It is proven, populations evolve when they enter a different environment. When you as a half-fish half-amphibia want to explore land you need lungs not gills, your heart and your whole body must evolve to survive in the new environment, No dehydration in the water but pure dehydration in the new environment, just solve the problem by evolving ... But how does the Dna know when to evolve a different heart, lung etc. ? Is it the genes (and amino acids and proteins in them) "controlling" the heart that see this ? I know the evolving is given from offspring to offspring and spread all over the population, but i dont know how they know when to evolve.