The Truth About Pheromones, Part 1

How we communicate chemically

Posted May 18, 2009

The topic of pheromones needs some explanation, so I'm going to start by giving you an overview of what pheromones are. The word "pheromone" was coined in 1959 by Peter Karlson, a German biochemist, and Martin Lüscher, a Swiss entomologist. It is derived from the Greek, pherein meaning "to carry" and hormon meaning "to excite"— in other words "carrier of excitement." Karlson and Luscher used this word to describe what they were witnessing in their insect lab-that a chemical substance released by one insect-in their case termites, seemed to affect the behavior of other termites around it. They coined the word "pheromone" to describe the general phenomenon that a chemical released by one animal could affect the physiology or behavior of other animals of within its species. Simply put, pheromones are chemical communication, and they are highly important for animals, like the social insects who use chemical signals as their primary mode of communication.

Pheromones also convey important information for many non-insect species, including primates. The reason for the bawdy connotation of "pheromone" in our modern parlance is because for mammals, one of the most important forms of messages they carry are communiqués about reproductive status and availability. For example, androstenone, a pig pheromone, turns a sow's attention to mating and nothing else, and induces her to assume the sexually ready position. This automatic reaction has been exploited by pig farmers wishing to spare the expense of keeping male studs. There is a commercially available spray of androstenone called "Boar-Mate" that given to a sow, eases the process of artificial insemination. A male rhesus monkey will even ignore an amorous female in heat if he can not detect the pheromones that signal her fertility. The fact that other mammals produce and react to pheromones which play an indispensible role in their sex lives is why people in the fragrance industry hold out hope for a human sex pheromone. If such a chemical aphrodisiac could be discovered and bottled it would be the biggest thing in history of cosmetics and fragrance.

Because many pheromones involve chemical secretions that are "smelled," or have a smell, this has led to the erroneous conclusion that pheromones are odors, which they are not. Pheromones are chemicals which may or may not be smelled at all. It is also the case that pheromones are not normally picked up and processed by the olfactory system, but rather by a separate structure called the vomeronasal organ (VNO) which connects to the accessory olfactory bulb, an independent structure from the main olfactory system. The VNO is located above the roof of the mouth and evolved to detect large molecules and molecules that are dissolved in liquid, which is why licking various body parts-as dogs do when they great each other—is a key way for pheromonal information to be received. We can only "smell" with our nose small airborne molecules.

All animals that have been documented to use pheromonal communication use their VNO for detecting them. One major problem for creating our billion dollar pheromonal potion is that we do not have a functioning VNO. Human embryos may have a VNO, but after birth this tissue disappears. There continues to be controversy surrounding this issue, but overwhelming evidence points to there being no functioning neural tissue in humans that corresponds to the VNO of other animals. Moreover, although it may be possible for the main olfactory bulb to process pheromones, the accessory olfactory bulb to which VNO nerves normally project, has not been found in humans. So what does this mean for us and pheromones? Stay tuned for next time...!

Rachel Herz is the author of The Scent of Desire and on the faculty at Brown University.

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