Using data from magnetic resonance imaging (MRI), autopsy, endocranial measurements, and other techniques, we show that (1) brain size is correlated with cognitive ability about .44 using MRI; (2) brain size varies by age, sex, social class, and race; and (3) cognitive ability varies by age, sex, social class, and race. Brain size and cognitive ability show a curvilinear relation with age, increasing to young adulthood and then decreasing; increasing from women to men; increasing with socioeconomic status; and increasing from Africans to Europeans to Asians. Although only further research can determine if such correlations represent cause and effect, it is clear that the direction of the brain-size/cognitive-ability relationships described by Paul Broca (1824–1880), Francis Galton (1822–1911), and other nineteenth-century visionaries is true, and that the null hypothesis of no relation, strongly advocated over the last half century, is false.
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Andreasen, N. C. (1993, November).Sex differences in the brain: Perspectives from neuroimaging. Paper presented at a meeting of the Society for Neuroscience, Washington, DC.
Andreasen, N. C., Ehrhardt, J. C., Swayze, V. W., Alliger, R. J., Yuh, W. T. C., Cohen, G., &Ziebell, S. (1990). Magnetic resonance imaging of the brain in schizophrenia.Archives of General Psychiatry,47, 35–44.
Andreasen, N. C., Flaum, M., Swayze, V., O’Leary, D. S., Alliger, R., Cohen, G., Ehrhardt, J., &Yuh, W. T. C. (1993). Intelligence and brain structure in normal individuals.American Journal of Psychiatry,150, 130–134.
Ankney, C. D. (1992). Sex differences in relative brain size: The mismeasure of woman, too?Intelligence,16, 329–336.
Ankney, C. D. (1995). Sex differences in brain size and mental abilities: Comments on R. Lynn and D. Kimura.Personality & Individual Differences,18, 423–424.
Armstrong, E. (1990). Brains, bodies and metabolism.Brain, Behavior & Evolution,36, 166–176.
Baker, J. R. (1974).Race. Oxford: Oxford University Press.
Beals, K. L., Smith, C. L., &Dodd, S. M. (1984). Brain size, cranial morphology, climate, and time machines.Current Anthropology,25, 301–330.
Bogaert, A. F., &Rushton, J. P. (1989). Sexuality, delinquency andr/K reproductive strategies: Data from a Canadian university sample.Personality & Individual Differences,10, 1071–1077.
Bouchard, T. J., Jr.,Lykken, D. T., McGue, M., Segal, N. L., &Tellegen, A. (1990). Sources of human psychological differences: The Minnesota study of twins reared apart.Science,250, 223–228.
Bouchard, T. J., Jr., &McGue, M. (1981). Familial studies of intelligence: A review.Science,212, 1055–1059.
Brandt, I. (1978). Growth dynamics of low-birth weight infants with emphasis on the perinatal period. In F. Falkner & J. M. Tanner (Eds.),Human growth (Vol. 2, pp. 557–617). New York: Plenum.
Bray, P. F., Shields, W. D., Wolcott, G. J., &Madsen, J. A. (1969). Occipitofrontal head circumference—An accurate measure of intracranial volume.Journal of Pediatrics,75, 303–305.
Broca, P. (1861). Sur le volume et la forme du cerveau suivant les individus et suivant les races.Bulletins et mémoires de la Société d’Anthropologie de Paris,2, 139–207, 301–321, 441–446.
Brody, N. (1992).Intelligence. New York: Academic Press.
Broman, S. H., Nichols, P. L., &Kennedy, W. A. (1975).Preschool IQ: Prenatal and early development correlates. Hillsdale, NJ: Erlbaum.
Broman, S. H., Nichols, P. L., Shaughnessy, P., &Kennedy, W. (1987).Retardation in young children. Hillsdale, NJ: Erlbaum.
Cattell, R. B. (1982).The inheritance of personality and ability. New York: Academic Press.
Clark, E. A., &Hanisee, J. (1982). Intellectual and adaptive performance of Asian children in adoptive American settings.Developmental Psychology,18, 595–599.
Cooke, R. W. I., Lucas, A., Yudkin, P. L. N., &Pryse-Davies, J. (1977). Head circumference as an index of brain weight in the fetus and new born.Early Human Development,112, 145–149.
