BIOL 4362 Laboratory 1
11 January - 1 February 2016
Human Mating Preferences
Sexual reproduction is the process by which two parents contribute genetic material to the
creation of progeny that differ genetically from both parental individuals. Variation
resulting from that process provides the raw material for evolution via natural selection, as
certain individuals are better adapted to their environment than others. That said, selection
does not favour individuals that squander energetically costly gametes and engage in
potentially risky copulatory behaviour in the production of offspring that have no
expectation of surviving to reproduce. A parent's fitness interests are best served by
producing offspring that are well adapted to the prevailing environmental conditions,
given that offspring are the primary vectors of parental fitness. Thus individuals of few, if
any species mate indiscriminately: rather, they select mates that advertise their exceptional
fitness either directly through the possession of certain morphological and behavioural
traits, or indirectly via the possession of superior resources.
Where females manifest mate choice, they commonly select males that control access to
high quality resources. In manifesting that choice, females reduce the probability that their
young will be depredated (e.g. Eisner and Meinwald 1995), and gain access to high quality
resources both for themselves and their dependent young (e.g. Stanford 1995, Thornhill
1976). While males controlling premium resources may be genetically superior to other
males, females also select mates by assessing male traits that correlate with underlying
male quality. "Choosiness" on the part of females thus selects for the expression of male
traits that advertise fitness, and can produce outlandish and costly male displays via this
intersexual or epigamic selection. Fisher's "runaway hypothesis" (1930) recognized that
where male traits become the focus of female mating preferences, selection can favour the
elaboration of those traits beyond any natural selective benefit to their bearers. The
"Hamilton-Zuk hypothesis" (Hamilton and Zuk 1982), suggests that females should prefer
males manifesting costly traits because the possession of those traits implies an underlying
resistance to parasites, which presumably would be transmitted to progeny. Zahvi's
"handicap hypothesis" (Zahavi 1975) suggests that females choose males manifesting
costly traits because the possession of those traits otherwise handicaps the male, and his
survival in the face of his handicap indicates his underlying genetic superiority.
Like females, males have also been documented to exhibit elements of mate choice. This
is commonly observed where males make substantial investments in offspring, either
through the provision of parental care or through the investment of limited resources
(Trivers 1972). Further, males commonly select among potential female mates on the
basis of cues that correlate with female fecundity (e.g. Gwynne 1981). While male
gametes are relatively inexpensive, male fitness interests are best served by mating with
females that can best propagate like copies of the male's genes to subsequent generations.
The expression of male versus female choosiness varies widely across animal taxa.
Among mammals, females are expected to be more selective in choosing mates than males
given their greater proportionate investment in gametes, and higher future costs in
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lactating to dependent young. Humans (Homo sapiens) are no exception to this pattern
(Alcock 2005). Males are reported to prefer younger females as mates (Buss 1989,
Kenrick and Keefe 1992) and prefer females with a waist to hip ratio of approximately
0.7:1 (Singh 1993). Both of these preferences have been interpreted as a product of
selection acting on males to choose fecund female mates. It is safe to say, however, that
human males are, on average, far less choosy and more promiscuous than females (e.g.
Buss and Schmitt 1993, Clark and Hatfield 1989, Kelly and Hare 2010). Unlike males,
female humans manifest a pronounced preference for older mates (Kenrick and Keefe
1992), who on average have greater access to resources critical to female reproduction
(Boone 1986, Buss 1989). Further, females prefer male partners manifesting greater facial
symmetry (Little et al. 2001, Penton-Voak et al. 2001). Symmetry is commonly
interpreted as a reflection of developmental stability (ibid), and hence female preferences
for such males serves to ensure that females obtain male gametes that will contribute to
the production of viable offspring. Once such a preference is fixed in the population,
females choosing symmetrical partners will also increase the likelihood that any sons they
produce will be preferred by females in subsequent generations (i.e. "sexy sons" sensu
Weatherhead and Robertson 1979).
