The evolution of eusociality in insects

Abstract Hamilton (1964a,b) formalized the modern approach to the evolution of social behaviour with his notion of inclusive fitness, and also noted that the exceptionally high relatedness among sisters might lead to a predisposition of the Hymenoptera to evolve eusociality because females could benefit more by raising sisters than own daughters. A decade later Trivers and Hare (1976) combined Hamilton ‘s kin selection theory with Fisher ‘s (1930) sex ratio theory and pointed out that hymenopteran workers benefit from the high sister relatedness only if they can bias the sex ratios in favour of females. These insights give sex allocation theory the central place in considering the evolution of eusociality. In the years since Hamilton ‘s seminal papers, opinion has varied greatly over whether malehaploidy was, after all, important in the evolution of eusociality. In this chapter we follow Pamilo (1991c) and evaluate the current status of views on malehaploidy as a predisposing agent to the evolution of eusociality in the light of sex allocation theory. We apply here the inclusive fitness formulation developed in the preceding chapter. The main aims in this approach are to see whether there is a difference between diploid and male-haploid genetic systems in how readily they allow the evolution of a worker caste, and to examine how different features of insect life cycles might affect such evolution.