NATURAL OUTCOME. “It is likely that incipient speciation and its reversal naturally characterize evolutionary dynamics of ecological speciation and adaptive radiation. Indeed the level of reproductive isolation between species of Darwin’s Finches varies between years with and without selection against hybrids. Such alternation between progress and regress in speciation during adaptive radiations may even increase the adaptability of genomes.”
http://www.sciencedirect.com/science/article/pii/S0960982206014138