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Evolutionary Psychology,Lecture 3.

Altruism and Co-operation

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Learning Outcomes.

At the end of this session you should beable to

!. E"plain #hat is meant by the terms $%inselection& and $reciprocal altruism&.

'. (iscuss %in selection and reciprocatione"planations for human and animal

cooperative ) altruistic behaviours.

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*houghts +or the (ay.

Let us try to teach generosity and altruism becausewe are born selfsh ichard (a#%ins /!012.

4ethics, morality, human conduct, and the human psyche are to be understood only i societies areseen as collections o individuals seeking their ownsel interest . .(. Ale"ander /!051.

Scratch an altruist and watch a hypocrite bleed .6hiselin /!017.

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Altruism. 

Altruism refers to an individual acting in a #ay that#ill decrease its o#n survival chances, but improvethe survival chances of another individual.

*he (ar#inian perspective emphasising $survival of

the 8ttest& gave the impression that sel8shness #asthe norm.

Pioneering #or% involving the study of animals livingin social groups in fact revealed that co-operationand altruism are 9ust as $natural& as sel8shness.

:f co-operation and altruism have evolved, then theymust have some adaptive bene8ts, researchers haveanalysed the conditions under #hich adaptations forengaging in such behaviour can be e"pected toevolve.

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E"amples of AnimalAltruism. ;ampire bats #ill regurgitate

and feed blood that they havecollected from their prey to ahungry conspeci8c/uirrels #ill #arnothers of the presence of apredator, even though ma%ingsuch a call may dra# theattention of the predator toitself /?herman, !011.

:n many species of socialinsects, #or%ers forgoreproduction entirely /theyare sterile in order to helpraise their sisters /

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*heories of Altruism.

!. @in ?election /Proposed by amilton, !027.

By helping relatives to reproduce /even at the costto your o#n reproductive success then your sharedgenes can spread. Assisting a close relative thereby

increases one&s $:nclusive +itness&. sing mathematical modelling, amilton sho#ed

that an altruistic gene can spread through thepopulation if it causes an individual to help arelative, #henever the cost to the individual is oDset

by the reproductive bene8t gained by the receiver. $amilton&s ule& r BFc 

#here rcoeGcient of relatedness, B  bene8t tothe recipient, c  cost to the giver.

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@in ?election in Action.

6round s>uirrels do not give an alarm call everytime a predator approaches. *hey only do so #henthere is a large proportion of their relatives #ithinearshot /?herman, !011.

;ampire bats are much more li%ely to share theirfood #ith relatives than #ith non-relatives/

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@in ecognition.

:t is important to be able to recognise %in, as the costsinvolved in mista%ing another individuals oDspring forone&s o#n are high, and the bene8ts fe#.

ODspring recognition should evolve more often in

colonial species, as there is a high ris% of misdirectingparental care.

E"amples.

Ban% s#allo#s /colonial do not accept strange chic%s

#hereas rough-#inged s#allo#s /solitary do. erring gulls /colonial ground-nesting recognise

oDspring and refuse strange chic%s, but @itti#a%es/colonial cliD-nesting do not recognise oDspring andaccept substitute oDspring.

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@in ecognition in6ulls. 

Data from Alcock, 1993

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@in ?election inumans.

?tudies amongst diverse human populationsconsistently support the e"istence of %in selection, somee"amples /cited in Barrett et al., '==' are as follo#s

+ood sharing is more common amongst close relatives.

Political alliances bet#een %in are more stable thanthose formed bet#een distantly related, or unrelatedindividuals and involve less preconditions.

*he passing on of #ealth to lineal descendants/e"cluding spouses is far more common than giving toless closely related or unrelated individuals.

Close relatives are preferentially sought out in times of

need and such help is less li%ely to be reciprocal. 

elatives typically receive more e"pensive presents. 

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o# Juch Pain

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+acial ?imilarity and *rust

(eBruine /'=='  argued that animals should besensitive to cues of genetic relatedness #hen ma%ingaltruistic decisions.

:n humans such decisions may be based around facial

appearance. Participants played a computerised game of trust in

#hich they had to decide #hether or not to sharemoney #ith an individual.

*hey #ere sho#n faces of their MopponentsM #hich #ere

either facially diDerent to themselves, or #hose faceshad been morphed to resemble their o#n.

Participants sho#ed signi8cantly more MtrustingMbehaviour #hen playing against opponents that

resembled themselves. 

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uman Adoption. 

*he adoption of unrelated children has been cited asevidence against %in selection as helping to rear unrelatedchildren #ill not produce genetic bene8ts to the $giver&.

o#ever,  ?il% /!00=  observed that among Polynesian

cultures, a substantial number of adopters cared forchildren #ho #ere cousin e>uivalents or closer. +amilies#ho had adopted children that #ere unrelated tended tobe agricultural families needing e"tra help.

?imilarly, in Chicago ?tac% /!017  reported that thema9ority of foster children #ere adopted by %in.

Adopting unrelated children is a recent

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Problems for @in?election.

@in selection does not e"plain observed incidences ofanimals helping non-relatives for e"ample

nrelated chimpanHees come to one another&s aid#hen threatened /de

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'. eciprocalAltruism.

Proposed by *rivers /!01!. 

Natural ?election may create psychologicalmechanisms designed to deliver bene8ts even to non-relatives, provided that such actions lead toreciprocal bene8cial actions in the future.

