Cooperative breeding is the joint raising of offspring by wo or more individuals, where at least one of them is not he genetic parent of the young. The key characteristics of ooperative breeding systems are diversity of social behaviours ithin and between groups and high variation of factors influncing conflict over reproduction (for review see Komdeur, 006). In the second half of the 20th century, development of esearch on cooperative breeding systems has been influenced by ame theory from human economy (e.g. Nash, 1950; Maynard mith, 1982; Hammerstein and Selten, 1994), by empirical studes on different systems (e.g. Brown, 1987; Taborsky, 1994; olomon and French, 1997; Koenig and Dickinson, 2004), and y mathematical models of fitness advantages of group living n behavioural ecology (initiated mainly by Hamilton, 1964 and y Vehrencamp, 1983). Cooperative breeding systems comprise subset of social systems with cooperative behaviour, but are f high importance to generate hypotheses, search for patterns nd mechanisms, and develop theories for the evolution of social ife. Mechanistic concepts to explain the evolution of cooperaion (see e.g. Dugatkin, 1997; Hammerstein, 2003) have been eveloped parallel to the discoveries of the diversity of cooperaive behaviours. In this context, evolutionary theory uses mainly ame theoretical arguments, where the strategy of one individal depends on the strategies of others in the population. Most pproaches use non-cooperative game theory (for review see cNamara et al., 2006) where individuals compete with each ther to maximize their fitness but where cooperation is not ssumed in advance. To solve Darwin’s puzzle of the evolution f cooperation by natural selection the Prisoner’s dilemma game formulated after the Flood–Dresher experiment, Flood, 1958), hat involves rational players trying to maximize individual pay-