The classification of species, however, began well before the eighteenth century. Aristotle distinguished species by habitat and means of reproduction, but Andrea Cesalpino produced the first significant taxonomy of plants in 1583, arranging the species in a hierarchical, graded order. His work was developed by Marcello Malpighi, who expanded his hierarchical system to include animals.
The English naturalist John Ray was the first to formulate the idea of species. His late seventeenth-century work is based on the taxonomy of Aristotle, but he provided a sounder scientific basis on which to make distinctions of various plants and animals from one another.
The single most important development in taxonomy, however, came from the Swedish botanist Carolus Linnaeus, who in 1737 superseded Ray by publishing the taxonomic system which is the basis of that used today. Whereas most previous taxonomies worked by beginning with large categories subdivided along logical lines, Linnaeus worked in the opposite direction, beginning empirically with individual species and grouping them according to their similarities. He borrowed Bauhin's system of nomenclature, and identified twenty-four classes of plants, categorizing them by the number of pistils and stamens: this classification based on reproductive organs soon became the standard system. Later he identified six classes of animals (quadrupeds, birds, amphibians, fishes, insects, and worms), following the work of Ray.
Although Linnaeus established the basis of taxonomy still in use today, those who followed him refined and corrected his sytem. Among the most important was Jean-Baptiste Lamarck, who was unsatisfied with Linnaeus's classification of invertebrates into only two classes, insects and worms. Lamarck distinguished mollusks, arthropods, crustaceans, insects, and other classes.
The classification of species carried with it considerable political and theological baggage. Voltaire, for instance, likened the hierarchical arrangement of species to political and religious hierarchies in the Philosophical Dictionary (1764). The debate became only more heated as taxonomy became entangled in arguments over evolution, as biologists began to explain both the similarities and differences of the species by placing them at different points along an evolutionary path. Early attempts to reconcile taxonomy with evolution were tentative and inconsistent: lacking an adequate empirical record (such as fossils), many theorists made wild speculations about the relationships between the species. But as the nineteenth century progressed and more evidence was collected, the gaps were filled and scientists reconciled the theory and the evidence without violence to either.
An important cousin of taxonomy is physical anthropology, the study and classification of the primates -- including human beings. Johann Friedrich Blumenbach's investigations of the primates paved the way for Buffon's more wide-ranging work.