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Running head: GUNS, TESTOSTERONE, AND AGGRESSION
Adapted Version of Guns, Testosterone, and
Aggression: An Experimental Test of a
Mediational Hypothesis
Jennifer Klinesmith
Tim Kasser
Francis T. McAndrew
Knox College
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Abstract
To test whether interacting with a handgun increases testosterone which, in turn,
increases aggressive behavior, 30 college men (ages 18-22) provided a saliva sample
(used to measure each man's testosterone level), interacted with either a gun or a
children's game for 15 minutes, provided a second saliva sample, and then added as
much hot sauce as they wanted to a cup of water that they thought another participant
would be forced to drink. In support of the hypothesis that interacting with a handgun
increases aggressive behavior, the men who interacted with the gun added more hot
sauce to the water than the men who interacted with the game. In support of the
hypothesis that testosterone partially mediates this gun-aggression relationship, (a) men
who interacted with the handgun had greater increases in testosterone than those who
interacted with the game, (b) increases in testosterone levels were correlated with
increases in aggression, and (c) controlling for changes in testosterone reduced the gunaggression correlation.
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Guns, Testosterone, and Aggression:
An Experimental Test of a Mediational Hypothesis
The “weapons effect”—that merely seeing a weapon increases aggression—is well-documented
(Anderson, Benjamin, & Bartholow, 1998; Bartholow, Anderson, Carnagey, & Benjamin, 2005;
Berkowitz & LePage, 1967; Bettencourt & Kernahan, 1997; Killias & Haas, 2002). However,
the physiological mechanism behind the weapons effect has not been investigated.
Perhaps the hormone testosterone is the physiological trigger for the weapons effect. After all, for
species ranging from chickens to monkeys, testosterone injections increase aggressiveness
(Ellis, 1986). Furthermore, some laboratory and field studies involving human participants have also found
strong positive relationships between testosterone and aggression (Archer, 1994; Campbell, Muncer, &
Odber, 1997; Dabbs, Carr, Frady, & Riad, 1995; Dabbs, Jurkovic, & Frady, 1991). Thus, it may be that
seeing a weapon triggers a surge in testosterone which, in turn, triggers aggression.
Although some evidence suggests that surges in testosterone trigger aggression, there is no direct
evidence that seeing a weapon triggers testosterone surges. However, some indirect evidence suggesting
that seeing a weapons could trigger an increase in testosterone comes from research on the “challenge
hypothesis” (Wingfield, Hegner, Dufty, & Ball, 1990).
Originally developed to explain aggressive behavior in male pair-bonded birds, the challenge
hypothesis proposes the following chain of events. First, threats to a male’s status trigger surges in
testosterone. Second, those testosterone surges then facilitate whatever competitive behaviors (including
potentially aggressive responses) are necessary for meeting the challenge.
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Studies across a wide range of nonhuman vertebrates has found evidence for the threattestosterone-aggression sequence central to the challenge hypothesis (Cavigelli & Pereira, 2000;
Ferree, Wikelski, & Anderson, 2004; Hirschenhauser, Taborsky, Oliveira, Canario, & Oliveira, 2004;
Muller & Wrangham, 2004). Thus far, human research has investigated and found support for the threattestosterone link. For example, researchers find that men's testosterone levels rise in response to insults
(Cohen, Nisbett, Bowdle, & Schwarz, 1996) and to competitions (Archer, 1991; Booth, Shelley, Mazur,
Tharp, & Kittok,1989; Gladue, Boechler, & McCaul, 1989; Mazur, Booth, & Dabbs, 1992;
Mazur & Lamb, 1980).
In this study, we examine whether the presence of a gun might act as a
stimulus signaling a threat to status. If so, the gun’s presence should increase men's testosterone
levels (the mediating variable), which, in turn, should increase men's aggressive behavior
(the dependent variable).
To measure changes in our potential mediating variable (testosterone), participants'
testosterone levels were measured both before and after interacting with a gun or a children's game.
To measure aggression (the dependent variable), we adapted Lieberman, Solomon, Greenberg, &
McGregor's (1999) procedure of letting each participant anonymously put hot sauce in a cup of
water that the participant believes another person will be forced to drink.
Based on past research, we hypothesized that interacting with the gun would increase
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aggression. Based on the challenge hypothesis, we hypothesized that interacting with the gun
would increase aggression by increasing participants' testosterone. Specifically, we predicted that (a)
interacting with the gun would increase testosterone levels, (b) increases in testosterone levels would be
positively correlated with levels of aggression, and (c) controlling for increases in testosterone would
shrink this gun-aggression correlation.
Method
Participants
Participants included 30 male college students (age range 18-22) who received extra
credit or a small monetary reward for their participation. To help control for the tendency for
men’s testosterone levels to vary depending on time of day (Nieschlag, 1974), we conducted all
sessions during the afternoon or early evening.
Procedure
When recruited, participants were informed that the study would examine taste
sensitivity in males and that they would therefore need to provide saliva for hormone
analysis; as such, participants were asked not to eat, drink, smoke, or brush their teeth one
hour prior to testing in order to minimize impurities in the saliva samples. When participants
arrived at the lab, a female experimenter confirmed that the participants had indeed followed
these instructions before she administered consent procedures. Next, participants
provided a 6-ml sample of saliva by spitting into a cup; this saliva was used to assess
pre-manipulation testosterone levels.
