ScienceDaily (Feb. 17, 2012) — It's no secret that battlefield trauma can leave veterans with deep emotional scars that impact their ability to function in civilian life. But new research led by Washington University in St. Louis suggests that military service, even without combat, has a subtle lingering effect on a man's personality, making it potentially more difficult for veterans to get along with friends, family and co-workers.

"Our results suggest that personality traits play an important role in military training, both in the sort of men who are attracted to the military in the first place, and in the lasting impact that this service has on an individual's outlook on life," says study lead author Joshua J. Jackson, PhD, an assistant professor of psychology in Arts & Sciences.

Published in the journal Psychological Science, the study found that men who have experienced military service tend to score lower than civilian counterparts on measures of agreeableness -- a dimension of personality that influences our ability to be pleasant and accommodating in social situations.

The study confirms that the military attracts men who are generally less neurotic, less likely to worry, less likely to be concerned about seeking out novel experiences. When compared with men in civilian pursuits, those entering the military also are more aggressive, more interested in competition than cooperation and less concerned about the feelings of others, the study finds.

"Military recruits are a little less warm and friendly to begin with and the military experience seems to reinforce this -- as after service, men score even lower on agreeableness when compared to individuals who did not go into the military," Jackson says. "Interestingly, this influence appears to linger long after the soldier has re-entered the workforce or returned to college."

Jackson points out that being less agreeable is not always a negative human trait. While it may make it more challenging to maintain positive relationships with friends and romantic partners, it can be seen as a positive influence on career success.

"On the flip side," he says, "people with lower levels of agreeableness are often more likely to fight their way up the corporate ladder and to make the sometimes unpopular decisions that can be necessary for business success."

Either way, this study offers evidence that experiences in basic training and other military service do shape the way people approach the world.

"These changes in personality appear to be small, but they could make a big difference in the lives of those who have served in the military," he says.

Jackson's research is based on a six-year study that tracked the personality traits of a group of young men in German high schools who chose to meet mandatory public service requirements through either military or civilian service.

Co-authored with Felix Thoemmes, Kathrin Jonkmann, Oliver Lüdtke and Ulrich Trautwein, all of the University of Tübingen in Germany, the study is among the first to empirically test whether a particular life experience can truly change an individual's personality, something that many psychologists have long considered to be unlikely.

As Jackson explains, psychologists generally view personality as one of the most stable and difficult-to-change human traits. While some studies have tracked small changes in personality over time, such as changes related to the aging process, there is little research on why these changes occur, or on what sorts of life experiences might contribute to the changes.

Jackson's research team saw the military as the perfect laboratory in which to test for personality-changing life experiences.

"The whole military experience is sold as an opportunity for a life-changing transformation," Jackson says. "Recruiting materials of military forces around the world bolster the idea of military experience as being a catalyst for change. For example, recent slogans in the United States, such as 'Be all you can be,' 'Accelerate your life,' and 'Aim high,' all imply that military experiences affect life trajectories.

"It's one of the few situations in life where an individual's daily actions and expectations are completely controlled by someone else. Where, from the moment you wake up in the morning until you go to bed at night, someone is actively working to break down anything that's individual about you and to build up something else in its place."

Researchers tested the men's personalities during high school and re-tested them three times in the six years following either civilian or military service. Not surprisingly, all of the participants scored higher on measures indicative of maturity, such as increased conscientiousness and less neuroticism.

And while the military group did show some increases in measures of agreeableness, the change was much lower than that measured for participants in the civilian service group.

"While the military often promises to 'make a man out of you,' our analysis suggests that much of the advertised post-military increase in maturity can be attributed to normal changes that most young men experience during this stage of their lives," Jackson says.

"And while military service doesn't seem to have much impact on other personality traits, such as levels of anxiety or gregariousness, it appears to have a small but significant influence on measures of agreeableness."

Jackson's findings may offer a new explanation for why military service members tend to differ from civilians in their rates of divorce, longevity, salaries and health issues.

"Often these differences are interpreted in terms of the social opportunities that either exist or don't exist for military members, but rarely is it suggested that military experience changes something about the person, which then influences these outcomes," Jackson says.

"It's not a cut-and-dried issue, but this study shows that changes in personality may be one reason that military service is associated with different rates of important life outcomes, like divorce or occupational attainment."