The fossil record shows that the number of kinds of organisms tends to increase over time. When there is no gene flow, the 2 groups will accumulate more and more differences over time.
Random mutations occur in some of the offspring.
Again you select which morph you want to survive and reproduce. Over many generations you'll be amazed at the change you can get. Based on Richard Dawkin's work on the evolution of complex features. Well worth exploring. Results of Evolution adaptation similarity homologies convergent evolution analogous structures biodiversity divergent evolution retention of homologous features but with often dramatic modification adaptive radiation More Links to Interesting Web Pages on Evolution University of California Museum of Paleontology home page leads you to numerous pages to explore evolution.