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ReferencesTudge,C.(2002).NATURALBORNKILLERS.NewScientist,174(2342),36.

NATURALBORNKILLERSTHEMAKINGSOFASUICIDEBOMBERLIEINTHEBIOLOGYTHATSHAPEDUSALL,SAYSCOLINTUDGEREVENGEmightmakeusfeelbetter,butintheenditisnotthepoint.Whatmattersistomaketheworld safer, and for thatweneed some inkling ofwhy peoplewhoare neithermadnorstupid kill people theyhaveneverevenmet.Weneeda feel for theconditions thatpromotesuchbehaviourandthemindsetthatleadstoit.Inshort,weneedsomeinsightintothatelusivequalityknownashumannature.

Butwhathasemergedmoststarklyfrom11Septemberisthatwehaven'taclueornone,atleast,thathasenabledtheworld'sleaderstoimproveonsimpleretaliation,whichmaybehightechinexecutionbutinstrategybelongstotheStoneAge.Toprobeourownnatureweshouldwhereverpossiblebringsciencetobear,becauseitsideasaretestableandsocanbeworkedonandimproved.Withluck,itcanmoveusbeyondmereopinion.Oneobviousapproachistolook at our own biology, for although we think of ourselves in ethereal termstheologiansspeakofthesoul,andAristotledeclaredthatwearepoliticalanimalswearealsocreaturesofbiology,evolvedlikeanyother,anditmustbesensibletoaskwhatthatimplies.Forthiswehavetoturntothebranchofbiologyknownasevolutionarypsychology.

Merebiologywould scarcely seemup to the taskof explainingwhy youngmenandwomenshouldsacrificetheirownlivesassuicidebombers.Theirbehaviourseemsbothshockingandincomprehensible, a cue for politicians to rage about fanaticism and resurrect the coldwarconceptofbrainwashing.Yetthetermfanaticismtakenalonehasnoexplanatoryvalue,andisoften racist: the implication is thatMuslims ingeneralandArabs inparticularareprone tosuchbehaviour,togetherperhapswiththenorthernIrish.Thisbehaviour,it'simplied,isinnatelypathological,anddefiesunderstanding.Itcannotbeseenaspartofourevolvednature.

Can'tit?Awholenumberofcreaturesfromallsectionsofthephylogenetictree,includingmany

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that have no brains to be washed and certainly follow no religion, are known to sacrificethemselvesinallkindsofcircumstances.Thedrivingforcesareclearlygenetic,asitispossibleinprincipletoshowhowsuchbehavioursmayfollowMendelianpatternsofinheritance,andtheunderlyingreasonscanbeanalysedaccordingtotherulesofgametheory.

TheubiquitousgutbacteriumEscherichia coli providesa casestudy (Selection, vol 1, p51).TwoscientistsatMichiganStateUniversity,RichardLenskiandGregVelicer,foundthatwhennutrients are in short supply, different strains of the bacterium engage in chemical warfare.Individualswithineachstrainproducetoxinscalledcolicinsthatkillbacteriaofotherstrainsbutnottheirown.Butthere'sasnag.Individualbacteriathatproducethetoxinkillthemselvesintheprocess, just as a honeybee does when it stings or, as Lenski and Velicer point out, like asuicide bomber (and they wrote their paper well before September 2001). Selfsacrificemakes evolutionary sense because the gene that promotes the behaviour is also containedwithinotherbacteriaofthesamegenotype.Allindividualsofagivengenotypewillcontainthecolicingene,butonlyafewactuallyproducethetoxinandsosacrificethemselvesonbehalfoftheothers.Gametheoryanalysiscanshowwhatproportionwillemergeassuicidebombers.

Humans,ofcourse,arenotbacteria.Itwould,however,beasignificantmetaphysicalconceittosupposethatwecanlearnnothingfromothercreatures.Wehavegenestoo,andtheyinfluenceourbehaviour.The rulesofgeneticsareuniversal, so thesamebroad forces that shape thegeneralbehaviouralstrategiesofallcreaturesmustapplytoustoo.Specifically,broadbiologicalprinciplestellusthat,whateverthespecies,itisnotsurprisingthatsomeindividualsinasocietyandnot just thosewhoarepathologicallyprone to fanaticismmightsacrifice themselvesfortherest.

Inourownspecies,suicidebombersandhijackerswillingtodieforthecausearemoreoftenyoungmenratherthanwomen.FemalesuicidebombershaverecentlystruckseveraltimesinIsrael, and the Tamil Tigers, who have carried out many more suicide bombings than thePalestinians,havealsoemployedwomenbombers,butyoungmalebombersare in thegreatmajority.Nooneissurprisedbythis,becauseamongallcategoriesofhumanbeingmaleandfemale,youngandoldit'syoungmenwhoare thebiggest risktakers,not just inmattersofphysicalprowessbutinallaspectsoflife.

