Birth Order Facts to Spark Sibling Rivalry

While it's not exactly a science, it does offer insights that seem to reaffirm conventional wisdom about sibling dynamics.

- BY Charlotte Hilton Andersen

1 FIRST PROPOSED by psychiatrist Alfred Adler in the 1920s, birth order theory is the idea that where you fall in your family can determine major aspects of your personality. Even when it doesn't describe you all that well, it's still fun to discuss-especially with your family.

2 ELDEST DAUGHTER syndrome refers to the parent-like responsibility first-born girls often feel toward their younger siblings. It can make them overachievers but also anxious, guilt-ridden people pleasers. Think about Katniss Everdeen, from The Hunger Games series, who risks her life to save her little sister's. Harry Potter author J. K. Rowling (also an eldest daughter), has said the studious, rule-abiding Hermione is an amplified version of herself.

3 MANY CEOS and moguls are eldest children. Among them: Andrew Carnegie, Sheryl Sandberg and Oprah Winfrey. Firstborns also tend to get better grades and often have higher IQs than their siblings, but researchers link this to the fact that eldest kids are more likely to get extra attention and resources from parents, giving them a leg up.

4 YOUNGER SIBLINGS Aas are often painted as carefree and lighthearted, maybe because they don't face the same expectations their older siblings do. Take Princes William and Harry: William is more straight-laced (and poised to become king), while Harry was able to step away from his royal duties.