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Cited by 2,765Evolutionary Game Theory and CooperationEvolutionary Psychology and Human BehaviorAnimal Behavior and Reproduction

Evolution of indirect reciprocity

Open access
Nowak, Martin A., Sigmund, Karl·2005·Nature
DOI 10.1038/nature04131
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Abstract

Natural selection is conventionally assumed to favour the strong and selfish who maximize their own resources at the expense of others. But many biological systems, and especially human societies, are organized around altruistic, cooperative interactions. How can natural selection promote unselfish behaviour? Various mechanisms have been proposed, and a rich analysis of indirect reciprocity has recently emerged: I help you and somebody else helps me. The evolution of cooperation by indirect reciprocity leads to reputation building, morality judgement and complex social interactions with ever-increasing cognitive demands.

AI snapshot

Written from the paper’s full text.

TL;DR

This review argues that indirect reciprocity—helping others to build a reputation that leads third parties to help you—can sustain cooperation when the cost-to-benefit ratio is low and social information is sufficient. It synthesizes evolutionary game theory and experimental economics, emphasizing reputation, moral judgment, and increasing cognitive demands.

Key findings

  • Direct reciprocity is repeated Prisoner’s Dilemma between the same two individuals; indirect reciprocity assumes any two players interact at most once and relies on reputation and community enforcement, so help is channelled towards those who help.
  • In binary-assessment models, first-order assessment has 4 rules, second-order 16, third-order 256, and combining action and assessment yields 4096 strategies; Ohtsuki & Iwasa proved only 8 (“leading eight”) are evolutionarily stable under certain conditions, all distinguishing justified from unjustified defection. STANDING and JUDGING belong to the leading eight; SCORING and SHUNNING do not.
  • Experiments show substantial donations, image score correlates with receiving money, more information enhances cooperation, donations are more frequent in earlier rounds, and the propensity to donate more than doubles if players know their action will be communicated. In one public-goods experiment, contributions do not deteriorate when indirect reciprocity rounds are sandwiched between public-goods rounds, and donations reward high contributors.
  • Indirect reciprocity requires the probability \(q\) of knowing another’s social score to exceed the cost-to-benefit ratio \(c/b\), analogous to Hamilton’s rule; simulations often use population sizes of 50 to 100 individuals, and language and cognition likely coevolved with indirect reciprocity.

Methods

  • Review/synthesis, not a primary empirical study; no new data are presented.
  • Draws on evolutionary game theory (repeated Prisoner’s Dilemma, indirect reciprocity models, replicator dynamics, individual-based simulations) and experimental economics/psychology (donation/helping games, public goods, trust games).
  • Main analysis is conceptual and comparative, citing models and experiments; no formal meta-analysis or systematic search is reported.

Limitations

  • The paper states that private reputation lists and errors in perception can undermine cooperation; gossip may spread false rumours; the coevolution of language and indirect reciprocity is “fascinating and yet unexplored”; population structure is debated; strategies depending on both donor payoff and recipient score “have not been analysed so far”; and group selection should not be confused with indirect reciprocity.
  • Evident from the text: as a review, it does not present new experiments or a systematic quantitative synthesis, and many cited experiments are described only briefly, with some references listed as working papers or in press.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1038/nature04131

Cites

95 of 95 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

18 of 152 cited sources checked · 6 supported · 2 flagged · accuracy not yet measured

  • Premisecitation
    § Public goods · p. 13

    After a couple of rounds the personal experience obtained with the given co-player becomes more decisive.

    “After a couple of rounds the personal experience obtained with the given co-player becomes more decisive 62 .”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [62] Bolton, G. E., Katok, E. & Ockenfels, A. Cooperation among strangers with limited information about reputation. J. Public Econ. 89, 1457–1468 (2005) source

      The Design of the experiment section (page unavailable) says that no two subjects were paired more than once and that subjects knew this. Its design therefore rules out gaining experience with a given co-player over several rounds; the paper instead studies decisions based on information about a new partner’s past actions. (LLM, conf=0.89)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured
  • Interpretationcitation
    § Direct versus indirect reciprocity · p. 8

    The step from direct to indirect reciprocity corresponds to the step from personal enforcement to community enforcement.

    “In this sense, the step from direct to indirect reciprocity corresponds simply to the step from personal enforcement to community enforcement 26-29 .”
    Quote in the paperNot a substantial claim2 of 4 sources checked
    • cites [26] Binmore, K. Fun and Games: A Text on Game Theory (Heath, Lexington, Massachusetts, 1992)
    • cites [27] Rosenthal, R. W. Sequences of games with varying opponents. Econometrica 47, 1353–1366 (1979) source
    • cites [28] Kandori, M. Social norms and community enforcement. Rev. Econ. Stud. 59, 63–80 (1992) source
    • cites [29] Ellison, G. Cooperation in the prisoner's dilemma with anonymous random matching. Rev. Econ. Stud. 61, 567–588 (1994) source
  • Premisecitation
    § Evolution of indirect reciprocity · p. 7

    The growth of e-auctions and other forms of e-commerce is based, to a considerable degree, on reputation and trust.

    “The growth of e-auctions and other forms of e-commerce is based, to a considerable degree, on reputation and trust 5-10 .”
    Quote in the paperNot a substantial claim3 of 6 sources checked
    • cites [5] Bolton, G. E., Katok, E. & Ockenfels, A. How effective are electronic reputation mechanisms? An experimental investigation. Manage. Sci. 50, 1587–1602 (2004) source
    • cites [6] Keser, C. Trust and reputation building in e-commerce. IBM Watson Research Center, CIRANO working paper no. 2002s-75 http://www.cirano.qc.ca/en/publication_detail.php?id=2002s-75 (2002).
    • cites [7] Dellarocas, C. Sanctioning reputation mechanisms in online trading environments with moral hazard. MIT Sloan School of Management working paper no. 4297–03 http://ssrn.com/abstract=393043 (2003). source
    • cites [8] Bolton, G., Katok, E. & Ockenfels, A. in Applications of Supply Chain Management and e-Commerce Research (eds Geunes, J., Akcali, E., Pardalos, P. M., Romeijn, H. E. & Shen, Z.-J.) 195–216 (Springer, Dordrecht, 2005) source
    • cites [9] Resnick, P., Zeckhauser, R., Friedman, E. & Kuwabara, K. Reputation systems. Commun. ACM 43, 45–48 (2000) source
    • cites [10] Lucking-Reiley, D., Bryan, D., Prasad, N. & Reeves, D. Pennies from eBay: The Determinants of Price in Online Auctions. Vanderbilt Univ., Univ. Arizona working paper (1999).

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Interpretationcitation
    § Binary assessment, or the world in black and white · p. 10

    A more sophisticated assessment rule should distinguish between justified and unjustified defection, taking into account the score of the receiver.

