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Function of Pheromones

One of the first discoveries of pheromones was in the 1930s. Entomologists noticed that female moths are able to excite male moths even when the males cannot see or hear them. They discovered that the males actually smell the fragrance of the females in the air with a very sensitive antennae. Eventually the scientists were able to isolate the fragrance and they found out it can stimulate millions of moths with just three hundred millionths of an ounce. ("Following our noses", Time Magazine, 1998, 151:73-2) It was determined that only a single molecule of this pheromone was needed to stimulate the receptor cells of the moths. Scientists later discovered that the pheromone was secreted from the abdomen of the moth and was a chemical named bombykol (named after the moth, Bombyx mori) and it's chemical structure was trans-10-cis-12-hexadecadienol. (Sociobiology: The Abridged Edition, 1980, 93)

Other discoveries soon followed, including the detection of pheromones in bee colonies. The queen bee emits pheromones that prevent other female bees from maturing sexually so the queen will remain dominant. Pheromones were also discovered in fish. The females release scent markers that cause male sperm counts to quintuple overnight. Other amphibians also emit a pheromone that warns others of their species to keep out of harm's way. The list goes on, including wolves and musk ox which claim territory by urinating on it, and voles which use their urine as an aphrodisiac to cause females to ovulate within 48hrs. ("The influence of social and endocrine factors on urine-marking by captive wolves (Canis lupus)", Hormone Behavior, 1990, 24:497-509)

Some of the most well known and studied pheromones exist in social insects, including honeybees, ants, and termites. The most popular uses of pheromones for these species include the caste system, or individual and class recognition, alarm, and assembly and recruitment. (Sociobiology: The Abridged Edition, 1980, 105)

First, we'll start with honeybees. There are a minimum of 32 compounds just in the head of honeybee queens. Two of the most popular contrasting pheromones in honeybees are 9-keto-2-decenoic acid and 9-hydroxy-2-decenoic acid. The first one is an inhibitor that operates in conjunction with other body scents and it reduces the tendency of the other worker bees to construct royal cells and to rear new queens, which would be rivals of the mother queen. It also inhibits ovarian development in the workers, which prevents them from becoming rivals to the queen. Every spring the production of this pheromone is slightly lowered to allow the production of a few new queens. The second pheromone causes clustering and stabilization of worker swarms and it helps to guide the swarms from one nest site to another. (Sociobiology: The Abridged Edition, 1980, 97, 107) Studies have also shown that the 9-ketodecenoic acid is initially transmitted by grooming between bees. This are of study is still not well developed, but it leads scientist to believe that other colony odors and pheromones are transferred by grooming. (Sociobiology: The Abridged Edition, 1980, 104)

Click here for a list of pheromone controlled honey bee activities (Pheromone Communication in Social Insects, 1998, 261)

Click here for picture of pheromone spread in a bee hive (Picture taken from: Pheromone Communication in Social Insects, 1998, 225)

Ants are another popular example of pheromone use. The Dufour's gland in fire ants secretes a pheromone that is an attractant that is effective on all castes during their adult lives. It is also used to recruit workers to new food sources, organize colony emigration, and as an alarm when used in conjunction with a cephalic secretion. Ants also use other numerous trail phermones which control the amount of workers leaving the nest. Studies have been done that show the number of individuals leaving the nest is a linear function of the amount of pheromone released. The ants that lay the pheromone trail actually lay a specific quantity of it based upon the circumstances. For example, if there is food that is more desirable, more phermone is emitted, which attracts more worker ants. It becomes a form of mass communication for the ants. (Sociobiology: The Abridged Edition, 1980, 99)

Termites use pheromones in many ways similar to those of ants. A well-known termite pheromone is 3-hexen-1-ol, which is used to attract other termites over several centimeters for recruitment and assembly. Another termite pheromone is used for alarm. If there is a breach in a nest wall, termites will release a pheromone as an alerting trail to all other termites in the nest to warn them of the danger. (Sociobiology: The Abridged Edition, 1980, 105)

One popular question today is do humans use pheromones to communicate with each other? According to an article in the journal Nature, the answer is yes. The article discusses a paper that was published by a psychologist named Martha McClintock. McClintock was actually able to control the speed of the monthly menstrual cycle of women by exposing them to a whiff of sweat from other women. McClintock believes that it is pheromones that control the ovulatory command and that this insight can lead to new insights in human communication and medical application. The one question is how far-ranging can the pheromones be? McClintock is pushing to use pheromones as fertility enhancers and other researchers are trying to develop mood-altering pheromones for depression. ("Regulation of ovulation by human pheromones", Nature, 1998, 392:177)

Another study that supports the possibility of pheromone communication between humans is currently under review and will be published in the Archives of Sexual Behavior in June 2002. The article is titled "Does Semen Have Antidepressant Properties?" and was written by Dr. Gordon Gallup, Jr. Dr. Gallup and his colleagues performed a study to determine the rate of depression in sexually active females compared to condom use, which was an indirect measure of the presence of semen in the reproductive tract. In the end, the results showed that females who engaged in sexual intercourse but never used condoms had significantly lower scores on the Beck Depression Inventory than females who used condoms. They also discovered that the frequency of sexual intercourse was related to the length of the couple's relationship. ("Does Semen Have Antidepressant Properties?", Archives of Sexual Behavior, June 2002)

The actual numbers from Gallup's study are amazing. The averages of the scores on the Beck Depression Inventory were significantly higher for sexually active females who used condoms, almost 50 times as high. Also, only 4.5% of sexually active females who never used a condom had attemtped suicide, in comparison to 7.4% for those who used condoms sometimes, 28.9% for those who used them usually, and 13.2% for those who always used them. Those who abstained from sexual intercourse had a 13.5% suicide attempt rate and oral contraceptives had no relationships similar to those of condom use. ("Does Semen Have Antidepressant Properties?", Archives of Sexual Behavior, June 2002)

Gallup discusses some other possibilities for his finidings in his article and shows how all of them were unrelated and not likey to be explanations. In then end, he concluded that since previous research has shown that semen is absorbed through the vagina, something in the chemical makeup of semen causes a change in the depressive symptoms of females. Gallup agrees that further studies and testing are needed to investigate the relationship between depression and semen and what causes it, but it does show the possibility of chemical communication, also known as pheromones, in humans. ("Does Semen Have Antidepressant Properties?", Archives of Sexual Behavior, June 2002)

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