Altruism, Spite, and Greenbeards REVIEW

18 Pages·2010·0.55 MB·English

REVIEW
Hamilton’sgeneralpointwasthatnaturalse-
lectionleadsorganismstoappeardesignedasif
Altruism, Spite, and Greenbeards
tomaximizetheirinclusivefitness,whichisthe
sum of fitness gained through producing off-
spring (direct fitness) and through affecting the
Stuart A. West* andAndy Gardner*
fitnessofrelatedindividuals(indirectfitness).The
Hamilton’stheoryofinclusivefitnessshowedhownaturalselectioncouldleadtobehaviorsthat easiestwayinwhichindirectfitnesscanbeob-
decreasetherelativefitnessoftheactorandalsoeitherbenefit(altruism)orharm(spite)other tained is through interactions with close kin, in
individuals.However,severalfundamentalissuesintheevolutionofaltruismandspitehaveremained whichcasegenesareidenticalbydescent(froma
contentious.Here,weshowhowrecentworkhasresolvedthreekeydebates,helpingclarifyhow commonancestor),andsothisisusuallyreferred
Hamilton’stheoreticaloverviewlinkstoreal-worldexamples,inorganismsrangingfrombacteriato toas“kinselection.”However,inclusivefitness
humans:Istheevolutionofextremealtruism,representedbythesterileworkersofsocialinsects, isnotsimplyaconceptthatrelatestointeractions
drivenbygeneticsorecology?Doesspitereallyexistinnature?And,canaltruismbefavoredbetween betweenrelatives;itisourmoderninterpretation
individualswhoarenotclosekinbutsharea“greenbeard”geneforaltruism? ofDarwinianfitness,providingageneraltheory
ofadaptation(6,7).
Darwin’s (1) theory of natural selection altruisticorspitefultraits,whicharecostlytothe
explains both the process and the pur- individuals that perform them. The paragon of ExtremeAltruismandthe
poseofadaptation(Fig.1).Theprocess altruism is thesterileworker caste within social- HaplodiploidyHypothesis 0
1
isthatheritablecharactersassociatedwithgreater insect colonies, which help rear the offspring of Thesterileworkersofthesocialinsectsareex- 0
rceupmroudlautcetiivnensautuccraelsspowpiulllabtieonsesl.eTctheidslfeoardasntdoathce- tmheoilrdquceeellns.Athnateqaultarulliysteicxatlrleymgeievxeamupplethaeriersoliwmne tpreenmdeenatltrruepisrtosd,uwchtioongiivneourpdearnytochhealnpceotohferisn.dIen- 1, 2
1
apparentpurposeofadaptation:charactersappear- survivaltobecomethenonviablestalkofafruiting theHymenoptera(ants,bees,andwasps)andter- h
c
ing as if designed to maximize the individual’s body,helpingothercellstodisperseintheformof mites,thisextremealtruismhasledtoadivision r
a
reproductivesuccess(fitness). spores (5). The problem is that such altruism oflaborbetweenindividualsandtheevolution M
ofthehighestlevelofsocialorganization,termed n
o
A Dynamics B Design eusociality. Depending upon how eusociality is g
defined,ithasevolved3to11timesintheHy- or
menoptera,aswellasintermites,thrips,aphids, g.
a
spiders,beetles,shrimps,andmolerats(8,9). m
A major topic of debate has been whether e
c
eusociality has evolved multiple times in hy- n
e
menopterans because of their haplodiploid ge- ci
s
netics or their ecology. Under haplodiploidy, w.
fertilized eggs develop into (diploid) females, w
sg= cov(v,g) p pm a Px v(p) aHnadmuinltfoenrtili(z3e)desguggsgedsetveedlopthianttob(ehcaapulosied)hmaaplleos-. wm
o
diploidyleadstoafemalebeingmorerelatedto r
Fig. 1. Darwinian adaptation—dynamics and design. (A) Natural selection is the genetic change in the her sisters (r = 0.75, assuming an outbred d f
populationowingtodifferentialreproductivesuccessofindividualorganisms.Forexample,amongancestral e
population in which females mate once) than d
Arcticfoxes,individualswithpalefurleftmoredescendantsthanindividualswithdarkfursothatgenesforpale a
pfuorrtaicocnuomfualnatyecdhianrathcteerpoapscurliabtaiobnle.tPorincea’tsu(r3a5l)seelqeuctaitoinon(Dforgm)aisliezeqsutahlitso,stthaetincogvtahraiatntcheebcehtawnegeeninanthinedhiveirdituaabll’es hfoerrHowamnioltfofnsp’srirnugle(rto=be0.s5a)t,istfhiiesdm(Faikge.s3iAte).asier wnlo
S
genetic(“breeding”)valueforthetrait(g)anditsrelativefitness(v).(B)Asaconsequenceofpastnatural However, haplodiploidy also leads to a fe- o
D
selection,today’sArcticfoxeslook“designed”tofittheirenvironment.Thisiscapturedbyanoptimization male being less related to a brother (r = 0.25),
program,whichstatesthatthephenotype(p)oftheorganismisfunctioningasiftomaximizetheindividual’s exactlycancelingthebenefitofincreasedrelated-
relativefitness(v;moregenerally,itsinclusivefitness)(6,7).[Credit:Biosphoto/CordierSylvain/PeterArnoldInc.] nesstosisters(10).Thehaplodiploidyhypothesis
isnotrescuedifthepopulationsexratioisbiased
Fisher(2)unitedDarwinismwithMendelian reducesthereproductivesuccessofthealtruist—so towardfemalesbecausethisbiasalsoreducesthe
geneticsbydescribingnaturalselectioninterms whyisitnotweededoutbynaturalselection? relative reproductive value of females, exactly
ofchangesingenefrequencies.Genesassociated Hamilton (3) showed that genes can spread cancelinganyrelatednessbenefits(11).Numer-
withgreaterindividualfitnessarepredictedtoin- notonlythroughtheirdirectimpactontheirown ous studies have examined whether certain life
creaseinfrequency,leadingtoanincreaseinmean transmission but also through their indirect im- historiescouldrescueHamilton’shaplodiploidy
fitness.This“fundamentaltheoremofnaturalse- pactonthetransmissionofcopiespresentinother hypothesisbymakingtheaveragerelatednessto
lection”wasintendedtocapturetheprocess(nat- individuals.Consequently,altruisticbehaviorscan siblings r > 0.5, but none appears generally
uralselection)andthepurpose(maximizationof befavoredifthebenefitsaredirectedtowardother applicable (SOM text). In contrast, others have
individualfitness)ofadaptation. individualswhosharegenesforaltruism(Fig.2). arguedthatwhatisspecialaboutthehymenop-
ThisisencapsulatedbyHamilton’srule(3),which terans is that their natural history leads to a
Altruism, Spite,and Inclusive Fitness statesthatatraitwillbefavoredbyselectionwhen relativelyhighbenefitofhelping(highb/cratio),
Inthe1960s,Hamilton(3,4)realizedthatmaxi- rb–c>0,wherecisthefitnesscosttotheactor,b such as advanced parental care and a powerful
mization of individual fitness could not explain isthefitnessbenefittotherecipient,andristheir stingthatfacilitatesgroupdefense(12).
