Natural environments are subject to weather, location, height, if water is nearby and what kind of water this is the neighboring environment, and so much more. These factors affect what plant species can grow in an area. And these, in their turn, affect what animals can live in that specific area. Taking all the other factors into account. Evolution is a way to make sure that species can keep surviving. It’s a process of elimination. If you can’t keep up with changes, or your new evolutionary trait is useless, it, or you, will likely die out.