Stevens, P. S. (24 Irving Street, Arlington, Mass. 02174) 1974. Space, Architecture, and Biology. Syst. Zool. 22:405-408.-When he analyzes an existing biological form, the taxonomist seldom considers alternative forms that might have existed in its stead. Consequently, he does not benefit from the lesson learned by the architect-Lwhose business it is to consider alternative forms-that physical organization is largely determined by the properties of space. A few examples suffice to show that space also imposes order on the development of biological form. In a marvelously sweeping statement, the late Swiss architect Le Corbusier said that the first act of existence is the taking possession of space. At first glance, the statement may not seem particularly meaningful. For architects, familiarity has made it a truism. But for biologists, t-he statement may merit a second look. To make the usurpation of space the handmaiden of material existence encourages a view of the genesis of form that offers special rewards to those who search for fundamental principles of organization. Let us compare the attitudes of the biologist and the architect toward the development of form. In the simplest terms, the biologist, or at any rate the taxonomist, starts with the design solution-the mollusk, say, or the fern-and seeks to reconstruct its evolutionary development, to retrace the steps in the maturation of its design. The architect, on the other hand, starts with an empty building site and chooses-wit-hin the constraints of budget, materials, orientation, and so forth-the best possible building to erect on it. At each step in the design process, he attempts to select the happiest solution. The difference in approach between these two professionals is elucidated by the words of the Stigmatine Fathers: Some people see things that are and say why? We dream of things that never were and say why not? The first half of that epigram describes 'Mr. Stevens is the director of the Architectural Planning Office of the Harvard Medical Area, Boston, Massachusetts.-Editor. the practical biologist who considers the things that are. The second part describes the architect who drifts above the clouds dreaming of remote possibilities. Lest the biologist feel slighted, however, he has only to witness how quickly the dreaming architect comes down to earth upon discovering that the empty site permits the materialization of only a few of all the lovely things that never were. The realistic alternatives are inevitably fewer than the designer first imagines. The space at his disposal contains its own constraints, and those constraints dictate the organization of all the elements that can take possession of it. That lesson benefits the biologist as well. Proceeding as he does by way of analysis rather than synthesis, the biologist seldom receives the message as forcefully as the architect. But the general space that all things share contains constraints, and those constraints dictate the organization of the elements that can take possession of it. In biology as well as architecture, the possible configurations are strictly limited. The fact that space imposes constraints on nature's productions should be a great boon to the biologist. Organization need not be ascribed totally to biological operators, inductors, evocators, and regulators. Much of the regulation is imposed by the space in which the form resides. The reason why that organizer has been difficult to see is that it is everywhere you look. Biologists have revealed two ways in which space affects the form of things.