Successful speciation may occur because certain adaptations provide for increased success in differential reproduction, i.e., natural selection. Nonetheless, speciation, radiation, and extinction are ephemeral on the geologic time scale. In the last lecture we discussed the mechanics of microevolution and the evolution of species. Other examples of microevolution are the diversity of fishes in western American springs. For example, the Commanche Springs pupfish has adapted to select areas in west Texas.
Macroevolution is another way to look at population change through the fossil record.
One sees these changes as major breaks because the fossil record may be discontinous and occurs over long time periods. The American grizzly bear is Ursus arctos and the black bear Ursus americanus . The genus, e.g., Canis , shows a closer degree of relation, than say the animal's family or order. Also note that the genus and species are always in italics or underlined in print. The technique is essentially the same for plants and other organisms.