1. Digit ratio (2D:4D), mate guarding, and physical aggression in dating couples
Kelsey Grossman
Laura Jimenez
Cousins, A. J., Fugere, M. A., & Franklin M. (2009), Digit ratio (2D:4D), mate guarding, and physical aggression in dating couples. Personality and Individual Differences, 46, 7,

2. Introduction
Mate guarding: a way for a male to assure that partner remains faithful and doesn’t succumb to infidelity
Makes sure male doesn’t spend energy raising a child that isn’t his own
Consists of monopolizing one’s mate and discouraging potential threats from making a move on his mate
2D:4D: digital ratio which indicates the levels of testosterone in the body
Higher levels of testosterone in utero are associated with lower digit ratio and with aggressive behavior
Is an unusual trait because it doesn’t change as much across the lifespan as do secondary sex traits
Aggressive behaviors are often associated with mate guarding
Studies that show a relationship between aggression and 2D:4D indicate that low 2D:4D women show more reactive aggression (anger in response to frustration and being provoked) and indirect aggression (sneaky, manipulative aggression, for example; spreading a rumor)

3. Hypothesis Men with lower 2D:4D will: Also,
1. Mate guard more than higher 2D:4D men
2. Make more intrasexual threats than men with higher 2D:4D
3. Be more physically aggressive toward male competitors than men with higher 2D:4D
4. Be more physically aggressive toward their partner than higher 2D:4D men
5. Be more physically aggressive when their partner cheated
Also,
6. Women will resist mate guarding more when they cheated
7. Women will resist mate guarding more when their partner has a higher 2D:4D, due to lower costs to her
8. Women’s 2D:4D will not be associated with any of the behaviors described above

4. Methods Participants 101 heterosexual dating couples
At least one member of the pair was enrolled in an Introductory Psych class
Mean relationship length was 18 months
SD = 16.24
Mean female age was 20
SD = 3.09
Mean male age was 21
SD = 3.85
Women demographics
55% white
34% Hispanic
3% Asian
7% other
Men demographics
56% white
36% Hispanic
2% Asian
4% other

5. Materials and Procedure
First all participants had their 2D:4D levels evaluated by measuring each side of the index finger and the ring finger on the right hand of each participant twice.
Measurements were averaged in order to create the ratio; index finger (2D) to ring finger (4D)
Then a 42 item male guarding scale with seven subscales was administered
Asked to rate whether each behavior listed had occurred during the past 6 months
From 0 (never) to 4 (very often)
Subscales included:
Vigilance
Protection
Monopolization
Possessiveness
Intrasexual threats
Intrasexual physical aggression
Threats and aggression toward partner
Also administered a scale which measured resistance behaviors
27 items; questions included, “I hid stuff from my girlfriend so she wouldn’t find it”
Each individual rated their resistance to specific behaviors during past 6 months on a 0 to 4 scale
Higher scores indicate more resistance to mate guarding
Lastly, each participant was asked to state whether they’d ever cheated on their current partner
84% Women (N = 84) said they had never cheated on their partner
16% Women (N = 16) said they had cheated
87% Men (N = 87) said they had never cheated on their partner
13% Men (N = 14) said they had cheated

6. Results 2 x 2 ANOVA Contrary to hypotheses:
There was no relationship between men’s 2D:4D and overall levels of self-reported mate guarding
There was no relationship between 2D:4D and intrasexual physical aggression
Consistent with hypotheses:
Men with a lower 2D:4D were more likely to state that they made intrasexual threats
Men with more masculine 2D:4D were more threatening and physically aggressive toward their partners
Men were more threatening and physically aggressive when their partner stated she cheated
Women were more resistant to mate guarding when they cheated on their current partner

7. Discussion
Overall mate guarding was not significantly correlated with 2D:4D
Low 2D:4D men were more threatening and physically aggressive toward their partners than high 2D:4D men
2D:4D was not correlated with behavioral aggression in women
Women were more resistant to their partner’s mate guarding when he had high 2D:4D
When the costs of resistance become too high, women may tolerate mate guarding

8. Critical Review Limitations: Strengths:
Unable to say whether participants’ 2D:4D is related to their current circulating hormone levels
Unable to say whether these results would differ for people who have children
Strengths:
The use of couples in romantic relationships
Uncommon and allows for assessment of interactions between partners
Linking two areas of research; 2D:4D and mate guarding

9. Quiz
1. Which level of 2D:4D indicates a higher tendency towards aggressive behavior and mate guarding?
A. Low 2D:4D
B. High 2D:4D
C. Both A and B
2. The woman participants in the study reported cheating more than the male participants (T/F)
3. Women may allow mate guarding by men with low 2D:4D because…
A. They respect them more than high 2D:4D
B. They think low 2D:4D are sexier than high 2D:4D
C. It is too costly to resist them
4. How many questionnaires did the participants completed?
A. 1
B. 2
C. 4
5. 2D:4D was correlated with behavioral aggression in women (T/F)
6. Men were more threatening and physically aggressive when their partner stated she cheated (T/F)