What My project is about understanding the evolution of cooperation among unrelated individuals and how it is linked to social network structure. Theory predicts that social network structure (the pattern of social interactions between the individuals in a population) is likely to be a key factor in the evolution and maintenance of cooperation between unrelated individuals, but very little is known about what role social network structures and dynamics play for cooperation in real-world populations. In my project I combine computer modelling with data from real-world natural animal populations and experiments in order to gain new knowledge about how cooperation evolves and is maintained. Why Cooperation among unrelated individuals is found across species, but it seems to contradict evolutionary theory and has therefore constituted a major puzzle for science for many years. A number of mechanisms have been proposed that can theoretically promote the evolution of cooperation among non-relatives, but it is not well understood to what extent these mechanisms apply in the real world, and how cooperation among non-relatives in natural, structured populations actually evolves. My project links two fields of research that so far have been largely separate, namely the theoretical modelling of evolution of cooperation in networks and the empirical study of animal social network structure. This can help advancing our understanding of the evolution of cooperation. How I use a combination of computer modelling, empirical data from real-world natural animal populations, and behavioural experiments. The data are obtained from the Trinidadian guppy (Poecilia reticulata), a fish species that has been used extensively in evolutionary research and shows non-random social network structures and cooperation among unrelated individuals. The computer models simulate evolution of cooperation in social networks and are built to incorporate empirical data. This allows me to investigate various hypotheses about the evolution of cooperation in structured populations. SSR Cooperation is a central pillar in human society. And in humans, as in other species, cooperation necessarily takes place within social structures. Understanding cooperation in social networks is therefore important for understanding our own society, evolution, and success as a species. In a broad perspective, knowledge about the link between social networks and cooperation could also potentially be used for promoting cooperation-supporting structures in society, which are of vital importance for sustainable use of resources and peaceful interactions.