Cheater-detection module

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The cheater-detection module in Social Contract Theory (SCT) is an evolved program for detecting cheaters in situations involving social exchange. [1]


The cheater-detection module is supported by experiments[2] on the Wason Selection Task which is a logical puzzle involving four cards, each of which have a number on one side and a color on the other. Two of these face the number side and two the color side as shown in Figure 1.

Figure 1

In such experiments participants are told about a rule like "if the number on a card is even, then its color on the other side is red." They are then asked which cards need to be flipped over for the rule to be upheld.

The correct answer is: 1. the card that is even (to check that it is red) and 2. the card that is brown (to check that it is not even). However only a minority (less than 20% of UCSB undergrads)[2] get this correct.

The Abstract Problem

Abstractly stated the problem is verifying the rule "If P then Q" by cards that have P, not P, Q, not Q on each face.

The correct answer is to flip P to check for Q, and not Q to check for P.

The Drinking Age Problem

When is phrased in terms of social rules such as: "if you are drinking alcohol, then you must be over 18" (Figure 2) then most subjects get the answer correct. One must flip over the card of 1. the 16 year old and 2. the beer drinker.[3]

Figure 2

Further Reading


  1. Ermer, E., Cosmides, L., & Tooby, J. (2007). Cheater detection mechanism. In R. F. Baumiester & K. D. Vohs (Eds.), Encyclopedia of Social Psychology (pp. 138-140). Thousand Oaks, CA: Sage Publications.
  2. 2.0 2.1 2.2 Center for Evolutionay Psychology. (n.d.). The Wason Selection Task. Here is the general structure of a wason selection task. Retrieved August 17, 2022, from
  3. Cosmides, L. (1985). Deduction or Darwinian Algorithms? An explanation of the "elusive" content effect on the Wason selection task. Doctoral dissertation, Harvard University. University Microfilms #86-02206.  Introduction, Chapter 1, Chapter 2, Chapter 3, Chapter 4, Chapter 5, Chapter 6, Chapter 7
  4. Tooby, J., & Cosmides, L. (n.d.). Social Exchange. Retrieved August 17, 2022, from