geneticrelatedness.ThisformofHamilton’srule
DepartmentofZoology,OxfordUniversity,SouthParksRoad, emphasizesinteractionsbetweentwoindividuals, TheMonogamy Hypothesis
OxfordOX13PS,UK.
but it can be extended to allow for interactions Recent work (8, 13) has suggested a possible
*To whom correspondence should be addressed. E-mail:
withmultipleindividuals[supportingonlinemate- resolutiontothisdebate,arguingthatstrictlife-
[email protected] (S.A.W); [email protected].
ac.uk(A.G.) rial(SOM)textandtableS1]. timemonogamy,inwhichfemalesonlymatewith
www.sciencemag.org SCIENCE VOL327 12 MARCH 2010 1341
REVIEW
tosiblings(r>0.5)hasbeenaredherring;whatis
A Altruism B Reciprocity
keyisthataveragerelatednessstaysat0.5.Other
redherringsincludethepossibilityforeusociality
Relative to have evolved via cooperation between sisters
Help Help Relative (theparasocialroute)becausethatwouldleadto
Actor or non-
Actor Help relative r<0.5(8)andthesuggestionthathighrelat-
edness is a consequence rather than a cause of
eusociality(15),inwhichcasetheobservedcor-
Nonrelative
Not altruism! relationwithmonogamywouldnotbepredicted
(9). Finally, the monogamy hypothesis suggests
C Spite D Greenbeard thatfactorsthatfacilitatemonogamy,suchaslife-
timestorageofspermbyfemales,arealsoimpor-
tantinexplainingthedistributionofeusociality.
Relative Bearded
Help
GettheRight Spite
Benefit Actor or Benefit
Actor Inclusive-fitness theory explains altruism but
Harm Harm alsohasadarkerside.Spitefultraits,whichare
harmful to both actor and recipient, may be
Nonrelative Nonbearded
favored (4). Considering the classic two-party 0
1
versionofHamilton’srule,ifcispositive(which 0
dFiirge.ct2ed.Mtoewcahradnrisemlastifvoers.a(lBtr)uRisemci,psrpoictiet,yainsdfarveocriepdrowcihtey.n(Ait)mAaltkreusistmhecaacntobremfaovroerleikdeilfyittoisrepcreeifveerehnetlipalilny icsosctolysttloytthoertheceipaicetnotr)),,thanendrbb–iscn>e0gactaivnebe(wsahtiicsfhieids 1, 2
1
thefuture.Reciprocityreliesuponafuturedirectfitnessbenefitforcooperationandsoisnotaltruistic.(C) ifrelatedness(r)isnegative. Negative relatedness h
Spitecanbe favoredif it is preferentiallydirectedtowardrelativelyunrelatedindividuals,whoseloss c
mayseemabizarreconcept,butitsimplymeans r
improves the fitness of relatives. (D) Greenbeards are favored by directing altruism toward fellow a
thattherecipientislessrelatedtotheactorthanisan M
greenbeardindividualsorspitetowardnonbeardedindividuals. averagememberofthepopulation(SOMtext). n
o
Another way to think about spite is to dis- g
onemaleintheirentirelife,iscrucialfortheevo- already lost the ability to mate and realize full tinguish between the primary recipient of the or
lution of eusociality. Monogamy leads to a reproductive potential (9). Furthermore, these harming behavior (the individual physically g.
a
potential worker being equally related (r = 0.5) specieshavehadthetimetoevolvedivisionof attacked) and those secondarily influenced as a m
toherownoffspringandtotheoffspringofher labor and specialized helping behaviors, giving byproduct of this (those experiencing reduced e
c
mother(siblings).Inthiscase,anysmallefficiency asubstantialb/c. competitionfromtheharmedindividual)(16,17). n
e
benefit for rearing siblings over their own off- Thebeautyofthemonogamyhypothesisisthat Fromthisperspective,spitecanbefavoredifthe ci
s
spring(b/c>1)willfavoreusociality(Fig.3B). itsimplifiesourunderstandingofhoweusociality actorismorerelatedtothesecondaryrecipients w.
Incontrast,evenalowprobabilityofmultiple evolved,emphasizingthattheinteractionbetween (whobenefit)thantotheprimaryrecipients(who w
mating means that potential workers would be kinshipandecologyisfundamentalandthatthey areharmed).Spitecanthereforebethoughtofas w
morerelatedtotheirownoffspring.Inthiscase, are not competing explanations (8, 13). For altruismtowardthesecondaryrecipients:Harm- m
o
costly helping would require a significant effi- example,thesearchforhowtoincreaserelatedness inganindividualcanbefavoredifthisprovidesa r
ciency advantage to rearing siblings over own d f
e
offspring(Fig.3C).Untilgrouplivingisestab- d
A B C a
lished,allowingtheevolutionofspecializedco- Haplodiploidy Monogamy Polyandry o
operativebehavioranddivisionoflabor,theratio hypothesis nl
Offspring Siblings Offspring Siblings Offspring Siblings w
b/ccannotbeexpectedtogreatlyexceed1.For r= 0.5 r> 0.5 r= 0.5 r= 0.5 r= 0.5 r < 0.5 o
D
example,feedingasiblingisunlikelytobehugely
morebeneficialthanfeedinganoffspringbythe
same amount. Consequently, in the absence of
strictmonogamythepopulationcannotevenget
startedontheroadtoeusociality.