$you scratch my back…&.

*his is not necessarily limited to the same speciese.g. cleaner 8sh.

:f the bene8t received is larger than the cost

incurred, then individuals #ho engage in suchbehaviour #ill out-reproduce those #ho do not.

Eg, in vampire bats, an individual #ill share food #itha conspeci8c /#hether related or not if the other hasshared food #ith that individual in the past/

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Conditions nder

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Jodelling uman

?ocial E"changes. 

$6ame *heory& #as developed by the mathematicianvon Neumann and the economist Jorgenstern in the!07=&s in an attempt to model the behaviour ofindividuals in economic and adversarial situations.

Jaynard-?mith /!05'  adapted it to model co-operation and competition in the social #orld.

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$nscrupulous (iner?cenario&.

A group of diners agree to divide the restaurant bille>ually, most co-operate by choosing similar pricedmeals but an individual can ta%e advantage by orderingthe most e"pensive meal, as the cost #ill be absorbedby the #hole group /6lance I uberman, !007.

:n a one-oD situation in a large social group it pays tocheat, ho#ever in a small group #ho meet regularly,such defection #ill be noticed and punished.

eciprocal social e"change has mutual costs)bene8tsbut one person can al#ays bene8t more than another if

they cheat - i.e. receive an act but do not reciprocate. *his constitutes a formidable barrier to the evolution of

social e"change.

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Prisoner&s (ilemma.

(escribed by A"elrod I amilton /!05!. :t is a game in#hich mutual co-operation bene8ts both players, but a$cheat& can gain a higher pay-oD.

:t is often described as a hypothetical situation in #hicht#o individuals have committed a crime, and are beingheld for >uestioning in separate cells, they are unableto communicate.

:t is in the best interests of both to say nothing, as theevidence is such that both may only receive a lightsentence.

o#ever, they are being >uestioned separately, and thela#yer oDers both freedom if they implicate the otherin the crime.

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Prisoner&s (ilemma PayoD

Jatri"Player BCo-operates

Player BDefects

Player ACo-operates

3 year sentenceeach.e#ard for mutualcooperation

? long sentencefor A, freedom forB.?uc%erMs payoD 

Player A

defects

* freedom for A,long sentence for B.*emptation todefect

P!= year sentenceeach.Punishment formutual defection

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uent move.

*his is an $Evolutionary Stable Strategy’ /E?? - i.e. once

established it cannot be displaced by another strategy. :n real life it pays to cheat in a one-oD e"change

encounter but if there is a li%elihood that you #illencounter the same person more than once, then mutualcooperation #ill serve both parties the best.

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:ndirecteciprocation.

*rivers /!01!  argued that an altruistic act need notnecessarily be reciprocated by the person directlyassisted but can be returned indirectly from otherindividuals.

E.g if you advertise yourself as an altruist thenindividuals #ill be more favourably inclined to deal #ithyou in future social e"change situations.

*his may e"plain blood donation, giving to beggars, anddonating to charities.

:t had been claimed that such actions indicate that

human behaviour is immune form evolutionary analysisand demonstrates a pure form of altruism.

Ale"ander /!051 suggested that giving blood is a verygood #ay of demonstrating your altruism at only amodest cost.

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Evidence for :ndirecteciprocation.

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An Alternative*heory.

6intis et al., /'==3 argues that  %in selection andreciprocity theories do not e"plain #hy cooperation isfre>uent amongst unrelated individuals in non-repeated interactions #hen gains are small.

?trong reciprocity is the predisposition to cooperate#ith others, and to punish those #ho violate thenorms of cooperation, at some personal cost, even#hen such costs may not be repaid.

:n support, +ehr I 6Qchter /'==' sho#ed that #henas%ed to play a game for monetary re#ard under MnopunishmentM or Mpunishment conditions$, punishmentof non-cooperators substantially increased theamount that groups invested for the good of thegroup.

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Additional Evidence +or?trong eciprocity.

*he concept of MfairnessM lies at the heart of manyhuman social interactions and can be modelled usingthe Mltimatum gameM.

ere a participant is given a sum of money and told

they can %eep it provided that they split the sum#ith another individual.

*he participant has to ma%e a one-oD oDer bet#een= -!==R of the total sum to the other person.

:f the second person agrees to the oDered sum then

both %eep these amountsS if they re9ect the oDerthen both receive nothing. No haggling is allo#ed.

According to one-oD game theory e"changes #e#ould e"pect that the 8rst participant #ould oDer asum of #ell belo# =R and that the receiver should

accept any sum as anything is better than nothing.

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*he $ltimatum 6ame& inAction.

o#ever #hen this game is played it is typically foundthat individuals oDer around =R, and more than half ofreceivers do not accept oDers less than '=R /?igmundet al., '=='.

:ndividuals do not behave completely sel8shly but placea high value on fair outcomes. eceivers are prepared toaccept smaller MgiftsM under the follo#ing conditions

*he giver is chosen by better performance on a >uiH.

*he givers oDer is randomly selected by a computer.

?everal responders compete to accept a proposers oDer.

?igmund et al., /'=='  proposed that our emotionalapparatus has been shaped over millions of years ofsmall group living in #hich it is hard to cheat more thanonce and #here #e e"pect conspeci8cs to notice ouractions and remember them.