Meanwhile, smell biologist Tim Jacob of Cardiff University in Wales, says that rotten egg smell is a good example of the vibration theory's appeal. Sulfur is a chemical hallmark of rotting organic material—something that is dangerous for us to eat. And molecules containing sulfur almost always smell horrible to us, he says—just as should be the case if evolution worked properly to favor our survival.
But there's no single shape or simple chemical property that sulfur universally confers to every kind of odorant molecule. On the other hand, sulfur does add signature vibrations to a molecule that a molecular vibration–sensitive nose might detect. "I do all my research without needing to know which model most accurately describes what's going on," Jacob says. But, he says of the vibration theory, "from a biological point of view it has great interest."
And that keeps fans of this fight watching and wondering: Which side will ultimately score the knockout punch? And who will need the smelling salts?