Darwin, C. (1871).The descent of man. London: Murray.
Dekaban, A. S., &Sadowsky, D. (1978). Changes in brain weights during the span of human life: Relation of brain weights to body heights and body weights.Annals of Neurology,4, 345–356.
DeMyer, M. K., Gilmor, R. L., Hendrie, H. C., DeMyer, W. E., Augustyn, G. T., &Jackson, R. K. (1988). Magnetic resonance brain images in schizophrenic and normal subjects: Influence of diagnosis and education.Schizophrenia Bulletin,14, 21–32.
Egan, V., Chiswick, A., Santosh, C., Naidu, K., Rimmington, J. E., &Best, J. J. K. (1994). Size isn’t everything: A study of brain volume, intelligence and auditory evoked potentials.Personality & Individual Differences,17, 357–367.
Egan, V., Wickett, J. C., &Vernon, P. A. (1995). Brain size and intelligence: Erratum, addendum, and correction.Personality & Individual Differences,19, 113–115.
Estabrooks, G. H. (1928). The relation between cranial capacity, relative cranial capacity and intelligence in school children.Journal of Applied Psychology,12, 524–529.
Eysenck, H. J. (1991a). Race and intelligence: An alternative hypothesis.Mankind Quarterly,32, 133–136.
Eysenck, H. J. (1991b). Raising IQ through vitamin and mineral supplementation: An introduction.Personality & Individual Differences,12, 329–333.
Fisch, R. O., Bilek, M. K., Horrobin, J. M., &Chang, P. N. (1976). Children with superior intelligence at 7 years of age.American Journal of Diseases in Children,130, 481–487.
Fisher, R. A. (1970).Statistical methods for research workers (14th ed.). New York: Hafner Press.
Flaum, M., Andreasen, N. C., Swayze, V. W., II,O’Leary, D. S., &Alliger, R. J. (1994). IQ and brain size in schizophrenia.Psychiatry Research,53, 243–257.
Frydman, M., &Lynn, R. (1989). The intelligence of Korean children adopted in Belgium.Personality & Individual Differences,10, 1323–1326.
Galton, F. (1888). Head growth in students at the University of Cambridge.Nature,38, 14–15.
Gottfredson, L. S. (1986). (Ed.) Theg factor in employment.Journal of Vocational Behavior,29, 293–450.
Gould, S. J. (1978). Morton’s ranking of races by cranial capacity.Science,200, 503–509.
Gould, S. J. (1981).The mismeasure of man. New York: Norton.
Gur, R. C., Mozley, P. D., Resnick, S. M., Gottlieb, G. L., Kohn, M., Zimmerman, R., Herman, G., Atlas, S., Grossman, R., Berretta, D., Erwin, R., &Gur, R. E. (1991). Gender differences in age effect on brain atrophy measured by magnetic resonance imaging.Proceedings of the National Academy of Sciences,88, 2845–2849.
Hack, M., Breslau, N., Weissman, B., Aram, D., Klein, N., &Borawski, E. (1991). Effect of very low birth weight and subnormal head size on cognitive abilities at school age.New England Journal of Medicine,325, 231–237.
Haier, R. J., Chueh, D., Touchette, P., Lott, I., Buchsbaum, M. S., Macmillan, D., Sandman, C., LaCasse, L., &Sosa, E. (1995). Brain size and cerebral glucose metabolic rate and nonspecific mental retardation and Down syndrome.Intelligence,20, 191–210.
Harvey, I., Persaud, R., Ron, M. A., Baker, G., &Murray, R. M. (1994). Volumetric MRI measurements in bipolars compared with schizophrenics and healthy controls.Psychological Medicine,24, 689–699.
Haug, H. (1987). Brain sizes, surfaces, and neuronal sizes of the cortex cerebri: A stereological investigation of man and his variability and a comparison with some species of mammals (primates, whales, marsupials, insectivores, and one elephant).American Journal of Anatomy,180, 126–142.
Henneberg, M., Budnik, A., Pezacka, M., &Puch, A. E. (1985). Head size, body size and intelligence: Intraspecific correlations inHomo sapiens sapiens.Homo,36, 207–218.
Herrnstein, R. J., &Murray, C. (1994).The bell curve. New York: Free Press.
