I should think we might fairly gauge the future of biological science, centuries ahead, by estimating the time it will take to reach a complete, comprehensive understanding of odor. It may not seem a profound enough problem to dominate all the life sciences, but it contains, piece by piece, all the mysteries. Smoke: tobacco burning, coal smoke, wood-fire smoke, leaf smoke. Most of all, leaf smoke. This is the only odor I can will back to consciousness just by thinking about it.

— Lewis Thomas, quoted in The Poetics of Smell as a Mode of Knowledge at BrainPickings. Hat tip to Becca!