Purves, W.K., G.H. Orians and H.C. Heller. The Science of Biology . What are the genetic characteristics of wide ranging species.
Evolution is a process of cumulative change.
Evolution by natural selection involves the differential reproduction by individual genotypes resulting in a change in the genetic composition of the population. There is variation in phenotypic characteristics among individuals. In a particular environment, individuals with certain characteristics have a higher probability of surviving and reproducing than do individuals with other characteristics. At least some of the characteristics that result in a difference in reproduction are heritable. Long periods of time have been available for evolutionary change to occur.