Even at the tender age of 3, children who will go on to be convicted of a crime are less likely to learn to link fear with a certain noise than those who don’t. This may mean that an insensitivity to fear could be a driving force behind criminal behaviour.
Adult criminals tend to be fearless, but whether this characteristic emerges before or after they commit a crime wasn’t clear, says Adrian Raine, a psychologist at the University of Pennsylvania in Philadelphia.
To find out, Raine and colleague Yu Gao turned to data from a 1970s study, collected as part of a decades-long project to understand the biological and environmental factors underlying mental illness.
Back then, researchers led by Raine’s former research supervisor had measured the sweat response of about 1800 3-year-olds in Mauritius when they were exposed to two different sounds. One sound was always followed by a noisy blare, the other by nothing. The children learned to anticipate which sound preceded the blare, and sweated in response to it – an indicator of fear.
Decades later, Raine’s own team looked to see if any of the subjects had criminal records and found 137 that did. The team discovered that, as toddlers, these people had sweated significantly less in anticipation of the blare compared with subjects of similar race, gender and background for whom no criminal record was found.