Presentation on theme: "Evolutionary Psychology, Lecture 3. Altruism and Co-operation."— Presentation transcript:
Evolutionary Psychology, Lecture 3. Altruism and Co-operation
Learning Outcomes. zAt the end of this session you should be able to: z1. Explain what is meant by the terms ‘kin selection’ and ‘reciprocal altruism’. z2. Discuss kin selection and reciprocation explanations for human and animal cooperative / altruistic behaviours.
Thoughts For the Day. z“Let us try to teach generosity and altruism because we are born selfish” Richard Dawkins (1976). z“…ethics, morality, human conduct, and the human psyche are to be understood only if societies are seen as collections of individuals seeking their own self interest”. R.D. Alexander (1987). z“Scratch an altruist and watch a hypocrite bleed”. Ghiselin (1974).
Altruism. zAltruism refers to an individual acting in a way that will decrease its own survival chances, but improve the survival chances of another individual. zThe Darwinian perspective emphasising ‘survival of the fittest’ gave the impression that selfishness was the norm. zPioneering work involving the study of animals living in social groups in fact revealed that co-operation and altruism are just as ‘natural’ as selfishness. zIf co-operation and altruism have evolved, then they must have some adaptive benefits, researchers have analysed the conditions under which adaptations for engaging in such behaviour can be expected to evolve.
Examples of Animal Altruism. zVampire bats will regurgitate and feed blood that they have collected from their prey to a hungry conspecific (Wilkinson, 1990). zGround squirrels will warn others of the presence of a predator, even though making such a call may draw the attention of the predator to itself (Sherman, 1977). zIn many species of social insects, workers forgo reproduction entirely (they are sterile) in order to help raise their sisters (Wilson, 1971).
Theories of Altruism. z1. Kin Selection (Proposed by Hamilton, 1964). zBy helping relatives to reproduce (even at the cost to your own reproductive success) then your shared genes can spread. Assisting a close relative thereby increases one’s ‘Inclusive Fitness’. zUsing mathematical modelling, Hamilton showed that an altruistic gene can spread through the population if it causes an individual to help a relative, whenever the cost to the individual is offset by the reproductive benefit gained by the receiver. z‘Hamilton’s Rule’ = r B>c zwhere r=coefficient of relatedness, B = benefit to the recipient, c = cost to the giver.
Kin Selection in Action. zGround squirrels do not give an alarm call every time a predator approaches. They only do so when there is a large proportion of their relatives within earshot (Sherman, 1977). zVampire bats are much more likely to share their food with relatives than with non-relatives (Wilkinson, 1990). zThis theory explained the most puzzling phenomena - that of the sterile insects - by a genetic quirk they are more related to their sisters than to their mothers or daughters (Trivers & Hare, 1976).
Kin Recognition. zIt is important to be able to recognise kin, as the costs involved in mistaking another individuals offspring for one’s own are high, and the benefits few. zOffspring recognition should evolve more often in colonial species, as there is a high risk of misdirecting parental care. zExamples. zBank swallows (colonial) do not accept strange chicks whereas rough-winged swallows (solitary) do. zHerring gulls (colonial ground-nesting) recognise offspring and refuse strange chicks, but Kittiwakes (colonial cliff- nesting) do not recognise offspring and accept substitute offspring.
Kin Recognition in Gulls. Data from Alcock, 1993
Kin Selection in Humans. zStudies amongst diverse human populations consistently support the existence of kin selection, some examples (cited in Barrett et al., 2002) are as follows: zFood sharing is more common amongst close relatives. zPolitical alliances between kin are more stable than those formed between distantly related, or unrelated individuals and involve less preconditions. zThe passing on of wealth to lineal descendants (excluding spouses) is far more common than giving to less closely related or unrelated individuals. Close relatives are preferentially sought out in times of need and such help is less likely to be reciprocal. zRelatives typically receive more expensive presents.
