Lab 7 – Investigating Sexual selection

Module 6 Lab: Human mate choice
In many human cultures there tends to be agreement over what constitutes attractiveness – with people from different societies often agreeing

that a given woman or man is ‘attractive’. It is less clear, however, what actual traits observers use to make this judgement. In this week’s

lab, we are going to test a number of hypotheses to determine if there is a good way to subjectively measure attractiveness.
Background
Sexual selection and good genes hypothesis: Many species display the phenomenon of sexual selection – where males display costly ornaments or

behaviors (although in some rarer cases it is females that display these costly ornaments or behaviors). According to parental investment

theory, the gender that has lower intrinsic investment in reproduction is forced to compete for the attentions of the gender with the higher

investment. There is still a fair amount of theoretical discussion concerning the costs and benefits of sexual selection. One perspective,

the ‘good genes’ concept, suggests that costly ornaments are essentially ‘honest signals’ that the bearer is carrying high quality genes. An

animal that is capable of maintaining a large feather display or complicated nest-building behavior must also be generally healthy and the

carrier of desirable genetic qualities.
Humans are not exempt from sexual selection theory. Males and females are dimorphic in size and also in secondary sexual characteristics. The

human face contains secondary sexual traits that include facial features that may develop or increase in size at puberty. Humans make

judgements about the attractiveness of prospective partners based in part on these facial cues. An attractive partner may elicit greater

efforts at courtship or more costly displays to gain the attentions of the would-be mate. But how do humans make these judgements about

attractiveness?
Facial Symmetry Hypothesis: One hypothesis regarding human attractiveness is facial symmetry. Symmetry is often correlated with genetic

heterozygosity in many animals, including humans (Thornhill and Gangestad 1993). Such heterozygosity may be linked to parasite resistance and

therefore symmetry may be an indicator of ‘good genes’. There is evidence that facial symmetry is positively correlated with scores of

attractiveness (Grammer&Thornhill 1994; Fink et al. 2006), and it may also act as a cue to an individual’s personality characteristics (Fink et

al. 2006).
Averageness Hypothesis: Another hypothesis is the averageness hypothesis (Thornhill&Gangestad 1993). Based on this idea, researchers compiled

photos of different people. They found that the more people’s faces were averaged together, the higher the attractiveness score became.

Thornhill and Gangestad suggest that facial averageness is attractive because of its association with heterozygosity. It should be noted that

the facial symmetry hypothesis and averageness hypothesis are not mutually exclusive.
Questions: In order to investigate these questions, you will be utilizing an interactive website to rate human faces for attractiveness and

also to create average faces (in which individual faces are blended together).
Instructions:
Access the website at http://www.faceresearch.org/demos/average
To create averages, select faces you want to average and they will be show boxed in yellow. To unselect an image, just click it again.
When you’ve selected the ones you want in your selection, click ‘average’. Between trials, click the reset button to clear your previous

selections.
Assignment instructions:
1. Assign attractiveness scores to the first 20 faces of each sex on a scale from 1 – 10.
2. Of the 20 faces, choose three women you assigned the lowest scores, and average their faces. Score the new composite face.
3. Of the 20 faces, choose three women with scores close to 5 and average their faces. Score the result
4. Of the 20 faces, choose three women with the highest scores and average their faces. Score the resulting face.
5. Average all 20 female faces. Score the resulting face.
6. Repeat steps 2-5, using male faces.
To Finish:
1. Submit an excel spreadsheet to Blackboard with tables of your results. (Excel sheet should include Steps 1-6) (1 pt)
2. Submit a Word document/lab report to Blackboard that includes an “Introduction”, “Materials and Methods”, “Results”, and “Discussion”

sections (minimum of 300 words) (4 pts). Please remember lab reports should be written in paragraph format and with sub-headers for each

section or else points will be deducted.
a. Introduction (1 pt)
i. Describe attractiveness and how this relates to sexual selection
ii. Describe the Facial Symmetry Hypothesis
iii. Describe the Averageness Hypothesis
iv. State your hypothesis
b. Materials and Methods (1 pt)
i. Same instructions as always, write this section as if someone not in our class must complete this lab/duplicate what you did by solely

using your lab report and the instructions you give them.
ii. Put in paragraph format and in past tense
c. Results (1 pt)
i. Must include tables and graphs depicting your results
1. One table of Steps 2-5 for females
2. One tables of Steps 2-5 for males
ii. Must include paragraphs that state your Results in words (in other words, your Results should not just be tables and graphs)
d. Discussion (1 pt)
i. Describe your Results and what these mean in regards to attractiveness and sexual selection, the facial symmetry hypothesis, the

averageness hypothesis, and your own created hypothesis. Are these hypotheses supported or rejected by your results?

References
Fink, B, et. al, 2006. Facial symmetry and judgements of attractiveness, health, and personality. Personality and Individual Differences 41:

491-499
Grammer, K, Thornhill, R 1994. Heritable true fitness and bright birds: A role for parasites? Science 218: 384-387
Thornhill, R, Gangestad, S 1993. Human facial beauty: Averageness, symmetry and parasite resistance. Human Nature 4: 237-269
Trivers, R. 1972. Parental investment and sexual selection. In B. Campbell (Ed.) Sexual selection and the descent of man, 1871-1971. (pp

136-179). Chicago. IL

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