The origin of cooperation between individuals remains one of the main puzzles of evolutionary biology. Eusocial insects are one of most striking examples of extensive cooperation in which some individuals forego reproduction to help others. Yet research on eusocial insects concentrates mainly on species with large societies whereas species which exhibit facultative eusociality (some individuals live socially, other solitarily) are well suited for studying the origin of eusociality. I plan to study small carpenter bees (genus Ceratina), This is a globally distributed genus with approximately 200 described species which is an excellent model system for studying social evolution in a comparative approach because of their large interspecific diversity in social and parental strategies. My research has three main goals. Firstly, I shall construct a high-resolution molecular phylogeny of Ceratina based on next generation sequencing as a necessary framework for my comparative approach, namely the remaining two goals. Secondly, I shall evaluate the importance of traits underpinning sociality, parental care, nesting biology and mating by mapping them on phylogenetic trees. Thirdly, I will study covariance between relatedness and sociality across Ceratina species; they exhibit extensive variability in relatedness between offspring because females of some species mate with one partner, some with several and others are parthenogentic, allowing me to test the role of relatedness in social evolution. Biologists commonly study one or a few species in detail. However, I plan use comparative approach to compare strategies of multiple species and map life history traits onto phylogeny. My unique integrative approach will advance understanding of social evolution, parental care, and cooperative behaviour in general.