te rle f   er-grp 
There are less obvious effects of oxytocin, too.
For example, do you think it can play a role in
prejudice, discrimination or maybe even conict?
It turns out it can, but these come as side effects
of increased bonding with your own group. The

following two studies will look at these seemingly
surprising negative effects of oxytocin.
De Dreu et al (2012) looked at the role of
oxytocin in inter-group conict—more specically,
defence-motivated non-cooperation
This was a double-blind experiment using the
independent measures design. The sample
consisted of 102 males and they self-administered
either a dose of oxytocin or placebo through nasal
spray. Participants were randomly assigned to
three-person groups and told that they would need
to compete against another group of three people.
Following this, each participant was paired with a
member of another three-person group and played
a modied version of the “Prisoner’s dilemma”.

TOK
“Prisoner’s dilemma” is probably the most commonly mentioned problem of game theory. Game theory is an interesting
interdisciplinary eld that combines mathematics, decision theory, economics and other areas. It is a theory that
models the behaviour of two or more rational agents whose actions and outcomes depend on each other.Things get
even more interesting when you compare the rational predictions of the mathematical theory (game theory) to real-life
behaviour of participants in these situations (behavioural game theory).
The standard “Prisoner’s dilemma” is as follows.Two members of a criminal gang are arrested. Each prisoner is kept in an
isolated chamber and they have no means of communicating with each other.They are interrogated independently and
each of them has to choose one of two actions.They are also given the same deal, which is presented in the form of a
matrix of outcomes, as shown in Figure 2.32.

▲ Figure2.32 Options for players of the “Prisoner’s dilemma”

Prisoner A

Prisoner B

Silent Betray

Silent Betray

–1

–2

0 –2
–3

0

If A and B each choose to betray the partner and testify against that person, they are both given two years in prison. If A
and B both remain silent, they only get one year each. If A chooses to testify against B, but B keeps silent, A will be free
and B will get three years in prison (and vice versa).

83

hoRMonE S anD BEhav iouR

Figure 2.33 shows an example of the game played
by participants in the study.

▲ Figure 2.33 The modied version of the “Prisoner’s
dilemma” played in the study
Outgroup member
Non-cooperation
Ind: 5
Gr: 1

Ind: 8
Gr: 8

Ind: 6
Gr: 6

Cooperation
Cooperation Non-cooperation
Participant

Ind: 7
Gr: 7

Ind: 7
Gr: 7

Ind: 6
Gr: 6

Ind: 5
Gr: 1

Ind: 8
Gr: 8

(Ind = individual; Gr = group)

Just as in the standard “Prisoner’s dilemma”, the
two participants are asked to choose, simultaneously
and independently, whether they want to
cooperate or compete. Although the decision is
made independently, both players see the pay-off
matrix. They can see the following possible
outcomes.
A If I (the participant) cooperate and he (the
outgroup player) also cooperates, I win 7 points,
the members of my group win 7, he wins 7
and the members of his group win 7. This is an
attractive option: everyone wins quite a lot.
B If I compete and he competes, we only win 6—
both I and my group members and he and his
group members. This is less attractive than
outcome A for all of us.
C If I cooperate but he competes, he and the
members of his group win 8—the largest

possible pay-off. At the same time, I only win 5,
and the members of my group only win 1. This
means that I am vulnerable to my opponent’s
non-cooperation, but my group members are
even more vulnerable.
D If he cooperates but I compete, outcome C is
reversed.
What decision would you make if you were playing
this game? Outcome A (cooperate-cooperate)
seems to be the most rational choice, but the
problem is that there always exists a temptation to
switch from cooperating to competing because this
will increase the pay-off from 7 to 8. You know this,
and you can probably decide that 7 is almost as good
as 8 and choose to cooperate. However, you also
know that your opponent has the same temptation.
Will he be reasonable and sacrice 1 unit of prot
for the common good? You hope so—but what if
he doesn’t, and goes for outcome C? In this case
you will suffer (not too much), but your group will
suffer a lot: its pay-off will be 7 times smaller. The
main question is: how likely is it that, in order to
prevent outcome C from happening, you will
strike rst and choose to compete rather than
cooperate? That’s what we call defence-motivated
non-cooperation.
TOK
Sometimes a war begins when one country strikes
another country pre-emptively, because it is afraid to
become the victim if it doesn’t strike rst.To what extent
do you nd this reasoning rational?
In general, can negative social events be the result of
positive, rational reasoning?
Participants were asked to make a choice
between cooperation and non-cooperation ve
times. The numeric rewards were varied on
these ve trials. The pay-offs from the game

TOK (continued)
It looks as if the most rational choice in this situation is to remain silent—this minimizes the total time spent in prison.
However, the problem is that both A and B have a temptation to testify against the partner and be free, so there’s a high
chance that the outcome will actually be two years in prison for each of them.
What would you do if you were in the situation that is the “Prisoner’s dilemma”?
What applications of game theory in various areas of knowledge can you think of?

84
2 BIOLOGICAL APPROACH TO BEHAVIOUR

were converted to real money and given to the
participants.
Results of the study showed that a player’s
defence-motivated non-cooperation:
● is more likely if vulnerability of the player’s
group is high (for example, suppose we change
1 to 0 in the pay-off matrix)
● does not depend so much on the player’s own
vulnerability
● is more likely in the oxytocin condition.
The researchers concluded that oxytocin-induced
non-cooperation is motivated by the desire to
protect vulnerable group members (and not
so much by the desire to protect oneself). This
reinforces the role of oxytocin in creating bonds
with the members of your ingroup, but also
shows how oxytocin has a reverse, negative
side—defensiveness and non-cooperation with
others.


what were the findings of the study