In support of this hypothesis, comparative
studieshavefoundmonogamytobetheancestral D E F
stateinalltheindependentoriginsofeusociality
studied(9,14).Monogamyoriginatedfirst,giving
ahighrelatedness,andthenwhenecologicalcon-
ditionsledtoahighenoughb/c,eusocialityevolved
(SOMtext).Importantecologicalconditionsin-
clude“lifeinsurance”benefitsofallowinghelpers
to complete parental care after the death of the
Fig. 3. Monogamypavesthewaytoeusociality.(A)Thehaplodiploidyhypothesisreliesonindividuals
mother(forexample,ants,bees,andwasps),and
beingmorerelatedtosiblingsthanoffspring,makingsiblingsworthmorethanoffspring.Asoriginally
“fortressdefense”benefitsofremainingtohelpuse envisioned,thisappearstohavebeenaredherring.(B)Themonogamyhypothesisemphasizesthatifan
or defend a food source, when opportunities for individualisequallyrelatedtoitssiblingsanditsoffspring,evenaveryslightefficiencybenefitforraising
successfulmigrationarelow(forexample,aphids, siblingstranslatesintoaselectiveadvantageforhelping.(C)Withoutstrictmonogamy,individualsaremore
beetles,termites,thrips,andshrimps)(12,14). relatedtotheiroffspringthantheyaretotheirsiblingssothatalargeefficiencybenefitisrequiredinorder
There are some eusocial species in which forsibling-rearingtobefavored.(D)SterileworkerscaringforbroodintheantCamponotusherculeanus.
queensmatemultiply.However,thisisaderived (E)AlifetimemonogamouspairfromthetermiteReticulitermesflavipes.(F)Nonbreedingworkersinthe
condition that has evolved after workers have shrimpSynalpheusregalis.[PhotosprovidedbyDavidNash,BarbaraThorne,andEmmettDuffy]
1342 12MARCH 2010 VOL327 SCIENCE www.sciencemag.org
REVIEW
benefittocloserrelatives(Fig.2C). toconspecificsthatlackanimmu-
Table1.Notspite:examplesoftraitsthathavebeensuggestedasspiteful
Thesetwodifferentencapsulations nitygene(22).Insomecases,cell
but actually provide a direct benefit to the actor and hence are selfish
ofspitearedifferentwaysoflook- death is required to release the
(table S2).
ingatthesamething,usingeithera bacteriocins into the environment,
two-orthree-partyHamilton’srule Taxa Suggestedspitefultraits Whyselfish,notspiteful and so it is clearly a costly trait
(SOMtext)(16,17).Iftheactoris (positive c). In addition, there is
Birds Protectionofterritories, Decreasedcompetitionfor
morecloselyrelatedtothesecond- geneticlinkagebetweenthebacte-
siblicideatneighboring resources,forselfor
aryrecipientsthantheprimaryre- riocin production and immunity
nests. offspring
cipients in a three-party rule, then genes so that close relatives both
Fish Eggcannibalism Decreasedcompetitionfor
thisleadstoanegativerelatedness produce and are immune to a
resources,foroffspring
inthetwo-partyrule. particular bacteriocin (22). Conse-
Humans Punishmentandrejectionof Leadstoincreased
Althoughmanybehaviorshave quently,thereleaseofbacteriocins
lowoffersineconomic cooperationinthelongterm
beensuggestedasspiteful,theyare killsnonrelatives,freeingupresources
games
usuallyexplainedasselfishbehav- forclone-mates.Experimentalwork
Mammals Infanticide,harassmentof Decreasedcompetition,for
iorsthatarecostlytotherecipient onbacteriocins has alsosupported
nondescendantjuveniles offspringormates
butprovideabenefittotheactor(c< the prediction that the relative ad-
andinjuredmales
0)(Table1).Thisbenefitisoftena vantageofspiteisgreaterwhenvar-
reductioninfuturecompetitionfor ianceinrelatednessishigher(giving
resources, for the actor or their offspring, with sterilesoldiercasteinpolyembryonicparasitoid anintermediatemeanrelatedness)becausethis 0
1
confusion arising because the direct fitness waspssatisfiesalltheseconditions(17).Females leads to interactions with both close relatives 0
cteornmseaqnudenncoetsowveerrethoenlilfyetcimonesiodfetrheedainctothre(SsOhoMrt laafyterthweihricehggthseownathspeeeggggssdoifvimdeotahsecxautearlplyillaanrsd, alantdednnoenssretloatitvhees,seaclloonwdianrgyaberenleaftiicviealryiehsig(Fhiegr.r4e)- 1, 2
1
text)(18).Whatmattersfornaturalselectionare consumethegrowingcaterpillarfromtheinside (21,23). h
c
fitnessconsequencesovertheentirelifetimeand (20). Although most larvae develop normally, a r
a
notsomearbitraryperiod.Forexample,herring fractionbecomeasoldiermorph.Developingasa Spiteful Words M
gullskillthechicksatneighboringnests,butthis soldieriscostlytotheactor,becausethesoldiersare As discussed above, spite can be considered a n
o
reducesthefuturecompetitionoverresourcesfor sterile, and costly to the recipient, because the formofaltruism.Consequently,itisusefultoask g
both themselves and their offspring. Further- soldiers seek out and kill other larvae within the whetherwegainanythingbydistinguishingspite or
more, there is no evidence that such examples host. Finally, soldiers preferentially kill larvae to from altruism. At one level, it can be useful to g.
a
involveasufficientsecondarybenefittorelatives. which they are less related (those that have emphasizethesimilarities,thatbotharefavored m
Indeed, it has even been suggested that the developedfromothereggs),freeingupresources becausetheyleadtoanincreaseintheinclusive e
c
conditions required are so restrictive that spite fortheirclone-mates. fitnessoftheactorthroughindirectfitnesscon- n
e
wouldberareornonexistent(11,12). Another example of spite is provided by sequences.Thiswillalsohelpavoiddebatesover ci
s
However, recent theory has shown that a the production of antimicrobial bacteriocins by whether certain traits should be classed as al- w.
positive relatedness to secondary recipients can manybacteria(21).Thesecompoundsarelethal truismor spite because the mathematics of any w
beobtainedmoreeasilythanpreviouslythought, w
suggesting that at least from a theoretical m
o
perspective spite is plausible (19) if there is (i) A B 4.0 r
lpbaeerhtgiateovrisov;rasr(iiaia)nimckeeindindaitsrceirlniamdteiivdninadetuisoasnls,btweotiwthweehhnoamrcmoitmnhge- efficient Spite Altruism efficient 23..00 oaded f
actor is relatively unrelated (making the actor n co n co 1.0 wnl
relatively more related to the secondary recip- o o o
ients); or (iii) strong local competition so that ecti ecti 0.0 D
harming the primary recipient provides appre- Sel Sel
ciable benefits to secondary recipients. When -1.0
0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0
theseconditionsaremet,spitefulbehaviorscan Kinship Kinship
be favored so as to reduce competition for rel-
C D
atives. Consider the extreme example of when
twogeneticallyidentical(clonal)individualsare
competingwithanonrelativetowhomtheyare
unrelated. One of the clone-mates could be
selected to harm the nonrelative, at a cost to
itself, if this harming reduces the nonrelative’s
ability to compete for resources and hence
benefitstheotherclone-mate.
