Gall conceived of the brain not as a single organ but as a mosaic of specialized parts that each governed a particular mental or emotional function. The size and development of each area, which Gall called faculties, implied a greater or lesser disposition toward the trait. These faculties included everything from reproduction to affection, vanity, and musical ability. Through his study, Gall came to believe that the shape of the brain matched the shape of the skull that encased it, so studying the bumps and indentations of the skull could reveal the function and character of the brain beneath. Later phrenologists came to believe that people could strengthen their positive brain organs. Like weightlifting builds muscle, the brain was an organ to be exercised.

While phrenology became very popular in Europe, it found its most devoted audience in the United States. One reason phrenology attracted so many followers was that it seemed to provide the toolbox for the American dream. All classes of society found much to admire in phrenology. The upper classes liked it because it reassured them that the social hierarchy that placed them on top was “natural”; the emerging middle class and working classes liked it because its meritocratic message confirmed their hope of advancement through personal striving and self-improvement.

Phrenology seemed to provide what the strict Calvinist religion of Puritanical America had not: a way to better what God gave you, empowering individuals to help shape their own future, and making man the master of his own mind. Moreover, phrenology also became commercialized in the United States, in large part due to the efforts of the Fowler family.

The Fowler brothers, Lorenzo Niles and Orson Squire, turned their interest in phrenology into a substantial business based in New York City in the 1830s. The eldest brother, Orson Squire Fowler, hadn’t set out to be a phrenologist. The son of a farmer and church deacon from upstate New York, Orson first pursued the ministry but found his true calling in phrenology. He began to lecture on the topic to his classmates at Amherst College in Massachusetts and offered head readings for two cents each. His enthusiasm soon infected his younger brother, Lorenzo, along with the rest of the family, including younger sister Charlotte; her husband, Samuel Wells; and Lorenzo’s wife, Lydia Folger. After graduation, the brothers put aside their plans for a life in the church for another kind of missionary work.

The Fowlers translated phrenology into a doctrine of perfectionism, a set plan designed to create a perfect social and moral system. Their version of phrenology attempted to bring together all the strands of science capable of improving the mind or benefiting mankind, which they believed would herald a new and better world. And like all true-blooded 19th century American entrepreneurs, they also just happened to sell the phrenological gear and accessories needed to make this happen.