    “A more sophisticated assessment rule should distinguish between justified and unjustified defection, and thus take into account the score of the receiver: someone withholding help from a 'bad' player should not pay with a reduced score 35,38,39,47 .”
    Quote in the paperNot a substantial claim1 of 4 sources checked
    • cites [35] Nowak, M. A. & Sigmund, K. A strategy of win-stay, lose-shift that outperforms tit-for-tat in the prisoner's dilemma game. Nature 364, 56–58 (1993) source
    • cites [38] Ferrière, R. Help and you shall be helped. Nature 393, 517–519 (1998) source
    • cites [39] Leimar, O. & Hammerstein, P. Evolution of cooperation through indirect reciprocation. Proc. R. Soc. Lond. B 268, 745–753 (2001) source
    • cites [47] Sigmund, K., Hauert, C. & Nowak, M. A. Reward and punishment. Proc. Natl Acad. Sci. USA 98, 10757–10762 (2001) source

      In “Bifurcation Through Reputation” (page unavailable), the paper models cooperators defecting against known nonpunishers, so a coplayer’s reputation can affect the decision to help. It does not describe an assessment rule that distinguishes justified from unjustified defection or say that withholding help from a bad player leaves the donor’s score unchanged. (LLM, conf=0.78)

      Experimental — accuracy not yet measured
  • Premisecitation
    § Binary assessment, or the world in black and white · p. 10

    A stable mix of discriminating and undiscriminating altruists which cannot be invaded by defectors is also obtained by assuming that as players grow older, their social network grows, and with it their information about their co-players' past.

    “A stable mix of discriminating and undiscriminating altruists which cannot be invaded by defectors, is also obtained by assuming that as players grow older, their social network grows, and with it their information about their co-players' past 54,55 .”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [54] Brandt, H. & Sigmund, K. The logic of reprobation: Assessment and action rules for indirect reciprocity. J. Theor. Biol. 231, 475–486 (2004) source

      Split into 2 atoms — 0 confirmed, 0 partially supported, 0 disputed, 0 misattributed, 2 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured
    • cites [55] Mohtashemi, M. & Mui, L. Evolution of indirect reciprocity by social information: The role of trust and reputation in evolution of altruism. J. Theor. Biol. 223, 523–531 (2003) source
  • May combine two claims. 52
  • Classified as probably not a substantial claim. 71

  • May combine two claims.

    Premisecitation
    § Costly experiments · p. 12

    In another experiment, those who give often end up with the highest payoff, so that there is a strategic advantage to generosity.

    “In another experiment 62 , however, those who give often end up with the highest payoff, so that there is a strategic advantage to generosity.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [62] Bolton, G. E., Katok, E. & Ockenfels, A. Cooperation among strangers with limited information about reputation. J. Public Econ. 89, 1457–1468 (2005) source

      The Conclusions (section 6; page not provided) report the opposite individual-level pattern: in every treatment, giving more gifts was negatively correlated with total payoff. Although giving raised the chance of receiving a gift, the paper says an additional gift cost the giver about 9 cents on average, rather than conferring the claimed payoff advantage. (LLM, conf=0.90)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation
    § Binary assessment, or the world in black and white · p. 10

    Costly punishment plays an undisputed role in other contexts, such as public goods games, ultimatum games and trust games, which shows that this form of discrimination is highly plausible.

    “The fact that costly punishment plays an undisputed role in other contexts, such as public goods games, ultimatum games and trust games 43-46 , shows that this form of discrimination is highly plausible.”
    Quote in the paperNot a substantial claim2 of 4 sources checked
    • cites [43] Dawes, R. M. Social dilemmas. Annu. Rev. Psychol. 31, 169–193 (1980) source
    • cites [44] Fehr, E. & Gächter, S. Cooperation and punishment in public goods experiments. Am. Econ. Rev. 90, 980–994 (2000) source
    • cites [45] Fehr, E. & Gächter, S. Altruistic punishment in humans. Nature 415, 137–140 (2002) source

      The public-goods experiment (p. 1) documents punishment that cost the punisher money, and “Altruistic punishment and cooperation” (p. 1) reports that it occurred frequently. The paper does not establish the cited point for ultimatum or trust games; those examples are not supported by this source. (LLM, conf=0.86)

      Experimental — accuracy not yet measured
    • cites [46] Fehr, E. & Fischbacher, U. The nature of human altruism. Nature 425, 785–791 (2003) source

      The Altruistic punishment section (p. 1) describes people punishing unfair offers in ultimatum games at a cost to themselves, and Strong reciprocity and multilateral cooperation (p. 3) discusses punishment of non-cooperators. But the paper’s discussion of trust games is in Altruistic rewarding (p. 2); it does not establish costly punishment in trust games. The inference about discrimination is the citing authors’ own conclusion. (LLM, conf=0.85)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation
    § Public goods · p. 13

    Observer Tit For Tat relies on reputation in the first round and on personal experience in all further rounds against the same co-player.

    “Observer Tit For Tat relies on reputation in the first round and on personal experience in all further rounds against the same co-player.”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [35] Nowak, M. A. & Sigmund, K. A strategy of win-stay, lose-shift that outperforms tit-for-tat in the prisoner's dilemma game. Nature 364, 56–58 (1993) source
    • cites [68] Güth, W., Königstein, M., Marchand, N. & Nehring, K. Trust and reciprocity in the investment game with indirect reward. Homo Oecon. 18, 241–262 (2001) source

      The Introduction (page unavailable) discusses direct and indirect rewards in investment games, but does not describe an Observer Tit For Tat strategy. Searches for the strategy name and for first-round reputation versus later personal experience found no passage addressing that distinction. (LLM, conf=0.76)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Findingcitation
    § [Figure Box 2a] · p. 15

    SHUNNING emerges as the winner in a computer tournament, if errors in perception are included and if there are only a few rounds in the game.

    “Yet it emerges as the winner in a computer tournament, if errors in perception are included and if there are only a few rounds in the game 56 .”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [56] Brandt, H. & Sigmund, K. Indirect reciprocity, image scoring, and moral hazard. Proc. Natl Acad. Sci. USA 102, 2666–2670 (2005) source

      The Results and Discussion (p. 4) report that, in simulations with errors of perception, a strategy that assigns a Bad score to anyone meeting a Bad coplayer did much better than standing. The passage does not say it won the tournament or that this result depended on there being only a few rounds. (LLM, conf=0.84)

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Box 3: Bidding for trust · p. 16

    Reputation mechanisms have played an important role in the emergence of medieval trade.

    “Reputation mechanisms have also played an important role in the emergence of medieval trade 78 .”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [78] Pfeiffer, T., Rutte, C., Killingback, T., Taborsky, M. & Bonhoeffer, S. Evolution of cooperation by generalized reciprocity. Proc. R. Soc. B 272, 1115–1120 (2005) source

      The Introduction discusses generalized reciprocity and briefly notes related work in economics; the Conclusions and discussion describe simulations of cooperation in small groups. Neither section addresses reputation mechanisms or the emergence of medieval trade (searched: medieval trade, reputation, merchants, and historical trade). (LLM, conf=0.76)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Findingcitation
    § Box 3: Bidding for trust · p. 16

    No player has an incentive to deviate if all other players adopt the label strategy, and the effect of an error will be overcome after T rounds.

