Local Convergence and Global Diversity: The Robustness of Cultural Homophily

Recent extensions of the Axelrod model of cultural dissemination (Klemm et al 2003) showed that global diversity is extremely fragile with small amounts of cultural mutation. This seemed to undermine the original Axelrod theory that homophily preserves diversity. We show that cultural diversity is surprisingly robust if we increase the tendency towards homophily as follows. First, we raised the threshold of similarity below which influence is precluded. Second, we allowed agents to be influenced by all neighbors simultaneously, instead of only one neighbor as assumed in the orginal model. Computational experiments show how both modifications strongly increase the robustness of diversity against mutation. We also find that our extensions may reverse at least one of the main results of Axelrod. While Axelrod predicted that a larger number of cultural dimensions (features) reduces diversity, we find that more features may entail higher levels of diversity.Comment: 21 pages, 8 figures, Submitted for presentation in Mathematical Sociology Session, Annual Meeting of the American Sociological Association (ASA), 200

About renegades and outgroup-haters: Modelling the link between social influence and intergroup attitudes

Polarization between groups is a major topic of contemporary societal debate as well as of research into intergroup relations. Formal modelers of opinion dynamics try to explain how intergroup polarization can arise from simple first principles of interactions within and between groups. Models have been proposed in which intergroup attitudes affect social influence in the form of homophily or xenophobia, elaborated as fixed tendencies of individuals to interact more with in-group members, be more open to influence from in-group members and perhaps even distance oneself from attitudes of outgroup members. While these models can generate polarization between groups, their underlying assumptions curiously neglect a central insight from research on intergroup attitudes. Intergroup attitudes are themselves subject to social influence in interactions with both in- and outgroup members. I extend an existing model of opinion formation with intergroup attitudes, by adding this feedback-effect. I show how this changes model predictions about the process and the conditions of polarization between groups. In particular, it is demonstrated how the model implies that intergroup polarization can become less likely if intergroup attitudes change under social influence; and how more complex patterns of intergroup relations emerge. Especially, a renegade minority (outgroup-lovers) can have a key role in avoiding mutually negative intergroup relations and even elicit attitude reversal, resulting in a majority of individuals developing a negative attitude towards their in-group and a positive one of the outgroup. Interpretations of these theoretical results and directions for future research are further discussed.Comment: 33 pages, 21 figures, Paper presented at ODCD 2017. Interdisciplinary Workshop on Opinion Dynamics and Collective Decision 2017, July 5-7, 2017 @ Jacobs University Bremen, German

Rational Exploitation of the Core by the Periphery? On the Collective (In)efficiency of Endogenous Enforcement of Universal Conditional Cooperation in a Core-Periphery Network

Raub and Weesie (1990) proposed a game theoretical model addressingeffects of network embeddedness on conditional cooperation between two actors.This work showed that network embeddedness can facilitate conditional coopera-tion by reducing uncertainty, in line with a number of follow-up contributions andconsistently with results from other modelling approaches. This research focusedmainly on interactions between two parties embedded in a network. In the presentpaper, I extend a closely related model towardsN-person collective good problems,combining conditional cooperation based on direct monitoring via network ties andobservation of group output in an uncertain environment. The focus is on a maxi-mally simple yet empirically relevant case, a core-periphery network in which onlycore-members can directly observe each other’s contributions to a collective effort,whereas peripheral members only observe a noisy signal indicating aggregated con-tributions. I propose the possibility of a‘rational exploitation of the core by the pe-riphery’. Strategy-profiles in which free-riding of peripheral members is toleratedwhile core-members cooperate conditionally, are not only individually rational butalso payoff-superior to profiles with universal conditional cooperation if uncer-tainty is sufficiently high and the number of peripheral members is sufficiently low

