The most influential psychophysiological theories of antisocial behavior assume that antisocial individuals are chronically underaroused. Psychophysiological indicators for underarousal include low heart rate, low skin conductance and more excessive slow-wave electroencephalogram [
26]. In this study we will focus on low heart rate. According to fearlessness theory, underarousal, indicated by low heart rate levels, is a marker of low levels of fear [
26,
27]. This may lead to criminal and violent behavior because a lack of fear might be to some extent be required to commit (violent) crimes, while fear on the other hand might inhibit crime. Moreover, a lack of fear, especially in childhood, reduces the effectiveness of social conditioning [
26,
27].
Stimulation-seeking theory explains the relationship between antisocial behavior and reduced arousal by arguing that low levels of arousal represent an aversive physiological state [
28]. Underaroused individuals engage in antisocial, criminal, and violent behavior because they seek stimulation in order to increase their arousal levels to an optimal or normal level. Fearlessness theory and stimulation-seeking theory are complementary theories rather than competing ones because underarousal may lead to (violent) crime by generating both fearlessness and stimulation-seeking [
26]. It is beyond the scope of this current study to test which of these two theories best explains the relationship between heart rate and antisocial behavior, but we will test whether the relationship is in the predicted direction.
In accordance with these theories, a meta-analysis by Ortiz and Raine [
6], covering 40 studies from seven different countries in both hemispheres, showed a relationship between low resting heart rate and antisocial behavior in children and adolescents. Previous studies showed that this relationship could not be accounted for by potential confounders such as physical characteristics, intelligence, drug and alcohol use, physical exercise or disadvantageous social factors [
29,
30,
31,
32]. In addition, several prospective studies showed that this relationship is in the predicted direction by ruling out the possibility that an antisocial lifestyle decreases heart rate levels [
29,
30,
31,
32,
33]. Based on these results, Ortiz and Raine ([
6], p. 154) concluded that “low resting heart rate appears to be the best-replicated biological correlate to date of antisocial and aggressive behavior in children and adolescents”. An effect of low heart rate on self-reported antisocial behavior [
34] and criminal convictions [
31,
32,
35] was also found among young adults. Lorber [
36] further showed in a meta-analysis that low resting heart rate is correlated with aggression among adults as well. Whether or not the association between low resting heart rate and offending is stronger for violent offending than non-violent offending remained unclear from these meta-analyses. Ortiz and Raine [
6] could not test this in their meta-study since too few studies compared between aggressive behavior and non-aggressive antisocial behavior. Lorber’s [
6] meta-study does not distinguish between aggressive and non-aggressive antisocial behavior for the adult population either. Wadsworth [
32], however, found lower heart rates among sexual and violent offenders than among non-violent offenders and non-criminal controls. More recently, low resting heart rate was shown to be related to both all crime and violent crime at age 50 in the CSDD [
37]. However, effect sizes could not be compared in this study since different types of regression analyses were used for all crime and violent crime. Using a large Swedish population study, Latvala and colleagues [
9] did show a stronger association of low resting heart rate with violent crime (in particular serious violent crime) than with non-violent crime. Also Murray and colleagues [
10] found that, among Brazilian males, a low resting heart rate at age 15 was more strongly associated with violent crime than with non-violent crime at age 18. Using prospective longitudinal data from the Mauritius Child Health Project, Choy and colleagues [
38] further showed that resting heart rates measured at age 11 were the lowest for those participants involved in serious violent offending at age 23. In line with these studies, Portnoy and Farrington [
39] found, in a recent meta-analysis, a larger effect size for the relationship between heart rate and violence than for all other forms of antisocial behavior (i.e., aggression, behavior problems, conduct disorder, offending, psychopathy). Based on fearlessness theory, stimulation-seeking theory and previous findings, we expect that:
In addition to those two main effects of parental crime and heart rate levels on criminal offending, heart rate levels may impact the intergenerational transmission of crime as a mediating or moderating factor.