RealSpite
Todemonstratespite,itmustbeshownthatatrait
Fig. 4. Populationstructure,altruism,andspite.(A)Theorypredictsthatasrelatednesswithinapatch
iscostlytotheactor(positivec)andcostlytothe increases,thereisanincreaseinaltruistictraitsandadomedrelationshipwithspitefultraits(3,15).(B)As
recipient (negative b). In addition, for spite to predicted, the relative benefit of bacteriocin production inPseudomonas aeruginosa shows a domed
haveevolvedbymeansofnaturalselection,the relationshipwithrelatedness(23)(C)Altruism:afruitingbodyoftheslimemoldDictyosteliumdiscoideum.
actor must be more closely related to the sec- (D)Spite:Apieceoffilterpapersoakedwithabacteriocin(leftspot)causesaninhibitionzonewherebacteria
ondary recipients (beneficiaries) than to the cannotgrow,inthesamewayasatraditionalantibiotic(rightspot;bottomspotshowsbothincombination).
primaryrecipientthattheyharm(Fig.2C).The [PhotosprovidedbyOwenGilbert,MargaretRiley,andSaraCody]
www.sciencemag.org SCIENCE VOL327 12 MARCH 2010 1343
REVIEW
casecanberearrangedsoastomakeaspitefulor wouldnotoccurinnaturebecausetheycouldbe biology. Theoretical work on spite and green-
altruistictwo-partyrule(16,17). easily invaded by “falsebeards” (cheats) that beards was spurred by biological examples but
However,therearealsoanumberofreasons displayedthebeardwithoutalsoperformingthe thenledtoaunifyingframeworkthatilluminated
whyitisusefultodistinguishspitefromaltruism behavior(27). detectionproblemsandsuggestedwheretolook
(17). From a behavioral perspective, there is a Thisassumptionhasbeenoverturnedbythe forfurtherexamples.Alloftheseexamplesillus-
clear difference between helping and harming. discoveryofanumberofaltruisticgreenbeards. tratethatthedistinctionbetweengenetics(r)and
Additionally, there are biologically interesting In the slime mold Dictyostelium discoideum, ecology (b/c) is both artificial and unhelpful.
differences between altruism and spite. For ex- individuals with the csa gene adhere to each What really matters is how they interact, as has
ample,localcompetitionforresourcestypically other in aggregation streams and cooperatively alwaysbeenemphasizedbyHamilton’srule.
selects for spite and against altruism (21); formfruitingbodieswhileexcludingnoncarriers
altruistic traits are predicted to show a positive of the gene (5). Other examples have been ReferencesandNotes
relationshipwithrelatedness(3),whereasspite- foundinyeast,abacterialplantpathogen,anda 1. C.Darwin,OntheOriginofSpeciesbyMeansofNatural
Selection,or,thePreservationofFavouredRacesinthe
fultraitsarepredictedtoshowadomedrelation- lizard (SOM text). In addition, spiteful green-
StruggleforLife(JohnMurray,London,UK,1859).
ship(Fig.4)(19,21);andkindiscriminationis beardshavebeendiscovered,includingtheGp-9
2. R.A.Fisher,TheGeneticalTheoryofNaturalSelection
key in the examples of spite, whereas altruism gene of the fire ant Solenopsis invicta (29). (Clarendon,Oxford,1930).
canoftenevolvewithoutkindiscriminationwhen Workerswiththeballeleatthislocususeodor 3. W.D.Hamilton,J.Theor.Biol.7,1(1964).
limiteddispersalkeepsrelativestogether(3). todeterminewhetherprospectivequeensalsocarry 4. W.D.Hamilton,Nature228,1218(1970).
5. D.C.Queller,E.Ponte,S.Bozzaro,J.E.Strassmann,
Spitecanalsobedefinedfromamechanistic this allele, dismembering them if they do not.
Science299,105(2003).
or psychological perspective in primates and Another example is provided by bacteriocin 6. A.Grafen,J.Evol.Biol.20,1243(2007). 0
humansasabehaviorthatharmsanotherorarises production,inwhichthebacteriocin-encodinggene 7. A.Gardner,Biol.Lett.5,861(2009). 01
cfraosmes,ahdaermsirinegtoishlaikrmelyatnoobtheefra(v2o4r,ed25b)e.cIanutsheeosen andTthheeoirmetmicuanlitwyogreknehaarsetcilgahrtilfyiedlinkwehden(22w).e 8. J3.6J4.,B3o1om91sm(2a0,0P9h)i.los.Trans.R.Soc.Lond.BBiol.Sci. 1, 2
9. W.O.H.Hughes,B.P.Oldroyd,M.Beekman, 1
averageit providesadirectbenefittotheactor wouldexpectgreenbeardstooccur(30).Green- F.L.W.Ratnieks,Science320,1213(2008). h
c
(c<0)andisselfish,notspiteful.Itiscrucialnot beardscanbecategorizedintofourgroups,with 10. R.L.Trivers,H.Hare,Science191,249(1976). r
a
tomixdefinitionsofspitebyraisingtheproblem different evolutionary dynamics, according to 11. R.Craig,Evolution33,319(1979). M
andrarityofevolutionaryspitethengoingonto whether they are altruistic (helping) or spiteful 12. J.E.Strassmann,D.C.Queller,Proc.Natl.Acad.Sci.U.S.A. n
104(suppl1),8619(2007). o
examineaharmingbehaviorthatprovidesadirect (harming) and always expressed (obligate; for 13. J.J.Boomsma,Curr.Biol.17,R673(2007). g
benefit to the actor, and therefore is not evolu- example, bacteriocins) or only expressed in 14. J.E.Duffy,K.S.Macdonald,Proc.Biol.Sci.277,575(2010). or
tionaryspiteful.Thespecificconditionsrequired response to the presence of the greenbeard in 15. E.O.Wilson,B.Hölldobler,Proc.Natl.Acad.Sci.U.S.A. g.
