Cranial capacity

races and 19th-20th century scientific ideas
Samuel George Morton (1799-1851), one of the inspirers of physical anthropology, collected hundreds of human skulls from all over the world and started trying to find a way to classify them according to some logical criterion. Influenced by the common theories of his time, he claimed that he could judge the intellectual capacity of a race by the cranial capacity (the measure of the volume of the interior of the skull). A large skull meant a large brain and high intellectual capacity, and a small skull indicated a small brain and decreased intellectual capacity. By studying these skulls he decided at what point Caucasians stopped being Caucasians, and at what point Negroes began. Morton had many skulls from ancient Egypt, and concluded that the ancient Egyptians were not African, but were white. His two major monographs were the Crania Europe (1839), An Inquiry into the Distinctive Characteristics of the Aboriginal Race of America and Crania Aegyptiaca (1844). In Crania Americana, he claimed that the mean cranial capacity of the skulls of Whites was 87 in³ (1,425 cm³), while that of Blacks was 78 in³ (1,278 cm³). Based on the measurement of 144 skulls of Native Americans, he reported a figure of 82 in³ (1,344 cm³) [sic].
Stephen Jay Gould (1941-2002), an American paleontologist, evolutionary biologist and historian of science, studied these craniometric works from a historical perspective in The Mismeasure of Man (1981). He showed that Samuel Morton had fudged data and "overpacked" the skulls with filler in order to justify his preconcieved notions on racial differences.
Morton's followers, particularly Josiah C. Nott (1804-1873) and George Gliddon (1809-1857) in their monumental tribute to Morton's work, Types of Mankind (1854), carried Morton's ideas further and claimed that his findings in fact supported the notion of polygenism, which claims that humanity originates from different lineages and is the ancestor of the multiregional hypothesis. Morton himself had been reluctant to explicitly espouse polygenism because it was a major challenge to the biblical account of creation. Charles Darwin opposed Nott and Glidon in his 1871 The Descent of Man, arguing for a monogenism of the species. Darwin conceived the common origin of all humans (the single-origin hypothesis) as essential for evolutionary theory.
Furthermore, Josiah Nott was the translator of Arthur de Gobineau's An Essay on the Inequality of the Human Races (1853-1855), which is one of the founding works of the group of studies that segregates society based on "race", in contrast to Boulainvilliers (1658-1722)'s theory of races. Henri de Boulainvilliers opposed the Français (French people), alleged descendants of the Nordic Franks, and members of the aristocracy, to the Third Estate, considered to be indigenous Gallo-Roman people who were subordinated by the Franks by right of conquest. Gobineau, meanwhile, made three main divisions between races, based not on colour but on climatic conditions and geographic location, and which privileged the "Aryan" race.
In 1873, Paul Broca (1824-1880) found the same pattern described by Samuel Morton's Crania Americana by weighing brains at autopsy. Other historical studies alleging a Black-White difference in brain size include Bean (1906), Mall, (1909), Pearl, (1934) and Vint (1934).

William Z. Ripley's map of the "cephalic index" in Europe, from The Races of Europe (1899).
Furthermore, Georges Vacher de Lapouge's racial classification ("Teutonic", "Alpine" and "Mediterranean") was re-used by William Z. Ripley (1867-1941) in The Races of Europe (1899), who even made a map of Europe according to the alleged cephalic index of its inhabitants.