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Impact of Medical Conditions on Human IQ in the United States

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Human Intelligence and Medical Illness

Part of the book series: The Springer Series on Human Exceptionality ((SSHE))

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Abstract

There is robust evidence that the IQ of young people has been rising progressively for many years. This rise in IQ – known as the Flynn Effect – is neither subtle nor recent. Careful analysis of the scientific literature suggests that the average IQ of young people is increasing at a rate of roughly 1 point every 2 years, and has probably been increasing for at least a century now. If IQ tests are not renormed frequently, the average person in 100 years would be a genius by our standards. How is this possible? Are human beings truly smarter now than they were in the past? Or do IQ tests fail to measure what they purport to measure? Are humans improving cognitively – either by a process of evolution or by an enhanced development – as rapidly as the test results would suggest? Or are test results the visible trace of a more subtle change in the human condition? We have hypothesized that the Flynn Effect is due to the progressive amelioration of medical challenges that have depressed human intelligence for as long as there have been humans. We contend that human IQ test scores are substantially reduced by features of the environment that are medical in nature: infestation with parasites, infection with microbes, exposure to toxicants, experience with various forms of chronic deprivation, and so on.

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References

  1. Steen, R. G. (1996). DNA & Destiny: Nature and Nurture in Human Behavior. New York: Plenum. 259 pp.

    Google Scholar 

  2. Flynn, J. (1984). The mean IQ of Americans: Massive gains 1932 to 1978. Psychological Bulletin, 95, 29–51.

    Article  Google Scholar 

  3. Prifitera, A., Weiss, L. G., & Saklofske, D. H. (1998). The WISC-III in context. In A. Prifitera & D. Saklofske (Eds.), WISC-III Clinical Use and Interpretation: Scientist-Practitioner Perspectives (pp. 1–38). New York: Academic.

    Chapter  Google Scholar 

  4. Flynn, J. R. (1998). Israeli military IQ tests: Gender differences small; IQ gains large. Journal of Biosocial Science, 30, 541–553.

    Article  PubMed  Google Scholar 

  5. Randhawa, B. S. (1980). Change in intelligence and academic skills of grades four and seven pupils over a twenty-year period. 22nd International Congress of Psychology. Leipzig, East Germany.

    Google Scholar 

  6. de Leeuw, J., & Meester, A. C. (1984). Over het intelligence-onderzoek bijde militaire keuringer vanaf 1925 tot heden [Intelligence-as tested at selections for the military service from 1925 to the present]. Mens en Maatschappij, 59, 5–26.

    Google Scholar 

  7. Rist, T. (1982). Det Intellektuelle Prestasjonsnivaet i Befolkningen Sett I lys av den Samfunns-Messige Utviklinga [The level of the intellectual performance of the population seen in the light of developments in the community]. Oslo, Norway: Norwegian Armed Forces Psychology Service.

    Google Scholar 

  8. Teasdale, T. W., & Owen, D. R. (2000). Forty-year secular trends in cognitive abilities. Intelligence, 28, 115–120.

    Article  Google Scholar 

  9. Bouvier, U. (1969). Evolution des cotes a quelques tests [Evolution of scores from several tests]. Brussels, Belgium: Belgian Armed Forces, Center for Research into Human Traits.

    Google Scholar 

  10. Elley, W. B. (1969). Changes in mental ability in New Zealand school-children. New Zealand Journal of Educational Studies, 4, 140–155.

    Google Scholar 

  11. Clarke, S. C. T., Nyberg, V., & Worth, W. H. (1978). Technical report on Edmonton Grade III achievement: 1956–1977 comparisons. Edmonton, Alberta: University of Alberta.

    Google Scholar 

  12. Uttl, B., & Van Alstine, C. L. (2003). Rising verbal intelligence scores: Implications for research and clinical practice. Psychology and Aging, 18, 616–621.

    Article  PubMed  Google Scholar 

  13. Vroon, P. A., de Leeuw, J., & Meester, A. C. (1984). Correlations between the intelligence levels of fathers and sons. In J. R. Flynn (Ed.), Utrecht, The Netherlands: Department of Theoretical Psychology and History of Psychology.

    Google Scholar 

  14. Colom, R., & Garcia-Lopez, O. (2003). Secular gains in fluid intelligence: Evidence from the culture-fair intelligence test. Journal of Biosocial Science, 35, 33–39.

    Article  PubMed  Google Scholar 

  15. Lynn, R., Hampson, S. L., & Mullineux, J. C. (1987). A long-term increase in the fluid intelligence of English children. Nature, 328, 797.

    Article  PubMed  Google Scholar 

  16. Daley, T. C., et al. (2003). IQ on the rise: The Flynn effect in rural Kenyan children. Psychological Science, 14, 215–219.

