A propensity to believe that fellow citizens will not act against our interests in social and economic transactions has been identified as key to the effective functioning of democratic polities. Yet the causes of this type of 'generalized' or 'social' trust are far from clear. To date, researchers within the social and political sciences have focused almost exclusively on social-developmental and political/institutional features of individuals and societies as the primary causal influences. In this paper we investigate the intriguing possibility that social trust might have a genetic, as well as an environmental basis. We use data collected from samples of monozygotic and dizygotic twins to estimate the additive genetic, shared environmental, and non-shared environmental components of trust. Our results show that the majority of the variance in a multi-item trust scale is accounted for by an additive genetic factor. On the other hand, the environmental influences experienced in common by sibling pairs have no discernable effect; the only environmental influences appear to be those that are unique to the individual. Our findings problematise the widely held view that the development of social trust occurs through a process of familial socialization at an early stage of the life course.

Borderline personality disorder (BPD) and substance use disorders often co-occur. Both disorders are heritable and family studies showed that there are familial factors that increase the risk for BPD as well as substance use/abuse. This is the first study that investigates whether the association of borderline personality traits (BPT) with substance use reflects an underlying genetic vulnerability or nongenetic familial influences. To this end we analyzed data of 5,638 Dutch and Belgian twins aged between 21–50 years from 3,567 families. Significant associations between BPT and high alcohol consumption (r = .192), regular smoking (r = .299), and ever use of cannabis (r = .254) were found. Bivariate genetic analyses showed that the associations of BPT and substance use had different etiologies. For regular smoking and for ever use of cannabis, the correlation with BPT was explained by common genetic factors. Interestingly, for high alcohol consumption and BPT the association was explained by unique environmental factors that influence both traits rather than common genetic factors.

Borderline personality disorder (BPD) and substance use disorders often co-occur. Both disorders are heritable and family studies showed that there are familial factors that increase the risk for BPD as well as substance use/abuse. This is the first study that investigates whether the association of borderline personality traits (BPT) with substance use reflects an underlying genetic vulnerability or nongenetic familial influences. To this end we analyzed data of 5,638 Dutch and Belgian twins aged between 21-50 years from 3,567 families. Significant associations between BPT and high alcohol consumption (r = .192), regular smoking (r = .299), and ever use of cannabis (r = .254) were found. Bivariate genetic analyses showed that the associations of BPT and substance use had different etiologies. For regular smoking and for ever use of cannabis, the correlation with BPT was explained by common genetic factors. Interestingly, for high alcohol consumption and BPT the association was explained by unique environmental factors that influence both traits rather than common genetic factors.The presentation of borderline personality disorder (BPD) with a comorbid substance use disorder (SUD) is common in clinical and population samples (Feske, Tarter, Kirisci, & Pilkonis, 2006; Tomko, Trull, Wood, & Sher, in press;Trull, Sher, Minks-Brown, Durbin, & Burr, 2000;Trull, Jahng, Tomko, Wood, & Sher, 2010). Also, higher rates of alcohol and drug abuse and dependence and a higher rate of new onsets of SUD are found in patients with BPD than in patients with other personality disorders (McGlashan et al., 2000;Walter et al., 2009;Zanarini et al., 2011). In a comprehensive review, Trull et al. (2000) report that almost 60% of the individuals diagnosed with BPD meets criteria for a general category of substance use disorder, almost 50% meets criteria for an alcohol use disorder (abuse or dependence) and almost 40% meets criteria for a drug use disorder (abuse or dependence). The co-occurrence of BPD and SUD is associated with an increased risk for suicide attempts, poorer school performance, a higher level of unemployment, more promiscuity, and more early termination from treatment (Karterud, Arefjord, Andresen, & Pedersen, Miller, Abrams, Dulit, & Fyer, 1993;van den Bosch, Verheul, & van den Brink, 2001).It is well established that genetic factors contribute to the liability for substance use (Agrawal & Lynskey, 2008). Heritability estimates between 36% and 72% were reported for several measures of alcohol use (Grant et al., 2009; Kendler, Myers, Dick, & Pescott, 2010;Sartor et al., 2010;Whitfield et al., 2004). Li, Cheng, Ma, and Swan (2003) conducted a meta-analysis for tobacco use and report a heritability estimate of 59%. A meta-analysis for cannabis initiation estimated the heritability to be 48% for males and 40% for females although the confidence intervals around these estimates for males and females overlapped (Verweij et al., 2010).For BPD and related traits, large scale twin and twin family studies report heritab...

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