Brain Size and Cognitive Ability
Psychonomic Bulletin & Review 1996, 3 (1). 21-36 Brain size and cognitive ability: Correlations with age, sex, social class, arid race J. PHILIPPE RUSHTON and C. DAVISON ANKNEY University of Western Ontario, London, Ontario, Canada 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, so- cial 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 socio- economic status; and increasing from Africans to Europeans to Asians. Although only further re- search 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 re- lation, strongly advocated over the last half century, is false. With new technologies increasingly available for scan- ning the brain, and renewed interest in the evolutionary basis of behavior, remarkable discoveries are being made that confirm relationships first established over 100 years ago. Four main procedures have been used to estimate brain size. In the past, these included weighing wet brains at autopsy, measuring the volume of empty skulls using filler, and measuring external head sizes and estimating volume. Recently, more sophisticated techniques have been added to the arsenal, including computer assisted tomogra- phy (CAT) and magnetic resonance imaging (MRI) to cre- ate, in vivo, three-dimensional images of the brain. Data derived from independent procedures enhance probabil- ity of finding truth. Paul Broca (1824-1880), the renowned French…