How does natural selection provide a mechanism for evolution to occur ?

Natural selection is where an animal will choose its mate based on it's view of whether or not it is of its own species so if a turtle mates with a tortoise, it will slowly evolve from the babies.

Natural selection is one of the basic mechanisms of evolution, along with mutation, migration, and genetic drift. Darwin's grand idea of evolution by natural selection is relatively simple but often misunderstood. To find out how it works, imagine a population of beetles: There is variation in traits.