Final Answer:
Gall assumed that an especially well-developed mental faculty or organ requires a larger and more prominent brain area.
Step-by-step explanation:
Gall, a phrenologist, believed that specific mental faculties or organs were associated with distinct regions of the brain. He hypothesized that a well-developed mental faculty would be reflected in the size and prominence of the corresponding area of the brain.
This assumption formed the basis of phrenology, a pseudoscience that attempted to link personality traits and mental abilities to the shape and size of specific brain regions.
In Gall's view, a larger and more pronounced area of the brain was indicative of a heightened development of the associated mental faculty. While phrenology has been discredited as a scientific practice, Gall's ideas were influential in early discussions about the localization of brain functions.
In summary, Gall assumed that an especially well-developed mental faculty required a larger and more prominent brain area, a concept central to the pseudoscience of phrenology.