According to Comeron et al. [41], long introns are favored because they increase the efficiency of natural selection by releasing The Hill-Robertson (HR) interference. The HR interference was basically described as genetic linkage between two sites under selection in finite populations, leading to decreasing effectiveness of natural selection [41]. The HR interference model predicts that selection efficiency should be different between genes that differ in exon-intron structures, so that genes with longer introns should be under weaker HR interference by increasing recombination between two sites in two neighboring exons. In other words, introns may have a role in relaxing intragenic HR interference between sites under the influence of natural selection in finite populations. Recombination gives the opportunity for two independently occurring favorable alleles at linked loci to be located together and thus enhances the efficiency of natural selection [40], which can be one of the plausible scenarios of how introns have been sustained through the evolutionary history of genes.