This tendencymaywellderivedirectly from reproductivephysiology.Femaleswhoare fertileandwanttohaveababyaregenerallyabletodoso.Malescaninprincipleimpregnateagreatmanymatesbutthisincreasesthecompetitionbetweenthem,sotheycaneasilyfinishupwithnomatesatall,andoftendo.Malescan'tbecertainof reproducingwithout takingrisks: theycannotsimplywaitforamatetocall.Thosewhoriskallmightdieintheattempt,butthisisnoworsegeneticallyspeakingthansittingaroundanddyingchildlesstheymight,byriskingall,doverywellindeed.Faintheartneverwonfairlady.

Youngmen'spropensityforriskiseasilyquantifiedinviolentcrime.Thusintheirclassicstudyoverseveraldecades,MartinDalyandMargoWilsonofMcMasterUniversityinOntarioshowedthat in all societies, young men commit the overwhelming majority of murders. Of course,humanbehaviourisextremelyflexibleandtheenvironmenthasahugebearingonthelikelihoodthatanyoneperson,maleor female,youngorold,willcommitmurder.MorewomencommitmurderinPhiladelphiathanmendoinIceland.Setuptherightcomparisonandyoucanfinda

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group of women who are more violent than a group of men. But still, male murderers inPhiladelphiaoutstripPhiladelphia'swomenmurderersby100to1,andthesameratioofmentowomenisfoundinthePhilippines,andScotland,andDenmark,andindeedinIceland,althoughthenumberofmurdersthereissosmallthatthestatisticshardlyregister.

Evolutionarypsychologistshavealsostudiedtheothersideofthecoin:notconflictandviolence,but sociality. Not all creatures are social but those that are clearly benefit in many ways.Commonsense,observationandallmannerof theoriesagree that sociality typically involvessomemeasureofunselfishness,andthisbydefinitionimpliesthatsocialityexactsaprice.Thevarious theories of altruism throw light on where unselfishness comes from. The lateevolutionarybiologistBillHamilton'snotionofkinselectionneatlyexplainedwhycreaturesareliabletohelptheirownkin,evenatcosttothemselves,andforanycreatureitsimmediatekinwillinevitablyformasignificantpartofitssociety.HisideasweretakenfurtherbyBobTrivers,ananthropologistatRutgersUniversityinNewJersey,toshowwhyevolutionmightalsofavourindividuals that helpothers theyarenot related to, in particular through reciprocal altruism:onehelpsanotherinthehopeandexpectationthatatsometimethefavourwillbereturned.

Moreprogresshasbeenmadeonthebackofthesefundamentalideas.JohnMaynardSmith'sanalysesofbehaviouralstrategythroughgametheory,developedattheUniversityofSussex,areparticularlyimportant.HisworkshowsthatsocietieswhichappeartoprovidewhatJeremyBenthamsometwocenturiesagocalledthegreatesthappinessforthegreatestnumbermaynotbeevolutionarilystable.Thussocietieswhichcontainonlyaltruisticdovesareaspeacefulascanbesincenobodywill fightanyoneelse.Butalldovesocietiesare liabletobeupsetbysomemutanthawkthatswaggersinandtakeseverythingwithoutopposition.Thehawkswillthriveandmultiplyuntil therearesomany that theystartclashingwithotherhawks,which isbadnewsforthehawks.Sothehawksaremoreorlessboundtoappearamongsocietiesofdoves,buttheirownhawkishnessstopsthembecomingtoonumerous.

Moregenerally, all societies require individuals tobehavewith somedegreeof altruism,andthatinturnmeansthattheyareallatriskfromfreeloaderswhotakethegoodiesanddonothinginreturn.Triverspredictedthatsocialcreaturesshouldbeadeptatdetectingcheatsandtakeadimviewofthem.EvolutionarypsychologistsJohnToobyandLedaCosmidesoftheUniversityof California, Santa Barbara, have tested this prediction in humans and so it turns out. Inlaboratoryteststheyshowthatpeoplefindithardtodetectviolationsofanif/thenrulelaidoutin logic but can do so easily and accurately if the violation represents cheating in a socialsituation.Theconclusionisthatourbrainshavespecificallyevolvedtospotcheating.Wehavenotsimplyevolvedageneralabilitytothinklogically.

The other side of this coin has been explored byRobert Frank ofCornellUniversity amongothers. In his books, including The WinnerTakeAll Society, he develops the notion thathumanshaveevolvedatremendouslystrongsenseofjustice.Ontheonehandweareacutelyawareofbeingdonedownontheotherwegotogreatlengthstoestablishourreputationsasgood,honestpeople.Inthis,wegofarbeyondwhatmightseemtobenecessary:forexample,weleavetipsforwaitersinrestaurantswewillnevervisitagain,becausewecan'tstopprovingtotheworldhowreliableweare.

