Lujiazui, Shanghai's financial district, includes the world's third- and sixth-tallest buildings. The city's population is 23 million.

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A museum employee stands beneath a mastodon skeleton on display at the U.S. National Museum, now the Smithsonian National Museum of Natural History, circa 1917. A new study revisits an old debate about the evidence for an early mastodon hunt in North America.

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Brain researchers say the big fluctuations in IQ performance they found in teens were not random — or a fluke. hide caption

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Auguste Rodin's The Thinker, shown outside the Detroit Institute of Arts, depicts a man engaged in what Daniel Kahneman might describe as System 2 — or slow, deliberative — thinking.

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