Serious physicists seem at present more aware than many biologists of its confusions and inadequacies. At the end of the nineteenth century, physicists'widely believed that classical physics gave the general outlines of a complete mechanical explanation of the universe. Since then, relativity and quantum theory have overturned such notions altogether. Of course, molecular biologists generally ignore the implications of physics, except when these implications support their own position. In this connection, it might be appropriate for them to consider that the nineteenth-century view of physics. Classical physics was swept aside and overturned, being retained only as a simplification and an approximation valid in a certain limited domain. Constructive metaphysics has its own thoughts, and science its own motives. If the word science means what it seems to mean here- primarily the search for particular facts - then it is powered emotionally by the familiar motive of detailed curiosity.