102,13367(2005). a
to favor evolutionary spite might make it rela- others (facultative; for example,Gp-9). For all m
16. L.Lehmann,K.Bargum,M.Reuter,J.Evol.Biol.19,
tivelyunlikelyinhumansandotherprimates.In- casesexceptthefacultativealtruisticgreenbeard, e
1507(2006). c
deed, spite may be rare in general because it is the greenbeard is selected against at low 17. A.Gardner,I.C.W.Hardy,P.D.Taylor,S.A.West,Am. n
e
hardtoobtainsituationsinwhichpopulationsare frequencies and only favored when it has Nat.169,519(2007). ci
structuredsothatharmingnonrelativesisanef- establisheditselftoacertainfrequency.Popula- 18. FKe.nRn..F3o8st,e2r,2T9.(W20en0s1e)l.eers,F.L.W.Ratnieks,Ann.Zool. w.s
ficientwayofhelpingrelatives. tionstructurecansolvethisproblembykeeping 19. A.Gardner,S.A.West,J.Evol.Biol.17,1195(2004). w
individuals with greenbeards together. The best 20. D.Giron,D.W.Dunn,I.C.W.Hardy,M.R.Strand, w
Greenbeards place to look for new greenbeards may be in Nature430,676(2004). m
Hamilton(3,26)pointedoutthatindirect-fitness microbes, in which asexual growth can lead to 21. A.Gardner,S.A.West,A.Buckling,Proc.Biol.Sci.271, ro
benefits require genetic relatedness per se and extreme population structuring; the relatively 1529(2004). d f
22. M.A.Riley,J.E.Wertz,Annu.Rev.Microbiol.56,117(2002). e
not kinship. Imagine a gene (or cluster of simple link between genotype and phenotype 23. R.F.Inglis,A.Gardner,P.Cornelis,A.Buckling,Proc. d
a
tightly-linked genes) that gives rise to a con- may prevent a decoupling of beard and social Natl.Acad.Sci.U.S.A.106,5703(2009). o
spicuous phenotype, uses this phenotype to trait (falsebeards), and genetic knockouts facil- 24. M.Hauser,K.McAuliffe,P.R.Blake,Philos.Trans.R.Soc. nl
w
Lond.BBiol.Sci.364,3255(2009).
discriminate between carriers and noncarriers itatethedetectionofgreenbeards(30). o
25. K.Jensen,J.Call,M.Tomasello,Proc.Natl.Acad.Sci.U.S.A. D
ofthegene,andleadstocostlyhelpingtoward Somemodelsforaltruisminhumans(31–34) 104,13046(2007).
other carriers of the gene (Fig. 2D). This gene and social insects (15) implicitly invoke green- 26. W.D.Hamilton,inBiosocialAnthropology,R.Fox,Ed.
could be favored by natural selection, even if beard mechanisms without realizing this, such (Wiley,NewYork,1975),pp.133–155.
27. R.Dawkins,TheSelfishGene(OxfordUniv.Press,Oxford,
carrierssharenoothergenesincommon.Thus, asthesuggestionthataltruisticindividualsdiffer
1976).
the crucial requirement for altruism is genetic from individuals whoare not altruisticinsome
28. L.Lehmann,L.Keller,J.Evol.Biol.19,1365(2006).
relatednessatthealtruismlocusandnotgenea- observable characteristic [such as being more 29. L.Keller,K.G.Ross,Nature394,573(1998).
logicalrelationshipoverthewholegenome. likelytosmileandlaugh(31,32)]ormodelsof 30. A.Gardner,S.A.West,Evolution64,25(2010).
Dawkinsproposedthehypotheticalexample “strongreciprocity”thatassumepunishmentand 31. R.H.Frank,Am.Econ.Rev.77,593(1987).
32. M.J.Owren,J.-A.Bachorowski,inEmotions:Current
ofagenethatgivesrisetoagreenbeardwhile altruismtobegeneticallylinked(33,34).How-
IssuesandFutureDirections,T.J.Mayne,G.A.Bonanno,
simultaneously prompting individuals with ever,thereisnoreasontosuspectthattraitssuch Eds.(Guilford,NewYork,2001),pp.152–191.
greenbeardstodirectcooperationtowardother assmilingorpunishmentwillbeencodedbythe 33. H.Gintis,J.Theor.Biol.206,169(2000).
green-bearded individuals (27). However, this samegeneorcloselylinkedgenesasthosethat 34. S.Bowles,H.Gintis,Theor.Popul.Biol.65,17(2004).
35. G.R.Price,Nature227,520(1970).
“greenbeard”mechanismcanalsooccurwithout leadtoaltruism.Consequently,falsebeardscould
36. WethankJ.Alpedrinha,K.Boomsma,A.Griffin,
avisibletag.Whatisrequiredmoregenerallyis arise,andtheseproposedexplanationsforaltruism M.Hauser,K.Jensen,L.KellerandP.Taylorfor
a single gene (or a number of tightly-linked wouldnotbeevolutionarilystable(30). commentsandtheRoyalSociety,EuropeanResearch
genes) encoding both the cooperative behavior Council,andLeverhulmeTrustforfunding.
and causing cooperators to associate (26, 28). Conclusions
SupportingOnlineMaterial
Greenbeards are oneof the twoways in which Aunifyingthemeinalltheissuesthatwehave
www.sciencemag.org/cgi/content/full/327/5971/1341/DC1
natural selection can favor altruistic behavior, discussedhereistheimportanceoftheinterplay SOMText
withtheotherbeinginteractionswithgenealog- between theory and data. The monogamy hy- TablesS1andS2
ical kin (3). However, despite this fundamental pothesiscutsthroughthesuperfluousdetailsby References
position it has been assumed that greenbeards focusing on a key aspect of the underlying 10.1126/science.1178332
1344 12MARCH 2010 VOL327 SCIENCE www.sciencemag.org
www.sciencemag.org/cgi/content/full/327/5971/1341/DC1

Supporting Online Material for

Altruism, Spite, and Greenbeards
Stuart A. West* and Andy Gardner*

*To whom correspondence should be addressed. E-mail: [email protected] (S.A.W);
[email protected] (A.G.)

Published 12 March 2010, Science 327, 1341 (2010)
DOI: 10.1126/science.1178332

This PDF file includes:

SOM Text
Tables S1 and S2
References
Supporting Online Material
for
‘Altruism, Spite and Greenbeards’, by Stuart A. West & Andy Gardner
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’0)/!%&/%!*++.)2/%’+$!’(!8/5+42)0!,&)$!/5/’3/E3)!E2))0’$1!(’%)(!/2)!3’6’%’$1!>&/E’%/%!
