The quantification of intelligence in nineteenth-century craniology: an epistemology of measurement perspective

Abstract

Craniology – the practice of inferring intelligence differences from the measurement of human skulls – survived the dismissal of phrenology and remained a widely popular research program until the end of the nineteenth century. From the 1970s, historians and sociologists of science extensively focused on the explicit and implicit socio-cultural biases invalidating the evidence and claims that craniology produced. Building on this literature, I reassess the history of craniological practice from a different but complementary perspective that relies on recent developments in the epistemology of measurement. More precisely, I identify two aspects of the measurement culture of nineteenth-century craniologists that are crucial to understand the lack of validity of craniological inference: their neglect of the problem of coordination for their presupposed quantification of intelligence and their narrow view of calibration. Based on my analysis, I claim that these methodological shortcomings amplified the impact of the socio-cultural biases of craniologists, which had a pervasive role in their evidential use of measurement. Finally, my argument shows how the epistemology of measurement perspective can offer useful tools in debates concerning the use of biological evidence to foster social discourse and for analyzing the relationship between theory, evidence, and measurement.

Imaging genomics reveals genetic architecture of the globular human braincase

“…It misused measurements, like the cervical index (the ratio of a skull’s maximum width to its length), to wrongly suggest racial differences in intellectual capabilities. These ideas were absorbed into phrenology, which claimed to predict personality, mental health, and criminal tendencies based on skull measurements, providing a pseudo-scientific basis for racist beliefs, slavery, colonialism, and later, 20th-century eugenics 99,100 . Despite being discredited as pseudoscience 101,102 , the remnants of racial craniology and phrenology still influence contemporary studies linking brain and behaviour 103 .…”

Epistemic circularity and measurement validity in quantitative psychology: insights from Fechner’s psychophysics

“…Most natural sciences can rely on shared perception as a criterion for metrological traceability, i.e., on the fact that inter-subjective agreement on what is being observed can be achieved, thus grounding the possibility to further infer causal empirical relationships among quantities. As the problem 8 These include, among others, medical measurement (McClimans, 2013), physical anthropology (Luchetti, 2022), perception studies (Barwich andChang, 2015), andpsychometrics (McClimans et al, 2017). 9 The reason for this difficulty is that the historical development of successful measurement procedures for a certain quantity or property is often intertwined with the empirical process of identification, confirmation and refinement of the relevant measurement laws that are required to infer information on the measurand from the result of a measurement process (Chang, 2004;Riordan, 2015;Luchetti, 2020).…”

“… 8 These include, among others, medical measurement ( McClimans, 2013 ), physical anthropology ( Luchetti, 2022 ), perception studies ( Barwich and Chang, 2015 ), and psychometrics ( McClimans et al, 2017 ). …”