Craniology, the study of variations in size, shape and proportion of the skull, was a popular though controversial branch of medicine in the late 19th century. It is a subsection of anthropometry, a branch of anthropology concerned with comparative measurements of the human body and body parts. It was believed that individual mental faculties were contained in neat compartments in the cerebral cortex, and the extent of these faculties was reflected in the configuration of the skull. The measurement of cranial features was used to classify people by race, criminal temperament, intelligence, etc. Alongside similar pseudoscience like phrenology, craniology became influential during the Victorian age in justifying racism, colonisation and dominance of ‘inferior people', especially Africans.
Dr Izydor Kopernicki, a leading Polish anthropologist, asked Conrad in 1881 to assist his craniological studies by collecting skulls during his travels and sending them to a museum in Kraków.