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Biology 202
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Maureen Kyin

Have you ever wondered how different species know when to mate and who to mate with? How can they tell the difference between someone of the same sex, much less whether another organism is of the same species? This can be answered by chemical signals kn own as pheromones. Pheromones are unique and highly specific chemical signals produced by an organism that signals its presence to other members of the same species. Each organism have different pheromones they release during mating that helps them to id entify each other and start the process of mating. Pheromones come not only in forms of sex attractants, but also as alarm pheromones, aggregation pheromones, and dispersion pheromones(1).

How do we know that such a chemical exists in organisms? In 1956, German scientists were able to identify the first ever pheromone in silkworm moths. After 20 years of research and over half a million female moths later, they were able to extract a pecu liar compound from certain glands located on the tip of the abdomen. When even a small amount of this substance was exposed to male moths, they would begin to beat their wings madly in a iflutter dancei. This indicated that they had detected the powerfu l sex attractant from the females that caused this type of behavior. After extracting extraneous matter and purifying the substance, scientists ended up with the first ever chemically pure pheromone. Since then, various other organisms have been studied and more is understood about the effects of pheromone, but not much is known about how pheromones work in more complex vertebrates such as humans.

The next logical question to ask is how are these chemical signals recognized? Studies have shown that pheromone is first recognized by the chemical receptors in the vomeronasal organ (VNO) and olfactory bulbs located in the nose; signals are then sent t o the hypothalamus of the brain. In an experiment conducted on virgin male mice where their VNO was removed, the mice were found to generally not mate with receptive females, even if the maleis olfactory nerves were not damaged. This showed that the VNO s are needed in order start certain chains of reactions already programmed in the brain. Further studies show that when male mice have begun to associate sexual activity with other cues from females, including smells they become less dependent on the VNO s. A sexually experienced male whois VNO is removed will mate almost as frequently as a male whois VNO is still intact(2).

One of the leading researchers in this hot topic is psychologist Martha McClintock of the University of Chicago. In a paper published in the journal Nature, she reported what may be the best evidence of human pheromones yet. In a straightforward experime nt, she was able to speed up and slow down the monthly menstrual cycles of a group of women by exposing them to the smell of sweat from other women.

In a simple experiment involving 29 student volunteers, she used pads to collect released molecules from the underarms of 9 women volunteers either before or just after ovulation. The substances collected from the pad were treated with isopropyl alcohol to mask any odor and applied to the upper lips of the other 20 women volunteers. This resulted in the acceleration or shortening of their menstrual cycles, depending on which of the swabs was applied under the nose. Volunteers who were treated with the pre-ovulation pads experienced shortened menstrual cycles by as much as 14 days in 68% of the women. When exposed to the ovulation-phase pads, a different 68% experienced cycles that were up to 12 days longer. From this she believed that the female ovul ation command was carried out by pheromones.

Still further research and information is needed in order to determine what these pheromones do to the human body. If they do exist, how does our body process them? Do we have a vomeronasal organ like those found in mammals and reptiles to help detect f or pheromones? Studies have long shown the presence of the VNO in humans, but humans lack the characteristic capsule and large blood vessels of other mammals. The connections between what looks like VNO receptor neurons and the brain have not been demon strated. However, the study conducted by McClintock already suggests the notion of chemical communication in humans. This evidence is shown by the synchronization of menstrual cycles among women who live together.

What about choosing the right partner for mating in humans? Do we choose solely on appearance and personality? Or do these chemical signals somehow come into play? Just recently, there have been magazine articles and news reports of human pheromones th at are synthetically made and guaranteed to attract someone of the opposite sex. Could this really be a secret love potion of the 90is or is it all just another hoax to swindle consumers out of money? There are numerous websites luring people by claimin g they have the secret formula for iinstant sex appeali and give tips on how to most effectively use their product and enhance it's effects on the opposite sex. Do humans have pheromones which help to woo others of the opposite sex?

One thing for sure is that all these products are made using the same essential ingredient: androstenone (the male pheromone) and androstenol (the female pheromone). It is these two chemicals which the brain processes unconciously causing physiological a nd behavioral changes. Unfortunately, not too much is known about these particular pheromones. Studies are being conducted on pigs, which are found to give off pheromones similar to those found in humans.

As we age, our olfactory acuity declines. This may be a reason for why as the older we get, the less inclination there is to be sexually active. Our nose and olfactory system are no longer able to detect these subtle chemical signals that others of the opposite sex or our partners release. Studies have shown that this loss of olfaction is not consistant in geographic regions nor is it the same for both males and females. Women were reported to have higher levels of olfactory functioning than men(3).

The possible benefits of using synthetic pheromones are being studied in different fields currently. For example, instead of using pesticides, can we instead use pheromones from insects to stop the process of mating? Or would the animals undergo some so rt of mutation, making them resistant to their old chemical signals, and develop a slightly different one? There are still many questions out there about these natural chemical signals which are released by organisms. Are they of more benefit than we th ink? Or are we making them out to be more than they really are? For now, only time and tedious research will tell.


1) University of Wisconsin at River Falls

2) Howard Hughes Medical Institute

3) HealthGate

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