Project Proposal s1

Project Proposal Bio 3B Saddleback College Spring 2010

The effect of the menstrual cycle on sexual selection for temporary and long-lasting relationships in Homo sapiens base on olfactory cues.

Cole Querry and Ken Tupper Department of Biological Sciences Saddleback College Mission Viejo, California 92692

Males who have a favorable body odor have been shown to be selected more often by females since their body is linked to their bilateral facial symmetry, which denotes good genetics. Since the menstrual cycle effects the hormone levels in women we hypothesized that women who are menstruating would be more susceptible to the odor of males who have a greater degree of facial symmetry. College aged women smelt and rated the attractiveness of a total of 8 T-shirts that were worn by men for a period of 24 hours. Then a second study was conducted where college aged women smelt 5 T-shirts that were worn by men for a 24-hour period. In this study the women were followed for a month smelling and ranking the shirts once every week. Results indicated that the female subjects did select the individuals with a greater degree of bilateral facial symmetry significantly more often. However the menstrual cycle did not have an effect on the amount of times the males with the greatest facial symmetry were chosen. The study also showed that there was no significant difference in female section of males with greater symmetry when their degree of difference was within 1%.

Introduction (Rikowski and Grammer 1999). Females use Physical attractiveness has become a these genetic characteristics as cues to biologically and culturally important ensure quality in a mate choice and during construct, giving a meaning to the pursuit of different periods of menstruation, women’s the perfect mate. What some are unaware of preference on a sexual mate and the level of is that these phenotypic traits of facial commitment can vary (Gangestad and symmetry and body odor can be related to Thornhill 1998). good genes. Evidence indicates that Based on favorable body odors of pheromones can be directly correlated to men, females should have a greater response facial symmetry cueing a high mate quality. to those pheromones and choose men with Many cultures define beauty in greater facial symmetry. Throughout the different ways, however all cultures show a different stages of the menstrual cycle, considerable agreement that bilateral facial women have fluctuation in the attractiveness symmetry to be attractive (Rhodes et al towards men who they would sleep with for 1998). Facial symmetry corresponds with a short-term relationship and who they the symmetrical development through stages would choose for a long-term relationship, of development, therefore, exemplifying or mate. Since during the week of genetic success against stress and time menstruation women have a peak in sexual desire (P.C. Regan 1996). It is believed that subject when there last menstruation was. during these peaks they would put greater Data was analyzed, and chi-squared selection pressure on which individual they contingency table was constructed. would choose for a mate. The second set of data were Women should put more selection collected through the months of March and pressure on the individual that they will April of 2010. Male subjects (n=5) choose for a long-term relationship since participated by wearing new freshly washed, this will be the individual who will be with odorless Tide detergent, t-shirts for a proving them with offspring. For this reason twenty-four hour period. Once the shirts this study will look at women’s selection for were prepared in the same manner as in the short-term and long-term relationships. first study, experimentation began with male subjects bathing with odorless Dove soap Materials and Methods and immediately putting on the freshly Experimentation began within the washed and sealed t-shirts. After the twenty- month of February of 2010 and data were four hour period, shirts were placed in the collected at Saddleback College and outside sealed bag once again to be smelled by the school. Eight white t-shirts were female subjects (n=9). Male subjects wore purchased then washed with odorless Tide the shirt one twenty-four hour period per laundry detergent to ensure there are no week in order to follow female subjects external odors contaminating the olfactory throughout a month span. The shirts were response. After the shirts had been washed, washed and sealed between every study to they were transferred into the dryer using prevent odor contamination. The women clean latex gloves and once dried, were asked once per week to smell t-shirts immediately sealed in a zip-sealed bag to and rank them on a scale from one to ten prevent odor contamination. The male based on desirability. Shirts were subjects (n=8) were given the shirts and had randomized each week to ensure no female to wear their given shirt for a twenty-four subject had an influence on another’s hour period. Each male subject, prior to recordings. Numbered from one to five, the wearing the shirt, showered with odorless shirts were tested by female subjects and the Dove soap and not allowed to apply any questionnaire was then filled out. Asking the lotions, deodorants, colognes, aftershave, or same series of questions from the first set of any other item that could alter their natural data tested: who would you choose for a body odors. Once the twenty-four hour one-night stand; who would you choose to period was over, male subjects immediately settle down with; are you menstruating; and took off the shirts and placed it back into the if no, when was your last menstruation. zip-sealed bags. On Tuesday February 23rd After the last set of data was collected, a chi- and Wednesday February 24th, 2010, female squared contingency table was constructed. subjects (n=53) were asked to smell each of Lastly, pictures were taken of all the shirts and fill out a questionnaire asking: male subjects from both studies in this to rank the shirts based upon favorability on experimentation (eight from the first set of a scale from one to ten, choose who they data collected and the five from the second would settle down with (based on scent), set of data). Pictures were taken at a choose who they would select for a one straight-on angle and the program ImageJ night stand, and ask if they were (National Institute of Health, USA) was menstruating. If the female subjects were used to measure facial symmetry. Three not menstruating, investigators asked a measurements were taken using ImageJ: A1, A2, and A3. A1 measured from the middle greatest degree of bilateral facial symmetry of the brow to the far tips of the right and were never significantly chosen more by the left eye; A2 measured from the tip of the by the menstruating group then by the non- nose to the outer tips of both earlobes; and menstruating group for long-term A3 measurement was taken from the cleft relationships. In the first study the individual beneath the nose to the outer tips of the right with the greatest bilateral facial symmetry and left side of the mouth, as shown in was chosen 55% of the time by the figure 1. Measurements of all subjects were menstruating group, with a P value of then transferred into MS Excel and the ratios 0.5711, this shows that there is no were then calculated finding subjects with significant difference in the amount of times greatest facial symmetry. Results were then chosen by the menstruating group compared tested as to how they ranked based on the to the non-menstruating group. The experimentation done by the female subjects individuals with a degree of bilateral facial in both sets of data collection. symmetry of 98% or greater had a P value of 0.2560 or greater. Ratio averages of the three facial symmetry measurements of each subject and selection percentage for the second study are shown in table 2. In the second study the individual with the greatest degree of bilateral facial symmetry was only chosen by the menstruating group 46% of the time, with a P value of 0.6711. In this study all the individuals had a degree of facial symmetry of 98% or greater and only one individual was chosen significantly more by the menstruating group over the non- menstruating group (P value= 0.0005). For short term relationships only one individual was chosen significantly more often by the menstruating group. In this study the menstruating group did not choose individuals with greater bilateral facial symmetry significantly more often then the non-menstruating group.

