"In almost any natural population of organisms, more offspring will be produced than are able to survive. The offspring will vary—in particular, they will vary with respect to characteristics that affect their abilities to survive and reproduce. Some organisms will survive longer and reproduce more frequently. If the advantageous characteristics are inheritable, then they will be transferred to descendants. As a result, they will become more prevalent in later generations. Over a large number of generations the common features of the population may be radically changed."