Science Saturday: Americans are WEIRD

This story came to me by way of a friend I left behind in Korea: "A slap in the face to evolutionary psychologists," is the context he provided. And I will gladly read anything that can credibly debunk evopsych because many in the field practice and perpetuate bad science.

For the link phobic, an anthropologist went to a relatively isolated tribe in Peru and ran a bunch of game theory experiments with them. These were experiments had been performed time and time again, with consistent and universalized results.

Until Henrich played some games with Machiguengas in Peru:

The test that Henrich introduced to the Machiguenga was called the ultimatum game. The rules are simple: in each game there are two players who remain anonymous to each other. The first player is given an amount of money, say $100, and told that he has to offer some of the cash, in an amount of his choosing, to the other subject. The second player can accept or refuse the split. But there’s a hitch: players know that if the recipient refuses the offer, both leave empty-handed. North Americans, who are the most common subjects for such experiments, usually offer a 50-50 split when on the giving end. When on the receiving end, they show an eagerness to punish the other player for uneven splits at their own expense. In short, Americans show the tendency to be equitable with strangers—and to punish those who are not.

Among the Machiguenga, word quickly spread of the young, square-jawed visitor from America giving away money. The stakes Henrich used in the game with the Machiguenga were not insubstantial—roughly equivalent to the few days’ wages they sometimes earned from episodic work with logging or oil companies. So Henrich had no problem finding volunteers. What he had great difficulty with, however, was explaining the rules, as the game struck the Machiguenga as deeply odd.

When he began to run the game it became immediately clear that Machiguengan behavior was dramatically different from that of the average North American. To begin with, the offers from the first player were much lower. In addition, when on the receiving end of the game, the Machiguenga rarely refused even the lowest possible amount. “It just seemed ridiculous to the Machiguenga that you would reject an offer of free money,” says Henrich. “They just didn't understand why anyone would sacrifice money to punish someone who had the good luck of getting to play the other role in the game.”

As it turns out, many experiments in psychology thought to be good science turned out to be using an incredibly small sample size: Westerners*. Just how small of a sample size is that?

A 2008 survey of the top six psychology journals dramatically shows how common that assumption was: more than 96 percent of the subjects tested in psychological studies from 2003 to 2007 were Westerners—with nearly 70 percent from the United States alone. Put another way: 96 percent of human subjects in these studies came from countries that represent only 12 percent of the world’s population.

Americans are WEIRD; that is to say they are Western, Educated, Industrialized, Rich, and Democratic. It goes without saying that these characteristics are not inherent in all of the world's cultures. Assuming that because you've got consistent results from running an experiment thousands of Americans you've found some grand evolutionary truth about our brains, cognition, or temperaments is a huge mistake. A truly freaky example:

This one is considered a classic illusion, right? Even though most of you know better, you'll still perceive B as being longer than A. Yet what seems to be an issue of pure cognition and perception is actually a factor of culture, living spaces, and environment.

Researchers found that Americans perceive the line with the ends feathered outward (B) as being longer than the line with the arrow tips (A). San foragers of the Kalahari, on the other hand, were more likely to see the lines as they are: equal in length. Subjects from more than a dozen cultures were tested, and Americans were at the far end of the distribution—seeing the illusion more dramatically than all others.

Why?

For instance, the different ways people perceive the Müller-Lyer illusion likely reflects lifetimes spent in different physical environments. American children, for the most part, grow up in box-shaped rooms of varying dimensions. Surrounded by carpentered corners, visual perception adapts to this strange new environment (strange and new in terms of human history, that is) by learning to perceive converging lines in three dimensions.

When unconsciously translated in three dimensions, the line with the outward-feathered ends (C) appears farther away and the brain therefore judges it to be longer. The more time one spends in natural environments, where there are no carpentered corners, the less one sees the illusion.

Perhaps, in time, this hypothesis about whence the difference arises will be debunked and a better one put in its place. But it's still a hypothesis about a demonstrable, testable, replicable difference in something once thought to be a universal perception.

So the next time you hear someone talk about how "humans/men/women have been shown to do X, Y, or Z," ask if the studies included people who aren't WEIRD. It might just make all the difference. How much? This story about the Karbi and the Khasi tribes in India just about sums it up.

Across both tribes and genders, people took about 40 seconds, on average, to complete the puzzle. In the patrilineal Karbi tribe, men completed the puzzle 36 percent faster than women. But in the matrilineal Khasi tribe, women and men were equally good at their task.

What that shows, Hoffman said, is that "even while holding biology constant, there is an effect of culture on the gender differences in spatial abilities."

This difference in spatial reasoning is cited time and time again as reasons why there aren't more women in STEM. "It's biological," people like to say, "it's just because men and women are wired differently." Similar "biological," evopsychological reasons come up time and time again to explain this or that difference: women aren't naturally promiscuous, women are naturally inclined towards motherhood, etc etc.

Look at what a huge difference a little culture makes.

*I loathe division by hemisphere but as a linguistic shortcut it's sometimes the easiest way to demarcate things.