(/%42/%’+$?7! E)*/4()! ’%! ,+430! 3)/0! %+! 9)/2! 2+4$0! *+6.)%’%’+$! 8+2! E2))0’$1! (’%)(;!
T+$(’0)2’$1! 3’8)! &’(%+29! 5/2’/E3)(7! *++.)2/%’5)! E2))0’$1! (.)*’)(! %)$0! %+! &/5)! 3+,)2!
6+2%/3’%9!2/%)(!/$0!3+,)2!2/%)(!+8!0’(.)2(/37!,&’*&!*+430!/3(+!3)/0!%+!12)/%)2!*+6.)%’%’+$!
8+2!%)22’%+2’)(!>28, 29?;!#$!6/$9!E’20!*/()(7!&)3.’$1!6/9!2).2)()$%!%&)!E)(%!+8!/!E/0!^+E7!’$!
2)(.+$()!%+!8/*%+2(!(4*&!/(!8/’3)0!E2))0’$1!/%%)6.%(!>30?!+2!/!3/*:!+8!(4’%/E3)!$)(%’$1!(’%)(!
>31?7!/$0!(+!%&)!b_c!2/%’+!*/$!E)!5)29!&’1&!04)!%+!/!3+,!c;!

Social behaviours and intentional language!
V2+6!/$!)5+34%’+$/29!.)2(.)*%’5)!/!%2/’%!+2!E)&/5’+2!’(!(+*’/3!’8!’%!&/(!8’%$)((!
*+$()C4)$*)(!8+2!E+%&!%&)!’$0’5’04/3!%&/%!.)28+26(!%&/%!E)&/5’+2!>%&)!/*%+2?!/$0!/$+%&)2!
’$0’5’04/3!>%&)!2)*’.’)$%?;!</6’3%+$!>2?!*3/((’8’)0!(+*’/3!E)&/5’+2(!/**+20’$1!%+!,&)%&)2!
%&)!*+$()C4)$*)(!%&)9!)$%/’3!8+2!%&)!/*%+2!/$0!2)*’.’)$%!/2)!E)$)8’*’/3!>’$*2)/()!0’2)*%!
8’%$)((?!+2!*+(%39!>0)*2)/()!0’2)*%!8’%$)((?!>F/E3)!]‘W"?;!
! L
F&)! /0/.%/%’+$’(%! /..2+/*&! .2+5’0)(! %&)! 8+26/3! ^4(%’8’*/%’+$! 8+2! %&)! 4()! +8!
’$%)$%’+$/3! 3/$14/1)7! (4*&! /(! /3%24’(6! /$0! (.’%)! >32?;! ].)*’8’*/3397! %&)! 09$/6’*(! +8!
$/%42/3!()3)*%’+$!3)/0(!%+!’$0’5’04/3!+21/$’(6(!%&/%!E)&/5)!/(!8’%$)((!6/-’6’D’$1!/1)$%(7!
/$0!&)$*)!E)&/5)!/(!’8!%&)9!&/5)!’$%)$%’+$!+2!.42.+()!/%!%&)!’$0’5’04/3!3)5)3;!#$%)$%’+$/3!
%)26(!0+!$+%!.2+5’0)!/!(4.)28’*’/3!13+((7!E4%!2/%&)2!*+$5)9!’6.+2%/$%!’$8+26/%’+$!/E+4%!
1)$)! 82)C4)$*9! 09$/6’*(;! #$! ./2%’*43/27! %&)! 6/-’6’D’$1! /1)$%! /$/3+19! &/(! E))$!
8+26/3’D)0!,’%&!2)(.)*%!%+!/$!’$0’5’04/3=(!3’8)%’6)!2).2+04*%’5)!(4**)((!@!$+%!8+2!^4(%!
(+6)!/(.)*%!+8!8’%$)((!>);1;!8)*4$0’%9?!+2!+5)2!(+6)!3’6’%)0!%’6)!(*/3)!+2!2)3/%’5)!%+!(+6)!
(4E()%!+2!12+4.!+8!%&)!.+.43/%’+$;!
U3%)2$/%’5)! )5+34%’+$/29! 0)8’$’%’+$(! +8! %)26(! (4*&! /(! /3%24’(6! E+%&! */4()!
*+$84(’+$! /$0! 3/*:! /! 8+26/3! ^4(%’8’*/%’+$! >33?;! V+2! )-/6.3)7! %&)! 4()! +8! \2)*’.2+*/3!
/3%24’(6=!0)8’$)(!/3%24’(6!+5)2!%&)!(&+2%M%)26!8’%$)((!*+$()C4)$*)(;!<+,)5)27!$/%42/3!
()3)*%’+$!+.)2/%)(!+$!3’8)%’6)!8’%$)((!*+$()C4)$*)(7!$+%!+5)2!(+6)!/2E’%2/29!(&+2%M%)26;!
H)*’.2+*/3!/3%24’(6!’(!$+%!/*%4/339!/3%24’(%’*!>V’1;!K?7!/$0!(+!E)%%)2!%)26)0!2)*’.2+*’%9=!
>33?;!F+!1’5)!/$+%&)2!)-/6.3)7!%&)!12+4.!()3)*%’+$!3’%)2/%42)!0)8’$)(!/3%24’(6!2)3/%’5)!%+!
%&)!8’%$)((!+8!+%&)2!’$0’5’04/3(!’$!%&)!12+4.!>34?;!<+,)5)27!$/%42/3!()3)*%’+$!+.)2/%)(!+$!
8’%$)((!2)3/%’5)!%+!%&)!.+.43/%’+$7!$+%!(+6)!/2E’%2/29!82/*%’+$!+8!’%;!F&)()!/$0!+%&)2!
)-/6.3)(!/2)!0’(*4(()0!’$!12)/%)2!0)%/’3!’$!%&)!8+33+,’$1!()*%’+$;!

O88)*%!+$!/*%+2! O88)*%!+$!2)*’.’)$%!
! b! M!
b! W4%4/339!E)$)8’*’/3! ])38’(&!
M! U3%24’(%’*! ].’%)843!
Table SOM1. Social Behaviors. U$! )5+34%’+$/29! *3/((’8’*/%’+$! (*&)6)! 8+2! (+*’/3!
E)&/5’+2(!%&/%!&/5)!E))$!()3)*%)0!8+2!E9!$/%42/3!()3)*%’+$!>2, 33?;!O88)*%(!/2)!6)/(42)0!’$!
