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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
Physical attractiveness has become a
biologically and culturally important
construct, giving a meaning to the pursuit of
the perfect mate. What some are unaware of
is that these phenotypic traits of facial
symmetry and body odor can be related to
good genes. Evidence indicates that
pheromones can be directly correlated to
facial symmetry cueing a high mate quality.
Many cultures define beauty in
different ways, however all cultures show a
considerable agreement that bilateral facial
symmetry to be attractive (Rhodes et al
1998). Facial symmetry corresponds with
the symmetrical development through stages
of development, therefore, exemplifying
genetic success against stress and time
(Rikowski and Grammer 1999). Females use
these genetic characteristics as cues to
ensure quality in a mate choice and during
different periods of menstruation, women’s
preference on a sexual mate and the level of
commitment can vary (Gangestad and
Thornhill 1998).
Based on favorable body odors of
men, females should have a greater response
to those pheromones and choose men with
greater facial symmetry. Throughout the
different stages of the menstrual cycle,
women have fluctuation in the attractiveness
towards men who they would sleep with for
a short-term relationship and who they
would choose for a long-term relationship,
or mate. Since during the week of
menstruation women have a peak in sexual
desire (P.C. Regan 1996). It is believed that
during these peaks they would put greater
selection pressure on which individual they
would choose for a mate.
Women should put more selection
pressure on the individual that they will
choose for a long-term relationship since
this will be the individual who will be
proving them with offspring. For this reason
this study will look at women’s selection for
short-term and long-term relationships.
Materials and Methods
Experimentation began within the
month of February of 2010 and data were
collected at Saddleback College and outside
the school. Eight white t-shirts were
purchased then washed with odorless Tide
laundry detergent to ensure there are no
external odors contaminating the olfactory
response. After the shirts had been washed,
they were transferred into the dryer using
clean latex gloves and once dried,
immediately sealed in a zip-sealed bag to
prevent odor contamination. The male
subjects (n=8) were given the shirts and had
to wear their given shirt for a twenty-four
hour period. Each male subject, prior to
wearing the shirt, showered with odorless
Dove soap and not allowed to apply any
lotions, deodorants, colognes, aftershave, or
any other item that could alter their natural
body odors. Once the twenty-four hour
period was over, male subjects immediately
took off the shirts and placed it back into the
zip-sealed bags. On Tuesday February 23rd
and Wednesday February 24th, 2010, female
subjects (n=53) were asked to smell each of
the shirts and fill out a questionnaire asking:
to rank the shirts based upon favorability on
a scale from one to ten, choose who they
would settle down with (based on scent),
choose who they would select for a one
night stand, and ask if they were
menstruating. If the female subjects were
not menstruating, investigators asked a
subject when there last menstruation was.
Data was analyzed, and chi-squared
contingency table was constructed.
The second set of data were
collected through the months of March and
April of 2010. Male subjects (n=5)
participated by wearing new freshly washed,
with odorless Tide detergent, t-shirts for a
twenty-four hour period. Once the shirts
were prepared in the same manner as in the
first study, experimentation began with male
subjects bathing with odorless Dove soap
and immediately putting on the freshly
washed and sealed t-shirts. After the twentyfour hour period, shirts were placed in the
sealed bag once again to be smelled by
female subjects (n=9). Male subjects wore
the shirt one twenty-four hour period per
week in order to follow female subjects
throughout a month span. The shirts were
washed and sealed between every study to
prevent odor contamination. The women
were asked once per week to smell t-shirts
and rank them on a scale from one to ten
based on desirability. Shirts were
randomized each week to ensure no female
subject had an influence on another’s
recordings. Numbered from one to five, the
shirts were tested by female subjects and the
questionnaire was then filled out. Asking the
same series of questions from the first set of
data tested: who would you choose for a
one-night stand; who would you choose to
settle down with; are you menstruating; and
if no, when was your last menstruation.
After the last set of data was collected, a chisquared contingency table was constructed.
