A new study looks at how birth order and family size impacts personality traits. Birth order theory is a perennial favourite topic on the internet: are firstborn children really the independent trailblazers they’re made out to be? Are middle children really the peacemakers who everyone in the family seems to forget exist? Are the youngest-born as laidback and chill as the cliche suggests?Apparently, social scientists are just as intrigued by these questions.In a new study, researchers from two Canadian universities looked at how birth order and family size impact personality traits, and found that there may be some truth to those long-held sibling stereotypes.The researchers ― psychology professors Kibeom Lee of the University of Calgary and Michael Ashton of Brock University in St. Catharines, Ontario ― found that middle children really do rank higher on measures of cooperation and modesty compared to their older, younger and only child counterparts. They also found that people from larger families were more likely to be cooperative and modest.