The behavior of animals is strongly influenced by pheromones — chemicals made by one animal and “smelled” by another. Mating, dominance among males, weaning, recognition of members of social groups, and level of stress are all influenced, even controlled, by pheromones. Inside of the nose of nonhuman mammals is a specialized organ for receiving pheromones, which then communicates through special neural pathways to the hypothalamus. Until the last few years, common wisdom has been that humans did not communicate using pheromones. Then four years ago, a pheromone receptor was found in the human nose.Flashback: Thirty years ago, a Wellesley College student, Martha McClintock, noticed that the menstrual cycles of women living together tended to become synchronized over time: within several months of the new school year, roommates tended to get their periods at the same time. She wondered if pheromones could trigger such a phenomenon. McClintock, who is now at the University of Chicago, demonstrated previously that pheromones cause rats to experience synchronization of their menstrual cycles. In an elegant new study, she demonstrates that women produce a pheromone in their armpits during the mid-follicular phase of the menstrual cycle that shortens the follicular phase of other women, and another pheromone during ovulation that lengthens the follicular phase of other women. There is considerable variability in the strength of response to pheromones. The chemical structure of the pheromones has not yet been determined. The pheromones are without a recognizable scent.

Comment: A new modality of human communication has been discovered, something beyond sight, sound, taste, scent, and touch: human pheromones. How much human behavior might be influenced (and ultimately manipulated) by pheromones? The answer could be profound.