Linnaeus and the New Classification

Carl Linnaeus (1707-1778) was a Swede who attended Upsalla University, where he became especially interested in the study of plants. It was likely at this time that he began to consider using the sexual parts of the plants as a basis for classifying them. In 1732 he became an official "collector" of specimens for the Academy of Sciences at Upsalla, and made a trip across the norther, arctic part of Sweden (Lapland).

Linnaeus' most famous work was his Systema Natura, the first, rather brief edition of which appeared in 1735. He issued elevent further editions for a total of twelve, expanding each until the work was a massive compilation and more importantly, systematic classification of each species of plant and animal then known to botany and zoology. (Elsewhere, Linnaeus also classified minerals and diseases).

Linnaeus followed two basic principles in the logic of his classification systems:

Linnaeus' great innovation in the classification of plants was to organize them according to the number of their "stamens" (male parts) and "styles" (female parts). The number of male parts determined the class; and within a given class, the number of female parts determined the order. Species were well-differentiated types within a genus.

Linnaeus broke new ground in the classification of animals as well. He determined the classes by considering the kind of heart and blood in each, and within each class, the order by a variety of considerations, including whether the animal was born alive or from an egg; breathed by gills or lungs; and had antennae or tentacles. Here is how this classification looked:

Type of heart and blood Further Distinctions Resulting Groupings
I: Heart with 1 ventricle (upper part of heart) and no auricles (lower part of heart)
Blood is cold and colorless
With tentacles 1. "Worms"
With antennae 2. Insects
II: Heart with 1 ventricle and 1 (ocassionally 2) auricles
Blood is cold and red
Breathes through gills 3. Fish
Breathes through lungs 4. Reptiles
III: Heart with 2 ventricles and 2 auricles
Blood is warm and red
Young are born through eggs (oviparous) 5. Birds
Young are born alive (viviparous) 6. Mammals

Note: "Worms" (Latin - "vermes") was a general class including real worms as well as all the simple organisms not included in the other orders. This group will be broken up by Lamarck into many orders.

Of particular interest is the fact that Linnaeus classified the human species in the animal kingdom. In different editions, he made numerous modifications to the details, but "man" was now part of the natural world, though distinguished by "his" soul. The term "homo sapiens" to describe our species (literally: "know thyself") is due to Linnaeus, in the third edition.

The significance of Linnaeus is manifold:

Finally, let's consider Linnaeus' position on the origin of species. Like almost all biologists of his time Linnaeus accepted the "fixity of species" (The exception was Georges Buffon, the French natural historian who intimated that species might evolve, but did not focus on this idea or place it the center of this thought). By fixity of species is meant the following claims: (i) God created each species individually and separately, with the form and functions we now observe today; (ii) Each species is perfectly adapted to its environment, with the consequence that none disappear, or become extinct.

Nonetheless, even Linnaeus began to doubt one aspect of the above claim -- and thought he had observed the origination of a new plant species. In writings in the Swedish journal Amoenitates Academicae he considered the possibility that the plant Peloria had arisent from the separate species Linaria. This speculation was quite secondary in his thinking, and in all editions of the System of Nature he defended species fixity. The notion of species evolution would be developed for the first time as the key thesis of a work in biology by Jean Baptiste Lamarck, the French biologist.