Though sometimes (namely after mowing the grass) it may seem like he (or she) smells more like a gorilla, that special person in your life has a personal smell that belongs only to him or her. Just like a fingerprint, genes code for mechanisms that produce unique odors that can be identified if not by you, more than likely by that person's mother. This whole concept, reviewed by Stephen Young, was first discovered while Edward and Jeanette Boyse happened to notice that their mice wouldn't mate with other mice who had the same genetic make-up (Young 1988). Since the mice obviously had no X-ray vision, nor the capability to practice genealogy, they drew the conclusion that they were sniffing each other's urine for a genetic difference; several experiments later, they were convinced that the sense of smell was definitely the key.
Intrigued, other scientists began manipulating genotypes to see just how few genes would have to be different before the mice would toss out their inhibitions. Researchers Kunio Yamazaki and Gary Beauchamp discovered that the major histocompatability complex, a string of genes that code for proteins involved in the immune system, was the key to all of this (Young 1988). All they had to do was manipulate a single gene on the MHC, and the mice would smell enough of a difference to mate. More testing was then done to hopefully confirm the idea of MHC involvement in personal odor. Prim Singh and his colleagues exposed rats to radiation and then performed bone marrow transplants using marrow from donor rats with different MHC genes. Several weeks after the transplant, glycoproteins coded for by the donor MHC began appearing, while the glycoproteins of the rat's original MHC disappeared. The recipient rat, therefore, took on the odor of the donor rat (Young, 1988).
Why would the MHC play such an important role in personal odors? It makes sense when you consider that the MHC is responsible for producing glycoproteins that sit on most cell surfaces in the body like name tags; these name tags say "Don't eat me!" when the cells of the immune system are on the prowl for foreigners. Since, on a cellular level, the MHC labels cells as "self," it makes sense that it could find a way to proclaim "self" on a multicellular, multi systematic level. Now, this is all still a little ambiguous, but more and more research is being done to investigate this idea.
Two ideas of how the MHC has accomplished its name tagging on a organismal level have been hypothesized. First, since the MHC is a strand of genes that is different for everyone, these genes code for different proteins (Young 1988). These proteins get into the bloodstream and eventually end up in the urine (or other glands which will be discussed later) where bacteria feast on them. The different types and concentrations of proteins serve as host to different types and concentrations of bacteria, which produce different types and concentrations of waste, which produce different types and concentrations of odor; therefore, different genes indirectly produce different odors. Another idea involves the glycoprotein name tags used on the cellular level. It is thought that these glycoproteins eventually make their way into the bloodstream, where they either break down and become small enough to become volatile in the urine or they remain intact but drag other, smaller chemicals with them into the urine from the blood and that it is these small chemicals that break off and become volatile--a "urinary potpourri," depending on the type of name tag that you have (Young 1988).
In addition to your individual scent, it is now believed that families possess related scents so that though each member has his own particular odor, the family smells are related. To investigate this idea further, Richard Porter conducted experiments involving mothers of newborns and tee shirts that had been worn by the infants (Porter 1994). He found that mothers easily identified their babies by scent alone, even if the mothers had had less than five hours of contact with the newborns. While conducting this study, the mothers told him repeatedly that the infants smelled like its siblings. To look into this phenomenon, he then asked unrelated subjects to try to match shirts that belonged to a particular family. For example, one experiment involved four shirts and a target shirt. The target shirt had been worn by a mother, and one of the four shirts had been worn by that mother's child. The unrelated subject had to match the child's shirt to that of the mother based on similarity of scent--a familial odor. The same type of experiment was done with clothing belonging to husbands and wives. There was no similarity in their odors. Porter concluded, therefore, that each family member contains a portion of the familial smell in his or her individual odor.
