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Bateson, M., Nettle, D. & Roberts, G.(2006). Cues of being watchedenhance cooperation in a real-worldsetting. Biology Letters, 2, 412–414.

Burnham, T.C. & Hare, B. (2007).Engineering human cooperation:Does involuntary neural activationincrease public goods contributions?Human Nature, 18, 88–108.

Buss, D.M. (1989). Sex differences inhuman mate preference. Behavioural

and Brain Sciences, 12, 1–49.Buss. D. (1994). The evolution of desire:

Strategies of human mating. NewYork: Basic Books.

Eagly, A.H. & Crowley, M. (1986). Genderand helping behaviour. PsychologicalBulletin, 100, 283–308.

Farrelly, D., Lazarus, J. & Roberts, G.(2007). Altruists attract. EvolutionaryPsychology, 5, 313–329.

Goldberg, T.L. (1995). Altruism towards

panhandlers: Who gives? HumanNature, 6, 79–89.

Griskevicius, V., Tybur. J. M., Sundie. J. etal. (2007). Blatant benevolence andconspicuous consumption: Whenromantic motives elicit strategiccostly signals. Journal of Personalityand Social Psychology, 93, 85–102.

Haley, J.J. & Fessler, C.M.T. (2005).Nobody’s watching? Subtle cuesaffect generosity in an anonymous

economic game. Evolution andHuman Behaviour, 26, 245–256.

Hamilton, W.D. (1964). The geneticevolution of social behavior I and II. Journal of Theoretical Biology, 7,1–52.

Hardy, C. & Van Vugt, M. (2006). Niceguys finish first: The competitivealtruism hypothesis. Personality andSocial Psychology Bulletin, 32,1402–1413.

Could Darwinian sexual selectionhelp us understand altruismtowards strangers? We proposethat altruism may be used as a‘peacock’s tail’ to attract females.We argue that altruism is anattractive mate signal to femalesbecause brave, heroic displays cansignal good gene quality, andbecause financial help andvolunteering signal the willingnessto care and invest in therelationship. Finally, wehypothesise that such findingscould have positive real-lifeimplications: by harnessing the sex appeal of altruistic behaviour,charities and volunteerorganisations could increaseprosocial behaviour.

Compared with other animals,humans are quite unusual in theiraltruism towards (genetic)

strangers. We regularly donate money inaid of the poor, give blood to help thesick, and even risk our lives to jump aftera drowning person whom we have nevermet. Why do we engage in theseseemingly irrational acts? Why do we goout of our way to help complete strangerswhen it involves a cost to ourselves?

From an evolutionary perspective,helping strangers is somewhat puzzling.Charles Darwin’s theory of naturalselection assumes that organisms shouldbe concerned about their own welfarerather than that of others. So whatadvantage does helping strangers give youwhen it involves a significant cost or risk?More broadly, if individuals are primarilyconcerned with their own welfare howcould any selfless behaviour have evolved?This question puzzled Darwin and othergreat scientists in biology, philosophy andpsychology for many centuries. Onehundred and fifty years after Darwin firstpublished The Origin of the Species we arestill questioning the origins of humanaltruism, but through empirical research in the behavioural sciences we are gettingcloser to an answer (Van Vugt & VanLange, 2006).

Survival of the kindestNatural selection favours individuals that are relatively better adjusted to theirphysical and social environment – hence,the fitter individuals are more likely tosurvive and reproduce. A common

misunderstanding about the evolutionaryapproach is what we mean by survival ofthe fittest. Although in everyday language‘fittest’ generally refers to the strongest,fastest, healthiest, and hardiestindividuals, in evolutionary biology itsimply concerns the ‘ability to pass ongenes to the next generation’. Thistherefore can refer to any feature of anorganism as long as it increases theirability to pass on their genes. In highlysocial species (such as honeybees andhumans) there will be positive selectionfor traits such as honesty, kindness,generosity and altruism. Altruismincreases an individual’s ability to pass ontheir genes if it involves helping a closerelative – we share 50 per cent of ourgenes with our biological parents,children, and siblings (kin selectiontheory: Hamilton, 1964) – or helpingthose who are likely to reciprocate at a later time (reciprocal altruism theory:Trivers, 1971).

