A new analysis of 14 studies comprising 50,000 people may provide the best evidence yet that personality is not fixed through life.

Subjects in the US and throughout Europe showed considerable changes in their personalities as they aged.

Many of the changes were broadly consistent, although some people did change in unique ways.

You might be fundamentally you for your entire life, but don’t expect your personality to stay the same.

That’s according to a major study of 50,000 people over the course of several decades, which found the traditional notion of personality – as fixed and unchanged after adolescence – is mostly untrue.

People included in the sample showed a common trend as they got older, declining in all five major personality metrics that psychologists have come to trust as the gold-standard.

Psychologists have been writing about personality for the better part of three centuries, beginning most famously with William James’ 1890 text “The Principles of Psychology.” Relying on personal observation, James wrote that personality is “set like plaster” after age 30.

In the century or so since “The Principles of Psychology” was published, psychologists have come to rethink personality in bits and pieces. In 2003, the American Psychological Association observed the changing consensus among members of the field: Personality was beginning to look more like it was ever-evolving, even through old age.

The latest study combined 14 longitudinal studies that gathered information about people’s personalities, including data from the United States, Europe, and Scandinavia. Many of the subjects had already reached adulthood, which gave the researchers unique perspective on personality changes. Typically, studies skew toward young people.

Of the Big Five personality traits – neuroticism, conscientiousness, openness, extroversion, and agreeableness – all five showed major fluctuations across individual participants’ lives. And all traits, except for agreeableness, showed downward trends of about 1-2% per decade across the overall studies.

In part, this suggested to researchers that the so-called “Dolce Vita” effect was real – that when people age, they enjoy fewer social responsibilities and can do more of what they want.

People can be less neurotic about conforming to the group, less open to trying new things in order to savour the classics, less conscientious as they become more selfish, and less extroverted as they keep more to themselves.

These trends appeared at nearly every stage of the 14 studies and held mostly steady across different geographical regions. Some regions deviated from the norm, however. People from the US showed considerably larger declines in extroversion as they aged, which signalled to the investigators that they were especially done with with seeming social.

People aren’t set in plaster, as William James asserted 128 years ago. They’re more like clay, constantly getting moulded by their changing circumstances.

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