Ho, K. C., Roessmann, U., Straumfjord, J. V., &Monroe, G. (1980a). Analysis of brain weight: I. Adult brain weight in relation to sex, race, and age.Archives of Pathology & Laboratory Medicine,104, 635–639.
Ho, K. C., Roessmann, U., Straumfjord, J. V., &Monroe, G. (1980b). Analysis of brain weight: II. Adult brain weight in relation to body height, weight, and surface area.Archives of Pathology & Laboratory Medicine,104, 640–645.
Hofman, M. A. (1991). The fractal geometry of convoluted brains.Journal für Hirnforschung,32, 103–111.
Hofman, M. A. (1993). Encephalization and the evolution of longevity in mammals.Journal of Evolutionary Biology,6, 209–227.
Hofman, M. A., &Swaab, D. F. (1991). Sexual dimorphism of the human brain: Myth and reality.Experimental Clinical Endocrinology,98, 161–170.
Holloway, R. L. (1980). Within-species brain-body weight variability: A reexamination of the Danish data and other primate species.American Journal of Physical Anthropology,53, 109–121.
Hooton, E. A. (1939).The American criminal (Vol. 1). Cambridge, MA: Harvard University Press.
Hunter, J. E., &Schmidt, F. L. (1990).Methods of meta-analysis: Correcting error and bias in research findings. Newbury, CA: Sage.
Jackson, D. N. (1993, July 17–21).Sex differences in intellectual ability. Paper presented at a meeting of the International Society for the Study of Individual Differences, Baltimore.
Jackson, D. N. (1995, May).Sex differences in general cognitive ability. Paper presented at a meeting of the International Behavioral Development Symposium: Biological Basis of Sexual Orientation and Sex-Typical Behavior, Minot State University, Minot, ND.
Jensen, A. R. (1980).Bias in mental testing. New York: Free Press.
Jensen, A. R. (1993a). Psychometric G and achievement. In B. R. Gifford (Ed.),Policy perspectives on educational testing (pp. 117–227). Boston: Kluwer.
Jensen, A. R. (1993b). Spearman’s hypothesis tested with chronometric information processing tasks.Intelligence,17, 47–77.
Jensen, A. R. (1994). Psychometricg related to differences in head size.Personality & Individual Differences,17, 597–606.
Jensen, A. R., &Johnson, F. W. (1994). Race and sex differences in head size and IQ.Intelligence,18, 309–333.
Jensen, A. R., &Sinha, S. N. (1993). Physical correlates of human intelligence. In P. A. Vernon (Ed.),Biological approaches to the study of human intelligence (pp. 139–242). Norwood, NJ: Ablex.
Jensen, A. R., &Whang, P. A. (1993). Reaction times and intelligence: A comparison of Chinese-American and Anglo-American children.Journal of Biosocial Science,25, 397–410.
Jensen, A. R., &Whang, P. A. (1994). Speed of accessing arithmetic facts in long-term memory: A comparison of Chinese-American and Anglo-American children.Contemporary Educational Psychology,19, 1–12.
Jerison, H. J. (1963). Interpreting the evolution of the brain.Human Biology,35, 263–291.
Jerison, H. J. (1973).Evolution of the brain and intelligence. New York: Academic Press.
Jernigan, T. L., Archibald, S. L., Berhow, M. T., Sowell, E. R., Foster, D. S., &Hesselink, J. R. (1991). Cerebral structure on MRI, part 1: Localization of age-related changes.Biological Psychiatry,29, 55–67.
Johnson, R. C., McClearn, G. E., Yuen, S., Nagoshi, C. T., Ahern, F. M., &Cole, R. E. (1985). Galton’s data a century later.American Psychologist,40, 875–892.
Kamin, L. J. (1974).The science and politics of IQ. Hillsdale, NJ: Erlbaum.
Kandel, E. R. (1991). Nerve cells and behavior. In E. R. Kandel, J. H. Schwartz, & T. M. Jessell (Eds.),Principles of neural science (3rd ed., pp. 18–32). New York: Elsevier.
Kimura, D. (1992). Sex differences in the brain.Scientific American,267, 119–125.
Klein, R. E., Freeman, H. E., Kagan, J., Yarborough, C., &Habicht, J. P. (1972). Is big smart? The relation of growth to cognition.Journal of Health & Social Behavior,13, 219–250.