How Much Pain Will You Suffer For Your Kin? zIn an interesting experiment Fieldman et al., (cited in Barrett et al., 2002) asked participants to maintain a painful position. The longer they held the position the more money they would earn. zIn different conditions participants could earn money for individuals differing in relatedness: zThemselves. zParent or sibling. zGrandparent / niece / nephew, a cousin. zUnrelated friend. zThe duration of maintaining the painful position varied as a direct proportion of relatedness, with more pain being sustained for closer relatives.
Facial Similarity and Trust? zDeBruine (2002) argued that animals should be sensitive to cues of genetic relatedness when making altruistic decisions. zIn humans such decisions may be based around facial appearance. zParticipants played a computerised game of trust in which they had to decide whether or not to share money with an individual. zThey were shown faces of their 'opponents' which were either facially different to themselves, or whose faces had been morphed to resemble their own. Participants showed significantly more 'trusting' behaviour when playing against opponents that resembled themselves.
Human Adoption. zThe adoption of unrelated children has been cited as evidence against kin selection as helping to rear unrelated children will not produce genetic benefits to the ‘giver’. zHowever, Silk (1990) observed that among Polynesian cultures, a substantial number of adopters cared for children who were cousin equivalents or closer. Families who had adopted children that were unrelated tended to be agricultural families needing extra help. zSimilarly, in Chicago Stack (1974) reported that the majority of foster children were adopted by kin. zAdopting unrelated children is a recent Western phenomenon. Alcock (1993) argues that the urge to produce children and look after them is so beneficial in reproductive terms that it has become deeply ingrained.
Problems for Kin Selection. zKin selection does not explain observed incidences of animals helping non-relatives for example: zUnrelated chimpanzees come to one another’s aid when threatened (de Waal & Luttrell, 1988). zVampire bats will feed non-relatives (Wilkinson, 1990). zHumans often engage in apparently altruistic acts such as: zGiving blood. zDonating to charity. zForgoing reproduction. zRescuing unrelated individuals (and even animals). zSacrificing their lives for moral or ethical principles. zHow can such behaviours be explained?
2. Reciprocal Altruism. zProposed by Trivers (1971). zNatural Selection may create psychological mechanisms designed to deliver benefits even to non-relatives, provided that such actions lead to reciprocal beneficial actions in the future. z‘you scratch my back…’. zThis is not necessarily limited to the same species e.g. cleaner fish. zIf the benefit received is larger than the cost incurred, then individuals who engage in such behaviour will out- reproduce those who do not. zEg, in vampire bats, an individual will share food with a conspecific (whether related or not) if the other has shared food with that individual in the past (Wilkinson, 1990).
Conditions Under Which Reciprocation Flourishes. z1. Individuals must associate for long-enough periods of time to develop reciprocal interactions. z2. The likelihood of one individual performing some social exchange with another should be predicted on the basis of their past associations. z3. The roles of giver and receiver should reverse at least once. z4. The short-term benefits to the recipient are greater than the costs to the donor. 5. Givers should be able to recognise and expel cheaters from the system. zDo such conditions apply to human social interactions?
Modelling Human Social Exchanges. z‘Game Theory’ was developed by the mathematician von Neumann and the economist Morgenstern in the 1940’s in an attempt to model the behaviour of individuals in economic and adversarial situations. zMaynard-Smith (1982) adapted it to model co-operation and competition in the social world. zWithin game theory, individuals behave rationally and choose the action that yields the highest payoff. zHuman social interactions can be mapped into game settings, as one individual can benefit from the actions of others at little cost to themselves. zThere are several forms:
‘Unscrupulous Diner Scenario’. zA group of diners agree to divide the restaurant bill equally, most co-operate by choosing similar priced meals but an individual can take advantage by ordering the most expensive meal, as the cost will be absorbed by the whole group (Glance & Huberman, 1994). zIn a one-off situation in a large social group it pays to cheat, however in a small group who meet regularly, such defection will be noticed and punished. zReciprocal social exchange has mutual costs/benefits but one person can always benefit more than another if they cheat - i.e. receive an act but do not reciprocate. zThis constitutes a formidable barrier to the evolution of social exchange.
