The Species Concept and Breeding Systems

Abstract

People group and organize entities or observations as a way of understanding the world. We also believe that the structures we generate doing this fundamental taxonomic activity approach the “true” organization of the natural world. Initially few characters, often of a single class, are available for organizing individuals into groups. As new characters, and especially those of a different nature or class, become available, the effectiveness of the original classification is tested and evaluated. An ideal taxonomy results in the same classification regardless of the nature of the characters used. In biology the species level was more effective than higher levels of classification in forming “natural” groups, i.e., those in which different classes of characters resulted in the same or similar groupings. In this century the greater effectiveness of the species level of classification could be rationalized through the gene pool shared by members of this evolutionary unit. Along with this new evolutionary definition of species came the discovery that morphologically similar Drosophila could sometimes be divided into more than one genetic species. These became known as sibling species.