    “No player has an incentive to deviate if all other players adopt this strategy, and the effect of an error will be overcome after T rounds.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [27] Rosenthal, R. W. Sequences of games with varying opponents. Econometrica 47, 1353–1366 (1979) source

  • May combine two claims.

    Findingnone given
    § Box 1: The good, the bad and the discriminating · p. 14

    In the case of direct reciprocity, the frequencies oscillate periodically, whereas in the case of indirect reciprocity, they converge to an equilibrium.

    “However, in the case of direct reciprocity, the frequencies oscillate periodically, whereas in the case of indirect reciprocity, they converge to an equilibrium.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingcitation
    § [Figure Box 2b] · p. 16

    Both STANDING and JUDGING belong to the leading eight, but neither SCORING nor SHUNNING.

    “Both STANDING and JUDGING belong to the leading eight, but neither SCORING nor SHUNNING.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [41] Nowak, M. A. & Sigmund, K. The dynamics of indirect reciprocity. J. Theor. Biol. 194, 561–574 (1998) source
    • cites [48] Sugden, R. The Economics of Rights, Cooperation and Welfare (Blackwell, Oxford, 1986)

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Findingcitation
    § Box 4: Games of direct reciprocity · p. 16

    In real Trust Game experiments, many donors transfer substantial amounts, and some obtain large returns, so that both players win.

    “In real experiments, many donors transfer substantial amounts, and some obtain large returns, so that both players win.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [79] Brandt, H. & Sigmund, K. The good, the bad and the discriminator. J. Theor. Biol. (in the press)

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [80] Imhof, L., Fudenberg, D. & Nowak, M. A. Evolutionary cycles of cooperation and defection. Proc. Natl Acad. Sci. USA 102, 10797–10800 (2005) source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingcitation
    § Box 4: Games of direct reciprocity · p. 16

    In real Public Goods experiments, many players contribute.

    “In real experiments, however, many players contribute.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [79] Brandt, H. & Sigmund, K. The good, the bad and the discriminator. J. Theor. Biol. (in the press)

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [80] Imhof, L., Fudenberg, D. & Nowak, M. A. Evolutionary cycles of cooperation and defection. Proc. Natl Acad. Sci. USA 102, 10797–10800 (2005) source

  • May combine two claims.

    Interpretationreasoning
    § Direct versus indirect reciprocity · p. 8

    In both cases (personal and population trigger), a lot of innocents would be punished, and errors cause havoc.

    “In both cases a lot of innocents would be punished, and errors cause havoc.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation
    § Direct versus indirect reciprocity · p. 9

    For direct reciprocity, game theoretical analysis and individual-based simulations have shown that a population of defectors can be invaded by a small cluster of retaliators or even by a single retaliator.

    “For direct reciprocity, game theoretical analysis and individual-based simulations have shown that a population of defectors can be invaded by a small cluster of retaliators 31 or even by a single retaliator 32 .”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [31] Nowak, M. A. & Sigmund, K. Evolutionary dynamics of biological games. Science 303, 793–799 (2004) source
    • cites [32] Nowak, M. A. & Sigmund, K. Tit for tat in heterogeneous populations. Nature 355, 250–253 (1992) source

  • May combine two claims.

    Premisecitation
    § Evolution of indirect reciprocity · p. 7

    Humans display a large amount of cooperation between non-relatives, in contrast to other eusocial species.

    “In contrast to other eusocial species, such as bees, ants or termites, humans display a large amount of cooperation between non-relatives 12-14 .”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [12] Wilson, E. O. Sociobiology (Harvard Univ. Press, Cambridge, Massachusetts, 1975)

      Not checked in the free run.

    • cites [13] Trivers, R. Social Evolution (Benjamin Cummings, Menlo Park, 1985)

      Not checked in the free run.

    • cites [14] Hamilton, W. D. Narrow Roads of Gene Land Vol. 1 (Freeman, New York, 1996) source

  • Classified as probably not a substantial claim.

    Interpretationreasoning
    § Direct versus indirect reciprocity · p. 8

    In the Prisoner's Dilemma, if both players cooperate, each receives b-c, which is better than defecting (0).

    “If both players cooperate, each receives b-c , which is better than what they would obtain by defecting, namely 0.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The cost of an altruistic act is smaller than the benefit.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Evolution of indirect reciprocity · p. 7

    Neuro-economic experiments show that moralistic emotions have a physiological basis.

    “Neuro-economic experiments show that these emotions have a physiological basis 15-17 .”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [15] Sanfey, A. G., Rilling, J. K., Aronson, J. A., Nystrom, L. E. & Cohen, J. D. The neural basis of economic decision-making in the ultimatum game. Science 300, 1755–1758 (2003) source
    • cites [16] Rilling, J. K. et al. A neural basis for social cooperation. Neuron 35, 395–405 (2002) source
    • cites [17] Fehr, E. The neural basis of altruistic punishment. Science 305, 1254–1258 (2004) source

  • Classified as probably not a substantial claim.

    Premisereasoning
    § Evolution of indirect reciprocity · p. 7

    Indirect reciprocity is based on reputation.

    “Indirect reciprocity, in this view, is based on reputation.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Interpretationreasoning
    § Direct versus indirect reciprocity · p. 8

    In the Prisoner's Dilemma, a unilateral defector earns b, the highest payoff, and the exploited co-operator pays cost c without benefit.

    “But a unilateral defector would earn b , which is the highest payoff, and the exploited co-operator would pay the cost c without receiving any benefit.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The cost of an altruistic act is smaller than the benefit.

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing), S4 (based). May combine two claims.

    Interpretationreasoning
    § Evolution of indirect reciprocity · p. 8

    The use of the same terms 'good' and 'bad' for pleasure/pain and moral judgements reveals empathy and reflects highly developed faculties for cognition and abstraction.

    “The same terms 'good' and 'bad' which are applied to pleasure and pain are also used for moral judgements: this linguistic quirk reveals an astonishing degree of empathy, and reflects highly developed faculties for cognition and abstraction.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation
    § Direct versus indirect reciprocity · p. 8

    Game theory shows that even if information is transmitted only locally and errors occur occasionally, cooperation can be sustained: there exist strategies such that no rational player has an interest to deviate unilaterally.

    “Game theory shows that even if information is transmitted only locally and errors occur occasionally, cooperation can be sustained: there exist strategies such that no rational player has an interest to deviate unilaterally 27 .”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [27] Rosenthal, R. W. Sequences of games with varying opponents. Econometrica 47, 1353–1366 (1979) source

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

    Interpretationreasoning
    § Evolution of indirect reciprocity · p. 8

    The step from experiencing good/bad based on own reproductive fitness to judging actions between third parties as good/bad is not obvious.

