Eusociality and Natural selection?
Group selection, in the extreme, yields eusociality due to the shared fate of the replicators in the group.  In a multicellular sexual organism, this "shared fate" of the "group" is the shared prospect that all replicators (alleles) have for making it into the next generation via the meotic lottery that produces the gamete.  Since they share this prospective fate they have an evolutionary incentive to cooperate in the construction of specialized cells that are, in effect, "sterile caste" members of the total "hive".  Similarly, if it is possible to subject all members of a group of individuals to a shared fate through multiple generations -- they will tend to evolve highly cooperative social structures.  However, one of the confusing aspects of the eusocial insect colonies is whether they evolved to be that way through shared fate of individual organisms, or some variant on the meotic lottery's shared fate of alleles.  The answer appears to be, primarily, that it is a peculiar form of meotic lottery in which the genes of the parents have extended phenotypes in the children that, in essence, parasitically castrate the vast majority of the children to help rear more offspring for the parents -- in particular the queen.  In this respect, one can view the evolution of eusociality in the social insects as a perverse form of individual selection where the genes of, say, the queen, cooperate in constructing not just the queen's body but, also, the entire hive.  The sterile castes are simply extended phenotypes of the queen (and the  drone with which she mates).

See "The Social Conquest of Earth" by E. O. Wilson for an in-depth treatment of eusociality and its evolution as set forth by Nowak et al in their recent paper "The Evolution of Eusociality".  See also "The Extended Phenotype" by Richard Dawkins -- in particular the chapter "Host Phenotypes of Parasite Genes".