People who have lower resting heart rates are on average more likely to commit crimes. Such a rather strange relationship was discovered by the researchers after a series of experiments.
All of these studies were conducted in developed countries with relatively low rates of violent crime, and also included only men. Recently, an international team of scientists decided to conduct a similar study in which they analyzed data on residents of the Brazilian city of Pelotas of both sexes. The crime situation in the city is extremely unfavorable, and the number of murders per capita is almost 20 times higher than in the UK.
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The scientists used data from the Brazilian cohort study (cohort studies usually involve long-term follow-up of a group of people), which included children born in the city of Pelotas in 1993. Initially, 5265 children were examined, repeated examinations at the age of 11, 15 and 18 years were carried out with approximately 80% of them. During each examination, in particular, resting heart rate was measured.
When surveyed at age 18, participants were asked, among other things, if they had committed crimes (and if so, which ones) in the last 12 months. Of course, the answers to such questions will not always be truthful, so official data on convictions and arrests were also used. Violent crimes included murder, battery and bodily harm, kidnapping, rape, illegal possession and use of weapons. All other crimes were considered non-violent, and traffic violations were not counted at all. A total of 26,6% of boys and 11,3% of girls surveyed at age 18 had already committed violent crimes.
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For boys, low resting heart rates (about 60 beats per minute) at ages 11, 15, and 18 were found to be strongly correlated with violent crime. For girls, only a slow heartbeat at the age of 18 mattered.
Crime in the disadvantaged areas of Brazil is due to many factors – poverty, corruption, gangs, drug trafficking, etc. The authors of the study were surprised that even with so many social factors, the influence of individual physiological differences is still clearly visible.
Scientists offer several possible explanations for such a connection, emphasizing that so far these are only hypotheses.
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It is hypothesized that a lack of activity in the nervous system can lead to a low heart rate and a constant craving for external stimulation and strong impressions, often resulting in antisocial behavior, including violent crime. These same features of the body may be associated with a reduced ability to experience a sense of fear – including fear of possible punishment. However, in a similar US study, fearlessness alone did not explain the association between slow heart rate and violent crime—it appears to be only a minor factor.
Подробнее см. J. Murray et al. «Low resting heart rate is associated with violence in late adolescence: a prospective birth cohort study in Brazil», International Journal of Epidemiology, January 2016.