Relatedness and the fraternal major transitions

Many of the major transitions in evolution involved the coalescence of inde pendent lower-level units into a higher organismal level. This paper examin es the role of kinship, focusing on the transitions to multicellularity in animals and to coloniality in insects. In both, kin selection based on high relatedness permitted cooperation and a reproductive division of labour. T he higher relatedness of haplodiploid females to their sisters than to thei r offspring might not have been crucial in the origin of insect societies, and the transition to multicellularity shows that such special relationship s are not required. When multicellular forms develop from a single cell, se lfish conflict is minimal because each selfish mutant obtains only one gene ration of within-individual advantage in a chimaera. Conditionally expresse d traits are particularly immune to within-individual selfishness because s uch mutations are rarely expressed in chimaeras. Such conditionally express ed altruism genes lead easily to the evolution of the soma, and the germ li ne might simply be what is left over. In most social insects, differences i n relatedness ensure that there will be potential conflicts. Power asymmetr ies sometimes lead to such decisive settlements of conflicts that social in sect colonies can be considered to be fully organismal.