Discussion Favorable body odor has been shown Figure 1. Three facial measurements (A1, to be linked to a higher degree of bilateral A2, A3) represent bilateral facial symmetry. facial symmetry, and a high degree of bilateral facial symmetry is linked to good Results genetics. Research has shown that women Ratio averages of the three facial will have peaks in there degree of sexual symmetry measurements of each subject and desire (P.C. Regan 1996). Therefore in our selection percentage for the first study are study we looked at if this peak in sexual shown in table 1. The male subjects with the desire would also affect their choice in male subjects causing the women to choose difference in the amount of times they were individuals with higher degrees of bilateral chosen for a long-term relationship or a facial symmetry more often during this peak short-term relationship. When the degree of of sexual desire. However in our study it symmetry is this close, the scent of males has been shown that the peak in sexual who have a greater degree of masculinity desire during the week of menstruation does have a more masculine scent that is not have an effect on the females’ choice of preferred by women (Cornwell, R. E. et al. male mates for a long-term relationship. 2004). In our first study there were two individuals who were chosen significantly more by the menstruating group. These two individuals did not have a high degree of Subject Subject Subject Subject bilateral facial symmetry and were very #1 #2 #3 #4 rarely chosen. The same thing happened Average with these two individuals in this study for Ratio 97.96 97.18 96.58 96.54 the short-term relationship. Therefore with a (%) larger sample size of women this apparent Selection anomaly may disappear. Therefore another Percentage 0 0 12.5 12.5 study where there is a larger sample size (Menstruating) would be beneficial to determine more Selection accurately if the peak in sexual desire during Percentage 6.6 0 8.8 2.2 the week of menstruation effects women’s (Non- selection based on body odor. menstruating) In the second study where we Subject Subject Subject Subject followed the same women for four weeks #5 #6 #7 #8 we only saw one individual who was chosen Average significantly more often by the menstruating Ratio 96.00 96.48 98.58 98.97 group for a long-term relationship, but this (%) individual also was not chosen often. Selection However in this study we did see one Percentage 12.5 0 25 1437.5 individual who was chosen significantly (Menstruating) more often for a short-term relationship, and Selection who was chosen a significant amount of the Percentage 4.4 11.1 35.5 31.1 time. This individual did not have the (Non- menstruating) highest degree of bilateral facial symmetry but he was chosen a significant amount of Table 1. Average ratio percentage and the time. To elaborate on this study it would selection percentage of male subjects in be beneficial to do an extended study where study 1 for long-term relationships. female subjects are followed for many months to see if they will choose the same individuals every time or more often then not when they are menstruating and on there peak time of sexual desire. In this study it was noted that when males are within 1% difference in the degree of facial symmetry there was no significant Subject Subject Subject Subject Subject #1 #2 #3 #4 #5 Average Ratio 98.58 98.97 96.48 98.68 98.07 (%) Table 2. Average ratio and Selection Percentage 38 12 12 26 12 selection percentage of male (Menstruating) subjects in study 2 for long-term relationships. Selection Percentage 36 14 4 25 21 (Non- menstruating)

References: Cornwell, R. E., Boothroyd, L., Burt, D. M., Feinberg, D. R., Jones, B. C., Little, A. C., Pitman, R., Whiten, S., and Perrett, D. 2004. Concordant preferences for opposite-sex signals? Human pheromones and facial characteristics. The Royal Society.

Gangestad, S. and Thornhill, R. 1998. Menstrual cycle variation in women’s preferences for the scent of symmetrical men. The Royal Society.

Regan, P. C. 1996. Rhythms of desire: the association between menstrual cycle phases and female sexual desire. Department of psychology, California State University Los Angeles, California.

Rhodes, G., Proffitt, F., Grady, J., and Sumich, A., 1998. Facial symmetry and the perception of beauty. Psychonomic society, inc.

Rikowski, A. and G., Karl 1999. Human Body odour, symmetry and attractiveness. The Royal Society.