The Viability of Cooperation Based on Interpersonal Commitment

A prominent explanation of cooperation in repeated exchange is reciprocity (e.g. Axelrod, 1984). However, empirical studies indicate that exchange partners are often much less intent on keeping the books balanced than Axelrod suggested. In particular, there is evidence for commitment behavior, indicating that people tend to build long-term cooperative relationships characterised by largely unconditional cooperation, and are inclined to hold on to them even when this appears to contradict self-interest. Using an agent-based computational model, we examine whether in a competitive environment commitment can be a more successful strategy than reciprocity. We move beyond previous computational models by proposing a method that allows to systematically explore an infinite space of possible exchange strategies. We use this method to carry out two sets of simulation experiments designed to assess the viability of commitment against a large set of potential competitors. In the first experiment, we find that although unconditional cooperation makes strategies vulnerable to exploitation, a strategy of commitment benefits more from being more unconditionally cooperative. The second experiment shows that tolerance improves the performance of reciprocity strategies but does not make them more successful than commitment. To explicate the underlying mechanism, we also study the spontaneous formation of exchange network structures in the simulated populations. It turns out that commitment strategies benefit from efficient networking: they spontaneously create a structure of exchange relations that ensures efficient division of labor. The problem with stricter reciprocity strategies is that they tend to spread interaction requests randomly across the population, to keep relations in balance. During times of great scarcity of exchange partners this structure is inefficient because it generates overlapping personal networks so that often too many people try to interact with the same partner at the same time.Interpersonal Commitment, Fairness, Reciprocity, Agent-Based Simulation, Help Exchange, Evolution

The Viability of Cooperation Based on Interpersonal Commitment

A prominent explanation of cooperation in repeated exchange is reciprocity (e.g. Axelrod 1984). However, empirical studies indicate that exchange partners are often much less intent on keeping the books balanced than Axelrod suggested. In particular, there is evidence for commitment behavior, indicating that people tend to build long-term cooperative relationships characterised by largely unconditional cooperation, and are inclined to hold on to them even when this appears to contradict self-interest. Using an agent-based computational model, we examine whether in a competitive environment commitment can be a more successful strategy than reciprocity. We move beyond previous computational models by proposing a method that allows to systematically explore an infinite space of possible exchange strategies. We use this method to carry out two sets of simulation experiments designed to assess the viability of commitment against a large set of potential competitors. In the first experiment, we find that although unconditional cooperation makes strategies vulnerable to exploitation, a strategy of commitment benefits more from being more unconditionally cooperative. The second experiment shows that tolerance improves the performance of reciprocity strategies but does not make them more successful than commitment. To explicate the underlying mechanism, we also study the spontaneous formation of exchange network structures in the simulated populations. It turns out that commitment strategies benefit from efficient networking: they spontaneously create a structure of exchange relations that ensures efficient division of labor. The problem with stricter reciprocity strategies is that they tend to spread interaction requests randomly across the population, to keep relations in balance. During times of great scarcity of exchange partners this structure is inefficient because it generates overlapping personal networks so that often too many people try to interact with the same partner at the same time

Can Ethnic Tolerance Curb Self-Reinforcing School Segregation? A Theoretical Agent Based Model

Schelling and Sakoda prominently proposed computational models suggesting that strong ethnic residential segregation can be the unintended outcome of a self-reinforcing dynamic driven by choices of individuals with rather tolerant ethnic preferences. There are only few attempts to apply this view to school choice, another important arena in which ethnic segregation occurs. In the current paper, we explore with an agent-based theoretical model similar to those proposed for residential segregation, how ethnic tolerance among parents can affect the level of school segregation. More specifically, we ask whether and under which conditions school segregation could be reduced if more parents hold tolerant ethnic preferences. We move beyond earlier models of school segregation in three ways. First, we model individual school choices using a random utility discrete choice approach. Second, we vary the pattern of ethnic segregation in the residential context of school choices systematically, comparing residential maps in which segregation is unrelated to parents' level of tolerance to residential maps reflecting their ethnic preferences. Thirdly, we introduce heterogeneity in tolerance levels among parents belonging to the same group. Our simulation experiments suggest that ethnic school segregation can be a very robust phenomenon, occurring even when about half of the population prefers mixed to segregated schools. However, we also identify a sweet spot in the parameter space in which a larger proportion of tolerant parents makes the biggest difference. This is the case when the preference for nearby schools weighs heavily in parents' utility function and the residential map is only moderately segregated. Further experiments are presented that unravel the underlying mechanisms.Comment: 55 pages, 18 figures, paper presented in lecture series Institute for Advanced Studies (IAS), University of Amsterdam, March 2, 202