Reinforcement

Reinforcement, or the strengthening of reproductive isolation in response to hybridization costs, is a case in which natural selection directly contributes to the origin of new species. From its conception, reinforcement has enjoyed alternate periods of enthusiasm and rejection, in which powerful verbal arguments identified obstacles that were subsequently solved by novel theory. Empirical data has provided some of the strongest arguments for the plausibility of reinforcement and for its frequency in nature, indicating that it is likely to be a common aspect of species divergence and the completion of speciation.