In order to appreciate this little window into the inner workings of your brain, please cover up the rest of this column, reading just one paragraph at a time.
A deck of cards has, on one side, a person's age; on the other, it has the drink they are holding, either alcoholic or non-alcoholic. They're breaking the law if they're under 18 with an alcoholic drink. I show you these four cards: TEQUILA, 33, SPRITE, 16. Which two cards do you need to turn over to see if the law is being broken?
Pretty simple, yes? If the tequila card has an age less than 18 on the reverse, or if the 16 card has an alcoholic drink on the reverse, the law's being broken. The 33 and Sprite cards make no difference. Everyone gets this right.
Now the surprising twist. Another deck of cards has a number on one side and a color on the other. You're looking at four cards: 5, PURPLE, 8, RED.
I tell you, "If a card has an even number on one face, it has the name of a primary color (red, yellow, blue) on the other face. Which two cards do you turn over to confirm whether I'm telling you the truth? Once you've figured it out, move on to the next paragraph. Warning: Apparently, fewer than 25 percent of people get this right.
Let's see. Turning the 5 over reveals nothing about my statement, which only referred to even-numbered cards. Similarly, finding an odd number on the back of the red card neither proves nor disproves my statement about even-numbered cards. However, finding an even number on the back of the purple card disproves it, while finding anything other than red, yellow or blue on the back of the 8 card also disproves my statement. So the correct answer is purple and 8.
I bet you found this harder than the first puzzle. (I sure did.) But here's the thing: The two puzzles are identical! I just switched 18+/18- for odd/even and alcoholic/non-alcoholic for primary/non-primary colors. Formally, the puzzles are the same.
So what gives? Why do most of us find the booze puzzle simple and the other one tricky (perhaps even getting it wrong)? This is the sort of conundrum that brain researchers glom onto in their efforts to understand how we think. According to neuroscientist David Eagleman in his book Incognito (from which I adapted these puzzles), our responses are evidence of "neural specialization." He writes, "The brain cares about social interaction so much that it has evolved special programs devoted to it: primitive functions to deal with issues of entitlement and obligation." On the other hand, "our brains aren't wired for general logic problems" of the second sort.
There's no way we can go back in time to check it out, of course, but doesn't it make total sense that when our brains were developing back in the Stone Age, and when our ancestors lived in groups of perhaps 100 or 200 people, it was essential for the survival of the group that everyone pulled their weight, fulfilling obligations ("You owe me for the food I gave you yesterday") and obeying social rules? Any loose cannons not living up to the expectations of the group would face being ostracized or expelled.
So next time someone offers you a puzzle dealing with conditional logic, like the second one above, try to reframe it in "people" terms. Suddenly your socially well-adjusted brain will figure it out, naturally.