Men engage in more criminal activity than women, but little is known about why this gender gap exists. For a long time, some psychologists chalked it up to differential parenting.

A new study from Olivia Choy, a recent Penn alum, titled “Explaining the Gender Gap in Crime: The Role of Heart Rate,” goes beyond traditional socialization theories to address the incomplete understanding of gender differences in offending by examining biological functioning and behavior, specifically heart rate.

Published in the journal Criminology, it is the first study to demonstrate that men’s lower resting heart rate partly explains their higher rate of criminal offending. 

Choy, who graduated in May with a Ph.D. from Penn’s Department of Criminology in the School of Arts & Sciences (SAS), conducted the research in the lab of Adrian Raine, a Penn Integrates Knowledge Professor.

“We give little girls toys and little boys toy guns,” says Raine, who holds appointments in SAS and the Perelman School of Medicine. “But this is not the complete answer. Biological variables like heart rate are at play, and the more we begin to pay attention to the biological contributions to crime causation, the more we may understand, and ultimately prevent, the higher crime rates in men.”

Researchers examined data obtained from a subsample of participants involved in the Mauritius Child Health Project. The original sample consisted of 1,795 children born in 1969-70 who were recruited into the study from Mauritius, an island country in the Indian Ocean, when they were 3 years old. When they were 11 years old, the children were given a major psychophysiological test. When they were 23 years old, assessments on their level of adult criminal offending in the past five years were made.

Resting heart rate accounted for 5 to 17 percent of the gender difference in crime.

Prior studies have shown that people with low resting heart rates seek stimulation to raise their level of arousal to a more optimal one. This stimulation-seeking theory converges with a theory arguing that these people have a low level of fear and may be more likely to engage in antisocial behavior, which requires a degree of fearlessness.

Choy observes that one way to get that stimulation is by engaging in antisocial behavior.

“A theory connects low levels of arousal to low heart rate, reflecting a low level of fear in individuals,” she says. “To commit a crime, you need a level of fearlessness, so these are two major explanations for why we see this relationship between low heart rate and antisocial behavior.”

She points out that differences in heart rates among male and female children are seen as early as 17 months of age. Both Choy and Raine believe that researchers need to pay more attention to the biological contributions to crime causation to ultimately prevent the higher crime rates in men.