The research, which was published in the journal Psychology and Ageing back in December 2019, was part of the longest study on narcissism.
It explored how narcissistic behaviour changes not only over time, but also by generation, surveying nearly 750 people aged between 13 and 77.
"In the debate about whether or not narcissism has been increasing in recent history, there is a lack of basic information about how narcissism changes across the adult life span," the paper said.
After surveying the study's participants, researchers found that qualities associated with narcissism - such as being full of yourself, being sensitive to criticism and imposing your opinion onto others - generally declined 'over time and with age'.
However, overall older generations found to be more sensitive than their younger counterparts.
The study's co-author William Chopik, associate professor at Michigan State University, said: "There's a narrative in our culture that generations are getting more and more narcissistic, but no one has ever looked at it throughout generations or how it varies with age at the same time."
Chopik said baby boomers, or 'individuals who were born earlier in the century', started off with 'higher levels of hypersensitivity, or the type of narcissism where people are full of themselves, as well as willfulness, which is the tendency to impose opinions on others."
He said: "There isn't much data on older generations, but now that baby boomers are ageing into that phase of life, it's a huge part of the population that we need to be looking at."
Chopik also hypothetisised that baby boomers may be more narcissistic than other generations because they 'grew up in a time when the government provided privileges like social security'.
Researchers found that behaviour tends to decline as we move through life, and as we come across certain milestones.
Chopik continued: "There are things that happen in life that can shake people a little bit and force them to adapt their narcissistic qualities.
"As you age, you form new relationships, have new experiences, start a family and so on. All of these factors make someone realise that it's not 'all about them.'
"And, the older you get, the more you think about the world that you may leave behind.
"There's a sense in which narcissists start to realise that being the way they are isn't smart if they want to have friends or meaningful relationships."
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