But fluid intelligence, the ability to analyze abstract situations involving novel sets of rules, plays an outsize role.

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But the research on fluid and crystallized intelligence indicates that fluid intelligence peaks around twenty and then declines without reversal.

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After the 50s, the decline in fluid intelligence becomes the dominant force and our ability to make sophisticated decisions, for most people, declines.

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That ability, known as fluid intelligence, also declines with age.

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Fluid intelligence refers to the ability to solve novel problems.

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The theory of fluid and crystallized intelligence provides some clues.

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"Intelligence is so fluid right now, " McCann told CNN.

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