    Article  PubMed  Google Scholar 

  17. Fuggle, P. W., et al. (1992). Rising IQ scores in British children: Recent evidence. Journal of Child Psychology and Psychiatry, 33, 1241–1247.

    Article  PubMed  Google Scholar 

  18. Girod, M., & Allaume, G. (1976). L’evolution du niveau intellectuel de la population francaise pendent le dernier quart de siecle [The evolution of the intellectual level of the French population during the last quarter century]. International Review of Applied Psychology, 25, 121–123.

    Article  Google Scholar 

  19. Steen, R. G. (2007). The Evolving Brain: The Known and the Unknown (p. 427). New York: Prometheus Books.

    Google Scholar 

  20. Gould, S. J. (1981). The Mismeasurement of Man. New York: W. W. Norton & Co. 352 pp.

    Google Scholar 

  21. Detterman, D. K., & Thompson, L. A. (1997). What is so special about special education? The American Psychologist, 52, 1082–1090.

    Article  PubMed  Google Scholar 

  22. Brand, C. (1987). Intelligence testing: Bryter still and bryter? Nature, 328, 110.

    Google Scholar 

  23. Daley, T. C., et al. (2003). IQ on the rise: The Flynn effect in rural Kenyan children. Psychological Science, 14, 215–219.

    Article  PubMed  Google Scholar 

  24. Steen, R. G. (1996). DNA & Destiny: Nature and Nurture in Human Behavior (p. 295). New York: Plenum.

    Google Scholar 

  25. Flynn, J. R. (1987). Massive IQ gains in 14 nations: What IQ tests really measure. Psychological Bulletin, 101, 171–191.

    Article  Google Scholar 

  26. Carpenter, P. A., Just, M. A., & Shell, P. (1990). What one intelligence test measures: A theoretical account of the processing in the Raven Progressive Matrices Test. Psychological Review, 97, 404–431.

    Article  PubMed  Google Scholar 

  27. Duncan, J., & Owen, A. M. (2000). Common regions of the human frontal lobe recruited by diverse cognitive demands. Trends in Neurosciences, 23, 475–483.

    Article  PubMed  Google Scholar 

  28. Flynn, J. R. (1998). Israeli military IQ tests: Gender differences small; IQ gains large. Journal of Biosocial Science, 30, 541–553.

    Article  PubMed  Google Scholar 

  29. Teasdale, T. W., & Owen, D. R. (2000). Forty-year secular trends in cognitive abilities. Intelligence, 28, 115–120.

    Article  Google Scholar 

  30. Teasdale, T. W., & Owen, D. R. (1987). National secular trends in intelligence and education: A twenty-year cross-sectional study. Nature, 325, 119–121.

    Article  Google Scholar 

  31. Johnson, S. (2005). Eveything Bad is Good for You. New York: Penguin Group

    Google Scholar 

  32. Pullman, H., Allik, J., & Lynn, R. (2004). The growth of IQ among Estonian schoolchildren from ages 7 to 19. Journal of Biosocial Science, 36, 735–740.

    Article  Google Scholar 

  33. Slyper, A. H. (2006). The pubertal timing controversy in the USA, and a review of possible causative factors for the advance in timing of onset of puberty. Clinical Endocrinology, 65, 1–8.

    Article  PubMed  Google Scholar 

  34. Herman-Giddens, M. E., et al. (1997). Secondary sexual characteristics and menses in young girls seen in office practice: a study from the Pediatric Research in Office Settings Network. Pediatrics, 99, 505–512.

    Article  PubMed  Google Scholar 

  35. Kaplowitz, P. B., Slora, E. J., Wasserman, R. C., Pedlow, S. E., & Herman-Giddens, M. E. (2001). Earlier onset of puberty in girls: relation to increased body mass index and race. Pediatrics, 108, 347–353.

    Article  PubMed  Google Scholar 

  36. Sun, S. S., et al. (2002). National estimates of the timing of sexual maturation and racial differences among US children. Pediatrics, 110, 911–919.

    Article  PubMed  Google Scholar 

  37. Pearce-Duvet, J. M. (2006). The origin of human pathogens: evaluating the role of agriculture and domestic animals in the evolution of human disease. Biological Reviews of the Cambridge Philosophical Society, 81, 369–382.

    Article  PubMed  Google Scholar 

  38. Fevre, E. M., et al. (2005). A burgeoning epidemic of sleeping sickness in Uganda. Lancet, 366, 745–747.

    Article  PubMed  Google Scholar 

  39. Cleaveland, S., Laurenson, M. K., & Taylor, L. H. (2001). Diseases of humans and their domestic animals: pathogen characteristics, host range, and the risk of emergence. Philosophical Transactions of the Royal Society of London B, 356, 991–999.

