Okay there is much confusion here. The primary problem is the failure to understand that the genius of Darwin’s Theory is that it recognizes Evolution is a two phased process. The first phase is Variation where a new allele is produced by genetic changes, often by sexual mixing of genes.
But Variation does not have the final say. Natural Selection does. Variation produces a variant of the existing species, but Natural Selection determines if that variation is viable or not. If that variation is viable , then it might replace the old species, or might break off into a new species. Also Natural Selection might determine that a species is no longer viable and it may go extinct because it is selected out.
Variation produces possible new life forms. Natural Selection determines which life forms are going to survival and flourish. Why is this important? It is important because the earth is constantly changing. The climate is changing. The terrain is changing. The environment is changing.
Suring the time of the dinosaurs the climate changed and the habitat that sustained the dinosaurs disappeared and so did they. Today habitat is disappearing and so are many species. All sorts of changes in the environment force species to change or die out. It is changes in the environment that causes species to adapt and change, as hominids have adapted and changed over many years. .