Systematics and the Levels-of-Organization Approach

Human beings have always been preoccupied with the diversity of organisms. The psychological basis for this preoccupation is not clear, but its practical implications are obvious. This intuitive point of view was shared quite logically by those who gave biology its initial orientation and early conceptual framework. When the growing science became too vast for any one man to comprehend, it was natural that it should have split into taxonomically oriented subdivisions. Thus, at the present day, we have botanists, zoologists, and microbiologists, and departments of botany, zoology, and microbiology. Sometimes, and for various historical or practical reasons, we have other departments even more restricted taxonomically, such as entomology, bacteriology, and nematology. Beginning in the last century, when investigations of organisms had become more detailed, additional specialized disciplines were created-for example, ecology, physiology, genetics, and morphology-but these almost always remained subdivisions of the main, taxonomically oriented areas of biology. Even when one of these specialties became the focus of an academic department, one could usually understand "Plant" or "Animal" to be an unwritten part of its name. Not only did the taxonomic subdivision of biology impose a structure on research in the field until well into the twentieth century, it likewise provided a convenient basis for the circumscription of departments in universities and colleges. As with any system which provides the structure for such departments, this one has tended to channel the training of students along predetermined lines and thus has become self-perpetuating. In recent years, however, the outlook, the methods, and even the objectives of biology are being altered radically. Factual knowledge has been growing at an enormous rate and new generalizations are being formulated that unite previously separated bodies of information. As a result of this ferment, we find ourselves practicing biology in one of the most stimulating and at the same time most difficult periods in the history of the science. Biology today is dominated by the themes of simplicity, of the similarity of fundamental processes throughout the living world, and of the statistical regularity of populations and communities. Formerly, biology was concerned almost exclusively with the kinds of organisms: the ways they are put together, how they develop and function, how they are classified. Most of us feel that we know intuitively the place of systematics in this traditional concept of biology. Now it is clear that we must ask ourselves: what is the place of systematics in the biology that is developing today? To attempt an answer to this question, we must first briefly consider why biology as a whole is changing and in what directions it may be going. Increasingly detailed investigations of cells and molecules have led in our time to the spectacular and impressive advances of molecular biology which clearly promise to give us a much broader and deeper understanding of vital phenomena than could have been imagined ten years ago. The consequent explosive growth of molecular biology has necessarily forced a reconsideration of the structure of biology as a whole. Being completely and unequivocally outside of the traditional subdivisions of biology, it has constituted a direct challenge to the entire system of organizing biological thought. The emphasis of molecular biology on the properties common to all organisms at the molecular level has reinforced the growing attention to comparable properties at other levels. As a result of this work, considerable progress already has been made at the cellular, organismal, and population levels of organiz-