Three different possible changes in the hybrid zone may occur over time. The first possible change, reinforcement, results when hybrids are less fit than either purebred species. Like a fork in the road, the species continue to diverge until hybridization no longer occurs. The second possible change, fusion, results when reproductive barriers weaken until two species become one. In this scenario species initially diverge, but then join together. In the third scenario, stability, fit hybrids continue to be