Questioning the cultural evolution of altruism

12 Pages·2011·0.27 MB·English

doi:10.1111/j.1420-9101.2011.02398.x
REVIEW
Questioning the cultural evolution of altruism
J.-B. ANDRE´*(cid:2) & O. MORIN(cid:3)
*CNRSUMR7206Eco-anthropologieetethnobiologie,MNHN,Universite´ParisDiderot,F75005Paris,France
(cid:3)DepartmentofCognitiveScience,CentralEuropeanUniversity,Budapest,Hungary
(cid:2)LaboratoireEcologieetEvolution,UMR7625,CNRS,EcoleNormaleSupe´rieure,Paris,France
Keywords: Abstract
conformistimitation; Theevolutionaryfoundationsofhelpingamongnonkininhumanshavebeen
cooperation; the object of intense debates in the past decades. One thesis has had a
culturalgroupselection; prominent influence in this debate: the suggestion that genuine altruism,
culturaltransmission; strictly defined as a form of help that comes at a net fitness cost for the
evolutionongraphs; benefactor, might have evolved owing to cultural transmission. The gene–
imitation; culturecoevolutionliteratureiswonttoclaimthatculturalevolutionchanges
sociallearning. the selective pressures that normally act to limit the emergence of altruistic
behaviours.Thispaperaimstorecall,however,thatculturaltransmissionyields
altruismonlytotheextentthatitreliesonmaladaptivemechanisms,suchas
conformistimitationand(insomecases)payoff-biasedtransmission.Thispoint
is sometimes obscured in the literature by a confusion between genuine
altruism,maladaptivebydefinition,andmutualisticformsofcooperation,that
benefitallpartiesinthelongrun.Theoriesofculturalaltruismdonotliftthe
selective pressures weighing on strictly altruistic actions; they merely shift
the burdenofmaladaptationfromsocialcognitiontoculturaltransmission.
the biological fitness of other(s) at a net fitness cost for
Introduction
the benefactor (Hamilton, 1964; see also West etal.,
In models or verbal arguments, many scholars have 2011, section 6.1.1). However, evolutionary theory
suggested that cooperation in human societies cannot predictsthataltruismcanevolveonlyifitispreferentially
emerge solely because of its benefits to individuals. expressedtowardsgeneticallyrelatedpartners(Hamilton,
Mechanisms such as reciprocity or reputation, they 1964; and see also Rousset, 2004; Lehmann & Keller,
argue, do not suffice (e.g. Boyd & Richerson, 1985, ch. 2006; West etal., 2007a,b), and the genetic relatedness
7; Boyd & Richerson, 1988; Fehr & Fischbacher, 2003). within most human societies is generally considered
They have thus proposed that genuinely altruistic ten- insufficient for this to occur. Therefore, the claim that
denciesmustconstitute,inawayoranother,thecement human societies, but not other animal societies, rely
ofhumansocieties.Thesetendenciesareoftenreferredto upon genuine altruism must be backed by some specific
as ‘strong reciprocity’ (Gintis, 2000; Gintis etal., 2003). evolutionaryarguments.Twoquiteindependentlinesof
Humanbeings,sotheyargue,arewillingtosacrificetime research have proposed that the solution to this puzzle
andresourcestotheexclusivebenefitofothers,andthis couldbefoundinthefactthathumansocialbehaviours
is why they are able to sustain cooperation on a large are culturally ratherthan geneticallytransmitted. Inthe
scale(Fehr&Fischbacher, 2003;Gintisetal.,2003). generalattempttogroundsocialsciencesintonaturalistic
Notonlydoesthissuggestionentailthathumanbeings foundations,theyplayanimportantrolebyconstituting
have altruistic motives in the psychological sense, it arguments in favour of an altruistic view of human
entails that they express altruistic behaviours in the cooperation.
evolutionary sense of that term: behaviours that increase Inthispaper,ouraimistodiscuss,clarifyandquestion
the common hypotheses at the core of all such cultural
explanations of altruism. We will first describe the
Correspondence:Jean-BaptisteAndre´,46Rued’Ulm,75005Paris,France.
mechanisms that may allow cultural transmission to
Tel.:[phone];fax:[phone];
e-mail:[email protected] favour the evolution of genuine altruism, even towards
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2532 J.-B. ANDRE´ AND O. MORIN
nongenetic kin (section ‘The Genetic and Cultural Evo- happenstobegroup-beneficial(i.e.altruistic)ratherthan
lution ofAltruism’). individual-beneficial (i.e. selfish). More recently, Leh-
Next, we will lay down one key assumption that any mann etal. (2008a) has shown that the same process
model of cultural altruism needs: social learning places occursalsounderanotherfamilyofimitationrulescalled
strong constraints on our capacity to behave adaptively. ‘one to many’ transmission, in which one, or a few,
In other words, altruism is a maladaptive side effect of individual(s)arechosenrandomlyineachgrouptoserve
social learning (section ‘When Biological Altruism as cultural model(s).
EvolvesCulturally,itisAlwaysaMaladaptiveByproduct Cultural group selection, however, could be said to
ofImitation’). come in two distinct versions. Some models predict the
As a consequence, biological altruism cannot be con- culturalevolutionofaltruisticbehavioursinastrictsense
ceived as arising from a process of gene–culture coevo- (e.g. Boyd & Richerson, 1985, ch. 7; Henrich & Boyd,
lution.Ifanything,geneticadaptationshouldpreventthe 2001; Gintis, 2003; Lehmann etal., 2008a). Yet, other
spread of cultural altruism. This fact is not straightfor- models, also pertaining to CGS, aim at explaining the
wardly denied in the literature we review, but we shall cultural evolution of cooperative behaviours that are not
giveexamplesof ambiguous claimsthat seem to suggest altruistic, that is, behaviours that increase both the
the contrary (section ‘Ambiguities in the Literature‘). recipient’sandtheactor’sfitness(e.g.Boyd&Richerson,
One important source of misunderstanding stems from 1990, 2002, 2009b). The points made in this paper are
confusionsbetween mutualisticcooperationthatbenefit meanttoapplytomodelsofthefirstcategory,nottothe
all individuals, and genuine biological altruism (section second. Thedistinction between thesetwokinds ofCGS
‘Cultural Group Selection: Disentangling Altruism and (the one based on biological altruism and the one based
Cooperation’). onmutuallybeneficialcooperation)iseasilyoverlooked,
We will conclude that any explanation for the exis- andsomefrequentconfusionsbetweenthetwowillhave
tence of altruistic behaviours expressed towards nonkin to be lifted.This shall bedone atthe endofthis paper.
