When we combine the adaptation principle with the discovery that people’s average level of happiness is highly heritable,11 we come to a startling possibility: In the long run, it doesn’t much matter what happens to you. Good fortune or bad, you will always return to your happiness setpoint—your brain’s default level of happiness—which was determined largely by your genes. In 1759, long before anyone knew about genes, Adam Smith reached the same conclusion: In every permanent situation, where there is no expectation of change, the mind of every man, in a longer or shorter time, returns to its
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