    “The step from there to judging, as 'good' or 'bad', actions between third parties, is not obvious.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation
    § Evolution of indirect reciprocity · p. 7

    The capacity for moral norms appears to be a human universal for which there is little evidence in other species.

    “but the capacity for moral norms appears to be a human universal for which there is little evidence in other species 19 .”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [19] Brown, D. E. Human Universals (McGraw-Hill, New York, 1991)

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given
    § Evolution of indirect reciprocity · p. 7

    The evolution of cooperation by indirect reciprocity leads to reputation building, morality judgement and complex social interactions with ever increasing cognitive demands.

    “The evolution of cooperation by indirect reciprocity leads to reputation building, morality judgement and complex social interactions with ever increasing cognitive demands.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning
    § Direct versus indirect reciprocity · p. 8

    A trigger strategy based on personal experience hurts the original wrong-doer only after many rounds, and a strategy triggered by the first defection in the population leaves cooperation at the mercy of the first wrong move.

    “But a trigger strategy prescribing each person to cooperate until the first defection is personally experienced, and thenceforth to defect, hurts the original wrong-doer only after many rounds. A strategy triggered by the first defection in the population leaves cooperation at the mercy of the first wrong move.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Direct versus indirect reciprocity · p. 8

    The folk theorem on repeated games states that if the probability for future rounds is sufficiently high, cooperation can be sustained by trigger strategies.

    “The so-called folk theorem on repeated games states that if the probability for future rounds is sufficiently high, cooperation can be sustained by so-called trigger strategies, which switch to relentless defection as soon as the co-player defects once 25 .”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [25] Fudenberg, D. & Maskin, E. The folk theorem in repeated games with discounting or with incomplete information. Econometrica 50, 533–554 (1986) source

  • Classified as probably not a substantial claim.

    Premisecitation
    § Binary assessment, or the world in black and white · p. 10

    A simpler model based on a binary score ('good' or 'bad') was proposed.

    “In order to analyse these questions, an even simpler model was proposed, based on a binary score, taking only the values 'good' or 'bad', depending on what the co-player did when last observed 39-41 .”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [39] Leimar, O. & Hammerstein, P. Evolution of cooperation through indirect reciprocation. Proc. R. Soc. Lond. B 268, 745–753 (2001) source
    • cites [40] Panchanathan, K. & Boyd, R. A tale of two defectors: The importance of standing for evolution of indirect reciprocity. J. Theor. Biol. 224, 115–126 (2003) source
    • cites [41] Nowak, M. A. & Sigmund, K. The dynamics of indirect reciprocity. J. Theor. Biol. 194, 561–574 (1998) source

  • May combine two claims.

    Interpretationcitation
    § Binary assessment, or the world in black and white · p. 10

    Such altruistic punishment is good for the community but costly for the punisher, and thus can be viewed as a social dilemma.

    “Such a form of altruistic punishment is good for the community, but costly for the punisher, and thus can be viewed as a social dilemma 42 .”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [42] Ohtsuki, H. & Iwasa, Y. How should we define goodness? Reputation dynamics in indirect reciprocity. J. Theor. Biol. 231, 107–120 (2004) source

  • May combine two claims.

    Premisecitation
    § Binary assessment, or the world in black and white · p. 10

    If the discriminating strategy distinguishes between justified and unjustified defection, the population can converge to discriminators only, which cannot be invaded by unconditional strategies.

    “Alternatively, if the discriminating strategy distinguishes between justified and unjustified defection, the population can converge to discriminators only, which cannot be invaded by unconditional strategies 39 .”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [39] Leimar, O. & Hammerstein, P. Evolution of cooperation through indirect reciprocation. Proc. R. Soc. Lond. B 268, 745–753 (2001) source

  • May combine two claims.

    Premisecitation
    § Binary assessment, or the world in black and white · p. 10

    In this scenario (occasional failure), a population consisting only of conditional and unconditional altruists is not subject to random drift, but selection leads to a well defined, stable mix of the two types.

    “In this scenario, a population consisting only of conditional and unconditional altruists is not subject to random drift, but selection leads to a well defined, stable mix of the two types.”
    Quote in the paperSubstantial claim0 of 5 sources checked
    • cites [39] Leimar, O. & Hammerstein, P. Evolution of cooperation through indirect reciprocation. Proc. R. Soc. Lond. B 268, 745–753 (2001) source
    • cites [49] Ohtsuki, H. & Iwasa, Y. The leading eight: social norms that can maintain cooperation by indirect reciprocity. J. Theor. Biol.(in the press) source
    • cites [50] Lotem, A., Fishman, M. A. & Stone, L. Evolution of cooperation between individuals. Nature 400, 226–227 (1999) source
    • cites [51] Lotem, A., Fishman, M. A. & Stone, L. Evolution of unconditional altruism through signalling benefits. Proc. R. Soc. Lond. B 270, 199–205 (2002) source
    • cites [52] Fishman, M. A., Lotem, A. & Stone, L. Heterogeneity stabilises reciprocal altruism interaction. J. Theor. Biol. 209, 87–95 (2001) source

  • May combine two claims.

    Interpretationreasoning
    § Binary assessment, or the world in black and white · p. 10

    A discriminating donor using first-order assessment refuses help to a 'bad' recipient, and therefore becomes 'bad', which reduces the chance of being helped in turn.

    “A discriminating donor using this assessment rule refuses help to a 'bad' recipient, and therefore becomes 'bad', which reduces the chance of being helped in turn.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

    Interpretationnone given
    § Binary assessment, or the world in black and white · p. 10

    This binary score model can be viewed as a basic system of moral assessment.

    “This can be viewed as a basic system of moral assessment.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning
    § Binary assessment, or the world in black and white · p. 10

    Both the lack of information and the prevalence of unconditional altruists may stabilise cooperation.

    “Therefore, both the lack of information and the prevalence of unconditional altruists may, surprisingly, stabilise cooperation.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning
    § Binary assessment, or the world in black and white · p. 10

    Punishing a player with a bad score creates another player with a bad score; this 'passing the buck along' can stop by encountering either a discriminator who is uninformed, or an undiscriminating altruist.

    “Punishing a player with a bad score creates another player with a bad score; but this 'passing the buck along' can stop in two ways, by encountering either a discriminator who is uninformed, or an undiscriminating altruist.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation
    § Binary assessment, or the world in black and white · p. 10

    In a population consisting entirely of discriminators, undiscriminating co-operators fare just as well and thus spread by neutral drift.