In this lab, we will examine human mate choice by gleaning data from online
"companion" ads. We will quantify relative choosiness of males and females and attempt
to determine whether the criteria employed by males and females in advertising for mates
conform to the predictions made by evolutionary theory. While similar data could be
obtained by administering surveys, the "companion ads" are in the public domain and thus
do not require ethics approval. Such ads also allow a large and meaningful data set to be
amassed with minimal effort (e.g. Bereczkei et al. 1997, Kelly and Hare 2010, Kenrick
and Keefe 1992, Pawłowski and Dunbar 1999, Waynforth and Dunbar 1995), and spare
you the humiliation of asking friends and family about their mating preferences!
Exercise
Each group of 2-3 students will be given "companion" ads gleaned from online dating
sites. Groups will receive advertisements from different cities to ensure the independence
of observations contributing to the overall data set. Within each of the categories "males
seeking females" and "females seeking males", quantify the following data from each ad:
1) the age of the advertiser,
2) age range of the companion sought [coded relative to the age of the advertiser as older
only (oo), includes more older (io), symmetrical about same age (s), includes more
younger (iy), or younger only (yo)],
3) the overall number of adjectives used by the advertiser to describe themselves,
4) the overall number of adjectives used in describing the desired mate,
5) the number of physical attributes the advertiser uses to describe themselves,
6) the number of physical attributes listed in describing the desired mate,
7) the number of material attributes the advertiser lists in describing themselves
(property, income, professional occupation or any other aspect of material wealth),
8) the number of material attributes used in describing the desired mate,
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9) the number of references to educational achievement made by the advertiser in
describing themselves,
10) the number of educational criteria listed for their desired mate,
11) the number of athletic activities the advertiser lists in describing their interests,
12) the number of athletic activities the advertiser lists in describing their desired mate,
13) whether you'd characterize the ad as blatantly portraying the advertiser as physically
attractive or "sexy" (yes = Y; no = N),
14) whether you'd characterize the ad as blatantly advertising for a physically attractive or
"sexy" partner (yes = Y; no = N),
15) whether you'd characterize the ad as blatantly portraying the advertiser as "well off"
financially (yes = Y; no = N),
16) whether you'd characterize the ad as blatantly advertising for a wealthy partner (yes =
Y; no = N).
Record your data on the sheets provided using each row to code data from a single
advertisement. Columns are numbered 1 through 16 representing each of the 16 variables listed
above. Where data are not available for any of the variables, place an "X" in the cell (variables
1-2), or a zero if applicable (variables 3-12). Be sure to record your subjective impression as
yes (Y) or no (N) for variables 13-16 in each case. Each group must code data from 25 "male
seeking female" ads and 25 "female seeking male" ads. Data must be entered into an Excel
spreadsheet following the format of the data-coding sheet (available on the course web page:
http://home.cc.umanitoba.ca/~harejf/BIOL4362/), and sent as an e-mail attachment to your
course Teaching Assistant (roberta4@myumanitoba.ca) by Monday January 18th. Note that
totals only are required for variables 3-12. For variables 13 through 16 provide the number of
"yes" responses but provide raw data only (data from each individual ad) for variables 1 and 2.
We will compile your data into a class data set, which will be made available on the course
web site for download as an Excel™ spreadsheet. It is this class data set that you will use to
complete the assignment below.
Assignment (10 marks, due 1 February 2016)
1. Construct a 5x2 contingency table contrasting preferred partner age (variable 2) for
males versus females. Perform a chi-square test on that contingency table to test for
significant differences in age preferences of male versus female advertisers and
interpret your findings.
2. Contrast males and females for variables 3 through 12 using Yates-corrected chi-square
tests and present the results of those tests in a table. Provide a brief interpretation of any
significant differences detected between males and females. (note that t-tests or their
nonparametric equivalent – Mann-Whitney U-tests – could also be used here treating
each ad as an individual replicate, though we'll keep the analysis simple!)
3. a) Is there evidence to support the predictions that males prefer physically attractive
mates while females prefer wealthy mates? Perform Yates-corrected chi-square tests
on variables 14 and 16 in arriving at your answer.
