Helping, i.e. behaviour increasing the fitness of others, can evolve when directed towards kin or reciprocating partners. These predictions have been tested in the context of food sharing both in human foragers and non-human primates. Here, we performed quantitative meta-analyses on 32 independent study populations to (i) test for overall effects of reciprocity on food sharing while controlling...

Reciprocal Altruism or reciprocity occurs when an individual performs a costly act for the benefit of another individual in anticipation of receiving beneficence via a costly act in return (Trivers 1971, Connor 1986, Rothstein and Pierotti 1988). Thus the key defining feature of reciprocity is that in any given exchange an individual would do better by, in the absence of punishment, not recipro...

The character associated to a quadratic extension field K of Q, χ : Z −→ C, χ(n) = (disc(K)/n) (Jacobi symbol), is in fact a Dirichlet character; specifically its conductor is |disc(K)|. This fact encodes basic quadratic reciprocity from elementary number theory, phrasing it in terms that presage class field theory. This writeup discusses Hilbert quadratic reciprocity in the same spirit. Let k ...

Lately, there has been an increased interest in signed networks with applications in trust, security, or social computing. This paper focuses on the issue of defining models and metrics for reciprocity in signed graphs. In unsigned directed networks, reciprocity quantifies the predisposition of network members in creating mutual connections. On the other hand, this concept has not yet been inve...

Reciprocity stabilizes cooperation from the level of microbes all the way up to humans interacting in small groups, but does reciprocity also underlie stable cooperation between larger human agglomerations, such as nation states? Famously, evolutionary models show that reciprocity could emerge as a widespread strategy for achieving international cooperation. However, existing studies have only ...

The purpose of this note is to provide an overview of Rational Reciprocity (and in particular, of Scholz’s reciprocity law) for the non-number theorist. In the first part, we will describe the background in number theory that will be necessary for a complete understanding of the material to be discussed in the second part. The second part focuses on a proof of Scholz’s reciprocity law using the...

We analyse two types of belief-dependant models of social preferences: guilt aversion and reciprocity. In particular, we test the relevance of their input variables (second-order beliefs and general dispositions for guilt/reciprocity). The data confirm the predictions of belief-dependant models. Both secondorder beliefs and a participant’s sensitivity to guilt/reciprocity are relevant for the d...

We experimentally test Dufwenberg and Kirchsteiger’s (2004) theory of sequential reciprocity in a sequential prisoner’s dilemma (SPD) and a mini-ultimatum game (MUG). Data on behavior and firstand second-order beliefs allow us to classify each subject’s behavior as a material best response, a reciprocity best response, both, or none. We found that in both games the behavior of about 80% of the ...

Parent-child attachment security and dyadic measures of parent-child positive and negative emotional reciprocity were examined as possible mediators and moderators of the connection between marital conflict and children's peer play behavior. Eighty parents were observed in a laboratory play session with their 15- to 18-month-old child. Subsequently, at 36 months children were observed interacti...

We study indirect reciprocity and strategic reputation building in an experimental helping game. At any time only half of the subjects can build a reputation. This allows us to study both pure indirect reciprocity that is not contaminated by strategic reputation building and the impact of incentives for strategic reputation building on the helping rate. We find that pure indirect reciprocity ex...