    “In a population consisting entirely of discriminators, undiscriminating co-operators fare just as well and thus spread by neutral drift.”
    Quote in the paperSubstantial claim0 of 5 sources checked
    • cites [39] Leimar, O. & Hammerstein, P. Evolution of cooperation through indirect reciprocation. Proc. R. Soc. Lond. B 268, 745–753 (2001) source
    • cites [49] Ohtsuki, H. & Iwasa, Y. The leading eight: social norms that can maintain cooperation by indirect reciprocity. J. Theor. Biol.(in the press) source
    • cites [50] Lotem, A., Fishman, M. A. & Stone, L. Evolution of cooperation between individuals. Nature 400, 226–227 (1999) source
    • cites [51] Lotem, A., Fishman, M. A. & Stone, L. Evolution of unconditional altruism through signalling benefits. Proc. R. Soc. Lond. B 270, 199–205 (2002) source
    • cites [52] Fishman, M. A., Lotem, A. & Stone, L. Heterogeneity stabilises reciprocal altruism interaction. J. Theor. Biol. 209, 87–95 (2001) source

  • May combine two claims.

    Premisecitation
    § Binary assessment, or the world in black and white · p. 10

    Various assumptions on the distribution of the number of rounds lead to a bi-stable system, where depending on the initial state, the population converges either to the fixation of defectors, or to a stable mix of altruists which cannot be invaded by defectors.

    “Various assumptions on the distribution of the number of rounds lead to a bi-stable system, where depending on the initial state, the population converges either to the fixation of defectors, or to a stable mix of altruists which cannot be invaded by defectors 52,53 .”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [52] Fishman, M. A., Lotem, A. & Stone, L. Heterogeneity stabilises reciprocal altruism interaction. J. Theor. Biol. 209, 87–95 (2001) source
    • cites [53] Fishman, M. A. Indirect reciprocity among imperfect individuals. J. Theor. Biol. 225, 285–292 (2003) source

  • May combine two claims.

    Premisecitation
    § Binary assessment, or the world in black and white · p. 10

    Only eight assessment rules of second and third order lead to cooperation and are evolutionarily stable.

    “Only eight of them lead to cooperation and, at the same time, are evolutionarily stable: a homogeneous population of players using such a strategy cannot be invaded by players using other strategies 41 .”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [41] Nowak, M. A. & Sigmund, K. The dynamics of indirect reciprocity. J. Theor. Biol. 194, 561–574 (1998) source

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing), S4 (based). May combine two claims.

    Interpretationnone given
    § Costly experiments · p. 12

    More generally, it seems that decisions often depend on both the donor's payoff and the recipient's score, but such strategies have not been analysed so far.

    “More generally, it seems that decisions often depend on both the donor's payoff and the recipient's score, but such strategies have not been analysed so far.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning
    § Public goods · p. 13

    Indirect reciprocity is situated somewhere between direct reciprocity and public goods.

    “Indirect reciprocity is situated somewhere between direct reciprocity and public goods.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Public goods · p. 13

    The widespread tendency to judge actions between third parties, and the readiness for cooperation combined with altruistic punishment (strong reciprocity) has been neatly captured in an experiment involving three players.

    “The widespread tendency to judge actions between third parties, and the readiness for cooperation combined with altruistic punishment (also known as strong reciprocity 69 ) has been neatly captured in an experiment involving three players 70,71 .”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [69] Pollock, G. B. & Dugatkin, L. A. Reciprocity and the evolution of reputation. J. Theor. Biol. 159, 25–37 (1992) source
    • cites [70] Gintis, H. Game Theory Evolving: A Problem-Centered Introduction to Modeling Stategic Interaction (Princeton Univ. Press, Princeton, 2000)
    • cites [71] Fehr, E. & Fischbacher, U. Social norms and human cooperation. Trends Cogn. Sci. 8, 185–190 (2004) source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning
    § Costly experiments · p. 11

    In the basic experimental setup for testing indirect reciprocity, players usually do not interact face-to-face, but are given some information about the past actions of their potential recipients, in order to eliminate confounding effects.

    “In order to eliminate confounding effects, players usually do not interact face-to-face, but they are given some information about the past actions of their potential recipients.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

    Interpretationnone given
    § Binary assessment, or the world in black and white · p. 11

    Gossip might be a way of achieving consensus, but can also be used for spreading false rumours and manipulating co-players.

    “Gossip might be a way of achieving consensus, but can also be used for spreading false rumours and manipulating co-players.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given
    § Costly experiments · p. 12

    Many experiments have shown that players who have just received a donation are more likely to give a donation in turn.

    “Many experiments have shown that players who have just received a donation are more likely to give a donation in turn.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductreasoning
    § Costly experiments · p. 11

    In the basic experimental setup, players know that their recipients will never be their donors on future occasions, and thus that there is no scope for direct reciprocity.

    “They know that their recipients will never be their donors on future occasions, and thus that there is no scope for direct reciprocity.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Public goods · p. 13

    Richard Alexander claimed that indirect reciprocity originates from direct reciprocity in the presence of interested audiences.

    “Richard Alexander claimed that indirect reciprocity originates from direct reciprocity in the presence of interested audiences 2 .”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [2] Alexander, R. D. The Biology of Moral Systems (Aldine de Gruyter, New York, 1987)

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning
    § Costly experiments · p. 12

    This indicates that they expect their refusal to lower their score in the co-players' eyes, and that they do not rely on the community's understanding.

    “This indicates that they expect their refusal to lower their score in the co-players' eyes, and that they do not rely on the community's understanding.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisenone given
    § Costly experiments · p. 12

    In this series of experiments, there is a significant positive correlation between the number of gifts given and received, but a slightly negative correlation between the number of gifts given and the total payoff obtained.

    “In this series of experiments, there is a significant positive correlation between the number of gifts given and received, but a slightly negative correlation between the number of gifts given and the total payoff obtained.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation
    § Costly experiments · p. 12

    Often there is evidence for a dual motivation: players give donations if the recipient's score is high or their own score is low.

    “Often there is evidence for a dual motivation players give donations if the recipient's score is high or their own score is low 35 .”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [35] Nowak, M. A. & Sigmund, K. A strategy of win-stay, lose-shift that outperforms tit-for-tat in the prisoner's dilemma game. Nature 364, 56–58 (1993) source

  • May combine two claims.

    Premisenone given
    § Costly experiments · p. 11

    Donations occur more frequently if the cost-to-benefit ratio is lower, or the starting account higher.

    “As expected, donations occur more frequently if the cost-to-benefit ratio is lower, or the starting account higher.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationnone given
    § Binary assessment, or the world in black and white · p. 11

    In small populations, random drift can strongly affect evolution.

    “In such small populations, random drift can strongly affect evolution.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Interpretationreasoning
    § Costly experiments · p. 12

    The discrepancy could be due to the larger number of rounds or to the fact that players were informed not only about the recipients' last move but their whole history of giving.

