Thanks to what form of selection did cross-finned fish survive in nature?

There are two main forms of selection. This is natural selection and artificial selection. Artificial selection was created by people to breed new species of animals and plants. Natural selection is provided by nature itself. All weak organisms die out. When stronger organisms appear with new adaptations and useful mutations, they have more chances of survival than relatives who have not developed such mutations. Quack-finned fish have survived thanks to natural selection, as they were able to adapt to the environment.