Discuss with students some examples of artificial selection. If they can see how artificial selection operates, natural selection becomes easy to understand. Darwin used artificial selection as a model to illustrate natural selection.
Describe how dog breeds, for example, are the result of thousands of years of artificial selection, with a wolf as the original animal about 14,000 years ago.
Other examples include the variety of foods of the cabbage family (brussels sprouts, kohlrabi, Chinese cabbage) that have all been developed from a single species of Brassica.
Lead a discussion with your students involving their beliefs (religious) on the origin of life on earth. Ask several students how they think they, as humans, got to be here. Then describe Creationism and Naturalist Evolution as two distant ends of the spectrum and point out that there is also the potential for some middle ground. Add your personal beliefs as you wish. (There is little harm in discussing your own personal beliefs so long as you do not impose them upon your students.) By introducing evolution in this manner, many students who fear discussing evolution will relax and feel more open to the subject.