Systems of Classification

BEFORE discussing the evidences of Evolution, or examining the arguments advanced in its support, it is advisable to have some idea of the different systems of classification which have obtained in various periods of the history of science, and to learn on what such systems were based. Have naturalists in all ages employed essentially the same systems of classification, or have their systems been widely different, if not contradictory? Are scientific classifications expressions of natural arrangements existing in animated nature, or are they but artificial devices for coördinating our knowledge of nature and facilitating our investigations? Have species, genera, families, orders, classes and branches, a real or an ideal existence? Are they manifestly disclosed in the plan of creation or are they but arbitrary categories hit upon by naturalists as convenient aids in arrangement and research? These are a few of the many questions which present themselves for an answer as we approach the subject of organic Evolution. Others there are also which might be discussed but we have not space for them now.

The system of classification of Aristotle, and of the naturalists of antiquity generally, was of the most primitive character. It recognized but two groups, γένος and εἷδος, genus and species. These terms, as a rule, had only a very vague meaning, and were frequently made to embrace groups of animals that we should now refer to orders and classes.