Americans were strongly drawn to theories of racial character. Samuel Morton, the most famous American anthropologist of his day, collected thousands of skulls from across the New World. He measured the size of the brain cavity and imagined that this gave him a measure of basic intelligence. He published the result in a book, Crania Americana (1839). An illustration from the book appears here. Partly Morton's work supported slavery, since not surprisingly it ranked the "Teutonic Family" of skulls highest, and the "Negro Group" lowest. But the book also helped support the claim that you could judge people's character by their physical makeup.
The relationship between body and character reached its height in the decades before the Civil War, with the study of Phrenology, or skull shape. Phrenologists claimed that skull shape revealed character development--certain bumps indicated creativity, certain shapes represented leadership faculties; a slight swelling in one part of the skull suggested a tendency to crime. The Phrenological skull represented here was used to study head shape for practitioners, who would offer "readings" that helped people figure out their aptitudes and their basic character