A Nutrition Theory of the Secular Increases in Intelligence; Positive Correlations Between Height, Head Size and Iq

S ummary . The thesis is advanced that the secular increases in intelligence over the last half century are largely due to improvements in nutrition. These have brought about increases in height, head size and brain size of approximately one standard deviation, about the same magnitude of increase as has taken place in intelligence. The thesis requires the existence of a positive correlation between head size and intelligence. Data for 310 9–10 year‐olds obtained a correlation of +0·21.