A Controversial History
The sense of smell has been a topic of debate from humankind's earliest days. The Greek philosopher Democritus of Abdera (460-360 B.C.) speculated that we smell "atoms" of different size and shape that come from objects. His countryman Aristotle (384-322 B.C.), on the other hand, guessed that odors are detected when the "cold" sense of smell meets "hot" smoke or steam from the object being smelled. It was not until the late eighteenth century that most scientists and philosophers reached agreement that Democritus was basically right: the smell of an object is due to volatile, or easily evaporated, molecules that emanate from it.
In 1821 the French anatomist Hippolyte Cloquet (1787-1840) rightly noted the importance of smell for animal survival and reproduction; but his theorizing about the role of smell in human sex, as well as mental disorders, proved controversial. Many theories of the nineteenth century seem irrational or even malignant today. Many European scientists of that period fell into the trap of an essentially circular argument, which held that non-Europeans were more primitive, and therefore had a more developed sense of smell, and therefore were more primitive. However, other thinkers—Cloquet for one—noted that an unhealthy fixation on the sense of smell seemed much more common in "civilized" Europeans than to "primitives." The first half of the twentieth century saw real progress in making the study of smell more rational. The great Spanish neuroanatomist Santiago Ramón y Cajal (1852-1934) traced the architecture of the nerves leading from the nose to and through the brain. Other scientists carried out the first methodical investigations of how the nose detects scent molecules, the sensitivity of the human nose, and the differences between human and animal olfaction. But much real progress on the workings of this remarkable sense has had to wait upon the recent application of molecular science to the odor-sensitive cells of the nasal cavity.