Phrenology, a system that analyzed the shape, size, and bumps of the head to determine mental ability and character, enjoyed popularity from the 19th century until the 20th century, when it was discredited and abandoned. Like physiognomy, scientists used phrenology to support inaccurate ideas, including the beliefs that personal traits were innate and dictated solely by nature, that traits like criminality and psychopathy were measurable and localized to specific parts of the brain, and that women, people of color, neurodivergent people, and other marginalized groups were inherently inferior.
U.S. physician Henry Shipton Drayton (1840–1923) and James McNeill (1846–1916) provide an overview of phrenological theory and practice in this work. Drayton was a major advocate for phrenology.