Undoubtedly, experiments are an essential part of the scientific method. Through the design of experiments, the use of reliable and accurate computational methods and the analysis of data, we could eventually solve the evolutionary puzzle and validate existing theories. Therefore, in the very tradition of Science, we aim at observing the world around us, collect data

Our first experiment was aimed at testing whether the structure of the underlying network through which interactions take place plays any role in the emergence and evolution of cooperative behavior. To this end, we designed the largest experiment conducted up to now involving humans playing a Prisoner’s Dilemma. Specifically, we ran two settings: one corresponded to a square lattice in which 625 individuals were arranged in such as way that each subject played with 4 neighbors; and the second setup, involving 604 volunteers, considered a heterogeneous (so-called Scale-free networks) graph in which the nodes represent individuals that interact following the links of the graph. In this latter setting, the number of neighbors of a given player varied from 2 to 16. Both experiments were carried out concurrently, i.e., 1229 were playing in real-time (for more information about the experimental methodology, see the SI of the paper linked below).

The hypothesis to be tested in this experiment is that of network reciprocity. During the late 2000’s, among the several mechanisms that were proposed to explain cooperative behavior among humans, the effect of the underlying network of contacts received very much attention. Essentially, theoretical models have shown that the larger the heterogeneity of the contact networks is, the higher the cooperation observed is. The main mechanism for the evolution of cooperation behind these models is based on the assumption of certain strategies, including the fact that people take into account the pay-offs of their contacts to choose their actions, i.e., to decide whether they play as a cooperator or as a defector. In contrast to theoretical provisos, some experiments that were carried out with people playing social games on regular (grid-like configurations) structures, suggested that when individuals face the decision to cooperate or act selfishly, they do not

Although cooperation and altruism in human societies have been widely studied, certain fundamental aspects have received little attention. One of them is whether the observed cooperation changes through an individual lifetime. An immediate question that follows from this matter is of methodological nature: as the vast majority of experiments are performed with subjects in their early twenties’, do the results obtained with those individuals are generalizable to other age ranges? For instance, it has been observed that children develop their social abilities in different stages and that the elderly could be more inclined to prosocial behavior. In order to provide grounded evidence in one sense or another, we have performed a series of lab-in-the-field experiments carried out over a very wide range of ages. Our experiment took place in the 1st Board Games Fair in Barcelona in December 2012, and consisted of groups of 4 participants playing simultaneously a 4-player Prisoner’s Dilemma. Participants with ages between 10 and 87 among visitors of the Fair were randomly recruited. In order to compare the behavior of subjects of different ages, we either placed them in a group with other players of similar age (we divided the age range as follows: 10–17,18–25, 26–35, 36–45, 46–55, 56–65, and 66 and over) or placed in a group with

While our first experiment showed that the underlying topology plays little role in the evolution of cooperation, many other mechanisms have been proposed to explain cooperative behavior. On the one hand, several authors have proposed that the network of contacts does play a role, but in order to observe it, one should allow for the formation and removal of links, i.e., the network should be dynamical in nature (as opposed to our first experiment, in which the networks were static). On the other hand, other mechanisms such as indirect reciprocity have been less explored experimentally. These mechanisms of reciprocity (no matter whether indirect or direct) are based on the concept of reputation: in pairwise encounters between members of a population, individuals may have information about previous actions of their opponents and act accordingly. Thus, reputation would enhance cooperation by favoring strategies that are based on the opponent’s cooperative stature. In order to study the effects of reputation in social dilemmas, we have carried out a series of laboratory experiments where people interact through an iterated prisoner’s dilemma on a network, allowing subjects to break and form links.

Socially relevant situations that involve strategic interactions are widespread among animals and humans alike. To study these situations, theoretical and experimental works have adopted a game-theoretical perspective, which has allowed to obtain valuable insights about human behavior. However, most of the results reported so far have been obtained from a population perspective and considered one specific conflicting situation at a time. This makes it difficult to extract conclusions about the consistency of individuals’ behavior when facing different situations, and more importantly, to define a comprehensive classification of the strategies underlying the observed behaviors. Here, we present the results of a lab-in-the-field experiment in which subjects face four different dyadic games, with the aim of establishing general behavioral rules dictating individuals’ actions.

One of the most elusive scientific challenges for over 150 years has been to explain why cooperation survives despite being a seemingly inferior strategy from an evolutionary point of view. Over the years, various theoretical scenarios aimed at solving the evolutionary puzzle of cooperation have been proposed, eventually identifying several cooperation-promoting mechanisms: kin selection, direct reciprocity, indirect reciprocity, network reciprocity, and group selection. Here, we report the results of repeated Prisoner’s Dilemma experiments with anonymous and onymous pairwise interactions among individuals.

Global supply networks in agriculture, manufacturing, and services are a defining feature of the modern world. The efficiency and the distribution of surpluses across different parts of these networks depend on the choices of intermediaries. This paper conducts price formation experiments with human subjects located in large complex networks to develop a better understanding of the principles governing behavior. Our first finding is that prices are larger and that trade is significantly less efficient in small-world networks as compared to random networks.

Common-pool resources require a dose of self-restraint to ensure sustainable exploitation, but this has often proven elusive in practice. To understand why, and characterize behaviors towards ecological systems in general, we devised a social dilemma experiment in which participants gain profit from harvesting a virtual forest vulnerable to overexploitation. Out of 16 Chinese and 15 Spanish player groups, only one group from each country converged to the forest’s maximum sustainable yield.