"Cooperation is an evolutionary riddle, as it defies the basic principles of natural selection. If during the course of evolution only the fittest survive, why should one sacrifice individual fitness for the benefit of unrelated others? Widespread cooperation in nature is indeed one of the most important challenge to Darwin’s theory of evolution and natural selection. Understanding the evolution of cooperation means understanding also the main evolutionary transitions that led from single-cell organisms to complex animal and human societies, and it is therefore little surprising that the subject consistently attracts attention across large contingents of social and natural sciences."