    Article  Google Scholar 

  40. Diamond, J. (2002). Evolution, consequences, and future of plant and animal domestication. Nature, 418, 700–706.

    Article  PubMed  Google Scholar 

  41. Scott, R. S., et al. (2005). Dental microwear texture analysis shows within-species diet variability in fossil hominins. Nature, 436, 693–695.

    Article  PubMed  Google Scholar 

  42. Eshed, V., Gopher, A., & Hershkovitz, I. (2006). Tooth wear and dental pathology at the advent of agriculture: new evidence from the Levant. American Journal of Physical Anthropology, 130, 145–159.

    Article  PubMed  Google Scholar 

  43. Bonfiglioli, B., Brasili, P., & Belcastro, M. G. (2003). Dento-alveolar lesions and nutritional habits of a Roman Imperial age population (1st-4th c. AD): Quadrella (Molise, Italy). Homo, 54, 36–56

    Google Scholar 

  44. Kerr, N. W. (1998). Dental pain and suffering prior to the advent of modern dentistry. British Dental Journal, 184, 397–399.

    Article  PubMed  Google Scholar 

  45. Lewis, M. E., Roberts, C. A., & Manchester, K. (1995). Comparative study of the prevalence of maxillary sinusitis in later Medieval urban and rural populations in northern England. American Journal of Physical Anthropology, 98, 497–506.

    Article  PubMed  Google Scholar 

  46. Stiehm, E. R. (2006). Disease versus disease: how one disease may ameliorate another. Pediatrics, 117, 184–191.

    Article  PubMed  Google Scholar 

  47. Pastori, C., et al. (2006). Long-lasting CCR5 internalization by antibodies in a subset of long-term nonprogressors: a possible protective effect against disease progression. Blood, 107, 4825–33.

    Article  PubMed  Google Scholar 

  48. Steen, R. G. (2007). The Evolving Brain: The Known and the Unknown. New York: Prometheus Books, pp. 437.

    Google Scholar 

  49. Hunt, S. A. (2006). Taking heart–cardiac transplantation past, present, and future. New England Journal of Medicine, 355, 231–235.

    Article  PubMed  Google Scholar 

  50. DiBardino, D. J. (1999). The history and development of cardiac transplantation. Texas Heart Institute Journal, 26, 198–205.

    PubMed  Google Scholar 

  51. Clark, D. A., et al. (1973). Cardiac transplantation in man: review of first three years’ experience. American Journal of Medicine, 54, 563–576.

    Article  PubMed  Google Scholar 

  52. Pui, C.-H., et al. (2005). Risk of adverse events after completion of therapy for childhood acute lymphoblastic leukemia. Journal of Clinical Oncology, 23, 7936–7941.

    Article  PubMed  Google Scholar 

  53. Glaser, V. P. (2000). Investigator profile: E. Donnell Thomas, M.D. Journal of Hematotherapy and Stem Cell Research, 9, 403–407

    Google Scholar 

  54. Tamura, T., et al. (2002). Cord serum ferritin concentrations and mental and psychomotor development of children at five years of age. Journal of Pediatrics, 140, 165–170.

    Article  PubMed  Google Scholar 

  55. McNeil, D. G. (2006). In raising the world’s IQ, the secret’s in the salt. New York: The New York Times

    Google Scholar 

  56. Tai, M. (1997). The devastating consequence of iodine deficiency. Southeast Asian Journal of Tropical Medicine and Public Health, 28(Suppl 2), 75–77.

    PubMed  Google Scholar 

  57. Fenzi, G. F., et al. (1990). Neuropsychological assessment in schoolchildren from an area of moderate iodine deficiency. Journal of Endocrinological Investigation, 13, 427–431.

    PubMed  Google Scholar 

  58. Aghini-Lombardi, F. A., et al. (1995). Mild iodine deficiency during fetal/neonatal life and neuropsychological impairment in Tuscany. Journal of Endocrinological Investigation, 18, 57–62.

    PubMed  Google Scholar 

  59. Becker, D. V., et al. (2006). Iodine supplementation for pregnancy and lactation-United States and Canada: Recommendations of the American Thyroid Association. Thyroid, 16, 949–951.

    Article  PubMed  Google Scholar 

  60. Ray, J. G., et al. (2002). Association of neural tube defects and folic acid food fortification in Canada. Lancet, 360, 2047–2048.

    Article  PubMed  Google Scholar 

  61. Barbaux, S., Plomin, R., & Whitehead, A. S. (2000). Polymorphisms of genes controlling homocysteine/folate meatbolism and cognitive function. Neuroreport, 11, 1133–1136.

    Article  PubMed  Google Scholar 

  62. Gomez-Pinilla, F. (2008). Brain foods: The effects of nutrients on brain function. Nature Reviews. Neuroscience, 9, 568–578.