Yet theorists are having a hard time in tweaking these evolutionary theories toexplain the kind of helping we see so oftenin humans, such as giving money to streetbeggars, donating blood and organs, andproviding aid relief to developing countries(Goldberg, 1995; Titmuss, 1970; Van Vugt,2001). Yet this year’s Comic Reliefdonation of over £65,000,000 shows howimportant and widespread such generousacts are. What possible fitness advantage isthere for a generous act?

Survival of the sexiestThe answer may lie (at least in part) inDarwin’s second big insight, the theory of sexual selection. Darwin was intriguedby features of organisms that did not looklike they would enhance the survival ofthose individuals. The classic example is the tail of the peacock. How can suchcolourful and large plumage evolve if itattracts predators and slows downescape? Perhaps, Darwin argued, such a tail might help the peacock to attractmates. Darwin was quite clear that anorganism’s ability to pass on their genes

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Iredale, W., Van Vugt, M. & Dunbar, R.I.M.(2008). Showing off in humans: Malegenerosity as a mating signal.Evolutionary Psychology, 6, 386–392.

Miller, G. (2000) The mating mind: Howsexual choice shaped the evolution ofhuman nature. New York: Doubleday.

Why might the preference for analtruistic mate be stronger in womenthan men?Are there differences in male andfemale helping behaviour? Couldaltruism as a mate signal explain thesedifferences?

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The peacock’s tail of altruismWendy Iredale and Mark Van Vugt look at the Darwinian psychology of helping and generosity

was not just down to the survival of theindividual but also to their ability toattract sexual partners for producingoffspring. Therefore, evolution shouldselect for traits that increase theattractiveness of the individual to theopposite sex, and the peacock’s tail is justone example.

As usual, Darwin was correct. Researchshows that peahens actively select formales with large colourful tails (Petrie,1994). Many other seemingly odd traits inthe animal kingdom have now proven tobe the result of sexual selection, such asbird song, the lion’s mane, even the bluebottom of the Mandrill. Recentlypsychologists have suggested that sexualselection might have also played a role inshaping various human traits such as facialbeauty, facial symmetry, women’s breasts,intelligence, language and creativity(Miller, 2000).

So is human altruism a peacock’s tail?Evolutionary psychologist Geoffrey Miller(2000) thinks so: ‘We have the capacityfor moral behaviour and moral judgmentstoday because our ancestors favouredsexual partners who were kind, generous,helpful and fair’ (p.292). Is that still thecase in modern society? The entrepreneurand Virgin founder Richard Branson fellin love with his now wife JoanTempleman and to impress her gave herone of the Virgin Islands as a present. Thecore theme of many fictional stories innovels and films is how being generousgives the main character a sexualadvantage (see Tessman, 1995, for areview). In Jane Austen’s Pride andPrejudice, for instance, Elizabeth’saffection towards Mr Darcy increaseswhen she hears of his help and generositytowards her family. In the 1988 filmComing to America, Eddie Murphy’scharacter impresses the women of hisaffections when he gives away a wad of$100 bills to two homeless men.

For altruism to be a sexually selectedtrait it must impress members of theopposite sex. Altruism signals manypositive qualities, such as being kind,resourceful and generous, which are

important partner qualities (Buss, 1994),and will attract mates. Roberts (1998)argues that because altruism acts as asignal of quality, individuals may competefor the most altruistic partners. Potentialmates will obviously be more impressedthe costlier the altruistic display (such asbeing gifted an island in the Caribbean).The costliness gives an indication of howfit the individual is (Zahavi, 1975). In thelanguage of evolutionary biology, altruismhas to be an ‘honest signal of someunderlying quality’. For example, a personwho has £100,000 in his bank account canafford to give away £50,000 to charity buta person who only has £50,000 cannotafford to giveall of it way. Ina similar vein,only a healthypeacock cangrow anornamental tailand the lesshealthy onescannot.

It alsohelps if there isan audience forthe display sothat theindividual canshow off theirqualities to aslarge a numberof potentialmates aspossible.Highly publicacts ofgenerosity suchas giving moneyto a televiseddonation fund where big donors receiverecognition fit the bill and should thereforeelicit ‘show off’ altruistic displays.