Prisoner’s Dilemma. zDescribed by Axelrod & Hamilton (1981). It is a game in which mutual co-operation benefits both players, but a ‘cheat’ can gain a higher pay-off. zIt is often described as a hypothetical situation in which two individuals have committed a crime, and are being held for questioning in separate cells, they are unable to communicate. zIt is in the best interests of both to say nothing, as the evidence is such that both may only receive a light sentence. zHowever, they are being questioned separately, and the lawyer offers both freedom if they implicate the other in the crime. zWhen the game is played once or only a few times then the best strategy is to inform on the other (defect).
Prisoner’s Dilemma Payoff Matrix
Which Strategy is Best? zReal life social exchanges may occur more than once and individuals will probably remember those who have defected (cheated) in the past. zAxelrod (1984) organised a tournament in which various computer programs played repeated prisoners dilemma games. A program called 'tit for tat' was a clear winner. This simple strategy always cooperated on the first move, and then copied its opponents move on every subsequent move. zThis is an ‘Evolutionary Stable Strategy’ (ESS) - i.e. once established it cannot be displaced by another strategy. zIn real life it pays to cheat in a one-off exchange encounter but if there is a likelihood that you will encounter the same person more than once, then mutual cooperation will serve both parties the best.
Indirect Reciprocation. zTrivers (1971) argued that an altruistic act need not necessarily be reciprocated by the person directly assisted but can be returned indirectly from other individuals. zE.g if you advertise yourself as an altruist then individuals will be more favourably inclined to deal with you in future social exchange situations. zThis may explain blood donation, giving to beggars, and donating to charities. zIt had been claimed that such actions indicate that human behaviour is immune form evolutionary analysis and demonstrates a pure form of altruism. zAlexander (1987) suggested that giving blood is a very good way of demonstrating your altruism at only a modest cost.
Evidence for Indirect Reciprocation. zWe would maybe predict that individuals will not donate blood or give to charity unless their actions are made known – i.e. by wearing a sticker or badge indicating their actions. zLow & Heinen (cited in Alcock, 1993) reported that students are significantly more likely to give to charity if they receive a pin or tag that advertises their participation. zMulcahy (1999) observed who gave money to beggars and then interviewed mixed-sex couples after the male had donated money. zMales at the early stage of a relationship were more likely to give than those in a long-established relationship. Thus the act of giving when accompanied by a female is not simply to do with impressing a current partner, but demonstrating one's generosity to a potential partner.
An Alternative Theory. zGintis et al., (2003) argues that kin selection and reciprocity theories do not explain why cooperation is frequent amongst unrelated individuals in non-repeated interactions when gains are small. zStrong reciprocity is the predisposition to cooperate with others, and to punish those who violate the norms of cooperation, at some personal cost, even when such costs may not be repaid. zIn support, Fehr & Gächter (2002) showed that when asked to play a game for monetary reward under 'no punishment' or 'punishment conditions‘, punishment of non-cooperators substantially increased the amount that groups invested for the good of the group.
Additional Evidence For Strong Reciprocity. zThe concept of 'fairness' lies at the heart of many human social interactions and can be modelled using the 'Ultimatum game'. zHere a participant is given a sum of money and told they can keep it provided that they split the sum with another individual. zThe participant has to make a one-off offer between % of the total sum to the other person. zIf the second person agrees to the offered sum then both keep these amounts; if they reject the offer then both receive nothing. No haggling is allowed. zAccording to one-off game theory exchanges we would expect that the first participant would offer a sum of well below 50% and that the receiver should accept any sum as anything is better than nothing.
The ‘Ultimatum Game’ in Action. zHowever when this game is played it is typically found that individuals offer around 50%, and more than half of receivers do not accept offers less than 20% (Sigmund et al., 2002). zIndividuals do not behave completely selfishly but place a high value on fair outcomes. Receivers are prepared to accept smaller 'gifts' under the following conditions: zThe giver is chosen by better performance on a quiz. zThe givers offer is randomly selected by a computer. zSeveral responders compete to accept a proposers offer. zSigmund et al., (2002) proposed that our emotional apparatus has been shaped over millions of years of small group living in which it is hard to cheat more than once and where we expect conspecifics to notice our actions and remember them.