H. Armstrong Roberts/ClassicStock via Getty Images The first study to test people’s personalities in adolescence and again in old age shows that compared to their younger selves, most people’s personalities in older adulthood are barely recognizable.

Physical appearance and fashion choices aside, you might think you’ll be essentially the same person in old age as you were in adolescence.

But the longest-running study ever conducted on human personality challenges this assumption.

The study, the first to test people’s personalities in adolescence and again in old age, shows that compared to their younger selves, most people’s personalities in older adulthood are barely recognizable.

With unprecedented access, psychologists at the University of Edinburgh in the United Kingdom investigated how character traits shift as people get older by following a cohort of Scottish adults from adolescence to old age. The findings, published in the journal Psychology and Aging, significantly challenge the idea of personality as a relative constant throughout life.

“It’s important to appreciate how rare these data are,” Dr. Ian Deary, a professor of differential psychology at the university and one of the study’s authors, told The Huffington Post Wednesday. “The questions are not ideal and the ratings methods are not ideal, but the original sample is amazingly good and the time between ratings is unsurpassed.”

The researchers first accessed data from a study conducted in 1950, in which a group of teachers filled out personality assessments for more than 1,200 14-year-old students. These measured six basic personality traits: self-confidence, conscientiousness, perseverance, desire to excel, originality and stability of moods.

Then, in 2012, the researchers managed to track down students from the 1950 study. Of the 635 participants that they were able to locate, 174 agreed to take a personality test similar to the one they had participated in 63 years earlier.

The participants, who were now 77 years old on average, each filled out a personality assessment measuring the same six characteristics on which they were rated as teenagers. They also brought along someone close to them, who assessed the participant using the same personality scale.

“Personality changes only gradually throughout life, but by older age it may be quite different from personality in childhood.”

In comparing the then-and-now test results, the researchers were surprised to find virtually no overlaps. The only traits that had some mild constancy were stability of moods and conscientiousness, but the correlations weren’t strong.

The younger and older self seemed to bear no resemblance for each person. It was “as if the second tests had been given to different people,” the study’s authors noted.

“The longer the interval between two assessments of personality, the weaker the relationship between the two tends to be. Our results suggest that, when the interval is increased to as much as 63 years, there is hardly any relationship at all,” the researchers wrote in conclusion. “Personality changes only gradually throughout life, but by older age it may be quite different from personality in childhood.”

Still, the results were unexpected, considering that most other research shows personality traits to be relatively stable even across decades. Personality stability as a psychological construct can be traced back to William James, the father of American psychology, who said in 1890 that after the age of 30, the personality is “set like plaster.” Once we reach adulthood, he believed, our personalities are unlikely to change in any significant way.

Consistent with James’ views, research has shown personality plasticity ― a measure of how much our character traits change ― to decline as a person moves past young adulthood. The scientific evidence generally shows that personality traits are stable over long periods, Deary noted, and one study even found traits to be stable over more than 40 years.

But the new findings hint at the idea that personality may be more malleable than researchers thought. Of course, this data isn’t totally conclusive.

Comparing teacher assessments with later self-testing isn’t nearly as reliable as having the participants themselves take the same personality test at both ages. Plus, the sample size by the end of the study was relatively small. But the dramatic results nonetheless suggest that personality may be more malleable than we’ve acknowledged.