Natalie Shapero recounts the evolution of the lie detector, as told in Geoffrey C. Bunn’s recent book The Truth Machine. At the end of the 19th century and the beginning of the 20th, criminality was viewed as an inherent trait and “an individual person was either inherently law-abiding or inherently degenerate”:
That’s where fiction comes in. This harsh conception of human predisposition caused problems for the burgeoning genre of the whodunit, which derives its suspense from the premise that anyone at all could be the culprit. In order to justify the suspicions thrown on each and every character, mystery writers of the early twentieth century had to embrace a new, equal-opportunity model of criminality. The detective novel, Bunn writes, presupposed the shift in attitude that came in the 1930s, when many people in the U.S. and the U.K. rejected a eugenics-oriented approach to eradicating crime and began to think of criminality as a behavior rather than an identity. To go with this new conception of crime, several detective novels of the day imagined a new kind of sleuthing technology: the lie detector, which could be strapped to any ordinary person and distinguish his moments of earnestness from his moments of deception.