Human Skeleton.
For comparison with bird's skeleton (opposite), lettered to show the answerable bones. From Belon's Book of Birds, 1555.
Aristotle found himself obliged to rectify the traditional classification of animals in order to remove gross anomalies. When learning decayed the traditional classification came back. Thus the Ortus Sanitatis (first published in 1475, and often reprinted) adopts the division into (1) animals and things which creep on the earth; (2) birds and things which fly; (3) fishes and things which swim. No consistent primary division of plants was proposed by Greek or Roman, nor by anyone else until the seventeenth century A.D.
This conflict of systems should have raised questions concerning the nature of classification and the relative value of characters. Some of the most striking resemblances found among animals and plants are only superficial; others, though far less obvious, are fundamental. Whence this difference? Why should scientific zoology make so little of the place of abode and the mode of locomotion; so much of the mode of reproduction and the nature of the skeleton? The answers were vague, and even the questions were rare and indistinct. But a metaphorical term came into use which was henceforth more and more definitely associated with fundamental, as distinguished from adaptive, likeness. Such likeness was called affinity,[1] though no attempt was made to explain in what sense the term was to be understood. As late as the year 1835 one of the first botanists in Europe (Elias Fries) could say no more about affinity between species than that it was quoddam supernaturale, a supernatural property.
A tolerable outline of a classification of animals was attained much earlier than a tolerable classification of plants. The characters available for the classification of plants are, to begin with, less obvious than those which the zoologist can employ. Moreover, the botanists were restricted to a narrower view of their subject. Zoologists, though they were expected to bestow the best part of their time upon vertebrates, were encouraged to study all animals more or less. Botanists, on the other hand, were practically obliged to concentrate their attention upon the classification of the flowering plants. The physician, herb-collector, and gardener cared nothing about any plants except such as bear flowers and fruit; but of these they expected full descriptions, and were clamorous for a system which would enable even a tyro to make out every species with certainty and ease. The task set before the botanist was comparable in respect of difficulty with the construction of a detailed and completely satisfactory classification of birds, which zoology has never yet been able to produce, while for the sake of this long-unattainable object almost everything else in botany was neglected.