Transcript for New Study Reveals Possible Effects Birth Order Has on Personality
That brings us to the next story on birth order. It's been debated for so long. They think the first born is generally the leader. Middle kids natural peacemakers. A new STD study saying everything you thing you know might be wrong? Reporter: This is one of the most hotly contested debates in psychology. What difference does it make the you were born first, middle, our youngest. A new study claims to have all the answers. Birth sord destiny, goes the old theory. The idea that our personalities and intelligence with preprogrammed simply by where we fall if relation to our siblings. The first born, a responsible leader who tepids to play by the rules. Prince William. Hillary Clinton. And beyonce are a few famous examples. The youngest child? Charming and popular. Think whoopi Goldberg, Jon Stewart Stephen Colbert. Middle children, sensitive and competitive. Brady bunch, we're talking about Jan. All I hear all day long at school is how great mar shall is at this, how wonderful mar shall did that. Mar shall, mar shall, mar shall. Reporter: Donald Trump is maidle child. So is Kim Kardashian. It doesn't define who you are. There are other factors that determine your personality and intelligence level. Reporter: A new study, one of the largest ever, put nearly half a million kids through a battery of personality and intelligence tests found that birth order made just a marginal difference. There was a small asew yags. 0.02. That's almost zero. Reporter: How does that explain a century of evidence? Why all of the actors who have ever played -- Bond, James bond. Reporter: How does it Ek plain why so many younger kids go into comedy. Or perhaps most telling. How does it explain why prince harry just seems cooler than wills. There's a possibility it's not our actual -- the actual order in which we're born but the social roles imposed on us. Reporter: In other words, F nurture, not nature may dictate how we behave. The study author is a first born. A scientist. Her brother is younger, an artist. I'm guessing most of you are younger? Baby. Baby. Oldest. I'm the middle. 2 of 4. The peacemaker. Marsha, Marsha, Marsha. What do you thing at home. Tweet us with the hashtag social square. Interesting topic. So is this.
This transcript has been automatically generated and may not be 100% accurate.