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b) Is there evidence that females or males advertise themselves in a manner that
conforms to the predictions given under 3a? Perform Yates-corrected chi-square
tests using variables 13 and 15 in arriving at your answer.
4. Suggest any one further aspect of the data collected in this lab that we have not
analyzed above, and that could be examined to provide greater insight into human
mating preferences. Explain in brief why an examination of the relationship you
propose would be worthwhile, and what result(s) you might expect to find.
References
Alcock, 2005. Animal behavior - An evolutionary approach, 8th Edition. Sunderland:
Sinauer Associates.
Bereczkei, T., Voros, S., Gal, A., & Bernath, L. (1997). Resources, attractiveness, family
commitment: reproductive decisions in human mate choice. Ethology, 103, 681-699.
Boone, J.L. III. (1986). Parental investment and elite family structure in preindustrial
states: a case study of late medieval-early modern Portuguese genealogies. Amer.
Anthropol., 88, 859-878.
Buss, D.M. (1989). Sex differences in human mate preferences: evolutionary hypothesis
tested in 37 cultures. Behav. Brain Sci., 12, 1-14.
Buss, D.M., & Schmitt, D.P. (1993). Sexual strategies theory: an evolutionary perspective
on human mating. Psych. Rev., 100, 204-232.
Clark, R.D., & Hatfield, E. (1989). Gender differences in receptivity to sexual offers. J.
Psych. Hum. Sex., 2, 39-55.
Eisner, T., & Meinwald, J. (1995). The chemistry of sexual selection. Proc. Nat. Acad.
Sci. U.S.A., 92, 50-55.
Fisher, R.A. (1930). The genetical theory of natural selection. Oxford: Oxford University
Press.
Gwynne, D.T. (1981). Sexual difference theory: Mormon crickets show role reversal in
mate choice. Science, 213, 779-780.
Hamilton, W.D., & Zuk, M. (1982). Heritable true fitness and bright birds: a role for
parasites? Science, 218, 384-387.
Kelly, T.C., & Hare, J.F. (2010). Pair-bonded humans conform to sexual stereotypes in
web-based advertisements for extra-marital partners. Evol. Psychol., 8, 561-572.
Kenrick, D.T., & Keefe, R.C. (1992). Age preferences in mates reflect sex differences in
reproductive strategies. Behav. Brain Sci., 15, 75-133.
Little, A.C., Burt, D.M., Penton-Voak, I.S., & Perrett, D.I. 2001. Self-perceived
attractiveness influences human female preferences for sexual dimorphism and
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Pawłowski, B., & Dunbar, R.I.M. (1999). Impact of market value on human mate choice
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Penton-Voak, I.S., Jones, B.C., Little, A.C., Baker, S., Tidderman, B., Burt, D.M., &
Perrett, D.I. (2001). Symmetry, sexual dimorphism in facial proportions and male
facial attractiveness. Proc. R. Soc. Lond. B., 268, 1617-1623.
Singh, D. (1993). Adaptive significance of female physical attractiveness: role of the
waist-to-hip ratio. J. Pers. Soc. Psych., 65, 293-307.
Stanford, C.B. (1995). Chimpanzee hunting behaviour. Am. Sci., 83, 256-261.
Thornhill, R. (1976). Sexual selection and nuptial feeding behavior in Bittacus apicalis
(Insecta: Mecoptera). Am. Nat., 119, 529-548.
Trivers, R.L. (1972). Parental investment and sexual selection. In B. Campbell (Ed.)
Sexual selection and the descent of man, 1871-1971, (pp. 136-179). Chicago: Aldine.
Waynforth, D., & Dunbar, R.I.M. (1995). Conditional mate choice strategies in humansevidence from lonely-hearts advertisements. Behaviour, 132, 755-779.
Weatherhead, P., & Robertson, R. (1979). Offspring quality and the polygyny threshold:
"the sexy son hypothesis." Am. Nat., 113, 201-208.
Zahavi, A., (1975). Mate selection - a selection for a handicap. J. Theor. Biol., 53,
205-214.
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