Evolution is the change in a gene pool of a population over time. It is the theory that groups of organisms change with passage of time, mainly as a result of natural selection, so that descendants differ from their ancestors. In order for this theory to hold true, some things must be observed. First, it is necessary to view populations as a collection of individuals, each harboring a different set of traits. A single organism is never typical of an entire population unless there is no variation within that population. Individual organisms do not evolve; they retain the same genes throughout their life. Second, when a population is evolving, the ratio of different genetic types is changing; each individual organism within a population does not change. With this established, many components of the evolution theory can be discussed.
             One of the major components of evolution theory is common descent. This is the theory that every group of organisms descended from a common ancestor, and that all groups of organisms, including animals, plants, and microorganisms, ultimately go back to a single origin of life on earth.
             Another component is the theory of gradualism. Simply stated, evolutionary change takes place through the gradual change of populations and not by the sudden production of new individuals that represent a new type.
             Multiplication of the species is a very important piece of the evolution theory. This theory explains the origin of the enormous organic diversity. It postulates that species multiply, either by splitting into daughter species or by "budding", that is, by the establishment of geographically isolated founder populations that evolve into new species.
             All of these pieces lead to natural selection. According to this theory, evolutionary change comes about throughout the abundant production of genetic variation in every generation. The relatively few individuals who survive, owing to a particularly well...