This paper contributes to the literature in three ways. First, the study more than doubles the number of
unique samples that address the in vivo brain volume and intelligence relationship. Second, it also
contributes by testing age and sex moderators of the relationship. The relationship is stronger for females
than males and is stronger for adults than children. Finally, it resolves a 169 year-old debate. Tiedmann
(1836) was correct to conclude that intelligence and brain volume are meaningfully related.