mustinvolvea lackof geneticadaptation.Themaladap- Even though CGS is the only theory explicitly devel-
tation may come either from an inability to weigh oped to explain the existence of cultural altruism
perfectly the cost and benefits of social actions (malad- towards nongenetic kin, its core mechanism operates in
aptations of social cognition) or from a tendency to another important family of models: the study of social
imitatemaladaptivebehavioursindiscriminately(malad- evolution in networks, also sometimes called ‘evolution
aptationsofculturalcognition).However,culturaltrans- on graphs’ (Skyrms, 2004; Nowak, 2006a,b; Ohtsuki
mission in itself does not change, let alone reverse, the etal., 2006; Taylor etal., 2007; Ohtsuki & Nowak, 2008;
selectivepressures acting onaltruism. Santos etal., 2008; Tarnita etal., 2009, see also Allison,
1992a for a verbal description of the same process). In
these models, individuals interact within networks, and
The genetic and cultural evolution of
neighbours on the network mutually imitate one
altruism
another. Innetworkmodels,individualstypicallyfollow
a family of rules called payoff-biased imitation. They
Twotheoriesof culturalaltruism
observe the action and resulting payoff of their neigh-
The idea that culture could yield the evolution of bours and preferentially imitate the action played by
altruism among nongenetic kin has been primarily put high-payoff individuals (payoff-biased imitation is also
forward in the theory of cultural group selection (CGS) sometimes used in CGS – Henrich & Boyd, 2001; Boyd
originally developed by Boyd & Richerson (1982, 1985, etal., 2003). Payoff-biased transmission is a cultural
2009a; Richerson & Boyd, 2005; Boyd etal., 2011; see equivalent of biological reproduction, in which payoff
also Allison, 1992a,b for similar ideas, Henrich & Boyd, affects cultural influence rather than biological fitness
2001; Fehr & Fischbacher, 2003; Gintis, 2003; Gintis (see Hofbauer & Sigmund, 1998). Network models are
etal.,2003;Henrich,2004;Henrich&Henrich,2007,for hence explicitly built to represent indifferently either
further applications of CGS; and Lehmann etal., 2007, genetic or cultural evolution. In either case, they show
2008aforapopulationgeneticsformalization).Boydand that altruism can evolve among neighbours because
Richerson’s idea is that social behaviours are culturally neighboursdosharecommongenes,orcommoncultural
transmitted in a way that tends to homogenize the items. In their cultural version, therefore, these models
phenotype of individuals within each group. They con- open the possibility that altruism evolves among genet-
sider,inparticular,onetypeof‘imitationrule’thatcould ically unrelated individuals.
have this consequence: conformist-biased imitation,
whereby individuals imitate whatever behaviour is the
Genetic andcultural evolution
most frequent in their local group. Conformist imitation
generatesastrongphenotypichomogeneitywithinsocial The mechanisms leading to the cultural evolution of
groups. Some form of group selection can then act to altruism in all models may be simply captured in the
favour the groups in which the shared cultural trait following way. Let us consider a social trait (helping,
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Culturalaltruism? 2533
punishment, or anything else), transmitted genetically. Simply stated, all this merely expresses the fact that,
Fromthemostbasicprinciplesofsocialevolutiontheory when two levels of replicators (genes and culture)
(detailed in Supporting Information), the effect of selec- coexist,thereisnoapriorireasonwhytheirevolutionary
tion on that trait can be measured by a simple and interests should always be aligned. Hence, the direction
general equation, Hamilton’s rule (Hamilton, 1963, of selection, measured in Hamilton’s rules, is not the
1964),whichstatesthatthetraitisfavouredbyselection same on both levels. A trait that would be maladaptive
when )C +R B >0. In this equation, )C is a partial onthegeneticlevelcanbefavouredbyselectionwhenit
g g g g
regression coefficient measuring the statistical relation- is transmitted on the cultural level, and vice versa. This
ship between the trait value of a focal ‘actor’ individual generalstatementisalmosttrivial,butitsimplicationsare
(e.g. altruism or selfishness) and the biological fitness of not, in particular in the case of altruism. Being an
thisindividualandiscalledthe‘direct’effectofthetrait autonomous evolving system, culture could, at least in
on fitness. B is a regression measuring the statistical principle, yield us to sacrifice ourselves, or at least help
g
relationshipbetweenthetraitvalueoftheactorandthe perfect strangers, at a net cost to biological inclusive
biological fitness of another individual (called the fitness.
‘recipient’ in the case of a helping behaviour) and is
called the ‘indirect’ effect of the trait on fitness. Finally,
Biological altruism
thethirdcoefficient,R ,isthegeneticrelatednessbetween
g
the actor and the recipient, measured as the regression, Here, we are interested in biologically altruistic traits,
on the focal trait, of the heritable component of the defined as traits with a negative effect on the biological
recipient’sphenotypeontheheritablecomponentofthe fitness of their carrier ()C <0) and a positive effect on
g
actor’s phenotype. thebiologicalfitnessofother(s)(B >0).Thesetraitsare
g
The same principles apply also for a social trait interesting because, under regular genetic evolution,
transmitted culturally, that is, encoded by a cultural they should only evolve when they benefit genetically
item (see Supporting Information). The trait is favoured related individuals.
by selection when )C +RB >0, except that, now, )C As we just explained, however, when a trait is
c c c c
measures the statistical relationship between the actor’s transmitted culturally, the relevant B and C parameters
trait value and the cultural reproductive success of his are not its effects on biological fitness. Hence, a biolog-
cultural item (the specific item encoding the trait), B icallyaltruistictraitisnotnecessarilyculturallyaltruistic.