Suchnotionscanbetestedindirectly.InSwitzerland,ErnstFehroftheUniversityofZurichand

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SimonGachteroftheUniversityofStGallengavestudentsacooperativetaskoftheprisoner'sdilemma kind: all benefit if everyone plays honourably, but those who cheat benefit moreprovided they don't get found out (New Scientist, 12 January, p 11). The students wererewardedwith realmoney if they didwell and fined if they did not. Theywere also able topunishfellowplayersbyimposingfinesbutonlybypayingapenaltythemselves,sothosewhopunishedothersa lotwere liable to finishupwith lessmoney than thosewhopunishedverylittle.Surprisinglythoughperhapsnotsosurprisingtothoseversedinevolutionarypsychologythestudentstendedtopunishcheatsseverely,eventhoughtheylostoutbydoingso.Peopleseem to hate cheats somuch that they are prepared to incur significant penalties to punishthem.Again,thistendencydoesnotseemconfinedtohumansitisnotjustapartofourownspecific culturaloverlay.JenniferScottat theWesleyanUniversity inConnecticuthas foundcomparablebehaviour ingorillas.Eventhealphamales,hugeanddominantthoughtheyare,areliabletobegivenabadtimebytheirsubordinatesiftheyappeartobehaveunjustly.

Onemore lineof thought, this timederiving fromDarwin's ideaofsexualselection,seems tosewthesedisparateobservationsintoaneatstory.Darwinproposedthenotionthatselectiondidnotactonlyoncharacteristicsthatmadecreaturesbetterabletosurvive,butalsoonthosethatmadethembetterabletoattractmates.HisideaswereneglecteduntilAmotzZahavitookthemupinthe1970stoexplorewhyanimalsdoweirdandwonderfulthingsfortheoppositesexthatarequiteuselessorevendamagingfordaytodaysurvival.Indeed,Zahaviproposedthatmatingdisplayswithfeathersandantlersandthunderousbassvoicesareimpressivepreciselybecausetheyaresocostly intimeandenergy.It isasthoughtheanimalweresaying:WhatwonderfulgenesImusthavetoabletodothisandsurvivetoo.

GeoffreyMiller, inTheMatingMind, suggests that all the greatest achievements of humans,including fine art andmusic and the ability to do calculus and speculate onGod, began asdisplays of prowess. Oneway to stand out from the crowd is simply to be passionate, andyoungmenareparticularlypronetopassionindeed,DalyandWilsonhaveproposedthattheextremeviolencesooftenevidentinyoungmalescanbeconstruedasaformofshowingoff.

Soaswedrawtogetherthevariousthreadsofevolutionarypsychologyitbecomeseasytoseehowyoungmen in particularwant both to display their bravery, andare deeply offendedbyinjustice,andonbothcountsmayrisktheirownliveseventothepointofcertaindeath.Whenthesepeopleareonoursidewecall themheroesandmartyrswhen theyarenot,we labelthemterrorists.

Whatdoesall thisaddupto?Thegeneralcontributionofevolutionarypsychologysofar is tosuggestthatevenflyinganaeroplanefullofpassengersintoabuildingfullofordinarypeopleisnotbeyondhumanunderstanding.Itshouldnotbedescribedsimplyinthemystifyinglanguageof psychopathology. It wastes everybody's time simply to smother the whole event and thepeople behind it in words like wicked and evil. This is the vocabulary of desperation:expressions of intellectual and moral abdication, as if such acts must forever be beyondunderstanding, so there is nothing sensible to be done except to purge the world of theirperpetrators, with as many bombs as it takes. Once we perceive that even such extremebehaviourisinprinciplecomprehensible,andthatitisveryprobablyrootedinthedeep,human,evolvedsenseof justiceand injustice,andperpetratedbyyoungpeoplewho feeldonedownand have a yen for martyrdom, then we at least have the basis for sensible and perhaps

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effectivestrategy.

Ofcourse,evolutionarypsychologydoesnotprovideanallembracingtheoryofhumannature.Itisnotasoloturn,toreplaceallotherwaysoflookingatourselves.Butitshouldbeacceptedalongsideothersourcesof insight, includingpsychology,sociology,philosophy, literature.Andthe common canard of the critics, that the hypotheses of evolutionary psychology are nottestableandthereforearenotscience, issimplynottrue.Theseareonlythebeginnings,too.Evolutionarypsychologyisnotapanacea,oranalgorithm,but itsurely isasignificantstepinwhatshouldbehumanity'squestforenlightenment.

PHOTO(COLOR)

PHOTO(COLOR)

PHOTO(COLOR):Wegotogreatlengthstoestablishourreputationsasgood,honestpeople

PHOTO(COLOR):Whenthesepeopleareonoursidewecallthemheroesandmartyrs:whentheyarenot,welabelthemterrorists

~~~~~~~~ByColinTudge

ColinTudge'slatestbooks,InMendel'sFootnotesandTheVarietyofLife,arenowavailableinpaperback.TheauthorisespeciallygratefultoOliverCurryattheLondonSchoolofEconomicsforhishelpinpreparingthisarticle

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