Biology 202

2006 First Web Paper

On Serendip

The process of finding a mate is a series of conscious and unconscious determinations made by the brain and body of the organisms seeking to reproduce. While men and women both emit and are affected by pheromones, females unknowingly respond to these chemical signals when searching for a partner. Most females swoon over the looks of handsome men, with defined muscle and beautiful symmetrical facial features, but fail to realize that attraction does not solely revolve around physical attributes: "it's not how you look on the outside but what's on the inside that counts". Perhaps this statement holds a scientific truth.

While looks might appear as the most important factor at the start of any relationship, what drives strong emotional feelings are a series of chemical signals being emitted by the male. These chemical signals, or pheromones, interact with specific sites in female nostrils to cause intense emotional feelings. These sites include a series of vemeronasal organs (VNOs) that process pheromone signals from men and connect directly to a part of the brain that manages basic drives and emotions. 1) Smell: The Forgotten Sense The pheromones act as emotional stimuli and carry an array of markers that can identify a particular male's major histocompatibility complex (MHC), or a cluster of genes that play an important role in immune function. 1) Smell: The Forgotten Sense To respond to continuously changing environmental selection pressures, the MHC and pheromone signals, work effectively with female mate preferences to ensure a diverse selection of allele combination for future progeny. The MHC influences both body odors and body odor preference in human females to ensure the production of genetically diverse offspring.

Pheromones themselves share similarities with odorants, or those chemicals detected by the body as odors, but both simple odors and pheromones stimulate different pathways within the brain. The difference between normal odorant signals and pheromone signals lies in the responses elicited by the brain. Odorant signals result in sensations of smell while pheromone signals trigger a characteristic behavior or psychological response. 2 ) Pheremones: What's in a name? Pheromones are processed by the vomeronasal system or accessory olfactory system, in the brain, which uses a specialized structure in the nose, the vomeronasal organ, to receive chemical signals. On the other hand, normal odor signals interact directly with the main olfactory system. 2 ) Pheremones: What's in a name? > In 1985 researchers at the University of Colorado isolated the VNOs within human nostrils and coincidentally VNOs connected directly to part of the brain responsible for drives and emotion by stimulation of the hypothalamus in the cortex of the brain. 1) Smell: The Forgotten Sense

The pheromones originate in the apocrine glands of the skin located in the axillae of the armpits and pubic region. 1) Smell: The Forgotten Sense > In humans the apocrine glands are focused in areas around the face, chest and wherever body hair exists and become activated after puberty, a time focused on finding a mate. 3) The World of Skin Care In male sexual maturation, the apocrine glands produce steroidal secretions derived from testosterone, as andorstenone (male sweat exposed to oxygen) and androstenol (fresh male sweat). 4) Male Pheromones and Sexual Attraction As a result, pheromones act as hormones or chemical messengers that are transported outside of the body to evoke responses in another. 5) Social Issues Research Centre

Current research suggests that influences of the MHC alter body odor, and male body odor preferences in females. Pheromones work with MHC specific cites as cues to persuade certain human mate choices. 1) Smell: The Forgotten Sense Recent studies support the theory that the MHC acts as a genetic marker of relatedness that prevents inbreeding and thus the exposure of deleterious allele combinations. The MHC consists of a large cluster of genes located on the short arm of Chromosome 6. 6) MHC-Dependent mate preferences in humans The MHC contains many base pair polymorphisms which allow for distinct individual immune defenses, and may define the chemical differences that are distinguishable among male pheromones. 7) The Majorhistocompatability Complex

Female attraction to male specific pheromone secretions, that represent differing immune identifiers, prevents producing multiple progeny with similar MHC loci. The diverse MHC among offspring of female mammals leads to diverse allele combinations that can in turn lead to a more diverse immune function. Through the discouragement of non-random mating, this specificity leads to a decrease in effective population size which changes the distribution of allele frequencies in the next generation. By choosing opposite allele types in the MHC the female is ensuring the energetic investment made by her nine month gestation period will result in a viable and healthy offspring. In mice, pregnant females that come in contact with male mice that contain similar MHC loci as the fathering male can spontaneously abort the fetus. 6) MHC-Dependent mate preferences in humans The spontaneous abortions are the cause of mother investment to the progeny and preventing the selective process. The great diversity of MHC loci and immune function result in a diverse heterogeneous society and thus allow heterogeneity to be promoted through sexual selection. If people of similar MHC loci mate then the offspring would be at a selective disadvantage due to a lack of diverse immune defense. By the spontaneous abortions, as seen in mice, the mother is eliminating the duplication of multiple equal MHC loci.

The question still remains as to what happens if the female has defective VNOs and cannot effectively identify a male with differing MHC loci. In this case the cycle of heterogeneity fails and perhaps the large percentage of immune dysfunctional individuals can attribute their deficiencies to defects in female mate choice. Perhaps these defective progeny as well inherit the defective VNO trait and add to the large genetic variability of immune diseases. This indicates a defective strain in the cycle of heterogeneity among individuals. Perhaps the complexity of relationships is out of individual control and remains under the harsh grip of chemical signals and input pathways.

Works Cited

1) Woronczuk, Julia and Medwid, Stephanie, and Neumann, Laura, and Eshelman, Sarah. "Smell and Attraction". Smell: The Forgotten Sense. January 22, 2006

2) Elia T. Ben-Ari. Pheremones: What's in a name?. Biological Sciences, Vol. 48, No. 7. (Jul, 1998),pp. 505-511

3) Dr. John Gray. The World of Skin Care. January 22, 2006.

4) Thorne, Frances and Neave, Nick and Scholey, Andrew and Moss, Mark, and Fink, Bernhard. Male Pheromones and Sexual Attraction. Neuroendocrinology Letters 2002.< http://www.nel.edu/23_4/NEL230402R03_Thorne.htm>

5) Rationis,Vox. "Sexual Attraction". Social Issues Research Centre. January 28, 2006< http://www.sirc.org/publik/smell_attract.html>

6) Claus Wedekind; Thomas Seebeck; Florence Bettens; Alexander J. Paepke. MHC-Dependent mate preferences in humans. The Royal Society : Biological Sciences, Vol. 260, No. 1359 (Jun. 22, 1995), 245-249.

7) RT. "The Majorhistocompatability Complex". January 24, 2006.http://www.wellcome.ac.uk/en/genome/genesandbody/hg05f005.html

Works Consulted
Gale Peter Largey, David Rodney Watson. The Sociology of Odors. The American Journal of Sociology, Vol. 77, No. 6. (May, 1972), pp. 1021-1034. < http://links.jstor.org/sici?sici=0002-9602%28197205%2977%3A6%3C1021%3ATSOO%3E2.0.CO%3B2-K>

Erik E. Filsinger, Richard A. Fabes. Odor Communication, Pheromones, and Human Families. Journal of Marriage and the Family, Vol. 47, No. 2.(May, 1985), pp. 349-359.Stable URL:


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