c
measures the statistical relationship between the actor’s For instance, a costly helping behaviour that would be
trait value and the reproductive success of the homolo- easily imitated (e.g. because it is psychologically attrac-
gousculturalitemcarriedbyarecipientindividualandR tive)wouldbebiologicallybutnotculturallyaltruistic.In
c
is the cultural relatedness between the actor and the this paper, however, we are not interested in cultural
recipient, measured as the regression of the culturally selfishness/altruism defined in this sense. The aim of
transmissiblecomponentoftherecipient’sphenotypeon cultural models, and therefore the aim of the present
the culturally transmissible component of the actor’s review,istounderstandhowactualbehavioursthathave
phenotype. the paradoxical property to reduce the biological inclu-
Aswesee,beingafullygeneralpartitioningofselective sive fitness of their carriers can evolve, that is, to
forces, the fundamental structure of Hamilton’s rule is understand how different transmission modes may or
unchanged by the transmission mode of a trait (genetic may not change the selective pressure upon biological
or cultural). However, the parameters of Hamilton’s rule altruism. Accordingly, in the following, when we speak
are affected. First, the relatedness, on a given trait, of ‘altruism’, wealwaysmean‘biological altruism’.
between an actor and a recipient, shall depend on the Models found in the literature typically consider the
wayinwhichthattraitistransmitted.Aslongascultural evolution of two types of biologically altruistic traits.
transmission is not purely vertical, the relatedness it Some consider exclusively the evolution of helping
yields probably differs from that yielded by genetic behaviours, whereby a helper provides a good or a
transmission (i.e. R „ R). Second, when cultural service to a recipient (Boyd & Richerson, 1985, ch. 7;
g c
transmission is not purely vertical, the statistical rela- Gintis,2003;Lehmann&Feldman,2008;Lehmannetal.,
tionshipbetweenthephenotypicexpressionofacultural 2008a). Others consider the joint evolution of helping
item (e.g. altruism or selfishness) and its transmission andpunishingbehaviours,wherebyapunisherpaysacost
successislikelytodifferfromthestrictbiologicaleffectof to reduce the fitness of other individuals, because they
this item. When a given phenotypic trait is transmitted have refused to provide help in a first stage of the game
culturally, the parameters that matter to determine the (Henrich&Boyd,2001;Boydetal.,2003;Guzmanetal.,
effect of natural selection on that trait are not its 2007;Lehmannetal.,2007).Theonlyimportantthingto
effects on biological fitness, but its (direct and indirect) understand,here,isthatthecharacterizationofatraitas
effects on the cultural fitness of the underlying cultural altruistic (or not) is independent of whether the trait
item, and these are likely to be different (i.e. consistsinhelpingorpunishing(Gardner&West,2004;
(B ,C ) „ (B,C)). Lehmann etal., 2007). A trait is altruistic if it increases
g g c c
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2534 J.-B. ANDRE´ AND O. MORIN
the direct biological fitness of other(s) at a net cost to tionsmightlastapproximately25years).Thesameholds
one’s own. Helping is altruistic when it comes at a net in network models. Ohtsuki etal. (2006) show that
personalcostforthehelper.Punishmentcanbealtruistic helpingevolvesiftherelativebenefitofhelp(b/c)islarger
also, if it comes at a net personal cost for the punisher, thanthenumber(k)ofsocialpartnersperindividual.This
and if it benefits nonpunished individuals by reducing can reasonably be achieved if ‘individuals’ are actually
the intensity of local competition, or by increasing the cultural items that reproduce every year (or more) and
averageamountof helpexpressed byothers. can interact with as few as approximately 5 other items
every cultural generation, not if they are biological
organisms reproducing every 25years and interacting
Thehypothetical culturalfacilitation of biological
with several hundreds of partners in their lives. The
altruism
migrationratesthathappentofavouraltruismingroup-
The effect of selection on any trait depends on its structured populations, the social graphs that happen to
transmission mode (see above, section ‘Genetic and favouraltruisminnetworkmodels,areempiricallymore
Cultural Evolution’). In itself, this is sufficient to entail reasonableunderculturalthangeneticevolution.
thataltruismmay,atleastinprinciple,evolveculturally
when its genetic evolution is impossible, and vice versa. Cultural transmission is more homogenizing. The bal-
However, models of the cultural evolution of altruism ance between homogenizing and diversifying forces is
make a more specific statement (at least in the case of alsotippedbycultureforasecondreason,relatedtothe
CGS). Not only do they claim that cultural and genetic specific forms that cultural transmission takes in many
evolution differ, they also claim that, under realistic models:conformist-biasedtransmission(Boyd&Richerson,
conditions,culturalevolutionisgenerallymorelikelythan 1985,ch.7;Henrich&Boyd,2001;Guzmanetal.,2007;
genetic evolution to yield altruism. In the following we Lehmann &Feldman, 2008;Lehmann etal.,2008a)and
reviewwhatwetaketobethetwomajormechanisms,at onetomanytransmission(Lehmannetal.,2007,2008a).
workseparatelyorinconjunction,thatlendcredibilityto With these modes of transmission, not only is cultural
this claim: (i) culture can ‘increase’ relatedness (i.e. reproductionfasterthanbiologicalreproduction,itisalso
R >R ) and (ii) culture can ‘reduce’ the direct cost of morehomogenizing(asingleorafewculturalitemsare
c g
altruism(i.e.C <C ). imitated by every individual). This reinforces even
c g
further the amount of cultural relatedness relative to
Cultural relatedness may be larger than genetic genetic relatedness.
