Genetical Control of Incomatibility in Angiosperms and Fungi

Abstract

ALTHOUGH the majority of organisms agree in showing some special control over their breeding systems, whether to encourage inbreeding or out-breeding, they display a great variety of devices by which control is achieved. In most animals the sexes are separate and so self-fertilization is impossible. In spite of this, however, a high degree of inbreeding can be achieved by controlled brother-sister mating, as in the grass-mite; or, on the other hand, inbreeding may be discouraged by various ancillary devices such as the production of unisexual broods or cyclical changes in sex. Discriminative behaviour in mating may also favour either outbreeding or inbreeding, or some combination of the two. In fact, it appears that the controlling devices are likely to depend for their working on any of the special characteristics and faculties of the organisms in questions. This is strikingly illustrated in man, whose unique power of combining the transmission of rules of conduct, by means of what has been called tradition, with their enforcement by communal action, is used to govern mating in many different ways to give various degrees of outbreeding. Human matings may vary in advantage for non-genetic reasons in civilized and semi-civilized communities; but the occurrence of mating control even among the most primitive tribes shows that control must have arisen originally for genetical reasons1.