%)26(!+8!3’8)%’6)!)88)*%(!+$!0’2)*%!8’%$)((;!<)3.’$1!E)&/5’+2(!/2)!b!%+!%&)!2)*’.’)$%7!/$0!
*/$!E)!64%4/339!E)$)8’*’/3!+2!/3%24’(%’*;!</26’$1!E)&/5’+2(!/2)!@!%+!%&)!2)*’.’)$%!/$0!*/$!
E)!()38’(&!+2!(.’%)843;!T++.)2/%’+$!’(!0)8’$)0!/(!/!&)3.’$1!E)&/5’+2!%&/%!&/(!)5+35)0!/%!
3)/(%!./2%’/339!04)!%+!%&)!)88)*%!+$!%&)!2)*’.’)$%!@!%&’(!’$*340)(!/33!/3%24’(%’*!E)&/5’+2(!/$0!
(+6)! 64%4/339! E)$)8’*’/3! E)&/5’+2(! >33?;! W+(%! (+*’/3! E)&/5’+2(! ,’33! &/5)! 8’%$)((!
*+$()C4)$*)(!8+2!%&2))!+2!6+2)!’$0’5’04/3(7!(+!,)!6/9!(/9!%&/%!/!E)&/5’+2!’(!/3%24’(%’*!’$!
2)3/%’+$!%+!’6./*%!4.+$!+$)!2)*’.’)$%7!/$0!(.’%)843!’$!2)3/%’+$!%+!’%(!’6./*%!4.+$!/$+%&)2!
2)*’.’)$%;!#%!’(!2)/(+$/E3)!%+!%)26!(4*&!/!E)&/5’+2!/(!/3%24’(6!’8!%&)!.2’6/29!2)*’.’)$%!’(!
%&)!E)$)8’*’/297!/$0!(.’%)!’8!%&)!.2’6/29!2)*’.’)$%!’(!%&)!5’*%’6;

Not altruism
F)26(! (4*&! /(! /3%24’(6! &/5)! 5)29! (.)*’8’*! 6)/$’$1(7! ,&’*&! *+$5)9! 4()843!
’$8+26/%’+$;!#8!%&)()!%)26(!/2)!6’(4()07!+2!2)0)8’$)07!%&)!2)(43%!’(!*+$84(’+$!>33?;!F&’(!
&/(!E))$!/!./2%’*43/239!3/21)!.2+E3)6!,’%&!%&)!%)26!/3%24’(6!>33?7!.;!a"cMaKL?7!,&’*&!&/(!
E))$! 2)0)8’$)0! ’$! 6/$9! ,/9(7! ’$*340’$1I! >/?! 2)*’.2+*/3! /3%24’(67! ,&)2)! &)3.’$1! ’(!
8/5+42)0!E)*/4()!’%!,’33!3)/0!%+!%&)!/*%+2!E)’$1!&)3.)0!E/*:!/%!/!3/%)2!0/%)!>35?J!>E?!/!
0)*2)/()!’$!%&)!8’%$)((!+8!%&)!8+*/3!’$0’5’04/37!2)3/%’5)!%+!%&)!+%&)2!6)6E)2(!+8!’%(!12+4.!
>2)3/%’5)39! *+(%39! %+! ’$0’5’04/37! 2)3/%’5)39! E)$)8’*’/3! %+! %&)! 12+4.J! (+6)%’6)(! %)26)0!
\,)/:!/3%24’(6=?!>34, 36-41?J!>*?!/!0)*2)/()!’$!8’%$)((!+5)2!%&)!(&+2%!%)26!>42, 43?J!>0?!
.3/9’$1!*++.)2/%)!’$!/!.2’(+$)2(=!0’3)66/!1/6)!>44?J!>)?!/!8/’342)!%+!&/26!+%&)2(!>45?J!>8?!
%&)!6)*&/$’(6!E9!,&’*&!+$)!’$0’5’04/3!’(!6+%’5/%)0!%+!&)3.!+%&)2(!>46?;!
! a
F&)!.2+E3)6!,’%&!/33!+8!%&)()!2)0)8’$’%’+$(!’(!%&/%!%&)9!’$*340)!(’%4/%’+$(!,&)2)!
*++.)2/%’+$! *+430! .2+5’0)! /! 0’2)*%! 8’%$)((! E)$)8’%7! /$0! &)$*)! *+430! E)! 64%4/339!
E)$)8’*’/3;!T+$()C4)$%397!%&’(!3)/0(!%+!/!E)&/5’+2!E)’$1!3/E)3)0!/(!/3%24’(%’*!,&)$!’%!’($=%!
*+(%39! /$0! /*%4/339! E)$)8’%(! %&)! /*%+2;! V+2! )-/6.3)7! *+$(’0)2’$1! 2)*’.2+*/3! &)3.’$1!
>)-/6.3)!/!/E+5)?7!*++.)2/%’+$!’(!+$39!8/5+2)0!>E)%,))$!$+$M2)3/%’5)(?!’8!’%!3)/0(!%+!/$!
+5)2/33!E)$)8’%!>%&2+41&!’$*2)/()0!3’:)3’&++0!+8!E)’$1!&)3.)0!’$!%&)!84%42)?7!’$!,&’*&!*/()!
’%!’(!64%4/339!E)$)8’*’/37!/$0!(+!2)*’.2+*/3!/3%24’(6!’(!$+%!/3%24’(%’*;!#$!%&)!+%&)2!*/()(!
>)-/6.3)(!EM8?!&)3.’$1!*/$!E)!64%4/339!E)$)8’*’/3!+2!/3%24’(%’*!>M_b?7!0).)$0’$1!4.+$!
6+0)3! 0)%/’3(! /$0! ./2/6)%)2! 5/34)(! /((46)0;! O3(),&)2)7! ,)! 0’(*4((! ’$! 0)%/’3! %&)!
*+$84(’+$! %&/%! %&’(! */$! 3)/0! %+! >33?;! ]4*&! 2)0)8’$’%’+$(! +E(*42)! %&)! 84$0/6)$%/3!
0’(%’$*%’+$!E)%,))$!,&)$!0’2)*%!+2!’$0’2)*%!8’%$)((!E)$)8’%(!/2)!2)C4’2)0!%+!)-.3/’$!%&)!
+E()25)0!*++.)2/%’+$!>33, 47, 48?;!F&’(!*/$!3)/0!%+!%&)!(’%4/%’+$!,&)2)!/!E)&/5’+2!’(!