relatedness
The(geneticorcultural)relatednessinagivengroup,or Theculturalcostsandbenefitsofbiologicalaltruismmay
neighbourhood,istheoutcomeofabalancebetweentwo differ from their biological counterparts
antagonistic forces: (i) sampling effects that occur each When we think of the effect of culture on biological
time reproduction takes place and tend to increase local altruism, we usually exclusively think of the increased
homogeneity and (ii) migration and mutation that relatedness. However, when comparing the effect of
reintroduce outside polymorphism and tend to decrease selection under genetic vs. cultural transmission, the
homogeneity. One of the effect of cultural transmission, other parameters of Hamilton’s rule must also be com-
inmodels,istoboosttheimportanceofsamplingeffects pared,namelythecost,C,andbenefit,B,ofaltruism.Let
relativetomigration. Thisoccurs intwo distinctways. us insist, however, to avoid any confusion. Here, we
considerculturallytransmittedtraitsthathappentohave
Cultural reproduction is faster. Itisempiricallyreason- the property to be biologically altruistic (i.e. )C <0 and
g
abletoassumethatmorereproductioneventstakeplace B >0), and we say that their cultural costs and benefits
g
for culture than for genes in one given amount of time. (C and B) are likely to differ from their biological costs
c c
‘Culturalgenerations’areshorter.Iftheculturalmigration and benefits (C and B ). By no means do we intend to
g g
rateisnotproportionatelylarger,thenthemigrationrate say that cultural transmission has an effect on the
pergenerationismechanicallylowerinculture,andhence biological effectsof traits.
cultural relatedness is larger. Interestingly, this occurs Toourknowledge,infact,theonlypaperinwhichthis
even if cultural transmission is subject to the same (or second outcome of culture has been explicitly high-
similar) selective forces than genetic transmission (i.e. lightedisamodelinwhichculturaltransmissionimpedes
under‘payoff-biased’transmission;e.g.Boydetal.,2003; rather than facilitates the spread of altruism. Under a
Ohtsukietal.,2006). form of payoff-biased transmission, Lehmann etal.
For instance, Boyd etal. (2003) consider a migration (2008a; see also Lehmann etal., 2007) show that the
ratebetweengroupswhere<1%ofindividuals‘migrate’ direct cost of altruism is larger under cultural than
everygeneration,whichyieldsastrongrelatedness.What genetic transmission (i.e. C >C , compare their equa-
c g
allows this is, of course, the fact that the generations tions16and22)becausetheeffectoflocalcompetitionis
considered in the model are cultural generation. Thus, stronger.Inthiscase,ceterisparibus,altruismislesslikely
generations last only a year (whereas biological genera- under culturalthan genetictransmission.
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Culturalaltruism? 2535
In other models, the cultural benefit-to-cost ratio of According to CGS theory, it is an adaptive strategy
altruistic traits (B/C) seems more favourable to their becausebehavioursexpressedbythemajoritytendtobe
c c
success than their biological counterpart (e.g. Boyd & more adaptive than average (Boyd & Richerson, 1985,
Richerson, 1985, ch. 7; Henrich & Boyd, 2001; Gintis, ch.7).Yet,CGSscholarsalsorecognizethatfrequencyis
2003). However,thisisnot explicitlyput forwardinthe a highly indirect, limited and easily mistaken proxy.
papers, and it would require more formalization to be Many things can cause a majority of individuals to
better understood. Essentially, we think this change in expressmaladaptivebehaviours(e.g.foundereffectsand
benefit-to-cost ratio arises because (i) altruistic behav- culturaldrift),andthesebehavioursarethenimitatedall
iours are assumed to be transmitted just as well (or the same, which is maladaptive. In other words, with
almostaswell)asselfishbehaviourswithinlocalgroups, respect to biological fitness, conformist imitation is
thatis,theindividualbiologicalcostofaltruism,doesnot mistake-prone, and this mistake-proneness is the very
translate into an equivalent cultural cost in local trans- reasonwhyitcanleadtotheacquisitionofmaladaptive
mission, whereas (ii) the collective benefit of altruism behaviours suchas altruism.
does translate into a cultural advantage that accrues Two theoretical results seem surprisingly at odds with
exactly equally to all the individuals in each group (e.g. the above reasoning, claiming to show that conformist
via a larger group survival, see e.g. Boyd & Richerson, imitation can be favoured by genetic evolution, even
1985, ch. 7; Gintis, 2003). In other words, and to put it whenitsonlyeffectistotriggertheimitationofaltruism
bluntly,inthesemodels,theindividualcostofaltruismis (Henrich & Boyd, 2001; Guzman etal., 2007). Both
reduced but its collective benefit is maintained. This modelsconsiderpunishmentratherthanprimaryhelping
probably accounts for a significant part of these models’ as the focal altruistic trait. In a model in which
outcome. conformist imitation allows the cultural spread of altru-
istic punishment, Henrich & Boyd (2001) show that
natural selection favours genes that predispose individ-
When biological altruism evolves
uals to imitate more faithfully the social behaviour of
culturally, it is always a maladaptive
others, and Guzman etal. (2007) show that natural
byproduct of imitation
selection favours genes that directly code for conformist
Onemightcapturethebasicargumentofthemodelswe imitation itself. In a situation where genetic evolution
review as stating that culture, being an autonomous should not lead to altruistic punishment, evolution
evolving system, may in principle yield altruism when would favour a genetic predisposition (Henrich & Boyd,
genes cannot. They suggest in particular that, under 2001) or a genetic learning rule (Guzman etal., 2007)
reasonableassumptions,altruismmightevolveculturally leadingindividualstoacquirealtruisticpunishment.How
more easily than genetically. However, the apparent isthat possible?
simplicitywithwhichtheyachievethiseffect,bychang- Theexplanationisthatbothresultsarepermittedbyan
ing the parameters of Hamilton’s rule, is misleading. It implicitassumption.InGuzmanetal.(2007),individuals
might hide the fact that these models rely on a crucial are assumedto be either conformist with respect to both
empirical assumption. helping and punishment or not conformist at all. Yet,
Genuinealtruismtowardsnonkin(or,moregenerally, whatisadaptiveinthismodelistofaithfullyimitatethe
genetically maladaptive altruism) can evolve and/or helping part of others’ behaviour (because when others
stabilizeculturallyifindividualsuseimitationrules,such cooperate they generally also punish, and therefore one
as conformist, one to many or payoff-biased imitation, shouldcooperateaswell).Butimitatingthepunishment
that result in its cultural diffusion. Yet, a maladaptive part of their behaviour is not adaptive (because punish-
behaviour, even imitated from someone else, is still a ment is simply always costly). However, being maladap-
maladaptive behaviour. When an individual behaves in tivedoesnotkeepthisnormfrombeingadopted,because
an altruistic manner towards nonkin, whether because no flexible imitation strategy exists, that would allow
she is‘directly’ mistaken,orbecauseshe hasmistakenly agentstocopythebeneficialnormbutnotthecostlyone.
imitated another altruist, she is simply expressing a In Henrich & Boyd (2001), punishing is not always
genetically maladaptive trait. Thus, cultural evolution detrimental to punishers, because several layers of
solves the problem of altruism only to convert it into punishment are authorized: agents who do not punish
another problem: the fact that individuals learn from maybepunishedforthis,andsoonupto thenthlevel.
others in a way that eventually leads them to acquire Inthiscase,allintermediatelevelsofpunishmentarein
maladaptive behaviours. Let us consider three examples thedirectinterestofindividuals’,andonlythenthlevelis
before reachinga generalconclusion. genuinelycostlybecauseitfacesnoupper-levelsanction.
