Selection for the inviability of sterile hybrids

Complementary lethal, semilethal, and dwarfing genes whose effects appear to be expressed only in (usually sterile) interspecific hybrids are not uncommon in plants. Accounting for these genes by Darwinian selection has been somewhat puzzling. However, if luxuriant, sterile hybrid progeny compete with and tend to eliminate their pure-species half-sibs, genes that are detrimental to the growth and development of hybrid progeny will be favored by Darwinian selection; the selective advantage lies in the improved fertility of parental plants. This account, which deals largely with the corky gene of New World cotton species, contrasts events that may occur in plant and animal species.