Firstborns have higher IQs than their siblings

July 4, 2007 at 1:45 am 19 comments

This short paper from Science reports tasty findings on the correlation between birth order and intelligence. While it’s generally accepted in the scientific community that older siblings generally have higher IQs due to different environmental influences, numerous possible factors make it tricky to prove causation from correlation. One criticism is that later siblings are likely to come from larger families, which relates to lower socioeconomic status and IQ.

A study of 241,310 Norwegians shows that sibling social order rather than biological factors is what causes the variation of intelligence in siblings. This study supports the popular confluence theory, which claims that intelligence is directly influenced by the intelligence level of the other family members. Thus, older siblings benefit from extra time spent with the parents, while younger siblings are negatively affected by the other children.

Birth order vs Intelligence

In nature vs nurture, nurture takes this round.

Kristensen, P. & Bjerkedal, T. (2007). Explaining the Relation Between Birth Order and Intelligence. Science, 316(5832), 1717. [PDF]


Entry filed under: Birth Order, Intelligence, Relationships.

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19 Comments Add your own

  • 1. tastyresearch  |  July 4, 2007 at 1:47 am

    If you’re interested in “pop science” birth order theories, Wikipedia has some charming descriptions of each sibling (as of 2007-07-04).

  • 2. Bo  |  July 11, 2007 at 7:47 pm

    Hey – you should taclke this new study about Cumulative Advantage and why people choose to make one thing (song, software startup, celebrity) popular over others.

    I found it at: (the actual NYT link requires subscription)

  • 3. Rebecca Aguilar  |  July 21, 2007 at 8:45 am

    Stephen Colbert interviewed Dr. Frank Sulloway, who wrote a book (Born to Rebel) about the influence of birth order on personality.

    The interview:

  • 4. L.A.  |  November 6, 2007 at 4:39 pm

    Look, my brother is a good man, but there is no truth to this theory when it comes to my family. I think it depends on the effort you put in.

  • 5. Ashley  |  November 7, 2007 at 4:24 pm

    I don’t really agree with the topic. My sister and I are about as smart as each other and she is older than me. She is six years older than me so by the time I came around I still got my parents attention and we are the only two in our family. My parents influenced my sister just as much as they did in me. My dad is also the third child in his family and he had the higher IQ.

  • 6. Josh  |  November 12, 2007 at 3:23 pm

    This is completely preposterous! As a younger child I can say that my brother and I have almost no differences in our IQs. I refuse to believe that he is any better than me in the brain region.

  • 7. Sammie  |  November 12, 2007 at 3:36 pm

    This topic for me is hard to comment on. In my family, I have an older sister and two older brothers, and a younger brother. We are all pretty smart but the first and third child are way smarter then us other 3. But we all got the same attention and love from our parents. I just believe that they picked up on things more easily or they paid more attention. I don’t think this research is true!

  • 8. amanda  |  November 14, 2007 at 3:14 pm

    I think that birth order doesn’t really have an effect of your I.Q. Although I am the first born and I get better grades than my brother, he is still pretty smart but he just doesn’t apply himself.

  • 9. Geoffrey  |  February 11, 2008 at 7:06 pm

    All of these comments asserting that birth-order correlations with I.Q. don’t exist are a little ridiculous.

    Someone didn’t just say “hey, I bet firstborns are smarter,” there’s a HUGE amount of evidence to show that they do have higher average I.Q. scores, and the fact that a handful of people don’t think their older brothers are that smart is completely insignificant.

    Nobody said that ALL firstborns EVERYWHERE are ALWAYS smarter, so you can’t unravel the whole thing with a single contradictory anecdote. There’s a mountain of evidence showing that a correlation does exist, and a pretty big one at that, so it’s going to take evidence of absolutely epically greater proportions than “I know some people who don’t fit this” to mount a counter-argument.

  • 10. Bryan  |  February 11, 2008 at 9:30 pm

    Well, comment #9 is actually from my older brother and I think he’s dumb. So that settles that.

  • 11. heather  |  January 29, 2009 at 10:36 am

    Being a younger sister, i know this is not true based on my family. I would say we are equal, although we are only one year apart, but she is older, and that does not mean to me that she has a higher iq. I do find this topic interesting though to see all the information found..

  • 12. Gry Dla Dzieci  |  June 8, 2009 at 3:36 am

    I think the main reason for that is that firstborns need to learn/find out everything themselves. Younger kids can just learn from their older brothers/sisters.

  • 13. Myrna  |  June 4, 2010 at 5:19 pm

    I dis agree on the topic “Firstborns have higher IQs than their siblings” because in our case. We are only two in the family. I and my elder brother both studied in The King’s Academy but I am the one who always excel in the class though he did also good job. I must say that it depends on the effort you put in order to learn.

  • 14. NISM  |  September 15, 2012 at 1:56 am

    I do not think that first baby has higher IQ than siblings …… younger bro is more intelligent than me…

  • 15.  |  June 24, 2013 at 4:12 am

    Thanks to share your experience with us, so you can re-examine their own personal bias and thinking habits. Great stuff, toogood to be true!

  • 16.  |  September 1, 2013 at 10:04 am

    Keep posting good stuf like this!

  • 17.  |  September 6, 2013 at 5:07 am

    This post seems to me very interesting. Nice work! I am thankful for your help in this issue.

  • 18. nyc marathon race day tips  |  June 4, 2014 at 11:07 pm

    This post is helpful with an analysis I am doing for a specific group of people. Do you have any other articles to suggest on this topic? Thanks

  • 19. Data seeker  |  November 19, 2014 at 8:48 pm

    Great post! Will it be possible to have the data used? For my statistics class, I am supposed to analyze data.


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