unitary, innate, linearly rankable intelligence"—such as craniometry, the measurement of skull volume and its relation to intellectual faculties. Gould alleged that much of the research was based largely on racial and social prejudices of the researchers rather than their scientific objectivity; that on occasion, researchers such as Samuel George Morton (1799–1851), Louis Agassiz (1807–1873), and Paul Broca (1824–1880), committed the methodological fallacy of allowing their personal "a priori" expectations to influence their conclusions and analytical reasoning. Gould noted that when Morton switched from using bird seed, which was less reliable, to lead shot to obtain endocranial-volume data, the average skull volumes changed, however these changes were not uniform across Morton's "racial" groupings. To Gould, it appeared that unconscious bias influenced Morton's initial results. Gould speculated,