Thurstone, three intelligence researchers who popularized the statistical modeling tool of factor analysis.

In the third section of the book, Gould introduces the work of Charles Spearman, Cyril Burt, and L.L. Yerkes, Gould traces the widespread acceptance of intelligence testing in 1920s America and detailshow this movement influenced the isolation of so-called “feeble-minded” people, encouraged the intelligence testing and labeling of children, and negatively impacted national immigration policy quotas. Gould examines the historical development of Alfred Binet’s IQ scale, his original intention for how the test would be used, and its transmutation into a means of proving intelligence to be a biologically-determined and inheritable number. The second part of the book focuses on the use of intelligence testing in the 20th century. However, because quantifiable approaches of measuring intelligence were established scientific theories, published research was not only accepted, it paved the way for other race-based theories of intelligence, including evolutionary recapitulation and criminal morphology. In reviewing the data collection tables and publications of Morton and Broca, Gould argues that once unconscious and prejudicial bias is removed, the scientific data shows there is no evidence for race-based intellectual difference. Gould surveys the early scientific findings in this field, and also reexamines the work of leading scientists Samuel George Morton and Paul Broca.

During this time, scientific investigation focused on compiling numerical data measuring the sizes of human brains in order to arrive at a rational, objective methodology for ranking racial intelligence. The first part of the book focuses on the science of craniometry, which was at the forefront of biological determinism during the 19th century.

The mismeasure of man