How Should Chemists Think?

The Vatican holds a fresco by Raphael entitled The School of Athens. Plato and Aristotle stride toward us. Plato’s hand points to the heavens, Aristotle’s outward, along the plane of the earth. The message is consistent with their philosophies—whereas Plato had a geometric prototheory of the chemistry of matter, Aristotle described in reliable detail how Tyrian purple (now known to be mainly indigo and dibromoindigo) was extracted from rock murex snails. Plato searched for the ideal; Aristotle looked to nature. Modern chemistry faces the quandary that Raphael’s fresco epitomizes. Should it follow the hand sign of Aristotle or that of Plato? Is nature as fertile a source for new materials as some assert it to be? Can we, for example, hope to make better composites by mimicking the microstructure of a feather or of a strand of spider’s silk? Are chemists better advised to seek their inspiration in ideal mathematical forms, in icosahedra and in soccer balls? Or should we hazard chance? To some, the division between natural and unnatural is arbitrary; they would argue that man and woman are patently natural, and so are all their transformations. Such a view is understandable and has a venerable history, but it does away with a distinction that troubles ordinary and thoughtful people. So I will distinguish between the actions, mostly intended, of human beings and those of animals, plants and the inanimate world around us. A sunset is natural; a sulfuric acid factory is not. The 1.3 billion head of cattle in this world pose an interesting problem for any definition. Most of them are both natural and unnatural—the product of breeding controlled by humans. The molecules that exist naturally on the earth emerged over billions of years as rocks cooled, oceans formed, gases escaped, and life evolved. The number of natural molecules is immense; perhaps a few hundred thousand have been separated, purified, and identified. The vast majority of the compounds that fit into the unnatural category were created during the past three centuries. Chemists have added some 70 million well-characterized molecules to nature’s bounty.