The depiction of the vibration theory as an alternative to
“shape” theory or a “lock-and-key” mechanism is misleading.
Odor chemistry involves many factors besides shape. Ethanol
and ethanethiol may have roughly similar shapes, but chemically
they are as different as roses and skunks. Using vibrations to
detect isotopes by odor is biochemically irrelevant because
animals have no need to make such distinctions. Olfaction is
a chemical sense, not a spectral sense. The relation between
odor similarity and chemical similarity is evident when one
considers not only shape but other concepts like molecular
weight, functional groups, polarity, acidity, basicity, and steric
interactions. Whether in humans or flies, odorants bind and
activate receptors through a combination of chemical features
no different from other types of receptor-based molecular signaling in biology (5).

Thomas P. Hettinger1

Department of Oral Health and Diagnostic Sciences, University of
Connecticut Health Center, Farmington, CT 06030