Still not convinced that body odor is a good thing? If you enjoy sex, then listen up. Chemicals called pheromones that are thought to be released by your body through the despised armpits (complete with hair) may be responsible for that enjoyment. Pheromones are hormone-derived aromatic messengers which control the sexual development and behavior of all individuals within a particular species of animal. “Pheromone” is derived in part from the Greek word "pherein" which means to transfer, and in part from the word "hormon" which means to excite (Kohl 1995). Until 1959, they were called "ecto-hormones," short for external hormones. Pheromones were associated with hormones because they are produced in the metabolism or breakdown of hormones, and, like hormones, they act on genes to control different behaviors. Because pheromone messages are carried by air from one animal to another instead of by blood to different organisms, joining the prefix "ecto" indicated they were different. In 1959, "pheromone" replaced the term "ecto-hormone" because more differences became clear.
There are two types of pheromones, signaling and priming. Signaling pheromones cause a more or less immediate change in behavior. Not much is known about this type, but it is suggested that they act on genes in cells that produce neurotransmitters. Priming pheromones control hormone and neurotransmitter production in different areas of the brain. They can trigger gonadotropin-releasing hormone (GnRH) production, which then regulates the level of different hormones, which in turn affects development, metabolism, and various behaviors (Kohl 1995). The effects of priming pheromones are evident in pregnant mice. Eric Keverne at the University of Cambridge has shown that if, within three days of mating, a pregnant mouse smells the odor of a mouse other than her mate, she will abort her pregnancy; therefore, the priming pheromones of another male can affect her physiology ( Keverne 1990 ).
Researchers have yet to decide if humans actually have pheromones, but most recent studies suggest that they do, in fact, exist in humans. This hypothesis is based on anatomical and physiological details in humans. Pheromones are believed to work in part through apocrine sweat glands, glands that have different structure than that of regular saline-secreting, or "eccrine" sweat glands. The apocrine glands are located on the armpits, genitalia, and chest: the hairier areas of the body. Apocrine glands give off proteins which bacteria use as their source of nutrition. These bacteria then excrete their waste products, resulting in different odors. Also found in axillary sweat are two steroids: 5 androst-16-en-3-alpha-ol, a musky smelling steroid, and 5 androst-16-en-3-one, which has a smell similar to that of urine. Both have chemical structures similar to that of the male sex hormone, testosterone (Young 1984). Recent studies have even discovered androstenone in human saliva, with higher concentrations detected in men's spittle than in that of women.
Stephen Young and James Kohl refer to studies in which pheromones change reactions of women to men and vice versa. A study at Birmingham University which sprayed canned androstenone at various concentrations onto a seat in a doctor's office waiting room found that women seemed to be attracted to the chair, while at the highest concentration men were repelled (Young 1984). At Guy's Hospital in London, androstenol was sprayed in several telephone booths at the London train station. Women were reported to be spending more time in the booths that were scented than in those that were not (Kohl 1995). Further, androstenol has been shown to enhance men's opinions of photographs of women and female interviewers assessments of male candidates (Young 1984).
There are also bizarre cultural uses for human pheromones. Vaginal secretions and odors are also thought to be pheromones. At New York University, a Nigerian student shared with his class stories from his home where women, suspecting their husband's attention was wandering, would use their vaginal secretions and menstrual fluids in a special soup with the hope of regaining his lost affection. Another example of the folk use of vaginal secretions was discovered in a special Brazilian coffee. Women filtered this coffee through their well-worn underwear hoping to gain a male friend's fondness (Kohl 1995). Recent studies focus on the organic acid in vaginal secretions, such as acetic acid, propanoic acid, and butanoic acid. These three acids are collectively known as copulin. Michael Kirk-Smith at Birmingham University has shown that female monkeys wearing copulin receive more sexual attention than those without it (Young 1984). There are two main effects of pheromones which are interrelated( Kohl 1995). First, in the hypothalamus, it is theorized that pheromones may control the production of GnRH that is responsible for starting the cycles of sex hormones that originate in the pituitary glands and involve the adrenal glands, ovaries, and testes. This long-term effect of hormone release affects all sexual development, physiology, and behavior. Second, it is believed that pheromones can trigger the production of GnRH that acts as a neurotransmitter. This affects neuron activity, further influencing sexual development and behavior.
