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: 1  There is variation in traits. 2  For example, some beetles are green and some are brown. 3  There is differential reproduction. 4  Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. 5  There is heredity. 6  The surviving brown ...