Kolakowski, D., &Malina, R. M. (1974). Spatial ability, throwing accuracy, and man’s hunting heritage.Nature,251, 410–412.
Kretschmer, E. (1936).Physique and character (2nd ed.). London: Routledge.
Krogman, W. M. (1970). Growth of head, face, trunk and limbs in Philadelphia White and Negro children of elementary and high school age.Monographs of the Society for Research in Child Development,35 (No. 136).
Lewontin, R. C., Rose, S., &Kamin, L. J. (1984).Not in our genes. New York: Pantheon.
Lynn, R. (1990). New evidence on brain size and intelligence: A comment on Rushton and Cain and Vanderwolf.Personality & Individual Differences,11, 795–797.
Lynn, R. (1991). Race differences in intelligence: A global perspective.Mankind Quarterly,31, 255–296.
Lynn, R. (1993a). Further evidence for the existence of race and sex differences in cranial capacity.Social Behavior & Personality,21, 89–92.
Lynn, R. (1993b). Nutrition and intelligence. In P. A. Vernon (Ed.),Biological approaches to the study of human intelligence (pp. 243- 258). Norwood, NJ: Ablex.
Lynn, R. (1994). Sex differences in intelligence and brain size: A paradox resolved.Personality & Individual Differences,17, 257–271.
Lynn, R., &Hattori, K. (1990). The heritability of intelligence in Japan.Behavior Genetics,20, 545–546.
Lynn, R., &Jindal, S. (1993). Positive correlations between brain size and intelligence: Further evidence from India.Mankind Quarterly,34, 109–123.
Lynn, R., &Shigehisa, T. (1991). Reaction times and intelligence: A comparison of Japanese and British children.Journal of Biosocial Science,23, 409–416.
Mascie-Taylor, C. G. N., &Gibson, J. B. (1978). Social mobility and IQ components.Journal of Biosocial Science,10, 263–276.
Michael, J. A. (1988). A new look at Morton’s craniological research.Current Anthropology,29, 349–354.
Miller, E. M. (1926).Brain capacity and intelligence (Monograph Series No. 4). Sydney: Australian Association for Psychology and Philosophy.
Miller, E. M. (1994). Intelligence and brain myelination: A hypothesis.Personality & Individual Differences,17, 803–832.
Morton, S. G. (1849). Observations on the size of the brain in various races and families of man.Proceedings of the Academy of Natural Sciences Philadelphia,4, 221–224.
Murdock, J., &Sullivan, L. R. (1923). A contribution to the study of mental and physical measurements in normal school children.American Physical Education Review,28, 209–330.
Osborne, R. T. (1980).Twins: Black and white. Athens, GA: Foundation for Human Understanding.
Osborne, R. T. (1992). Cranial capacity and IQ.Mankind Quarterly,32, 275–280.
Packard, G. C., &Boardman, T. J. (1988). The misuse of ratios, indices, and percentages in ecophysiological research.Physiological Zoology,61, 1–9.
Pagel, M. D., &Harvey, P. H. (1988). How mammals produce largebrained offspring.Evolution,42, 948–957.
Pakkenberg, H., &Voigt, J. (1964). Brain weight of the Danes.Acta Anatomica,56, 297–307.
Passingham, R. E. (1979). Brain size and intelligence in man.Brain, Behavior & Evolution,16, 253–270.
Pearl, R. (1906). On the correlation between intelligence and the size of the head.Journal of Comparative Neurology & Psychology,16, 189–199.
Pearlson, G. D., Kim, W. S., Kubos, K. L., Moberg, P. J., Jayaram, G., Bascom, M. J., Chase, G. A., Goldfinger, A. D., &Tune, L. E. (1989). Ventricle-brain ratio, computed tomographic density, and brain area in 50 schizophrenics.Archives of General Psychiatry,46, 690–697.
Pearson, K. (1906). On the relationship of intelligence to size and shape of head, and to other physical and mental characters.Biometrika,5, 105–146.
Pedersen, N. L., Plomin, R., Nesselroade, J. R., &McClearn, G. D. (1992). A quantitative genetic analysis of cognitive abilities during the second half of the life span.Psychological Science,3, 346–353.
