SwitzerlandCooperation applies the situations where two or more individuals obtain a net benefit by working together. Cooperation is widely spread in nature and takes several forms, ranging from behavioral coordination to sacrifice of one's own life for the benefit of the group. This latter form of cooperation is known as "true cooperation", or "altruism", and is found only in few cases. Truly cooperative robots would be very useful in conditions where unpredictable events may require costly actions by individual robots for the success of the mission. However, the interactions among robots sharing the same environment can affect in unexpected ways the behavior of individual robots, making very difficult the design of rules that produce stable cooperative behavior. It is thus interesting to examine under which conditions truly cooperative behavior evolves in nature and how those conditions can be translated into evolutionary algorithms that are applicable to a wide range of robotic situations.Building on earlier intuitions by Haldane (1955), Hamilton (1964) suggested that altruism can evolve if the cooperator is genetically related to the recipient of help. In this case, even if the cooperator cannot propagate its own genes to the next generation, its altruistic act will increase the probability that a large portion of those genes will be propagated through the reproduction of the recipient of the altruistic act. The theory of kin selection (Maynard-Smith 1964), which developed from Hamilton's model, predicts that the ratio of altruistic individuals in a population is related to the degree of kinship, or genetic relatedness, among individuals. Another explanation for the evolution of altruistic cooperation is provided by the theory of group selection, which argues that altruistic cooperation may also evolve in groups of genetically unrelated individuals that are selected and reproduced together at a higher rate than the single individuals composing the group (Wynne-Edwards 1986). This could happen in situations where the synergetic effect of cooperation by different individuals provides a higher fitness to the group with respect to other competing groups. In those situations, cooperating individuals can be seen as a superorganism that becomes the unit of selection. It has been suggested that group selection may be a driving force behind the transition from unicellular to multicellular organisms (Michod 1999).In the context of evolution experiments with robots (Floreano and Mattiussi, 2008;Nolfi and Floreano, 2000), the hypotheses of kin selection and of group selection translate into the genetic composition of the group of robots and into the method used to select individuals for reproduction. If we consider only the extreme conditions, individuals in a team could be genetically homogeneous (clones) or heterogeneous (they differ from each other); and the fitness could be computed at the level of the team (in which case, the entire team of individuals is reproduced) or at the level of the individual (in which case...