"Social evolution is at the core of evolutionary biology, largely through the seminal work of WD Hamilton on inclusive fitness and the role of genetic relatedness in shaping social interactions and the social organisation of insect societies. Extensions to Hamilton’s original ideas have given a profound insight into the balance that exists between selfless cooperation and egoism within eusocial insect societies, spawning such concepts as worker policing and conflict resolution. These form one element of social evolution. The other element concerns the major evolutionary transition from solitary to truly social (eusocial), yet it has remained largely ignored. This is because the most widely studied social insects (ants, some bees, some vespid wasps) are obligately eusocial, unsuitable models to investigate the evolution of sociality. The sphecid or sand wasps provide an ideal group, although they have been largely neglected. Though most are solitary, a few are facultatively social and exhibit reproductive division of labour. Here I propose to investigate a facultatively social species which exhibits a division of labour in large (10-30 nestmates) groups. The study will integrate behavioural observations in the field to document patterns of nestmate activities with microsatellite genetic analysis of individuals to determine reproductive success. These analyses will tease apart the relative importance of relatedness versus ecological factors, size and age in determining the extent to which an individual cooperates for the good of the society and foregoes reproduction. Experimental manipulations in the field will be used to test explicit hypotheses over the role of relatedness in modulating cooperation. The neglected sphecid wasps offer novel insights into the role of relatedness in social interactions and caste differentiation that may challenge current views of social evolution. Genetic analyses (development of microsatellite markers) form the major training element."