RELATEDNESS ASYMMETRY AND THE EVOLUTION OF EUSOCIALITY

Kin selection theory, the relatedness asymmetry hypothesis, and various modifications of these, as they apply to the evolution of social insects are reviewed. The general validity of kin selection theory is affirmed as well as the theoretical validity of the relatedness asymmetry hypothesis. However, many criticisms are made concerning the relevance of the relatedness asymmetry hypothesis as an explanatory mechanism for real groups of social insects. Its invalid assumptions and lack of unique explanatory power are discussed. The relatedness asymmetry hypothesis has been widely held to explain the frequency of social evolution in the haplodiploid Hymenoptera, and the fact that only the highly related diploid females are workers. However, it is argued that these features are not uniquely explained by the relatedness asymmetry hypothesis and, in fact, do not constitute strong support for the hypothesis. In place of relatedness asymmetries, it is proposed that exaptations (sensu Gould & Vrba 1982) for nest defense are the key enabling factors in all origins of eusocial arthropods.