

Just why theGombe andTalchimps have developed suchdifferent hunting strategies isdifficult toexplain, andwe plan tospend sometimeatGombe in the hope offinding out.Inthe mean- time, themere existence ofdifferences is interesting enoughandmay perhaps force changes inour understanding of human evolution. Mostcurrently ac- cepted theories proposethatsome three million yearsago,adramatic climate change inAfrica eastofthe Rift Valley turned denseforest intoopen, drierhabi- tat. Adapting tothe difficulties oflife under thesenewconditions, ourances- tors supposedly evolvedintocooperative hunters andbegan sharing foodthey caught. Supporters ofthis idea point out that plant andanimal remains indicative 11.Dim Forest, BrightChimps ofdry, open environments havebeen found atall early hominid excavation sites inTanzania, Kenya,SouthAfrica, and Ethiopia. Thatthelarge majority of apes inAfrica todaylivewest ofthe Rift - Valley appears tomany' anthropologists to lend further support tothe idea that a change inenvironment causedthe common ancestorofapes andhumans to evolve alongadifferent linefrom those remaining inthe forest.

Our observations, however,suggest quite another lineofthought. Lifein dense, dimforest mayrequire moreso- phisticated behaviorthaniscommonly assumed: compared withtheir savanna relatives, Talchimps showgreater com- plexity inboth hunting andtool use.Tal chimps usetools innineteen different ways andhave sixdifferent waysof making them,compared withsixteen uses andthree methods ofmanufacture at Gombe.

Anthropologist colleaguesofmine have toldmethat thediscovery that some chimpanzees areaccomplished us- ers ofhammerstones forcesthemtolook with afresh eyeatstone toolsturned up at excavation sites.Theimportant role played byfemale Talchimps intool use also raises thepossibility thatinthe course ofhuman evolution, -women may havebeendecisive inthe development of many ofthe sophisticated manipulat- ive skills characteristic ofour species.

Tal mothers alsoappear topass ontheir skills byactively teaching theiroff- spring. Wehave observed motherspro- viding theiryoung withhammers and then stepping into help when theinex- perienced youngsters encounterdiffi- culty. Thishelpmayinclude carefully showing howtoposition thenut orhold the hammer properly. Suchbehavior has never beenobserved atGombe.

Similarly, foodsharing, foralong time saidtobe unique tohumans, seems more general inforest thaninsavanna chimpanzees. Talchimp mothers share with their young upto60 percent ofthe nuts they open, atleast untilthelatter become sufficiently adept,generally at about sixyears old.They alsoshare other foods acquired withtools, includ- ing honey, ants,andbone marrow.

Gombe mothers sharesuchfoods much less often, evenwiththeirinfants. Tal 65 2.:. PRIMATES chimps alsoshare meatmore frequently than dotheir Gombe relatives, some- times dividing achunk upand giving portions away,sometimes simplyallow- ing. beggars tograb pieces.

Any comparison betweenchimpan- zees andourhominid ancestors canonly be suggestive, notdefinitive. Butourstud- ies lead ustobelieve thattheprocess of hominization mayhave begun inde- pendently ofthe drying ofthe environ- ment. Savanna lifecould evenhave delayed theprocess; manyanthropologists have been struck byhow slowly homi- nid-associated remains,suchasthe hand ax, changed aftertheir firstappearance in the Olduvai age.

Will wehave thetime todiscover more about thehunting strategies orother, perhaps asyet undiscovered abilitiesof 66 these forest chimpanzees? Africa's tropical rainforests, andtheir inhabi- tants, arethreatened withextinction by extensive logging,largelytoprovide the Western worldwithtropical timberand such products ascoffee, cocoa,andrnb- ber. Ivory Coast haslost 90percent of its original forest,andlessthan 5per- cent ofthe remainder canbeconsidered pristine. Theclimate haschanged dra- matically. Theharmattan, acold, dry wind fromtheSahara previously un- known inthe forest, hasnow swept through theTalforest everyyearsince 1986. Rainfall hasdiminished; allthe rivulets inour study region arenow dry for several months ofthe year.

In addition, thechimpanzee, biologi- cally veryclose tohumans, isin demand for research onAIDS andhepatitis vac-cines.

Captive-bred chimpsareavail- able, butthey costabout twenty times more thanwild-caught animals.Chimps taken fromthewild forthese purposes are generally young,theirmothers hav- ing been shotduring capture. Forevery chimp arriving atits sad destination, nine others maywellhave diedinthe forest oron the way.> Such priorities- cheap coffee andcocoa andchimpan- zees~o notdothe economies ofThird World countries anygood inthe long run, andthey bring suffering anddeath to innocent victimsinthe forest. Our hope isthat Brotus, Falstaff, andtheir families willsurvive, andthat weand others willhave theopportunity tolearn about themwellintothefuture. But there isno denying thatmodem times work against themandus.