In the third chapter of Human Diversity: The Biology of Gender, Race, and Class, while discussing sex differences in neurocognitive functioning, Charles Murray presents a simple test of visuospatial skills, the Piaget water-level test.

Go ahead and give it a try.

Don’t worry, it’s not a trick question.

After you’re finished, go ahead and read the text below the diagram:

The test-taker is asked to draw a line to show how the water line would look in the tilted bottle. The correct answer is a horizontal line relative to the earth. Halpern reports that the best estimate, summarizing results over many studies, is that about 40 percent of college women get it wrong. Effect sizes favoring males range from –0.44 to –0.66. In Halpern’s words, “It is difficult to understand why this should be such a formidable task for college women.” And yet the result has been replicated many times, has been confirmed internationally, and is just about impossible to explain as a product of culture or socialization (if you doubt that, give it a try).

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