Is your Brother or Sister smarter than you?

They just might be! It all comes down to where you are located in the birth order amongst all your Siblings. Yes, you read that correctly, and it’s not only intelligence, it may affect other parts of the your personality as well! According to a study published by PNAS in September 2015 (Proceedings of the National Academy of Sciences of the United States of America) where they studied data from over 20,000 respondents across the U.S, U.K and Germany, they found some interesting information regarding the effects of birth order on Intelligence, Extroversion, Emotional Stability, Agreeableness, Conscientiousness and Imagination. Does your position of birth order in your family affect your personality traits, and overall life course?

Quick Background:

This is a question that scientists have been trying to answer for a long time. Sir Francis Galton, a pioneer in Eugenics, and who coined the phrase “Nature vs Nuture” had early on apparently analyzed a group of scientists and determined that Eldest Sons enjoy special treatment by their Parents which may result in them doing well intellectually.


(Sir Francis Galton)


There was also a study conducted by Alfred Adler that reported the first borns may feel priviliged but also may have a fear of dethronement from that position so may have traits of being a neurotic. Subsequently, later born children who were paid more attention to by their parents may lack social empathy.


(Alfred Adler)


Findings from another big study conducted by Frank Sulloway, asserted that firstborns, as are they are usually physically larger than their siblings during a young age will tend to be more dominating and less agreeable. Younger siblings will be more dependent on social support in order to assert themselves, and therefore would be more extraverted. He also predicted that firstborns were prone to be more anxious and more readily “fly off the handle”, whereas later borns were more vulnerable to depression, more self conscious and impulsive. In terms of intelligence, Sulloway claimed that firstborns performed better on psychometric intelligence tests.


(Frank Sulloway)


Although the hypotheses of the study above were later confirmed by several other studies, there were a lot of other studies conducted that were only able to confirm part of the hypotheses. Many reasons for the differing results had been proposed, and most of them point to flaws or differences in the design of the research. Some of the reasons proposed were that fact that most of the research that was conducted with “within family”, and also that most of these ratings were collected from one sibling who rated all the rest. Personal beliefs could easily skew these ratings, thereby lowering the confidence level of the hypotheses.


Current Study by PNAS

The study published by PNAS attempted to remove these limitations mentioned above, and included data from the United States, Great Britain and Germany. It also included both “within-family” and “between-family” samples in the data. The inferred results were very interesting.

  • They found that there was an effect of approximately 1.5 IQ points based on birth order position. A firstborn had a 52% chance of having a higher IQ than the second born. In families of 2 children, the older sibling had a higher IQ in 6 of 10 cases.
  • They also found that birth order position had no effect on the following four traits: Extroversion, Emotional Stability, Agreeableness or Conscientiousness.
  • There were no birth order effects on Imagination.
  • Self reported intellect saw the same effect as intellect as reported above.


To conclude and summarize the results, they did not find any effect of birth order on the traits of Extroversion, Emotional Stability, Agreeableness or Conscientiousness. They did however find an effect on Intellect. This was confirmed individually by the data collected in all three countries. They also achieved a power of 95% with which to detect a mean difference as subtle as 5% between the intellect of a first born vs a second born. Now before you get excited (if you are a firstborn yourself), and start sharing this with your younger brothers and sisters, do note that scientists in this study have also said that there results could vary based on factors that they did not involve in their research:

  • Birth order effects may be visible within the family, however may not be significant in behaviour and relationships outside of the context of the study.
  • Results may vary as the respondents in their research were all from the Western world, and family dynamics could give different results.


They also mentioned, that although the birth order effects on Intellect are significant in terms of findings of the research, in reality the different in IQ levels were an insignificant difference. Well, even though the real-world impact of this data may not significant, it doesn’t mean that we shouldn’t share this with our younger brothers and sisters just to have a wee bit of sibling fun! 🙂