Why is punishment at this last degree nevertheless
adopted by evolved imitation rules? The answer is that
Conformist imitation
in Henrich & Boyd (2001), just as in Guzman etal.
Conformist imitation consists in imitating the behaviour (2007), the same genetic predisposition is assumed to
expressed by the majority of individuals in one’s group. affect equally the imitation of all social traits – whereas
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the more adaptive strategy would consist in imitating adaptivenessoftheirbehaviour.Inasocialnetworkorin
onlythosetraitsthatbenefittheindividual.Theimitation a group-structured population, altruists have a larger
of the last layer of punishment is hence a costly side payoffthan‘selfish’individuals,butthatisbecausetheir
effectofthe (adaptive)imitationof otherlayers. neighbours are more altruistic than average, not because
Overall, even though these two models are presented they are altruistic (see Allison, 1992a). This is precisely
as exceptional instances in which conformist imitation the difference between a phenotypic correlation emerg-
evolves even when its only effect is to trigger the ing from reciprocity and a correlation emerging from
imitation of altruism, they have nothing exceptional in co-ancestry. In the latter, the correlation is not the
this respect. As in all other models, altruism is a costly reflection of an underlying causal relationship between
side effect of a relative maladaptation of imitation the actor’s phenotype and the recipient’s. Helpers do
rules. have a larger payoff because they happen to interact
NotethatLehmann&Feldman(2008)alsosurprisingly more often with helpers, but helping does not cause an
foundthatunbiasedconformistimitation(inwhicheach increase in one’s payoff. Imitating high-payoff indivi-
individual imitates a random member of her group), as duals thus leads to the mistaken acquisition of an
wellasonetomanytransmission(inwhicheverygroup altruisticbehaviourthatdidnotcausetheirlargepayoffs.
member imitates the same peer), can be favoured by Altruism, there again, is a consequence of the learning
geneticevolutioninamodelinwhichtheironlyeffectis rule’s proneness to mistakes.
to favour the cultural spread of helping (towards
nonkin). But a closer look offers an interpretation of
Social learning constrains behaviouraladaptation
this result. When random imitation occurs (unbiased
conformism, or one to many transmission), individuals Being a genetically maladaptive trait, altruism towards
candirectly benefit frombeinghelpers, becausethismay nonkin entails a lack of adaptation on the side of genes,
influence the phenotype of others in their group and whetherbecauseindividualsmistakenlyactaltruistically,
prompt them to help in return through imitation. This orbecausetheymistakenlyimitateotheraltruists.Hence,
effectobtainswheneachindividualhasalargeexpected cultural transmission does not change the nature of the
influence on others, which is exactly what Lehmann & selective pressures, acting upon genes, with respect
Feldman(2008)find(thisoccurswhensocialgroupsare to altruism. What cultural transmission does is only to
small; see also Boyd & Richerson, 1988). Under such introduce an intermediate control variable (the rules of
circumstances, owing to a type of selective pressurealso social learning) in the evolution of social traits, which
at work in the evolution of reciprocity, where the changestheconstraintsapplyingtobehaviours,andlimit
expression of helping by one individual increases their potential for adaptation in different ways (see
thetendency of others to express it, imitation can be Lehmannetal.,2008b).Thisisinterestingandimportant,
favoured because of its effect on helping. However, but doesnot byitself cancelthe paradoxofaltruism.
bydefinition, helping is not altruistic in this case, being
directly reciprocated.
Strong constraintsgenerate strongmaladaptations
What is more, in their models, students of cultural
Payoff-biasedimitation
altruism assume particularly strong constraints over
At first, payoff-biased imitation is even more perplexing social learning. They assume that individuals learn from
than conformist transmission. Payoff-biased imitation others using stereotyped rules. Individuals copy the most
lookslikeaperfectmannertotakebehaviouraldecisions. frequent behaviour of their group, or the behaviour of
As long as the observed ‘payoff’ is a faithful measure of theirhighestpayoff-peer,buttheyareunabletoevaluate
biological fitness, payoff-biased imitation should be the actual properties of the behaviour (e.g. ‘Does it
immune to the mistaken acquisition of genetically involve to spend some resources?’ and ‘Does it entail a
maladaptive behaviours. This intuition explains why, in physicalrisk?’).Theabilityofthesesimplerulestosubtly
contrast with conformism, scholars who use payoff- control cultural acquisitions is hence limited and opens
biased imitation do not (to our knowledge) raise the the possibility of many maladaptive decisions, including
question of its evolutionary rationale. However, it turns theimitationofaltruism.Assumingonlysimpleimitation
out that this intuition can be erroneous. With payoff- rulesislikeimposingaverystronglimitoverthegenetic
biased imitation, one does risk to acquire maladaptive adaptation of behaviour.
