Posts filed under ‘Intelligence’

Firstborns have higher IQs than their siblings

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]

July 4, 2007 at 1:45 am 22 comments

Why beautiful people are more intelligent

This paper breaks down the theorem “beautiful people are more intelligent” into 4 assumptions. These assumptions are short and sweet and evidence is provided in the actual paper.

  1. Men who are more intelligent are more likely to attain higher status
  2. Higher status men are more likely to mate with more beautiful women
  3. Intelligence is heritable
  4. Beauty is heritable

Hence, it logically follows that beautiful people are more intelligent.


Note that while the correlation between beauty and intelligence is statistically significant (p < .05), the strength of the relationship is fairly weak (d = .07), compared to for example, beauty and popularity (d = .65).

Kanazawa, S. & Kovar, J. L. (2002). Why beautiful people are more intelligent. Intelligence, 32(3), 227-243. [PDF]

September 4, 2006 at 2:09 pm 70 comments


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