Pfefferbaum, A., Mathalon, D. H., Sullivan, E. V., Rawles, J. M., Zipursky, R. B., &Lim, K. O. (1994). A quantitative magnetic resonance imaging study of changes in brain morphology from infancy to late adulthood.Archives of Neurology,51, 874–887.
Pool, R. (1994).Eve’s rib: Searching for the biological roots of sex differences. New York: Crown.
Porteus, S. D. (1937).Primitive intelligence and environment. New York: Macmillan.
Raz, N., Torres, I. J., Spencer, W. D., Millman, D., Baertschi, J. C., &Sarpel, G. (1993). Neuroanatomical correlates of age-sensitive and age-invariant cognitive abilities: Anin vivo MRI investigation.Intelligence,17, 407–422.
Reed, T. E., &Jensen, A. R. (1993). Cranial capacity: New Caucasian data and comments on Rushton’s claimed Mongoloid-Caucasoid brain size differences.Intelligence,17, 423–431.
Reid, R. W., &Mulligan, J. H. (1923). Relation of cranial capacity to intelligence.Journal of the Royal Anthropological Institute,53, 322–331.
Resnick, S. M. (1995, May).Gender differences in brain structure and function in the elderly. Paper presented at a meeting of the International Behavioral Development Symposium: Biological Basis of Sexual Orientation and Sex-Typical Behavior, Minot State University, Minot, ND.
Rosenthal, R. (1984).Meta-analytic procedures for social research. Newbury Park, CA: Sage.
Rushton, J. P. (1988a). Race differences in behaviour: A review and evolutionary analysis.Personality & Individual Differences,9, 1009–1024.
Rushton, J. P. (1988b). The reality of racial differences: A rejoinder with new evidence.Personality & Individual Differences,9, 1035–1040.
Rushton, J. P. (1992a). Cranial capacity related to sex, rank, and race in a stratified random sample of 6,325 U.S. military personnel.Intelligence,16, 401–413.
Rushton, J. P. (1992b). Life history comparisons between Orientals and Whites at a Canadian university.Personality & Individual Differences,13, 439–442.
Rushton, J. P. (1994). Sex and race differences in cranial capacity from International Labour Office data.Intelligence,19, 281–294.
Rushton, J. P. (1995).Race, evolution and behavior: A life-history perspective. New Brunswick, NJ: Transaction Publishers.
Rushton, J. P., &Ankney, C. D. (1995). Brain size matters: A reply to Peters.Canadian Journal of Experimental Psychology,49, 562–569.
Rushton, J. P., &Osborne, R. T. (1995). Genetic and environmental contributions to cranial capacity estimated in Black and White adolescents.Intelligence,20, 1–13.
Scarr, S., Weinberg, R. A., &Waldman, I. D. (1993). IQ correlations in transracial adoptive families.Intelligence,17, 541–555.
Schaie, K. W., &Strother, C. R. (1968). A cross-sequential study of age changes in cognitive behavior.Psychological Bulletin,70, 671–680.
Schreider, E. (1966). Brain weight correlations calculated from original results of Paul Broca.American Journal of Physical Anthropology,25, 153–158.
Schreider, E. (1968). Quelques corrélations somatiques des tests mentaux.Homo,19, 38–43.
Schultz, R. T. (1991).The relationship between intelligence and gray-white matter image contrast: A MRI study of healthy college students. Unpublished doctoral dissertation, University of Texas, Austin.
Snyderman, M., &Rothman, S. (1987). Survey of expert opinion on intelligence and aptitude testing.American Psychologist,42, 137–144.
Snyderman, M., &Rothman, S. (1988).The IQ controversy, the media, and public policy. New Brunswick, NJ: Transaction.
Sommerville, R. C. (1924). Physical, motor and sensory traits.Archives of Psychology,12, 1–108.
Sorokin, P. (1927).Social mobility. New York: Harper.
Sternberg, R. J. (1988).The triarchic mind: A new theory of human intelligence. New York: Penguin.
Stott, D. H. (1983). Brain size and “intelligence.”British Journal of Developmental Psychology,1, 279–287.
Stringer, C. B., &Andrews, P. (1988). Genetic and fossil evidence for the origin of modern humans.Science,239, 1263–1268.
Stumpf, H., &Jackson, D. N. (1994). Gender-related differences in cognitive abilities: Evidence from a medical school admissions testing program.Personality & Individual Differences,17, 335–344.