behaviours, but only a specific category of maladaptive The assumption that evolution has not been able to
behaviours: altruistic ones. Altruism is the flaw, so to provide human beings with better mechanisms than
speak,of payoff-biasedimitation. stereotypedrulesofimitation,inimportantdomainssuch
This flaw manifests itself when interacting individuals associalbehaviour,isquiteasurprisingone.Forinstance,
are phenotypically correlated because an individual’s the rule of payoff-biased imitation used in models of
payoff then partly depends on her neighbours’ strategy. evolutionongraphsrestsontheassumptionthathumans
Consequently, their payoff is a poor indicator of the areabletotrackothers’fitnessgainsincomplexcircum-
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Culturalaltruism? 2537
stances, but unable to understand the simple fact that tion (e.g. Richerson & Boyd, 2005, ch. 5; Boyd &
unreciprocated help is costly, while being helped is Richerson, 2006). Yet, they also often seem well aware
beneficial(seethesection‘Payoff-BiasedImitation’). of the fact that, as products of evolution, humans are
This raises the question: Why do scholars follow unlikely to be so crudely adapted that they are ready to
assumptions of this sort? The answer, we think, is that imitate anything. Individuals shall use simple imitation
it is part of the implicit way of looking at things in rules, they often agree, only when they have no better
cultural evolution. Under the influence of dual-inheri- sourcesofinformation.Forinstance,RichersonandBoyd
tance theory (Cavalli-Sforza & Feldman, 1981), scholars state that conformist transmission can operate only if
see culture as a supplementary system of inheritance, ‘individuals have difficulty evaluating the costs and
parallel to genes. Hence, like genes, cultural items are benefits of alternative cultural variants’ (Richerson &
assumed to be transmitted according to simple stereo- Boyd,2005,p.206;seealsoHenrich&Henrich,2007,p.
typed rules (e.g. biparental inheritance for nuclear 66).
genes). This leaves a lot of autonomy to culture and For this reason, they have put forward the idea of
thus yields a lotofmaladaptations. ‘altruistic punishment’ (Boyd & Richerson, 1992; Hen-
rich & Boyd, 2001; Fehr & Gachter, 2002), according to
which people primarily cooperate because they fear
Weaker constrains wouldgenerate weaker
punishment (i.e. the helping actions per se are not
maladaptations
altruistic but directly beneficial to individuals), but the
Yet, the ability to modulate one’s social behaviour in norms of punishment are themselves grounded in the
functionofothers’couldalsobeseenasacomplexform fact that people are ready to punish even at one’s
of adaptive plasticity, rather than a supplementary personal cost (i.e. the second-order retributive actions are
system of inheritance. Instead of a general drive to genuinelyaltruistic).Thisisinterestingbecause,punish-
imitate others, we could be endowed with a domain- ment being less frequently expressed (in equilibrium,
specific ability to construct our social behaviour, in line mostindividualscooperateandareneverpunished),itis
with the contingent strategies found in reciprocity biologically‘cheaper’inaveragethanhelping.Therefore,
(Trivers,1971).Eventhoughtheycouldneverbeperfect so the argument goes, individuals shall have more
and adaptive in all circumstances, such abilities would difficulty detectingthecostofpunishment thanthecost
leavemuch lessspace for maladaptive altruism. ofhelpingandarethusmorelikelytousecontent-blind
This debate is an old matter in the dual-inheritance imitationintheformer(Henrich&Boyd,2001;Henrich
literature and dates back to the foundation of the field & Henrich,2007, pp.66–67).
(Cavalli-Sforza & Feldman, 1981; Lumsden & Wilson, Leavingasidethefactthatitisnotclear(atleasttous)
1981).Defendersofsimpleimitationheuristicsarguethat how the mere rarity of punishment makes it more likely
we are bound to use stereotyped transmission strategies to be imitated, it is important to understand that the
for all purposes, because cultural behaviours and inno- reservationsofthesescholarsontheamountofmistaken
vations can take an infinite variety of aspects. No imitations in humans, however interesting and reason-
genetically encoded mechanism could have prepared us able they may be, are also, de facto, reservations on the
todealwithallofthem(Richerson&Boyd,2005,ch.5; amountofgenuinealtruismpresentinsocieties.IfBoyd,
Boyd & Richerson, 2006). We do not aim to enter, or Richerson,Henrichandothersarereadytoconsiderthat
evenlesstosettle,thisdebatehere.Wesimplynotethat humansimitatealtruismonlyinrareinstancesinwhich
RichersonandBoyd’sgeneralargumentiscertainlywell they have difficulty evaluating its costs (e.g. only for
applicabletodecisionsthatwe,asaspecies,haveseldom punishment),theymustalsoagreethatgenuinealtruism
(or never) been confronted with (e.g. the making of a israre.
kayak or a bow). But it is unclear to us how this same
argument applies in a domain, such as social life, to
Ambiguities in the literature
whichourancestorshavebeenconfrontedforlong.The
possible ways of helping others, although they are
Gene–culture coevolution
infinitely numerous, do share some general properties,
and evolution is likely to have endowed us with innate Many statements found in the literature do honestly
abilitiesthathelpusdealspecificallywiththesesituations present altruism as a costly side effect of social learning,
(as somerecent experiments in preschool children seem which entails that genes that make the cultural acquisi-
to suggest, see e.g. Hamlin etal., 2007; Warneken etal., tion of altruism more likely cannot be favoured by
2010; Hamann etal.,2011). selection because of their effect on altruism, but at best
in spite of this effect (see e.g. Boyd & Richerson, 1985,
p. 227;Gintis, 2003).
Weaker maladaptationsare only weaklyaltruistic
Otherstatements,however,revolvingaroundtheidea
Boyd,RichersonandHenrichdooftenargueinfavourof of gene–culture coevolution, are less clear.For instance,
the existence of stereotyped imitation in cultural evolu- inawidelycitedreview,Gintisetal.(2003)definestrong
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2538 J.-B. ANDRE´ AND O. MORIN
reciprocity as a ‘predisposition to cooperate with others models as in others, a costly side effect of the imitation
and to punish those who violate the norms of cooper- of beneficial traits. Therefore, the statement that ‘there
ation, at personal cost, even when it is implausible to isnoneedtoassumethatcostlyconformismisaspin-off
expect that these costs will be repaid’, which is genet- from individually beneficial conformism’ is simply
ically maladaptive by definition, and yet claim that wrong.
‘strong reciprocity is adaptive in the sense of emerging
fromagene–culturecoevolutionaryprocess’(theempha-
Cultural groupselection: disentangling altruismand
sisisours).RichersonandBoydprovideanotherexample
cooperation
in a recent book, when they state that gene–culture
coevolution ‘set up an arms race that drove social Third, as we already acknowledged, CGS comes in two
evolution to ever greater extremes of in-group cooper- significantly different versions, and this leads to some
ation’suchthateventually‘peoplewerereadytopunish ambiguities. The first version is the target of this paper.