    “The discrepancy could be due to the larger number of rounds - the advantage showed up only after a dozen of rounds - or to the fact that players were informed not only about the recipients' last move but their whole history of giving.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning
    § Costly experiments · p. 11

    In the basic experimental setup, interactions both with co-players and with experimenters are kept as anonymous as possible, usually under double-blind conditions.

    “The interactions both with the co-players and with the experimenters are kept as anonymous as possible, usually under double-blind conditions.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation
    § Costly experiments · p. 12

    Players faced with a full history of all previous rounds take in general a longer time to reach their decision, suggesting that they attempt to take into account, not only their recipient's last move, but also that of their recipient's recipient.

    “Players faced with a full history of all previous rounds take in general a longer time to reach their decision, suggesting that they attempt to take into account, not only their recipient's last move, but also that of their recipient's recipient.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [64] Engelmann, D. & Fischbacher, U. Indirect reciprocity and strategic reputation building in an experimental helping game. Univ. Zürich working paper no. 132 http://www.iew.unizh.ch/wp/iewwp132.pdf (2002). source

  • May combine two claims.

    Premisecitation
    § Costly experiments · p. 12

    There is evidence for 'upstream' indirect reciprocity in cyclical networks: short loops and a high benefit-to-cost ratio favour cooperation.

    “There is evidence for 'upstream' indirect reciprocity in cyclical networks: as expected, short loops and a high benefit-to-cost ratio favour cooperation 65 .”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [65] Milinski, M., Semmann, D., Bakker, T. C. M. & Krambeck, H. J. Cooperation through indirect reciprocity: Image scoring or standing strategy? Proc. R. Soc. Lond. B 268, 2495–2501 (2001) source

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Interpretationcitation
    § Binary assessment, or the world in black and white · p. 11

    It could be that co-operators fare less well than defectors within each group, but that groups of co-operators fare better than groups of defectors.

    “It could be that co-operators fare less well than defectors within each group, but that groups of co-operators fare better than groups of defectors 57 .”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [57] Takahashi, N. & Mashima, R. The emergence of indirect reciprocity: Is the standing strategy the answer? Hokkaido Univ. working paper no. 29 http://lynx.let.hokudai.ac.jp/COE21/pdf/029.zip (2003).

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Interpretationnone given
    § Public goods · p. 13

    Indirect reciprocity is a game between two players only, the donor and the recipient, but it has to be played within a larger group.

    “On one hand, it is a game between two players only, the donor and the recipient, but on the other hand it has to be played within a larger group.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationnone given
    § [Figure Box 2b] · p. 16

    Both SCORING and Tit-for-tat are not evolutionary stable, but their ability to catalyze cooperation in adverse scenarios and their simplicity constitute their strength.

    “Both strategies are not evolutionary stable, but their ability to catalyze cooperation in adverse scenarios and their simplicity constitute their strength.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given
    § Box 2: Let a thousand morals bloom · p. 15

    There are 16 second order assessment rules.

    “There are 16 second order rules.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Premisenone given
    § Box 3: Bidding for trust · p. 16

    In the Trust Game, donors who trust their responder will expect to gain from transferring money.

    “In the Trust Game, donors who trust their responder will expect to gain from transferring money.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationnone given
    § [Figure Box 2b] · p. 16

    SCORING is expected to play a similar role in indirect reciprocity as Tit-for-tat in direct reciprocity.

    “We expect, however, that SCORING plays a similar role in indirect reciprocity as Tit-for-tat in direct reciprocity.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationnone given
    § Box 1: The good, the bad and the discriminating · p. 14

    In each case, there are many other discriminating strategies, which are likely to take over eventually.

    “In each case, there are many other discriminating strategies, which are likely to take over eventually.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisereasoning
    § [Figure Box 2b] · p. 15

    There are 2^3 = 8 different assessment rules.

    “Hence, there are 2 3 =8 different assessment rules.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S2 (checkable), S4 (based).

    Interpretationreasoning
    § Cerebral expansion · p. 14

    It is very likely that games of indirect reciprocity provided the selective scenario that led to cerebral expansion in human evolution.

    “It is very likely that games of indirect reciprocity provided the selective scenario that led to cerebral expansion in human evolution.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Premisenone given
    § Box 4: Games of direct reciprocity · p. 16

    A responder with an income-maximising strategy should send nothing back in the Trust Game.

    “A responder with an income-maximising strategy should send nothing back.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning
    § Box 4: Games of direct reciprocity · p. 16

    Any donor expecting this should therefore transfer nothing.

    “Any donor expecting this should therefore transfer nothing.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Box 3: Bidding for trust · p. 16

    Trust plays an essential part in many types of economic transactions.

    “Trust, 'a lubricant of social life' 77 , plays an essential part in many types of economic transactions.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [77] Boyd, R. & Richerson, P. J. The evolution of indirect reciprocity. Soc. Networks 11, 213–236 (1989) source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisereasoning
    § Box 4: Games of direct reciprocity · p. 16

    If all players contribute, they multiply their endowment by the factor r.

    “If all do, they multiply their endowment by the factor r.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationreasoning
    § Cerebral expansion · p. 14

    Indirect reciprocity based on reputation serves as a link between diverse forms of cooperative interaction.

    “Indirect reciprocity based on reputation serves as a link between diverse forms of cooperative interaction.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisenone given
    § Box 3: Bidding for trust · p. 16

    In the Indirect Reciprocity game, donors know that they can expect no direct return, even if their recipient is trustworthy.

    “In contrast, donors in the Indirect Reciprocity game know that they can expect no direct return, even if their recipient is trustworthy.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationnone given
    § Cerebral expansion · p. 14

    The reputation of players may be determined not only by their own actions but also by their associations with others.

    “The reputation of players may not only be determined by their own actions, but also by their associations with others.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given
    § [Figure Box 2a] · p. 15

    There are 16 action rules.

    “There are 16 action rules.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisenone given
    § Box 2: Let a thousand morals bloom · p. 15

    In a world of binary moral judgements, there are four ways of assessing donors in terms of first order assessment: always consider them as good, always consider them as bad, consider them as good if they refuse to give, or consider them as good if they give.

    “In a world of binary moral judgements, there are four ways of assessing donors in terms of 'first order assessment': always consider them as good, always consider them as bad, consider them as good if they refuse to give, or consider them as good if they give.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisereasoning
    § [Figure Box 2a] · p. 15

    If a strategy is viewed as the combination of an action rule and an assessment rule, there are 4096 strategies.

    “If we view a strategy as the combination of an action rule and an assessment rule, we obtain 4096 strategies.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationnone given
    § [Figure Box 2b] · p. 16

    In extended versions of indirect reciprocity, where donors can sometimes deceive others about the reputation of the recipient, SCORING is the 'fool-proof' concept of 'I believe what I see'.

