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, Plausible scenarios are easy to construct. Morton, measuring by seed, picks up a threateningly large black skull, fills it lightly and gives it a few desultory shakes. Next, he takes a distressingly small Caucasian skull, shakes hard, and pushes mightily at the foramen magnum with his thumb. It is easily done, without conscious motivation; expectation is a powerful guide to action. In 1977 Gould conducted his own analysis on some of Morton's endocranial-volume data, and alleged that the original results were based on a priori convictions and a selective use of data. He argued that when biases are accounted for, the original hypothesis—an ascending order of skull volume ranging from Blacks to Mongols to Whites—is unsupported by the data. Bias and falsification The Mismeasure of Man presents a historical evaluation of the concepts of the intelligence quotient (IQ) and of the general intelligence factor (g factor), which were and are the measures for intelligence used by psychologists. Gould proposed that most psychological studies have been heavily biased, by the belief that the human behavior of a race of people is best explained by genetic heredity. He cites the Burt Affair, about the oft-cited twin studies, by Cyril Burt (1883–1971), wherein Burt claimed that human intelligence is highly heritable. IQ, g, statistical correlation, and heritability As an evolutionary biologist and historian of science, Gould accepted biological variability (the premise of the transmission of intelligence via genetic heredity), but opposed biological determinism, which posits that genes determine a definitive, unalterable social destiny for each man and each woman in life and society. The Mismeasure of Man is an analysis of statistical correlation, the mathematics applied by psychologists to establish the validity of IQ tests, and the heritability of intelligence. For example, to establish the validity of the proposition that IQ is supported