Abstract

Due to its multi-functionality and versatility, play is one of the most difficult behaviours to define. If defining play is a difficult matter, playing (and, especially, playing fairly) may be even more difficult. In play two opposing components coexist: cooperation and competition. This competitive/cooperative interaction serves to test a partner's willingness to invest in a relationship and, simultaneously, to demonstrate one's own willingness to accept vulnerability. A fair player must balance these two forces acting concurrently. To be fully expressed, play (the most plastic and versatile behaviour!) requires plastic and versatile societies, where the inter-individual relationships have a high degree of freedom and are not bridled into codified schemes or crystallized roles. Indeed, the competitive counterpart of play is more developed in those species showing social systems based on despotic relationships; while the cooperative propensity in play is linked to more relaxed and egalitarian relations. The correct management of a playful interaction requires also complex social abilities, so this is why playing has been considered a powerful means to gain social competence. In this chapter, we will provide an overview on the function of play in the regulation of social relationships and we will show that the results obtained on non-human primates can be also theoretically expanded to different human systems. Finally, we will focus on the complex communicative system which scaffolds each playful interaction.