    “In extended versions of indirect reciprocity, where donors can sometimes deceive others about the reputation of the recipient, SCORING is the 'fool-proof' concept of 'I believe what I see'.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationnone given
    § Cerebral expansion · p. 14

    In human evolution, there was a tendency from the simple cooperation promoted by kin or group selection to the strategic subtleties of direct and indirect reciprocity.

    “In human evolution, there was a tendency from the simple cooperation promoted by kin or group selection to the strategic subtleties of direct and indirect reciprocity.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Premisenone given
    § Box 2: Let a thousand morals bloom · p. 15

    There are 256 third order assessment rules.

    “There are 256 third order assessment rules.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisenone given
    § [Figure Box 2b] · p. 16

    SCORING judges the action and ignores the stories.

    “SCORING judges the action and ignores the stories.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Premisenone given
    § Cerebral expansion · p. 14

    Indirect reciprocity requires monitoring interactions among other people, possibly judging intentions in such interactions, and keeping up with the ever changing social network of the group.

    “Indirect reciprocity, in addition, has to monitor interactions among other people, possibly judge the intentions that occur in such interactions, and keep up with the ever changing social network of the group.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning
    § Public goods · p. 13

    The donations in the indirect reciprocity game, which are channelled towards those who contributed much to the public goods, can be viewed as rewards.

    “The donations in the indirect reciprocity game, which are channelled towards those who contributed much to the public goods, can be viewed as rewards.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisenone given
    § Public goods · p. 13

    Many players show an initial willingness to contribute to the public goods a substantial amount of their endowment, but this willingness often vanishes within a few rounds.

    “It is known that many players show an initial willingness to contribute to the public goods a substantial amount of their endowment, but this willingness often vanishes within a few rounds.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisereasoning
    § Box 4: Games of direct reciprocity · p. 16

    Since each player receives only the fraction r/N in return for their own contribution, the income-maximising strategy in the Public Goods game is to contribute nothing.

    “Since each player receives, in return for the own contribution, only the fraction r/N , the incomemaximising strategy is to contribute nothing.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationnone given
    § Box 3: Bidding for trust · p. 16

    Settling on this strategy, for instance on the specific number T, seems to require an institution able to guarantee honest labelling.

    “But settling on this strategy, for instance, on the specific number T, seems to require an institution able to guarantee honest labelling.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Interpretationreasoning
    § Cerebral expansion · p. 14

    Moralistic assessment of other members in the population, even if they are only observed at a distance, provides a powerful tool for channelling support toward those who collaborate, and thus an incentive to join group efforts.

    “The moralistic assessment of the other members in the population, even if they are only observed at a distance, provides a powerful tool for channelling support toward those who collaborate, and thus an incentive to join group efforts.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

    Interpretationnone given
    § Box 3: Bidding for trust · p. 16

    This very crude form of assessment seems to suffice for the purpose of reputation-building, and seems to be reasonably proof against manipulation.

    “This very crude form of assessment seems to suffice for the purpose of reputation-building, and seems to be reasonably proof against manipulation.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Interpretationreasoning
    § Box 3: Bidding for trust · p. 16

    In the Indirect Reciprocity game, all a donor can gain from the transfer is an increased reputation for altruism and trustworthiness.

    “All they can gain from the transfer is an increased reputation for altruism and trustworthiness.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

    Premisenone given
    § Cerebral expansion · p. 14

    Direct reciprocity requires precise recognition of individual people, a memory of past interactions with them, and enough brain to conduct multiple repeated games simultaneously.

    “Direct reciprocity requires precise recognition of individual people, a memory of the various interactions one had with them in the past, and enough brain to conduct multiple repeated games simultaneously.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Premisenone given
    § Figure legends · p. 22

    Helping another individual is costly but buys the reputation of being helpful.

    “Helping another individual is costly but buys the reputation of being helpful.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Box 6: Social viscosity · p. 17

    Altruism toward genetic relatives can evolve by kin selection provided Hamilton's rule holds: the coefficient of relatedness r between donor and recipient must exceed the cost-to-benefit ratio of the altruistic act.

    “Altruism toward genetic relatives can evolve by kin selection provided Hamilton's rule 14 holds: the coefficient of relatedness, r , between the donor and the recipient has to exceed the cost to benefit ratio of the altruistic act,”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [14] Hamilton, W. D. Narrow Roads of Gene Land Vol. 1 (Freeman, New York, 1996) source

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing). May combine two claims.

    Interpretationreasoning
    § Figure legends · p. 22

    While language might help to compare and synchronize private reputation lists, ultimately reputation is in the eyes of the beholder.

    “While language might help to compare and synchronize these lists 41 , ultimately reputation is in the eyes of the beholder.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [41] Nowak, M. A. & Sigmund, K. The dynamics of indirect reciprocity. J. Theor. Biol. 194, 561–574 (1998) source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationnone given
    § Box 6: Social viscosity · p. 17

    Kin selection works in 'viscous' populations where chances are high that neighbours are genetic relatives.

    “Kin selection works in 'viscous' populations where chances are high that neighbours are genetic relatives.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisenone given
    § Figure legends · p. 22

    The observers, the donor and the recipient can inform others about what has happened.

    “The observers, the donor and the recipient can inform others about what has happened.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisenone given
    § Figure legends · p. 22

    Indirect reciprocity is built on reputation.

    “Indirect reciprocity, in contrast, is built on reputation.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Premisereasoning
    § Box 4: Games of direct reciprocity · p. 17

    The Public Goods game for N=2 players has the structure of a Prisoner's Dilemma.

    “The Public Goods game for N =2 players has the structure of a Prisoner's Dilemma.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisenone given
    § Box 4: Games of direct reciprocity · p. 17

    Two players who cooperate earn more than two players who defect; a defector cheating on a cooperator earns the highest payoff, and the exploited cooperator earns the lowest.

    “Two players who cooperate earn more than two players who defect; but a defector cheating on a cooperator earns the highest payoff, and the exploited cooperator earns the lowest.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Premisenone given
    § Figure legends · p. 22

    Direct reciprocity is captured in the framework of the repeated Prisoner's Dilemma.

    “Direct reciprocity is captured in the framework of the repeated Prisoner's Dilemma.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given
    § Box 5: Upstream and downstream · p. 17

    An individual who has been at the receiving end of a donation may feel motivated to donate in turn.

    “An individual who has been at the receiving end of a donation may feel motivated to donate in turn.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given
    § Box 5: Upstream and downstream · p. 17

    An entirely different approach to indirect reciprocity is based not on the reputation of the recipient but on the experience of the donor.

    “An entirely different approach to indirect reciprocity is based, not on the reputation of the recipient, but on the experience of the donor.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Premisenone given
    § Box 4: Games of direct reciprocity · p. 17

    If two players in a trust game are simultaneously in the role of the donor and then simultaneously in the role of the responder, they play two rounds of a Prisoner's Dilemma.

