In any scientific endeavor, it is the understanding of process, rather than the description of pattern that is ultimately of interest. Only when we know why a pattern exists, that is, when we understand its cause, can we make generalizations with any real degree of confidence. This is as true of systematics and evolutionary biology as it is of any other field (Eldredge and Cracraft 1980).

The detailed investigation of microevolutionary processes has lagged behind the description of microevolutionary patterns just as a deep understanding of evolutionary forces has been retarded in other areas, such as behavioral ecology, biogeography, and macroevolution. For example, we realize that a cline may be the result of gene flow, natural selection, or even random drift, but, as with other areas of evolutionary biology, it is common merely to assert that selection was responsible for the pattern. Consequently, anything more than a subjective understanding of microevolutionary mechanisms has been slow to develop. What is needed to proceed beyond this illusion of knowledge are analytical models and statistical tests to examine the concordance of patterns to the expectations of given processes. Consistency with one's world view is not understanding; alternatives must be eliminated through quantification.

What we know about microevolutionary processes today has come mainly through quantitative studies of morphological variation.