These biochemical messages are called pheromones. In animals this perceptional sense complements sight, hearing, smell, taste, and touch. The term pheromone was first used in the l950s to describe the essence which female silkworm moths release into the air to entice males to mate with them. Bees whose hive is threatened will answer the call of a pheromone that commands them to swarm and sting in concert, thus driving away the intruder. A few molecules of a pheromone floating past a male hamster's nose will send him on a frenzied hunt for the female ready to receive his amorous advances.
Animals acting out pheromone orders can make almost comical mistakes.
If one of the pallbearers picks up the scent of death in the process of disposing of the body, he may find himself the target of ejection. As in a good mystery, the elements of the human pheromone story lay strewn about in puzzling bits and pieces for about a century until scientists, using deductive powers like those of Sherlock Holmes, made sense of the clues. In any case, no one knew what function this organ performed. No great increase of curiosity about the human VNO followed. One prominent neuroanatomist, writing in the 1930s, suggested that the human VNO was best thought of as an evolutionary relic, a nonfunctioning piece of leftover anatomical equipment.