Height and intelligence

A positive correlation exists between human IQ and height within populations.^[1] Correlation coefficients of the effect observed in these studies are typically about 0.2, meaning that variation in height explains about 4% of the variation in IQ.^[2]^[3]

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The correlation between the two factors is therefore weak, although statistically significant, and these studies do not imply that there are no short people who are 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. Similar strength correlations have been found in early and late childhood and adulthood in both developed and developing countries, and the correlation continues to exist after controlling for social class and parental education.

Explanations of the correlation

The reasons for the association between height and intelligence remain unclear, but possible explanations include that height may be a marker of nutritional status, prenatal maternal stress, or general mental and physical health during development. Studies have shown however, that common genetic factors influence variation in both height and intelligence, and are responsible for some of the effect^[4], 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^[5].

Another suggested reason for the correlation between height and intelligence may stem from the correlation between height and self esteem. The theory is that height indirectly affects intelligence because height during teenage years boosts self esteem, and higher self esteem in turn leads to better performance academically^{[citation needed]}. More importantly, it is not a person's full-grown adult height that matters, but a person's height while in high school. Income-wise, it has been discovered that tall men who were short in high school earn like short men, while short men who were tall in high school earn like tall men.^[6] This seems to rule out discrimination as a factor, since it would be hard for employers to know their employees' heights in the past. It suggests that another factor is at play.

References

^ Wilson DM, Hammer LD, Duncan PM et al. Growth and intellectual development. Pediatrics 1986;78:646–50.
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.
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.
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.
Teasdale, T. W., Srensen, T. I. A., & Owen, D. R. (1989). Fall in association of height with intelligence and educational level. British Medical Journal, 298, 1292-1293.
Tuvemo, T., Jonsson, B., & Persson, I. (1999). Intellectual and physical performance and morbidity in relation to height in a cohort of 18-year-old Swedish conscripts. Hormone Research, 52, 186-191.
Humphreys, L. G., Davey, T. C., & Park, R. K. (December 1985). "Longitudinal correlation analysis of standing height and intelligence". Child Development 56: 1465–1478.
^ Humphreys, L. G., Davey, T. C., & Park, R. K. (December 1985). "Longitudinal correlation analysis of standing height and intelligence.". Child Development 56: 1465–1478.
^ Donald B. Egolf and Lloyd E. Corder (March 1991). "Height differences of low and high job status, female and male corporate employees". Sex Differences 5-6: 365-373.
^ Silventoinen K., Posthuma D., van Beijsterveldt T., Bartels M. & Boomsma D.I. 2006. Genetic contributions to the association between height and intelligence: evidence from Dutch twin data from childhood to middle age. Genes Brain and Behavior 8: 585-595
^ 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
^ Nicola Persico, Andrew Postlewaite and Dan Silverman (October 2004). "The Effect of Adolescent Experience on Labor Market Outcomes: The Case of Height". The Journal of Political Economy 112: 1019-1053.

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Category: Human height

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