The products of ecological speciation rarely engage in wholesale hybridization with their progenitors, because the ecological barriers between them are unusually strong. This strength may simply be the result of directional selection, or they may arise from the differential survival of incipient species with the strongest barriers. A case is made for the latter. Those incipient species most similar in niche space to their progenitors would be most subject to hybridization with them. This would lead to a reduction in population growth and/or mongrelization of their gene pools associated with such, and ultimately the demise of the derivative. The most ecologically divergent derivatives would suffer less from this process referred to as isolate selection, and have the greatest chance of becoming a thriving new species. Long-distance hybridization has been demonstrated in crop and wild populations. The incidence of long-distance hybridization is inversely correlated with population size. The ecological derivatives struggling to invade new habitats would be especially vulnerable to hybridization.