Lastly, pictures were taken of all
male subjects from both studies in this
experimentation (eight from the first set of
data collected and the five from the second
set of data). Pictures were taken at a
straight-on angle and the program ImageJ
(National Institute of Health, USA) was
used to measure facial symmetry. Three
measurements were taken using ImageJ: A1,
A2, and A3. A1 measured from the middle
of the brow to the far tips of the right and
left eye; A2 measured from the tip of the
nose to the outer tips of both earlobes; and
A3 measurement was taken from the cleft
beneath the nose to the outer tips of the right
and left side of the mouth, as shown in
figure 1. Measurements of all subjects were
then transferred into MS Excel and the ratios
were then calculated finding subjects with
greatest facial symmetry. Results were then
tested as to how they ranked based on the
experimentation done by the female subjects
in both sets of data collection.
Figure 1. Three facial measurements (A1,
A2, A3) represent bilateral facial symmetry.
Results
Ratio averages of the three facial
symmetry measurements of each subject and
selection percentage for the first study are
shown in table 1. The male subjects with the
greatest degree of bilateral facial symmetry
were never significantly chosen more by the
by the menstruating group then by the nonmenstruating
group
for
long-term
relationships. In the first study the individual
with the greatest bilateral facial symmetry
was chosen 55% of the time by the
menstruating group, with a P value of
0.5711, this shows that there is no
significant difference in the amount of times
chosen by the menstruating group compared
to the non-menstruating group. The
individuals with a degree of bilateral facial
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 nonmenstruating 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
to be linked to a higher degree of bilateral
facial symmetry, and a high degree of
bilateral facial symmetry is linked to good
genetics. Research has shown that women
will have peaks in there degree of sexual
desire (P.C. Regan 1996). Therefore in our
study we looked at if this peak in sexual
desire would also affect their choice in male
subjects causing the women to choose
individuals with higher degrees of bilateral
facial symmetry more often during this peak
of sexual desire. However in our study it
has been shown that the peak in sexual
desire during the week of menstruation does
not have an effect on the females’ choice of
male mates for a long-term relationship.
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
bilateral facial symmetry and were very
rarely chosen. The same thing happened
with these two individuals in this study for
the short-term relationship. Therefore with a
larger sample size of women this apparent
anomaly may disappear. Therefore another
study where there is a larger sample size
would be beneficial to determine more
accurately if the peak in sexual desire during
the week of menstruation effects women’s
selection based on body odor.
In the second study where we
followed the same women for four weeks
we only saw one individual who was chosen
significantly more often by the menstruating
group for a long-term relationship, but this
individual also was not chosen often.
However in this study we did see one
individual who was chosen significantly
more often for a short-term relationship, and
who was chosen a significant amount of the
time.
This individual did not have the
highest degree of bilateral facial symmetry
but he was chosen a significant amount of
the time. To elaborate on this study it would
be beneficial to do an extended study where
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
difference in the amount of times they were
chosen for a long-term relationship or a
short-term relationship. When the degree of
symmetry is this close, the scent of males
who have a greater degree of masculinity
have a more masculine scent that is
preferred by women (Cornwell, R. E. et al.
2004).
Subject
#1
Subject
#2
Subject
#3
Subject
#4
Average
Ratio
(%)
97.96
97.18
96.58
96.54
Selection
Percentage
(Menstruating)
0
0
12.5
12.5
6.6
0
8.8
2.2
Subject
#5
Subject
#6
Subject
#7
Subject
#8
Average
Ratio
(%)
96.00
96.48
98.58
98.97
Selection
Percentage
(Menstruating)
12.5
0
25
1437.5
4.4
11.1
35.5
31.1
Selection
Percentage
(Nonmenstruating)
Selection
Percentage
(Nonmenstruating)
Table 1. Average ratio percentage and
selection percentage of male subjects in
study 1 for long-term relationships.
Subject
#1
Subject
#2
Subject
#3
Subject
#4
Subject
#5
Average
Ratio
(%)
98.58
98.97
96.48
98.68
98.07
Selection
Percentage
(Menstruating)
38
12
12
26
12
36
14
4
25
21
Selection
Percentage
(Nonmenstruating)
Table 2. Average ratio and
selection percentage of male
subjects in study 2 for long-term
relationships.
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.