33,168 research outputs found
Stability of cooperation under image scoring in group interactions
Image scoring sustains cooperation in the repeated two-player prisoner's
dilemma through indirect reciprocity, even though defection is the uniquely
dominant selfish behaviour in the one-shot game. Many real-world dilemma
situations, however, firstly, take place in groups and, secondly, lack the
necessary transparency to inform subjects reliably of others' individual past
actions. Instead, there is revelation of information regarding groups, which
allows for `group scoring' but not for image scoring. Here, we study how
sensitive the positive results related to image scoring are to information
based on group scoring. We combine analytic results and computer simulations to
specify the conditions for the emergence of cooperation. We show that under
pure group scoring, that is, under the complete absence of image-scoring
information, cooperation is unsustainable. Away from this extreme case,
however, the necessary degree of image scoring relative to group scoring
depends on the population size and is generally very small. We thus conclude
that the positive results based on image scoring apply to a much broader range
of informational settings that are relevant in the real world than previously
assumed.Comment: 6 two-column pages, 4 figures; accepted for publication in Scientific
Report
Groupwise information sharing promotes ingroup favoritism in indirect reciprocity
Indirect reciprocity is a mechanism for cooperation in social dilemma
situations, in which an individual is motivated to help another to acquire a
good reputation and receive help from others afterwards. Ingroup favoritism is
another aspect of human cooperation, whereby individuals help members in their
own group more often than those in other groups. Ingroup favoritism is a puzzle
for the theory of cooperation because it is not easily evolutionarily stable.
In the context of indirect reciprocity, ingroup favoritism has been shown to be
a consequence of employing a double standard when assigning reputations to
ingroup and outgroup members; e.g., helping an ingroup member is regarded as
good, whereas the same action toward an outgroup member is regarded as bad. We
analyze a model of indirect reciprocity in which information sharing is
conducted groupwise. In our model, individuals play social dilemma games within
and across groups, and the information about their reputations is shared within
each group. We show that evolutionarily stable ingroup favoritism emerges even
if all the players use the same reputation assignment rule regardless of group
(i.e., a single standard). Two reputation assignment rules called simple
standing and stern judging yield ingroup favoritism. Stern judging induces much
stronger ingroup favoritism than does simple standing. Simple standing and
stern judging are evolutionarily stable against each other when groups
employing different assignment rules compete and the number of groups is
sufficiently large. In addition, we analytically show as a limiting case that
homogeneous populations of reciprocators that use reputations are unstable when
individuals independently infer reputations of individuals, which is consistent
with previously reported numerical results.Comment: 25 pages, 7 figures. The Abstract is shortened to fill in arXiv's
abstract for
Emergence of social networks via direct and indirect reciprocity
Many models of social network formation implicitly assume that network properties are static in steady-state. In contrast, actual social networks are highly dynamic: allegiances and collaborations expire and may or may not be renewed at a later date. Moreover, empirical studies show that human social networks are dynamic at the individual level but static at the global level: individuals' degree rankings change considerably over time, whereas network-level metrics such as network diameter and clustering coefficient are relatively stable. There have been some attempts to explain these properties of empirical social networks using agent-based models in which agents play social dilemma games with their immediate neighbours, but can also manipulate their network connections to
strategic advantage. However, such models cannot straightforwardly account for reciprocal behaviour based on reputation scores ("indirect reciprocity"), which is known to play an important role in many economic interactions. In
order to account for indirect reciprocity, we model the network in a bottom-up fashion: the network emerges from the low-level interactions between agents. By so doing we are able to simultaneously account for the effect of both direct reciprocity (e.g. "tit-for-tat") as well as indirect
reciprocity (helping strangers in order to increase one's reputation). This leads to a strategic equilibrium in the frequencies with which strategies are adopted in the population as a whole, but intermittent cycling over different strategies at the level of individual agents, which in turn gives rise to social networks which
are dynamic at the individual level but stable at the network level
On the stability of cooperation under indirect reciprocity with first-order information
Indirect reciprocity describes a class of reputation-based mechanisms which
may explain the prevalence of cooperation in large groups where partners meet only once.
The first model for which this has been demonstrated was the image scoring mechanism.
But analytical work on the simplest possible case, the binary scoring model, has shown
that even small errors in implementation destabilize any cooperative regime. It has
thus been claimed that for indirect reciprocity to stabilize cooperation, assessments of
reputation must be based on higher-order information. Is indirect reciprocity relying
on frst-order information doomed to fail? We use a simple analytical model of image
scoring to show that this need not be the case. Indeed, in the general image scoring
model the introduction of implementation errors has just the opposite effect as in the
binary scoring model: it may stabilize instead of destabilize cooperation
Local reputation, local selection, and the leading eight norms
Humans are capable of solving cooperation problems following social norms. Social norms dictate appropriate behaviour and judgement on others in response to their previous actions and reputation. Recently, the so-called leading eight norms have been identified from many potential social norms that can sustain cooperation through a reputation-based indirect reciprocity mechanism. Despite indirect reciprocity being claimed to extend direct reciprocity in larger populations where direct experiences cannot be accumulated, the success of social norms have been analysed in models with global information and evolution. This study is the first to analyse the leading eight norms with local information and evolution. We find that the leading eight are robust against selfish players within most scenarios and can maintain a high level of cooperation also with local information and evolution. In fact, local evolution sustains cooperation under a wider set of conditions than global evolution, while local reputation does not hinder cooperation compared to global reputation. Four of the leading eight norms that do not reward justified defection offer better chances for cooperation with quick evolution, reputation with noise, larger networks, and when unconditional defectors enter the population
Understanding reciprocity
This paper surveys the evolutionary game theoretic literature on reciprocity in human interactions, dealing both with long-term relationships and with sporadic interactions. Four basic themes, repetition, commitment, assortation, and parochialism, appear repeatedly throughout the literature. Repetition can give rise to the evolution of behavior that exhibits reciprocity-like features but a vast array of other behaviors are also stable. In sporadic interactions, reciprocity can be stable if the propensity to punish selfish actions can induce opportunists to cooperate, if reciprocators themselves behave opportunistically when they expect others to do so, or if matching is sufficiently assortative.Reciprocity, Evolution, Assortation, Commitment, Parochialism
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