Birth order is thought to have a definitive influence on an individual's personality and other traits. First-born children are generally reliable and structured, while middle-born children tend to be rebellious people pleasers with large social circles, and last-born children are manipulative attention seekers who tend to be fun-loving yet self-centered.
By contrast, an only child tends to be mature for his age, conscientious and diligent. Only children may be perfectionists and are natural leaders.
Birth order traits and the hierarchy created by birth orders is generally thrown askew in a blended family when parents divorce and remarry. Birth order traits are also often off-kilter when there is a wide gap in ages between the children.