Evolution as a self-limiting process

Evidence is presented that diploid evolution is largely finished and that sexual reproduction is incapable of supporting progressive evolution. Since the first meiotic division is a form of diploid reproduction, it is proposed that this presexual (gynogenetic) event provides the basis for macroevolutionary change. The first meiotic division can serve both to preserve the original genome and also produce in a single step new paired chromosome rearrangements. Chromosome restructuring characterizes the differences which distinguish species such as our closest living primate relatives. Since chromosome restructuring is not likely to be precisely reversed, this hypothesis offers an explanation for the irreversible nature of organic evolution. The semi-meiotic hypothesis finds support from the nonhomologous devices which have evolved to determine the sexes, as well as the nonhomologous origins of the sex cells in the various vertebrate taxa. The parthenogenetic turkey and the diploid commensal protozoon Spirotrichosoma both offer living examples of the semi-meiotic mechanism. A brief critique of the Darwinian hypothesis is presented. Since the karyotypic differences which characterize species were apparently not produced sexually, I propose they were produced semi-meiotically as I have suggested.