Ant and bee colonies have long fascinated biologists because of their hierarchical social structure and the apparently altruistic behaviour of female workers in rearing the queen's young rather than reproducing themselves. In colonies headed by a single queen, this makes evolutionary sense in that the workers are as closely related to the princesses and princes they nurture as they would be to their own children. Thus the genes underlying this behaviour would be successfully transmitted through the generations due to "kin selection".