An example of a neurotransmitter affected by pheromone release is phenylethylamine (PEA) (Kohl 1995). PEA is found at synapses at the end of some nerve cells where it helps electrical impulses jump from neuron to neuron. It acts as a stimulant of the limbic system; the scent of a loved one sends a storm of messages to the limbic brain via PEA. These messages are then sent to the hypothalamus, which is responsible for the production of an andrenocoricotropic hormone (ACTH) releaser which in turn stimulates the pituitary gland to produce ACTH. Once ACTH is carried from the blood by the adrenal gland receptors, corticosterone is produced. This will increase the breakdown of glucose. This pathway, stimulated by PEA, is responsible for the feeling of being "in love." Now, men, don't get jealous. You may have heard somewhere that women have a keener sense of smell and can pick up on your pheromones a lot better, but there is no proof that you cannot enjoy these smells just as much. After reading study after study, it seems that no one can agree on whether or not there is a difference between men and women in their ability to distinguish certain odors. Some claim that females are far superior sniffers; others insist that there is no proof to verify that claim. The only thing that is definite is that there needs to be more research done in the area of gender-related smell.
As far back as 1899, there have been reports that females have a better sense of smell (Koelega 1994). One of the most highly publicized studies, The National Geographic Smell Survey done in 1986 claims that there are definite trends in female superiority in both detection of odors and in the ability to correctly identify them (Gilbert and Wysocki 1987). However, as Harry Koelega points out, there are problems with that survey, including an uncontrolled response bias. Koelega, once a believer that women are more able to detect smells, conducted a study with the intention of clearing up the matter permanently. He used 112 subjects over a period of four sessions and averaged the results. Unfortunately, there was no pattern to the results. Women showed superiority in some odors but not others; no conclusions could be drawn except that the matter is still unresolved (Kolega 1994).
Of the students who correctly identified their own shirts, three were female, and two were male. The four females correctly distinguished male or female about 50% of the time. The males correctly distinguished an average of about 50% also. With such a small experimental group, it is impossible to place any significance on these results; however, the comments made by the students regarding "female smells" and "male smells" are very interesting.
Of the tee shirts that were worn by males but mistaken for those worn by females, words used to describe those shirts included “weak odor,” “scentless,” “sweet,” “fruity,” “light,” “clean,” and “good.” The shirts that were worn by females but mistaken for those worn by males were described as “sweaty,” “musky,” “spicy,” “smoky,” “mildewy,” “smelly,” and “strong.” This leads to the conclusion that people assume that stronger or more offensive odors belong to men, possibly accounting for some of the discrepancies in those gender studies.
Females, then, are associated with things that are “sweet” and “clean,” while men are assumed to be “smelly” and “sweaty.” Somewhere along the way, society teaches that women are supposed to smell this way and that allowing your body odor to rear its ugly head is unacceptable. Just look at the shelves of the nearest drug store: men’s “deodorant” comes in “masculine” scents like “musk,” “sport,” and “spice,” while women’s “antiperspirant” is available in “powder” and “baby fresh” scents. All attempts at finding the exact components of these fragrances failed. It would be interesting to find these chemicals and to see just how it is decided whether a particular odor should be used in products manufactured for men or for women.
The odor prejudice brings us full circle. Humans seem to be the only animals concerned with hiding their smells, so it would be interesting to see how relationships would change if all of our anti-perspirants, perfumes, and powders were taken from us. We think that this just may be a solution to the dramatic rise in the divorce rate in this country. Well, that may be a bit dramatic, but who knows? The next time you are looking for a little love and affection, don’t be shy. Bypass that shower after an afternoon of mowing the lawn! Be sure and let us know what happens.
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