0)(*2’E)0! /(! /3%24’(%’*7! E4%! */$! E)! )-.3/’$)0! E9! 0’2)*%! 8’%$)((! E)$)8’%(! >’;);! E9! ()38M
’$%)2)(%)0!+2!()38M2)1/20’$1!E)&/5’+2(?;!W+2)!8+26/3397!%&)()!2)0)8’$’%’+$(!/2)!6’(3)/0’$1!
E)*/4()!%&)!(.2)/0!+8!/!1)$)!’(!0)%)26’$)0!E9!’%(!+5)2/33!>3’8)%’6)?!8’%$)((!*+$()C4)$*)(7!
2)3/%’5)! %+! +%&)2(! ’$! %&)! E2))0’$1! .+.43/%’+$7! /$0! $+%! ’%(! *+$()C4)$*)(! +5)2! (+6)!
/2E’%2/2’39!0)8’$)0!\(&+2%M%)26=7!+2!2)3/%’5)!%+!(+6)!(4E()%!+8!%&)!.+.43/%’+$7!(4*&!/(!,’%&!
,&+6!%&)9!&/..)$!%+!’$%)2/*%!>4, 33, 49, 50?;!
#%! ’(! /3(+! ,+2%&! *+6./2’$1! %&)! 0’(%’$*%’+$! E)%,))$! /3%24’(6! /$0! %&)! 5/2’+4(!
2)0)8’$’%’+$(!,’%&!Y++6(6/=(!>19, 20?!)6.&/(’(!+8!%&)!’6.+2%/$*)!+8!%&)!0’(%’$*%’+$!
E)%,))$!+E3’1/%)!/$0!8/*43%/%’5)!)4(+*’/3’%9!>51?;!U(!3+$1!/(!)4(+*’/3’%9!’(!$+%!+E3’1/%)!
>’;);!)5)29!6)6E)2!+8!/!&)3.)2!*/(%)!’(!/88)*%)0?!%&)2)!’(!(%’33!/!>/3E)’%!+8%)$!8/’$%39!6’$+2?!
0’2)*%!8’%$)((!’$%)2)(%!%+!E)!&/0!’$!%&)!84%42)!82+6!(,’%*&’$1!0)5)3+.6)$%/3!./%&,/9!%+!
.)2(+$/3! E2))0’$1;! F&’(! ’(! ,&9! Y++6(6/! */%)1+2’D)(! 8/*43%/%’5)! )4(+*’/3’%9! 4$0)2!
*++.)2/%’5)!E2))0’$1;

Spiteful or selfish?
F&)2)! /2)! $46)2+4(! )-/6.3)(! +8! &/26’$1! %2/’%(! ,&’*&! &/5)! E))$! /214)0! %+!
2).2)()$%!)5+34%’+$/29!>+2!</6’3%+$’/$?!(.’%)7!E4%!,&’*&!*/$!E)!)-.3/’$)0!E9!0’2)*%!
E)$)8’%(!%+!%&)!/*%+27!/$0!,&’*&!%&)2)8+2)!2).2)()$%!()38’(&!$+%!(.’%)843!%2/’%(!>52, 53?;!#$!
%/E3)!]‘WK!,)!(466/2’D)!/!$46E)2!+8!)-/6.3)(7!1+’$1!’$%+!12)/%)2!0)%/’3!%&/$!’$!%/E3)!
";!V+2!6/$9!+8!%&)()!*/()(7!%&)!8/*%!%&/%!%&)!%2/’%!*/$!E)!)-.3/’$)0!E9!0’2)*%!E)$)8’%(!&/(!
/32)/09!E))$!.+’$%)0!+4%;!X)!,+430!3’:)!%+!)6.&/(’D)!%&)!/00’%’+$/3!.+’$%7!%&/%!’$!/33!+8!
%&)()!*/()(7!%&)2)!’(!$+!)5’0)$*)!%&/%!%&)!&/26!*/4()0!E9!%&)()!%2/’%(!.2+5’0)(!/!E)$)8’%!%+!
()*+$0/29!2)*’.’)$%(!%+!,&+!%&)!/*%+2!’(!6+2)!*3+()39!2)3/%)0!%&/$!%&)!.2’6/29!2)*’.’)$%!
>’;);!%&)2)!’(!/$!/..2)*’/E39!$)1/%’5)!2)3/%)0$)((?;!
#$!6/$9!+8!%&)()!)-/6.3)(!%&)!0’2)*%!E)$)8’%(!%+!%&)!/*%+2!+8!%&)!%2/’%!/2)!6/0)!
)-.3’*’%;!V+2!)-/6.3)!ZF&)!.2’6/29!’6.)%4(!8+2!’$8/$%’*’0/3!E)&/5’+2!’(!%&)!)3’6’$/%’+$!+!
+88(.2’$1!+8!+%&)2!’$0’5’04/3(!%+!’$*2)/()!%&)!.2+E/E’3’%9!+8!2).2)()$%/%’+$!+8!+$)=(!+,$!
+88M!(.2’$1!’$!%&)!(4E()C4)$%!1)$)2/%’+$[!>54?;!#$!(4*&!*/()(7!%&)!6’(3/E)3’$1!/(!(.’%)!
())6(! %+! 8+33+,! 82+6! /! 3/*:! +8! /..2)*’/%’+$! %&/%! %&)! *&/2/*%)2’D/%’+$! +8! E)&/5’+2(!
0).)$0(!4.+$!%&)’2!+5)2/33!>%+%/3!+2!3+$1M%)26?!8’%$)((!*+(%(!%+!%&)!/*%+27!/$0!$+%!(+6)!
/2E’%2/29!)$)21)%’*!+2!+%&)2!*+(%!6)/(42)0!+5)2!/!(&+2%M%)26!.)2’+0;!U$+%&)2!:)9!.+’$%!’(!
%&/%!,&/%!6/%%)2(!’(!%&)!/5)2/1)!*+$()C4)$*)(!+8!/!%2/’%7!$+%!’$0’5’04/3!*/()(;!F&’(!’(!
E)*/4()!%&)!*3/((’8’*/%’+$!’(!E/()0!4.+$!8’%$)((!*+$()C4)$*)(7!/$0!$/%42/3!()3)*%’+$!/*%(!
+$!%&)!/5)2/1)!8’%$)((!*+$()C4)$*)(!+8!/!%2/’%;!V+2!)-/6.3)7!(4..+()!%&/%!/112)((’+$!,/(!
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