Why do original artworks sell for big bucks at auction while reproductions languish at yard sales? How is that pair of earrings your grandmother gave you different from every identical pair? Who taught you that autographs are worth anything? It's not brainwashing, according to recent research—we're born to value items with unique histories.

Evidence comes from two studies reported in Cognition by psychologists Bruce Hood of the University of Bristol and Paul Bloom of Yale. They asked kids ages 3 to 6 to throw their favorite playthings into a "copying machine" and then decide which they wanted to keep: the original or the smoke-and-mirrors "clone." Kids with the strongest attachments to their blanky preferred box No. 1 far more than the others did.

And kids had no qualms about a copy of an anonymous piece of precious metal but preferred an object purportedly owned by Queen Elizabeth II over its duplicate; they believed that two things could be materially identical but might differ in some special way—this spoon was the Queen's!

Susan Gelman of the University of Michigan has done similar work and agrees that we naturally imbue unseen "essences" to things. Essentialism may in part be an evolutionary response to fear of contagion. In a world full of germs, an object's historical path can be more important than its surface appearance. "Essentialism seems to provoke magical reasoning—witchcraft, blessings, et cetera," Gelman says. "And yes, it also explains why we prefer authentic things, including autographs, original works of art, and Britney Spears' chewed gum."

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