A lot of studies have shown that we are keen to show ourselves off as beingaltruistic. People are significantly morelikely to give to charity if they receive a pinor tag that advertises their participation(Low & Heinen, 1993). Similarly, Hardy

and Van Vugt (2006) found in their labstudies that when individuals make apublic donation – when others arewatching – they give more to the publicgood than if they had made theirdonations in private. Even the presence ofphotographic and computer eyes has beenshown to increase generosity and honesty(Bateson et al., 2006; Burnham & Hare,2007; Haley & Fessler, 2005).

Do men ‘show off’ altruism to attract women?What does this mean for helping andgenerosity? Imagine you are on a first

date with someone andwhilst having yourromantic dinner you areapproached by a charityworker asking fordonations to a charitablecause. Are you more orless likely to make adonation than when youare eating alone or with a group of ordinaryfriends? Would men andwomen act the same?

There is no doubt thatthe most desired trait in asexual partner for bothsexes is kindness (Buss,1989). Yet it is also truethat men and women value different attributesdifferently in sexualpartners. Research into

lonely heart adverts showsthat women tend to reveal andenhance information abouttheir physical attractiveness and men pay more attention to

these cues. Similarly, women tend to paymore attention to information about aman’s wealth, status, and commitment andmen tend to emphasis these traits in theiradverts (Waynforth & Dunbar, 1995). Thisdifference stems from differences inlifetime reproductive success and parentalinvestment, which is a feature of allmammalian species. Like other mammals,

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Howard, J.A., Blumstein, P. & Schwartz,P. (1987). Social or evolutionaryTheories? Some observations onpreferences in human matingselection. Journal of Personality andSocial Psychology, 53, 194–200.

Iredale, W., Van Vugt, M. & Dunbar, R.I.M.(2008). Showing off in humans: Malegenerosity as a mating signal.Evolutionary Psychology, 6, 386–392.

Jensen-Campbell, L., Graziano, W.G. &

West, S.G. (1995). Dominance,prosocial orientation, and femalepreferences: Do nice guys reallyfinish last? Journal of Personality &Social Psychology, 68, 427–440.

Kelly, S. & Dunbar, R.I.M. (2001).Whodares wins: Heroism versus altruismin women’s mate choice. HumanNature, 12, 89–105.

Latané, B. (1970). Field studies ofaltruistic compliance. Representative

Research in Social Psychology, 1,49–61.

Low, B.S. & Heinen, J.T. (1993).Population, resources, andenvironment: Implications of human behavioural ecology forconservation. Population andEnvironment, 15, 7–41.

Miller, G. (2000). The mating mind: Howsexual choice shaped the evolution ofhuman nature. London: Heinemann.

Mulcahy, N.J. (2002). Altruism towardsbeggars as a human mating strategy.In L. Barrett, R.I.M. Dunbar & J.Lycett (Eds.) Human evolutionarypsychology. Basingstoke: Palgrave.

Petrie, M. (1994). Improved growth andsurvival of offspring of peacocks withmore elaborate trains. Nature, 317,290–291.

Phillips, T., Barnard, C. & Ferguson, E.(2008). Do humans prefer altruistic

Does who you are with affectwhether you donate?

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human females tend to invest more in theiroffspring than human males, at the veryleast in terms of gestation and lactation.Furthermore, women are limited in thenumber of children they can have in alifetime compared to men; during a nine-month period when a woman producesone child, a male could have mated manytimes and produced many offspring. Thesedifferences change the pay-offs of themating game, with implications for whatmen and women are looking for in apartner and what partners then signal.Men pay more attention to looks becausethey are more concerned with cues ofhealth and fertility; such as hour-glassfigure, unblemished skin and lustrous hair.Women are the choosier sex because theyinvest more and they pay more attention to cues indicating that the man is going to provide resources and stick around. Inturn, men who signal these qualities aremore attractive as sexual partners. One of the ways in which men can signal theirresource quality is by driving around in a Porsche or buying aPicasso. However, this doesnot give any informationabout whether they arewilling to share theseresources with a potentialmate. It is thereforeprobably better for a manto engage in a conspicuous act ofgenerosity, such as buying an expensivegift like a tropical island or founding acharity.