Susanne, C. (1979). On the relationship between psychometric and anthropometric traits.American Journal of Physical Anthropology,51, 421–423.
Swaab, D. F., &Hofman, M. A. (1984). Sexual differentiation of the human brain: A historical perspective. In G. J. De Vries, J. P. C. De Bruin, H. B. M. Uylings, & M. A. Corner (Eds.),Progress in brain research (Vol. 61, pp. 361–374). Amsterdam: Elsevier.
Teasdale, T. W., &Pakkenberg, B. (1988). The association between intelligence level and brain volume measures: A negative finding.Scandinavian Journal of Psychology,29, 123–125.
Terman, L. M. (1926/1959).Genetic studies of genius: Vol. 1. Mental and physical traits of a thousand gifted children (2nd ed.). Stanford, CA: Stanford University Press.
Tobias, P. V. (1970). Brain-size, grey matter and race—Fact or fiction?American Journal of Physical Anthropology,32, 3–26.
Topinard, P. (1878).Anthropology. London: Chapman & Hall.
Van Valen, L. (1974). Brain size and intelligence in man.American Journal of Physical Anthropology,40, 417–424.
Voigt, J., &Pakkenberg, H. (1983). Brain weight of Danish children.Acta Anatomica,116, 290–301.
Voyer, D., Voyer, S., &Bryden, M. P. (1995). Magnitude of sex differences in spatial abilities: A meta-analysis and consideration of critical variables.Psychological Bulletin,117, 250–270.
Waldman, I. D., Weinberg, R. A., &Scarr, S. (1994). Racial group differences in IQ in the Minnesota Transracial Adoption Study: A reply to Levin and Lynn.Intelligence,19, 29–44.
Waller, J. H. (1971). Achievement and social mobility: Relationships among IQ score, education, and occupation in two generations.Social Biology,18, 252–259.
Weinberg, R. A., Scarr, S., &Waldman, I. D. (1992). The Minnesota Transracial Adoption Study: A follow-up of IQ test performance at adolescence.Intelligence,16, 117–135.
Weinberg, W. A., Dietz, S. G., Penick, E. C., &McAlister, W. H. (1974). Intelligence, reading achievement, physical size and social class.Journal of Pediatrics,85, 482–489.
Wickett, J. C., Vernon, P. A., &Lee, D. H. (1994).In vivo brain size, head perimeter, and intelligence in a sample of healthy adult females.Personality & Individual Differences,16, 831–838.
Wigdor, A. K., &Garner, W. R. (1982). (Eds.)Ability testing: Uses, consequences, and controversies. Washington, DC: National Academy Press.
Willerman, L., Schultz, R., Rutledge, J. N., &Bigler, E. D. (1991).In vivo brain size and intelligence.Intelligence,15, 223–228.
Willerman, L., Schultz, R., Rutledge, J. N., &Bigler, E. D. (1994). Brain structure and cognitive function. In C. R. Reynolds (Ed.),Cognitive assessment: A multi-disciplinary assessment (pp. 35–55). New York: Plenum.
Winick, M., Meyer, K. K., &Harris, R. C. (1975). Malnutrition and environmental enrichment by early adoption.Science,190, 1173–1175.
Witelson, S. F., Glezer, I. I., &Kigar, D. L. (1995). Women have greater density of neurons in posterior temporal cortex.Journal of Neuroscience,15, 3418–3428.
Yeo, R. A., Turkheimer, E., Raz, N., &Bigler, E. D. (1987). Volumetric asymmetries of the human brain: Intellectual correlates.Brain & Cognition,6, 15–23.
We thank E. Hunt, D. N. Jackson, A. R. Jensen, S. Johnson, P. Kyllonen, H. L. Roediger III, E. Tulving, J. Wickett, L. Willerman, and several anonymous reviewers for valuable comments and suggestions. This review draws on what we have previously published individually and jointly elsewhere.
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Rushton, J.P., Ankney, C.D. Brain size and cognitive ability: Correlations with age, sex, social class, and race. Psychonomic Bulletin & Review 3, 21–36 (1996). https://doi.org/10.3758/BF03210739
- Body Size
- Cognitive Ability
- Brain Size
- Stratify Random Sample
- Head Size