All participants were then led into a room containing a television, a chair, and a table
with an object and some paper on it. For experimental participants, the object was a pellet
gun identical in size, shape, and feel to a Desert Eagle automatic handgun; for control
participants, the object was the children's game Mouse Trap™. Participants were told that the
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study was investigating whether taste sensitivity was associated with the attention to
detail required for creating instructions concerning these objects. Participants were therefore
asked to spend 15 minutes handling the object and writing a set of instructions about
how to assemble and disassemble the object; a drawing of the object was also provided
for participants to label the object's parts. The handgun and children's game were relatively
similar in number and complexity of parts.
After 15 min, the experimenter re-entered the room, asked the participant to
stop working on the instructions, and obtained a post-manipulation saliva sample from the participant.
Participants were told they would next perform the taste sensitivity portion of the study.
They were given a cup filled with 85 grams of water and a single drop of Frank's Red
Hot Sauce. Participants were told that the sample had been prepared by a previous participant,
were instructed to take a sip of the sample, and were then asked to rate the taste of the
sample on a scale provided.
The experimenter left and then returned with a tray containing a cup of 85 grams
of water, a nearly full bottle of Frank's Red Hot Sauce, and a lid. Participants were asked to
prepare a sample for the next participant by placing as much hot sauce in the water as they
wanted. Each participant was assured that neither the person who drank it nor the experimenter would
know how much hot sauce he had put in the water, as the lid was to
be put on the cup after the hot sauce was added. The experimenter then left the room,
and participants signaled when they were finished adding the hot sauce. The cup was then
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removed from the room, and the experimenter weighed it again to obtain a measure of the
amount of hot sauce, in grams, the participant added to the water. This served as our
aggression measure (see Lieberman et al., l999).
Because of the potentially arousing nature of the experiment, we wanted to ensure that all
participants were reasonably calm when they left the lab. Therefore, all participants next
watched a relaxing video of nature scenes and classical musical. Given that participants had
been deceived, we next debriefed them, emphasizing that they should not feel badly
about any aggressive behavior they exhibited. Interestingly, several participants were
disappointed when told that the sample of hot sauce and water they had prepared would not
actually be given to the next participant. No participants expressed suspicion as to the true
nature of the study.
Results
As a first step to determining whether testosterone mediated the handgun-aggression effect, we
needed to establish that handguns did indeed increase aggression. They did: Participants who
interacted with the gun added more hot sauce to the water (M = 13.61 grams, SD = 8.35) than did those who
interacted with the children's game (M = 4.23 grams, SD = 2.62; t (28) = -4.16, p <.01 = .99; d
= 1.52). As a second step to determining whether interacting with a gun increased aggression by
increasing participants’ testosterone, we tested to see whether interacting with the gun increased
testosterone levels. It did: Those participants who interacted with the handgun showed more of an increase
in testosterone from pre-manipulation to post-manipulation (M = 62.05 picograms [a picogram is a trillionth
of a gram] per milliliter, SD = 48.86) than did those who interacted with the children's game (M = 0.68
pg/ml, SD = 28.57), t (28) = -4.20, p <.01; d = 1.53).
As a third step to determining whether interacting with a gun increased testosterone, which, in turn
increased aggression, we tested to see whether there was a relationship between testosterone levels and
aggression. There was: Changes in testosterone level were positively and significantly correlated with
amount of hot sauce participants put in the cup (r = .64, p < .01).
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As a fourth step to determining whether testosterone mediated the gun-aggression effect, we
examined whether the correlation between the predictor variable (i.e., gun vs. game) and the outcome
variable (i.e., grams of hot sauce added) decreased once we statistically controlled for the effects of the
purported mediating variable (i.e., changes in testosterone). In support of the hypothesis that testosterone
partially mediates the gun-aggression relationship, statistically controlling for changes in testosterone levels
resulted in a partial correlation between gun and aggression of -.36—which is smaller than the gunaggression correlation (r = -.62). To determine whether this decrease represents a statistically significant
(reliable) difference, we computed Sobel’s test for mediation, using this website. The results of that test
Suggested that testosterone did indeed mediate the gun-aggression relationship (Sobel’s test = 2.09,
P < .05).
Discussion
Past research shows that both testosterone and exposure to guns are associated
with aggressive behavior, but no studies, to our knowledge, have examined how the two
factors might work together. The present results demonstrated that men who interacted
with a gun showed a greater increase in testosterone levels and more aggressive behavior
than did men who interacted with a children's game. Our analyses also suggested that
part of the reason that guns increase aggression is by increasing in testosterone
levels.
Such findings not only are consistent with the challenge hypothesis (Wingfield et
al., 1990), but provide new support for it both by examining a new type of "challenging"
stimulus (the handgun) and by assessing not just increases in testosterone but increases in
aggression. Additionally, the results argue against some interpretations that have suggested that
experimental effects of guns on aggression are due to subtle demand characteristics. That is,
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it seems unlikely that subtle experimenter pressures could significantly increase participants'
testosterone levels; instead, it seems more reasonable to believe that the presence of the gun had this effect.
Future research could explore a variety of avenues for correcting some of the
limitations of the present study. For example, systematic replications could determine whether the results
would hold for (a) for women, (b) people with extensive experience with guns, such as hunters and
soldiers, and (c) people confronting an individual who had angered them.
In short, the present study both replicates and extends previous research on the gun-aggression relationship.
Replicating past research (e.g., Berkowitz & LePage, 1967; Bettencourt & Kernahan, 1997; Killias & Haas, 2002), it
found that answer to the question of whether the presence of guns contributes to violence seems to be
“yes.” Extending past research, it found evidence suggesting that, part of the answer to the question of how guns
contribute to violence is, at least for men, by increasing testosterone levels.
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