Are men more likely than women to be conspicuously helpful in the presenceof a potential mate? An interesting way to test this hypothesis is to examine whodonates to a street beggar. If you observebeggars and make a record about whogives most money to them – a loneindividual, a same-sex dyad or group, a mixed-sex dyad or group – we wouldexpect that men would donate the mostespecially in the presence of a female. TonyGoldberg (1995) examined sex differencesamong individuals giving money to streetbeggars and found that lone mendisproportionately gave to female street

beggars; whereas, Bibb Latané (1970)found that the presence of a femalecompanion increased giving to both maleand female street beggars. Mulcahy (2002)carried out a similar study and found ininterviews afterwards that men in the earlystages of their relationship weresignificantly more likely to give to beggarsthan men in long-term committedrelationships, no doubt to impress theirnew partner.

In a lab experiment we recently foundessentially the same result. Men andwomen played various economics gamesfor money and they were either notobserved or there was an (attractive) same-sex or opposite-sex observer in the sameroom watching them. After the games hadfinished they were then asked whatpercentage of their earnings they woulddonate to charity. Men donatedsignificantly more in the presence of anattractive woman, but women’s donationsdid not go up in the presence of anattractive man (Iredale et al., 2008).

Similarly, Farrelly et al.(2008) found that duringcooperative games, malesshowed a greater biastowards cooperating withopposite-sex partners

than did females. What about helping acts

that involve no money? Men are also morelikely to engage in helping that involvesphysical bravery – heroism – presumablybecause it signals their physical strengthand willingness to take risks. Out of the6955 people who have received theCarnegie heroism award – awarded topeople in the United States and Canadawho have risked their lives in savinganother’s life – only 9 per cent were female(Eagly & Crowley, 1986).

Griskevicius et al. (2007) examinedwhether public philanthropy, conspicuousdisplays of consumption and benevolencecould be elicited by romantic motives.They found that priming men with matingmotives increases conspicuous helpingwhen the act signalled was heroic (e.g.diving into icy water after a stranger falls

from a boat in a storm) but not mundanehelping (e.g. teaching underprivilegedyouths to read).

Men are also more likely to help insituations of intergroup competition. VanVugt et al. (2007) compared sex differencesin pubic goods donations. They found thatmen contributed more to their group ifthey were competing against anothergroup, whereas female cooperation wasunaffected by intergroup competition.

Thus, men show off their qualities aspotential sexual mates by engaging inconspicuous helping displays, such asbeing generous and heroic towards others.Logically men should only show off theirgenerosity if this is a trait that women findattractive in potential mates. Do they?

Do women prefer altruistic males?If you asked most women what they lookfor in a man, it is likely that they will useterms such as attractive, interesting,considerate and kind. We know thatwomen have a greater preference towardsaffectionate and compassionate mates(Howard et al., 1987) and prefer thosewho talk positively about giving help(Jensen-Campbell et al., 1995).Researchers at Nottingham Universityrecently found that altruism such as‘donates blood regularly’ and ‘volunteeredto help out in a local hospital’ wereconsidered attractive traits in a mate,particularly for females (Phillips et al.,2008). Kelly and Dunbar (2001) foundthat altruistic males are preferred as long-term mates, yet heroes (voluntary risktakers) are preferred over altruists at leastfor short-term mating purposes (i.e.having consensual sex).

We conducted a study to examinewhether females are attracted towardsaltruistic men. We showed a group offemale students at the University of Kent avideo of an attractive male actor displayingeither costly altruism (donating £30 to a street beggar), not so costly altruism(donating £1 to a street beggar), or noaltruism (walking past the street beggar).

“females are attractedto males who displaycostly altruism”

mates? Testing a link between sexualselection and altruism towards non-relatives. British Journal ofPsychology, 99, 555–572.

Roberts, G. (1998). Competitive altruism: From reciprocity to thehandicap principle. Proceedings of theRoyal Society of London B, 265,427–431.

Tessman. I. (1995). Human altruism as acourtship display. Oikos, 74,157–158.

Titmuss, R.M. (1970). The gift relationship.London: Allen and Unwin.

Trivers, R. (1971). The evolution ofreciprocal altruism. Quarterly Reviewof Biology, 46, 35–57.

Van Vugt, M. (2001). Communityidentification moderating the impactof financial incentives in a naturalsocial dilemma: A water shortage.Personality and Social PsychologyBulletin, 27, 1440–1449.

