The evolution of sexual reproduction as a repair mechanism. Part I. A model for self-repair and its biological implications.

The theory is presented that the sexual process is a repair mechanism which maintains redundancy within the sub-structure of hierarchical, self-reproducing organisms. In order to keep the problems within mathematically tractable limits (see Part II), a simple model is introduced: a wheel with 6 spokes, 3 of them vital and 3 redundant, symbolizes the individual (cell or organism). Random accidents destroy spokes; the wheels replicate at regular cycles and engage periodically in pairing and repair phases during which missing spokes are copy-reproduced along the intact spokes of the partner wheel. The hierarchical structure of such a system is analysed and an 'autonomous unit' is defined: this is the unit of minimal hierarchical complexity which is capable of perpetuating autonomously all higher and all lower levels of the hierarchy; this is the central unit of selection. Four basic, physical parameters are isolated which determine the essential features of any eucaryotic life cycle: 1. The number of levels of the hierarchy (unicellular, multicellular, colonial, etc.); 2. the relation between the phases of replication (asexual generations) and repair (sexual generations); 3. the duration of potential repair (haplo-diplo-phase); 4. the position of the sexual partners within the hierarchy (selfing, monecy, dioecy, reproductive individuals within colonies, etc.). The evaluation of fitness components is considered in relation to trends of reproductive patterns in evolution.