    Article  PubMed  Google Scholar 

  63. Malek, M. A., et al. (2006). Diarrhea- and rotavirus-associated hospitalization among children less than 5 years of age: United States, 1997 and 2000. Pediatrics, 117, 1887–1892.

    Article  PubMed  Google Scholar 

  64. Patrick, P. D., et al. (2005). Limitations in verbal fluency following heavy burdens of early childhood diarrhea in Brazilian shantytown children. Child Neuropsychology, 11, 233–244.

    Article  PubMed  Google Scholar 

  65. Lorntz, B., et al. (2006). Early childhood diarrhea predicts impaired school performance. Pediatric Infectious Disease, 25, 513–520.

    Article  Google Scholar 

  66. Prado, M. S., et al. (2005). Asymptomatic giardiasis and growth in young children; a longitudinal study in Salvador, Brazil. Parasitology, 131, 51–56.

    Article  PubMed  Google Scholar 

  67. Muniz, P. T., et al. (2002). Intestinal parasitic infections in young children in Sao Paulo, Brazil: Prevalences, temporal trends and associations with physical growth. Annals of Tropical Medicine and Parasitology, 96, 503–512.

    Article  PubMed  Google Scholar 

  68. Simsek, Z., Zeyrek, F. Y., & Kurcer, M. A. (2004). Effect of Giardia infection on growth and psychomotor development of children aged 0–5 years. Journal of Tropical Pediatrics, 50, 90–93.

    Article  PubMed  Google Scholar 

  69. Celiksoz, A., et al. (2005). Effects of giardiasis on school success, weight and height indices of primary school children in Turkey. Pediatrics International, 47, 567–571.

    Article  PubMed  Google Scholar 

  70. Hamvas, A. (2000). Disparate outcomes for very low birth weight infants: genetics, environment, or both? Journal of Pediatrics, 136, 427–428.

    Article  PubMed  Google Scholar 

  71. Short, E. J., et al. (2003). Cognitive and academic consequences of bronchopulmonary dysplasia and very low birth weight: 8-year-old outcomes. Pediatrics, 112, e359–e366.

    Article  PubMed  Google Scholar 

  72. Hack, M., et al. (2002). Outcomes in young adulthood for very-low-birth-weight infants. New England Journal of Medicine, 346, 149–157.

    Article  PubMed  Google Scholar 

  73. Taylor, H. G., et al. (2000). Middle-school-age outcomes in children with very low birthweight. Child Development, 71, 1495–1511.

    Article  PubMed  Google Scholar 

  74. Hack, M., et al. (1994). School-age outcomes in children with birth weights under 750 g. New England Journal of Medicine, 331, 753–759.

    Article  PubMed  Google Scholar 

  75. Grunau, R. E., Whitfield, M. F., & Fay, T. B. (2004). Psychosocial and academic characteristics of extremely low birth weight (≤ 800 g) adolescents who are free of major impairment compared with term-born control subjects. Pediatrics, 114, e725–e732.

    Article  PubMed  Google Scholar 

  76. National Center for Children in Poverty. (2006). Basic facts about low-income children: birth to age 18

    Google Scholar 

  77. Brooks-Gunn, J., Klebanov, P. K., & Duncan, G. J. (1996). Ethnic differences in children’s intelligence test scores: role of economic deprivation, home enviroment, and maternal characteristics. Child Development, 67, 396–408.

    Article  PubMed  Google Scholar 

  78. Lupien, S. J., et al. (2001). Can poverty get under your skin? Basal cortisol levels and cognitive function in children from low and high socioeconomic status. Development and Psychopathology, 13, 653–676.

    Article  Google Scholar 

  79. Smith, J. R., Brooks-Gunn, J., & Klebanov, P. K. (1997). Consequences of living in poverty for young children’s cognitive and verbal ability and early school achievement. In G. J. Duncan & J. Brooks-Gunn (Eds.), Consequences of Growing Up Poor (pp. 132–189). New York: Russell Sage Foundation.

    Google Scholar 

  80. Feldman, M. A., & Walton-Allen, N. (1997). Effects of maternal mental retardation and poverty on intellectual, academic, and behavioral status of school-age children. American Journal of Mental Retardation, 101, 352–364.

    PubMed  Google Scholar 

  81. Steen, R. G. (1996). DNA & Destiny: Nature and Nurture in Human Behavior (p. 295). New York: Plenum.

    Google Scholar 

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    R. Grant Steen

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Steen, R.G. (2010). Impact of Medical Conditions on Human IQ in the United States. In: Human Intelligence and Medical Illness. The Springer Series on Human Exceptionality. Springer, New York, NY. https://doi.org/10.1007/978-1-4419-0092-0_9

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