Van Vugt, M., De Cremer, D. & Janssen,D. (2007). Gender differences incooperation and competition: Themale warrior hypothesis.Psychological Science, 18, 19–23.

Van Vugt, M. & Van Lange, P.A.M. (2006).Psychological adaptations forprosocial behavior: The altruismpuzzle. In M. Schaller, D. Kenrick &J. Simpson (Eds.) Evolution and socialpsychology (pp.237–261). New York:

Psychology Press.Waynforth, D. & Dunbar, R.I.M. (1995).

Conditional mate choice strategies in humans: Evidence from ‘lonelyhearts’ advertisements. Behaviour,132, 755–779.

Zahavi, A. (1975). Mate selection: Aselection for a handicap. Journal ofTheoretical Biology, 53, 205–214.

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We found that females rated the male actormore attractive the greater the costs theyincurred. This suggest that females areattracted to males who display costlyaltruism, presumably because giving £30to a street beggar is an honest signal ofsome underlying trait.

What do altruists signal?Finally, we could ask what it is that males are signalling when they engage inconspicuous helping acts. The literaturehas put forward two hypotheses: the‘good-genes’ hypothesis and the ‘caring’hypothesis (Kelly & Dunbar, 2001; Miller,2000). The good-genes hypothesissuggests that altruism signals underlyinggenetic qualities, in the same way thepeacock’s tail is a costly handicap. Bybeing able to survive and carry thehandicap, the individual signalssomething about their underlying geneticquality – not only can they survive butthey can help others survive. The caringhypothesis suggests that altruismindicates that the person is willing toinvest in the relationship and in possibleoffspring.

Recently we conducted a study to testwhy women were attracted to altruisticmen. We asked two questions: are therecertain types of altruistic acts that are moreattractive than others; and do femalesassociate altruism with any importantmate qualities such as good genes,

resources or relationship commitment?Women from the University of Kentwatched a video clip of the same maleeither donating blood (volunteering),donating money to a beggar (financialaltruism), rescuing a stolen bag (heroicaltruism), or failing to display any of thesebehaviours. We asked females to rate themale in the video they saw in terms ofsexual attractiveness, and to rank orderlonely heart adverts from most likely toleast likely to have been written by themale in the video. The lonely heart advertsvaried in terms of good gene quality(either the lonely heart advert describedthe male as a healthy male, good at sports,or as a rather weak generally unwellindividual), resource potential (either amale with high earning ambitions or withno interest in becoming rich), andrelationship quality (either looking tocommit to a relationship or only lookingfor a bit of fun).

As expected, women rated the maleactor significantly more attractive when he

displayed altruism.Furthermore, womenranked the male actorrescuing the bag assignificantly physicallystronger and healthier. Thissupports the good-genehypothesis that risky andphysically costly altruisticacts signal gene quality. Inaddition females rated themale who gave money to a beggar as more likely tohave high potentialresources. This suggeststhat altruists are mostlikely to be associated withresources if they show offfinancial altruism. Finally,women rated the male asmore committed to arelationship when he gaveblood or donated moneythan when he rescued thebag. This research thusshows that altruism as a

mate signal can work in twoways: brave heroic displays cansignal good gene quality,whereas financial help and

volunteering signal the willingness to careand invest in the relationship.

ImplicationsWe have shown that altruism is a matingstrategy that is most often used by men toattract women. This ‘altruism is sexy’hypothesis has implications for charitiesand volunteer organisations. If it is sexyto donate and help others then perhapsorganisations that want to encouragepublic acts of altruism could use this toincrease donations. It may benefit theseorganisations to emphasise to potentialdonors that altruism is a quality that isattractive to the opposite sex and they canuse attractive female models to encouragealtruism much in the same way that carand home improvement adverts useattractive female models sell their goods.In addition, to attract volunteers theseorganisations could emphasiseopportunities to meet members of theopposite sex.

I Mark Van Vugtis in the Department ofSocial and OrganisationalPsychology, VU UniversityAmsterdamm.van.vugt@psy.vu.nl

I Wendy Iredaleis a postgraduate studentat the University of Kentwi4@kent.ac.uk

Manoeuvring to signal resource quality?