[...] even when personal interests were not directly at Here, wecall it the ‘altruistic’ versionbecause itaims to
stake’ (Richerson & Boyd, 2005, p. 214). Even more explainhowculturemayyieldtheevolutionofaltruistic
surprisingly, Henrich & Boyd (2001) write in their behaviours stricto sensu. In contrast, the second version,
abstract that ‘prosocial genes favouring cooperation and called here ‘mutualistic’, aims to explain the cultural
punishmentmayinvade’,andGuzmanetal.(2007)write evolution of cooperative behaviours that are not altru-
in their conclusion that conformism coevolves geneti- istic (see West etal., 2007b), that is, behaviours that
callywithculturalaltruismwith‘noneedtoassumethat increase both the recipient’s and the actor’s fitness
costly conformism is a spin-off from individually bene- through incentives such as reciprocity, reputation or
ficial conformism’. retribution,performingwhatisknowningametheoryas
These are misleading, if not simply false, statements. ‘equilibrium selection’ (e.g. Boyd & Richerson, 1990,
They certainly cannot help readers to comprehend the 2002,2009b).Althoughthesetwoversionshaveinitially
fact that altruism can be nothing but a costly side effect been explicitly distinguished (e.g. in Boyd & Richerson,
of imitation and can even help spreading the false idea 1990), this is no more the case in recent writings that
that, thanks to culture, altruism towards nonkin ends neglect to distinguish genuine altruism from mutualistic
up being adaptive, even from a gene’s point of view. cooperation(e.g.Richerson&Boyd,2005,ch.6;Boyd&
There are at least three sources of ambiguity that play a Richerson, 2009a).
role here. We rapidly mention two of them. We then For instance, Richerson & Boyd (2005) begin their
devote a specific subsection to the third and most chapter six byexplaining why genetic group selection is
important one. limited to small groups of close kin, whereas CGS is
First, the idea that the two sides of an interaction possible in larger groups (pp. 201–204). Even though
coevolve can mean quite different things. Coevolution theyneverexplicitlydefineit,thisstronglysuggeststhat
can be antagonistic when the two sides have conflicting they deal with genuine altruism (they even mention the
interests. Or it can be ‘reinforcing’ when the two sides caseofsocialinsects).Butthentheygoontoexplainthat
havealignedinterests.Regardingbiologicalaltruismwith human‘tribalsocialinstincts’evolvedgeneticallybecause
nonkin,bydefinition,genesandculturehaveconflicting people lacking these instincts were punished and ostra-
interests. Hence, altruism can be the outcome of a cized (p. 214), which corresponds to the mutualistic
coevolution between genes and culture only in the versionoftheirtheorywherecooperationisindividually
former sense, not in the latter. The claim that gene– beneficial.Finally,theyimplicitlymovebacktoaltruism
culture coevolution can lead to altruism is thus literally whentheyaskwhygenesthatpreventtheacquisitionof
true,butitismisleading.Itgivesthefalseimpressionthat costlycooperativebehavioursdonotinvade(p.214).Ina
altruism is even stronger when genes come into play, more recent review, Boyd & Richerson (2009a) seem to
whereas it is the exact opposite that is true. The correct be mostly dealing with the mutualistic version of their
statement is that cultural evolution can lead to altruism, theory,mentioningtheproblemofequilibriumselection
andthatgeneticcounter-evolutionisnotalwaysfullyable (p. 3281), and stating that genetic instincts have
to prevent it. This is not what readers are likely to ‘coevolved with culturally transmitted social norms’
understand when they read that ‘strong reciprocity is (p.3287). However, they still choose to define cooper-
adaptive in the sense of emerging from a gene–culture ationasa‘costlybehaviourperformedbyoneindividual
coevolutionaryprocess’. that increases the payoff of others’ (p. 3283), which is
Second, as we already discussed, Henrich & Boyd really altruism and therefore falls under the scope of the
(2001) and Guzman etal. (2007) claim to show that other version ofCGS.
genes coding for imitation can be favoured even when We fear that such expositions of CGS, which fail to
their ‘only’ effect is to yield altruism, but they forget to distinguish mutualism and altruism, could lead to
mention that this results from a constraint over the important misunderstandings of the assumptions and
adaptation of learning (see section ‘Conformist Imita- explanatorypowerofthetheory.Thealtruisticversionof
tion’). The imitation of costly altruism is, in these CGS can explain the existence of genuinely altruistic
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Culturalaltruism? 2539
behaviours (e.g. strong reciprocity), but it relies on the
Conclusion
existence of a mismatch between genes and culture (the
mistaken imitation of costly cultural traits), not on a We do sometimes behave in a strictly altruistic manner
reinforcingcoevolutionofthetwo.Onthecontrary,the towards nonkin. For instance, economic experiments
mutualisticversionofCGScanonlyexplaintheexistence have shown that, even when perfect anonymity is
of cooperative, not altruistic, behaviours, but it can be guaranteed, some experimental subjects still give away
the outcome of adaptive learning mechanisms and thus monetary resources to help or punish others, with no
emerge from a reinforcing coevolution of genes and clear individual benefit (although anonymity does
culture.Confusionsbetweenthetwoversionsarehence strongly reduce subjects’ generosity, see Hoffman etal.,
dangerous,becauseonecan takethe mildrestrictions of 1996). Our aim here has not been to discuss this
oneversiontobethesufficientconditionsfortheother. literature.Wediscussedonespecifickindofevolutionary
For instance, and most symptomatically, in their widely explanation of altruism: culturalexplanations.
