The explosive accumulation of new knowledge in the biological sciences in the last decades has advanced our understanding of the basic mechanisms that underlie most biological phenomena. These advances, however, have not been uniform but have varied considerably among the different biological problems. In some cases, e.g., biochemical genetics, radical advances have been made which have changed our ideas and our approaches. In other cases, even with work which has yielded much detailed new knowledge, our under­ standing of basic mechanisms remains very inadequate. Among the lines of work that have not yet led to dramatic conceptual advances is the problem of control of biological activities. This problem is, of course, basic both to any full understanding of life as a whole, and to any real understanding of its most minute phenomena. Indeed, the myriad of biological activities that we can observe by direct or indirect means are all under the sway of most exquisitely precise mechanisms. Any malfunctioning of these mechanisms has serious consequences, not only for the particular function itself, but for all the related and interlinked activities.