Height and intelligence

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Epidemiological studies have shown that intelligence is positively correlated with height in human populations[1][2][3][4]. Similar associations have been found in early and late childhood and adulthood in both developed and developing countries, and associations persisted after controlling for social class and parental education. This does not imply that many short people are not highly intelligent, or that changes in physical height have a direct effect on cognitive ability. Indeed, intelligence is believed to be influenced by many different factors, and individuals with a wide range of intelligence can be observed at any given height.

The reasons for the association between height and intelligence remain unclear, but possible explanations include that height may be a biomarker of nutritional status or general mental and physical health during development, that common genetic factors may influence both height and intelligence[5], or that both height and intelligence may be affected by adverse early environmental exposures. A large recent twin pair study of the height-intelligence relationship showed that both shared environment (59%) and shared genetics (35%) are responsible for significant portions of the observed correlation between intelligence and height[6].

Height has also been shown to have a positive correlation with adult income, raising the possibility that workplace discrimination based on height has a direct impact on income levels (see heightism). A recent study using four data sets from the US and UK found that after controlling for difference in cognitive test scores, there was no detectable independent effect of height itself on adult earnings, indicating that the height premium in adult earnings can be explained by childhood scores on intelligence tests[7] However, others believe that height has a significant independent impact, pointing to specific instances of height-based discrimination[1]. The relationship between height, cognitive ability, and discrimination based on height remains a subject of debate.

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An addition to this article should be that correlation does not mean causation. Anyone who has ever taken a statistics class knows that many things can be correlated, but that causation is not implied simply due to that correlation. The classic example is, "Rock music and acne correlate, but that does not mean that rock music causes acne. It simply shows that there is statistical coincidence between them because many teenagers listen to rock music and many teenagers have acne."

[edit] References

  1. ^ Wilson DM, Hammer LD, Duncan PM et al. Growth and intellectual development. Pediatrics 1986;78:646–50.
  2. ^ Walker SP, Grantham-McGregor SM, Powell CA, Chang SM. Effects of growth restriction in early childhood on growth, IQ, and cognition at age 11 to 12 years and the benefits of nutritional supplementation and psychosocial stimulation. J Pediatr 2000; 137:36–41.
  3. ^ Tanner JM. Relation of body size, intelligence test scores and social circumstances. In: Mussen PH, Largen J, Covington M (eds). Trends and Issues in Developmental Psychology. New York: Holt, Rinehard and Winston Inc., 1969.
  4. ^ Pearce MS, Deary IJ, Young AH, Parker L. Growth in early life and childhood IQ at age 11 years: the Newcastle Thousand Families Study. Int J Epidemiol 2005;34:673–77.
  5. ^ Silventoinen K., Posthuma D., van Beijsterveldt T., Bartels M. & Boomsma D.I. in press. Genetic contributions to the association between height and intelligence: evidence from Dutch twin data from childhood to middle age. Genes Brain Behav. doi: 10.1111/j.1601-183X.2006.00208.x
  6. ^ Sundet JM, Tambs K, Harris JR, Magnus P, Torjussen TM. Resolving the genetic and environmental sources of the correlation between height and intelligence: a study of nearly 2600 Norwegian male twin pairs. Twin Res Hum Genet. 2005 Aug;8(4):307-11
  7. ^ Anne Case, Christina Paxson. Stature and Status: Height, Ability, and Labor Market Outcomes. National Bureau of Economic Research, Working Paper No. 12466, August 2006
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