cited review on human altruism (Fehr & Fischbacher, Any explanation for a maladaptive trait, whether it
2003), have a specific section on gene–culture coevolu- involves culture or not, must rely on the fact that
tion, where they state that it can ‘provide a solution to naturalselectionhasbeenunabletooptimizeit.Cultural
thepuzzleofstrongreciprocity’.Nowhereinthissection altruism is sometimes thought of as an alternative to
is the underlying assumption of genetic maladaptation maladaptation, but this is a misunderstanding. Like any
mentioned. evolutionary account of a maladaptation, cultural evo-
lutionmodelsdorelyontheinabilityofnaturalselection
to remove the maladaptation. The only difference
Howtodisambiguateculturalgroupselectiontheory
between cultural accounts of altruism, and others, has
Toavoidanyriskofmisinterpretation,itwouldbeuseful to do with the kind of maladaptation involved (Fig. 1):
if, for each version of their theory (or mixture of Do they come from the limitations of our social cogni-
versions), proponents of CGS could spell out together (i) tion, or from those of our capacities for cultural learn-
its underlying assumptions (e.g. regarding the degree of ing?
mismatch between genes and culture) and (ii) its
explanatorypower(e.g.regardingtheamountofgenuine
Imperfections of socialcognition
altruism in human behaviour). In view of most of their
recentarticles(inparticularHenrich&Henrich,2007,ch. Genuine altruism could emerge as a consequence of
3;Boyd&Richerson,2009a,b;Boydetal.,2011),itseems imperfections of human social cognition. We are
tous(butwemightbewrong)thatBoyd,Richersonand endowed with evolved predispositions to handle
Henrich now endorse a primarily mutualistic version of social behaviour. They help us manage our reciprocal
their theory, in which helping is mostly individually exchanges and reputation. These predispositions should
beneficial, and genetic instincts can coevolve with, and be adapted, in average, to maximize our genetic fitness,
reinforce,culturalhelping(notethatthiswasnotthecase but we cannot expect them to be perfect (especially not
inearlierwritings,e.g.Boyd&Richerson,1985,p.227). in experimentalsettings).
However, if they do currently favour such a view, CGS Virtuallyeveryaspectofourphenotypeistheproduct
scholars must also explicitly state that their theory does of compromises: compromises between the costs and
not support many claims, found in the literature, about benefits of complexity; compromises between one func-
the alleged selflessness of humans. For instance, a tion and another; etc. For instance, a ‘snake-detecting’
moderate version of their theory cannot support the ability cannot both detect all snakes with near-certainty
claimthathumancooperationisa‘hugeanomaly’(Fehr and never generate false positives (this has been termed
& Fischbacher, 2003), or that it is ‘fundamentally the ‘smoke detector principle’ by Nesse, 2001). Relative
incompatible with the biologists’ model of the self- maladaptations are unavoidable in snake detection.
regardingreciprocalaltruist’(Gintisetal.,2003;seeWest Similarly, the set of cognitive modules that play a role
etal., 2011, for more examples). Initially, the originality inoursocialdecisions(tohelpornothelp,punishornot
of CGS lied in its ability to explain cooperation in punish,etc.)mustunavoidablybesubjecttoconstraints.
anonymous contexts (in which it cannot have direct Therefore, relative maladaptations are unavoidable in
benefits),andithasbeeninvokedinmanyclaimsonthis this domain as well (see West etal., 2011 section 6.6.1).
issue(e.g.Fehr&Fischbacher,2003;Gintisetal.,2003). As an illustration, in the vein of the smoke detector
Yet, a primarily mutualistic version of CGS loses this principle, one may imagine that it could generally be
specific explanatory power. At best, with such a view, adaptive to overestimate the importance of being coop-
one can explain that humans sometimes make mistakes erative in social situations, for the sake of one’s reputa-
intheirsocialdecisions(e.g.bycooperatingwhenitturns tion. Yet, this would come at the cost of false positives:
out to have no benefit), not that they generally and we would sometimes behave in a cooperative manner
systematically differ from nonhumans by being ready to when itturns out that there was no benefit to gain (see
helpandpunishwithnoinclusivefitnessbenefits. e.g. Hagen &Hammerstein, 2006).
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2540 J.-B. ANDRE´ AND O. MORIN
Fitness
+
Social Mistaken reactions Accurate reactions Social
cognition to social situations to social situations cognition
Cultural Adoption of detrimental Adoption of useful Cultural
learning rules behaviours behaviours learning rules
COOPERATION
Altruism with non-kin mutAulatrliusitsicm c woiothp ekriantion
Fig.1Culturedoesnotchangetheselectivepressureongenes,whichalwaystendstomaximizeinclusivefitness.Relativemaladaptationscan
neverthelessoccur,becausetheactionofnaturalselectionisconstrained.Inthecaseofcooperativebehaviours(thatbenefitatleastone
recipient),relativemaladaptationsmayhaveatleasttwoorigins.Socialcognitionmaybeimperfect,leading(amongothermaladaptive
behaviours)toaltruismwithnoinclusivefitnessbenefits.Likewise,culturallearningrulesmaybeimperfect,leadingtotheadoptionof
maladaptivebehaviours,someofwhichmayhappentobealtruistic.Influentialversionsofculturalgroupselectionconsiderthatbiological
altruismisparticularlyimportantinhumansbecauseofthissecondmechanism.
different. It is not, and we think that the respective
Imperfectionsof culturalcognition
merit of cultural and social explanations of genuine
Theoriginalityoftheculturalaccountsofaltruismisthat, altruism are easier to compare when seen as similar in
ratherthanrelyingonthenecessaryimperfectionofthe this respect.
setofevolvedmechanismsinvolvedspecificallyinsocial
decisions, they rely on imperfections of another, more
Acknowledgments
transversal,setofevolvedmechanisms:themechanisms
we use to learn from others. Because we generally We thank Laurent Lehmann for key discussions. We
imitate others, so the argument goes, we often end up thank Franc¸ois Rousset, Nicolas Baumard, Nicolas Cla-
imitating also their maladaptive courses of actions. idie`re,ClaireElMoudenandFrancescaGiardiniforvery
Scholars also explain this relative imperfection by the helpful remarks and ideas. We thank two anonymous
existence of a compromise. In the domain of social referees for their sometimes critical but often useful
learning,theyargue,wefaceatrade-offbetweentherisk comments ona previous versionofthispaper.
to imitate maladaptive behaviours, and the benefit of
imitating interesting novelties. Cultural altruism is thus
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