Aristotle Categorized Species as Immutable, the Theory of Evolution Upended This

Aristotle noted three characteristics of his concept of species. First, each species is a whole. It is comprehensive, representative of all the objects embraced within it, and any one of these objects may be used as an example of all others. The species tree, for example, embraces all trees whether they are used for timber or for firewood; and any given tree may exemplify the species which includes all trees.

Second, any one species comprises objects which have common or identical elements or characteristics. Aristotle emphasized form. Each kind of thing is produced under its own form. All oaks have the same form, regardless of their location, whether they stand on the eastside of the house or the west. Thus species is the representation of the common, typical, and standard form of the individual objects which it comprises.

Third, a species is permanent. In addition to being comprehensive and representative of the common form of its component parts, a species is permanent and unchanging. After an individual tree dies, for example, the species of tree continues to exist unimpaired. Similarly, one stone may crumble into dust, but the species of stone still exists. It does not matter that individual objects come into being and cease to be, either cyclically or otherwise, the species in which they are embraced has an unending existence.

The publication of Darwin s Origin of the Species sixty years ago wrought havoc in contemporary thought. Why? Because people were so completely under the influence of Aristotelian thought patterns. Aristotle had taught that every species is permanent and unchanging; but now Darwin was theorizing that each species had had its origin, and that it was subject to change——a challenge indeed to a two thousand year old traditional manner of thinking. It is not to be wondered at that Darwin's theory upset so many of his contemporaries. It ran exactly counter to the tradition which had dominated so many generations, and which had resulted in people taking for granted the unchanging nature of species.

The reason that this type of thinking constitutes such an important milestone in the history of philosophy is that the concept of species is essential to thought and the first step toward knowledge. When one is walking in the woods, for example, and asks the identity of a tree or a weed, and he is told that it belongs to such and such a species he can place it right away, and recognize its relationship to other trees or weeds. The greatest single contribution of Aristotle was his invention of the concept of species, a concept which enables us to classify things under common headings in accordance with their common characteristics.

Aristotle's system of thought, which defined and categorized the world, gave humans the ability to discuss and debate with common references. But it was flawed in that it defined classifications as immutable and unchanging.