CLASSIFICATION, as Dr. Elliott Coues has well said, is a natural function of "the mind which always strives to make orderly disposition of its knowledge and so to discover the reciprocal relations and of the things it knows. Classification presupposes that there do exist such relations, according to which we may arrange objects in the manner which facilitates their comprehension, by bringing together what is like and separating what is unlike; and that such relations are the result of fixed, inevitable laws. It is, therefore, Taxonomy (τάςις, array; νόμος, law) or the rational, lawful disposition of observed facts."
A perfect taxonomy is one which would perfectly express all the facts in the evolution and development of the various forms. It would be based on morphology, the consideration of structure and form independent of adaptive, or physiological, or environmental modifications. It would regard those characters as most important which had existed longest unchanged in the history of the species or type, thus considering all knowledge derived from paleontology. It would regard as of minor importance those traits which had risen recently in response to natural selection or to the forced alteration through pressure of environment, while fundamental alterations as they appear one after another in geologic time would make the basal characters of corresponding groups in taxonomy. In greater or less degree, the life history of the individual, through the operation of the law of heredity, repeats the actual history of the group to which the individual belongs. For this reason the characters appearing first in the individual are likely to have greatest importance in classification.τ