    “If two players, in a trust game, are simultaneously in the role of the donor, and then simultaneously in the role of the responder, they play two rounds of a Prisoner's Dilemma.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisecitation
    § Figure legends · p. 22

    In a natural extension of the basic model of indirect reciprocity, an action between a donor and a recipient is observed by a subset of the population.

    “In a natural extension of the basic model of indirect reciprocity, an action between a donor, A, and a recipient, B, is observed by a subset of the population 35 .”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [35] Nowak, M. A. & Sigmund, K. A strategy of win-stay, lose-shift that outperforms tit-for-tat in the prisoner's dilemma game. Nature 364, 56–58 (1993) source

  • May combine two claims.

    Interpretationreasoning
    § Figure legends · p. 22

    Therefore, the reputation of a person is not simply a label visible to all others; instead each person has a private list of the reputation of others.

    “Therefore, the reputation of a person is not simply a label that is visible to all others, but instead each person has a private list of the reputation of others.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisenone given
    § Figure legends · p. 22

    There are many possibilities of error in indirect reciprocity: the action or intention of the donor can be interpreted differently by different people, some individuals may receive conflicting information, and some may receive no information at all.

    “There are many possibilities of error: the action or the intention of the donor can interpreted differently by different people, some individuals may receive conflicting information from different sources, some individuals may not receive any information at all.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

    Premisenone given
    § Box 6: Social viscosity · p. 17

    The probability that brothers share a 'selfish gene' is 1/2; the same probability for cousins is 1/8.

    “The probability that brothers share a 'selfish gene' is ½; the same probability for cousins is 1/8.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationnone given
    § Box 5: Upstream and downstream · p. 17

    In both upstream and downstream reciprocity, the decision to give help can be interpreted as a misdirected act of gratitude.

    “In both cases, the decision to give help can be interpreted as a misdirected act of gratitude.”
    Quote in the paperNot a substantial claim
101 of 101

  • The paper relies on this without support.

    Natural selection favours selfish individuals who maximize their own resources at the expense of others.

    “Natural selection favours the strong and selfish who maximize their own resources at the expense of others.”

  • The paper relies on this without support.

    Many biological systems, and especially human societies, are organized around altruistic, cooperative interactions.

    “But many biological systems, and especially human societies, are organized around altruistic, cooperative interactions.”

  • The authors state this as an assumption.

    The cost of an altruistic act is smaller than the benefit.

    “We shall always assume that the cost is smaller than the benefit, so that if the act is returned, both individuals experience a gain.”

  • The authors state this as an assumption.

    In each round both players decide simultaneously.

    “For simplicity, we shall assume that in each round both players decide simultaneously.”

  • The authors state this as an assumption.

    In indirect reciprocity, any two players interact at most once with each other.

    “In the context of indirect reciprocity, any two players are supposed to interact at most once with each other.”

  • The authors state this as an assumption.

    Each player can experience many rounds, but never with the same partner twice.

    “Each player can experience many rounds, but never with the same partner twice.”

  • The authors state this as an assumption.

    In the indirect reciprocity model, within a well-mixed population, individuals meet randomly, one as donor, one as recipient.

    “A similar model of indirect reciprocity assumes that within a well-mixed population, individuals meet randomly, one in the role of the potential donor, the other as potential recipient (Fig 2).”

  • The authors state this as an assumption.

    Each individual experiences several rounds of this interaction in both roles, but never with the same partner twice.

    “Each individual experiences several rounds of this interaction in both roles, but never with the same partner twice.”

  • The authors state this as an assumption.

    All that counts is the total payoff.

    “Again, all that counts is the total payoff.”

  • The authors state this as an assumption.

    Typically, one considers a well-mixed population where individuals meet randomly and play a series of Prisoner's Dilemma games with each other.

    “Typically, one considers a well-mixed population where individuals meet randomly and play a series of Prisoner's Dilemma games with each other.”

  • The authors state this as an assumption.

    What counts is the total payoff.

    “What counts is the total payoff.”

  • The authors state this as an assumption.

    In the binary score model, a player's score is 0 at birth, increases whenever that player helps and decreases whenever the player withholds help.

    “A player's score is 0 at birth, increases whenever that player helps and decreases whenever the player withholds help.”
12 of 12

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Cites

Flagged first, then by citations

Research works printed but not linked: 6

  1. Wilson, E. O. Sociobiology (Harvard Univ. Press, Cambridge, Massachusetts, 1975)
  2. Trivers, R. Social Evolution (Benjamin Cummings, Menlo Park, 1985)
  3. Brown, D. E. Human Universals (McGraw-Hill, New York, 1991)
  4. Sugden, R. The Economics of Rights, Cooperation and Welfare (Blackwell, Oxford, 1986)
  5. Dufwenberg, M., Gneezy, U., Güth, W. & van Damme, E. Direct vs indirect reciprocity: An experiment. Homo Oecon. 18, 19–30 (2001)
  6. Brandt, H. & Sigmund, K. The good, the bad and the discriminator. J. Theor. Biol. (in the press)

Cited by

Sorted by citations

Related

Authors
Nowak, M. A., & Sigmund, K.
Affiliations
  • Harvard University (US)
  • University of Vienna (AT)
Corresponding author
Sigmund, Karl
ORCID
Venue
Nature
Publisher
Springer Science and Business Media LLC
Published
2005-10
Volume
437
Issue
7063
Pages
1291-1298
ISSN
  • 0028-0836 (ISSN-L)
  • 1476-4687
DOI
10.1038/nature04131
OpenAlex
W2157592153
Semantic Scholar
9f4a89877e0d7513834801bfe2c71823632d213f
Cited by
2,762
References
90
Citations by year
2026: 137 · 2025: 151 · 2024: 162 · 2023: 170 · 2022: 126 · 2021: 170 · 2020: 159 · 2019: 135 · 2018: 158 · 2017: 120 · 2016: 166 · 2015: 130 · 2014: 142 · 2013: 132 · 2012: 140
FWCI
224.45
Type
journal article
Language
en
Open access
Licence
www.springer.com/tdm (tdm)
Locations
  • Nature (publishedVersion)
  • PubMed (publishedVersion)
  • IIASA PURE (International Institute of Applied Systems Analysis) (submittedVersion)
  • RePEc: Research Papers in Economics (submittedVersion)
Funders
  • John Templeton Foundation
  • Harvard University
Topics
  • Social Sciences › Sociology and Political Science › Evolutionary Game Theory and Cooperation
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Evolutionary Psychology and Human Behavior
  • Life Sciences › Agricultural and Biological Sciences › Ecology, Evolution, Behavior and Systematics › Animal Behavior and Reproduction
Keywords
indirect reciprocity, evolution of cooperation, altruism, reputation, morality, social evolution, natural selection, human social behavior
MeSH terms
Altruism, Cooperative Behavior, Biological Evolution, Humans, Models, Biological, Morals, Trust

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-23.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-23.

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