Background

The Origin of Scientific Classification

Human observers through the ages have lived in awe of the creatures that share the Earth with them. By way of human nature, this fosters a desire to classify them in some systematic way: to impose order on the diversity of life. Aristotle (384-322 B.C.) the father of zoology, began the science that we call taxonomy. Aristotle saw for the first time that it was feasible, as well as beneficial, to work out a logical classification of animals. He came up with the term species, meaning a group in which all members have common attributes. Genus embraced a larger grouping whose members have a general similarity in size, shape, and external features.

Aristotle separated living from non-living things. According to him, living things posses a soul. he used this term almost indistinguishably from psyche or even life, so he was almost saying in circular fashion that a living being has the quality of life.

Living things evidence a number of attributes, and plants at the lowest level posses only one of them, self-nutrition. At the next level, animals have the ability to feed themselves plus a varying degrees faculties for locomotion, sensing, and desire. At the top level are humans , who posses all the attributes of animals below them plus the power to think. At the basis of this arrangement is the idea of hierarchy, in which each level includes the qualities of the levels below.

Aristotle, like most Greeks of his time, was impressed with what were then considered the four elements- fire, water, earth, and air. Their supposed qualities- hot versus cold, moist versus dry- were significant to him. He rated hot above cold, moist above dry. Blood, being both hot and moist, was regarded as a prime characteristic by which to distinguish animals.

Aristotle's Classification of Animals ©
1. Blooded animals                                                                     2. Bloodless animals
     A. Hairy, live birth quadrupeds (mammals)                               A. Malakia (squid and octopus)
     B. Birds                                                                                       B. Crustacea
     C. Cetacea (sea mammals)                                                        C. Testacea (molluscs)
     D. Fish                                                                                         D. Insects
     E. Snakes
     F. Egg laying quadrupeds (reptiles and amphibians)

Below the animals in Aristotle's classification were organisms he could not distinguish as wholly animals or plants, such as jellyfish and sponges. At the bottom of the scale were higher plants, and non-living matter.

Aristotle's system of classification remained the model for more than 2000 years. It became known as the
scala naturae, the ladder of nature.