Following Our Noses

If you're an animal, there are few things as valuable as a good nose. In a world without speech, it's often scent alone that tells you if a stranger is in the mood to mate or in distress, is preparing to attack or about to retreat in fear. The chemicals that carry these odorless messages are called pheromones, and while most animals produce them, the highest animals--humans--were thought to be above such crude olfactory signals.

Last week all that changed. In a paper published in the journal Nature, psychologist Martha McClintock of the University of Chicago reported what may be the...