Recent work on bullying perpetration includes the hypothesis that bullying carries an evolutionary advantage for perpetrators in terms of health & reproductive success; paper confirms the last, but health is worse

Benefits of Bullying? A Test of the Evolutionary Hypothesis in Three Cohorts. Tina Kretschmer, Chaïm la Roi, Rozemarijn van der Ploeg, René Veenstra. Journal of Research on Adolescence, August 27 2021. https://doi.org/10.1111/jora.12675

Abstract: Recent work on bullying perpetration includes the hypothesis that bullying carries an evolutionary advantage for perpetrators in terms of health and reproductive success. We tested this hypothesis in the National Child Development Study (n = 4998 male, n = 4831 female), British Cohort Study 1970 (n = 4261 male, n = 4432 female), and TRacking Adolescents’ Individual Lives Survey (n = 486 male, n = 521 female), where bullying was assessed in adolescence (NCDS, BCS70: age 16, TRAILS: age 14) and outcomes in adulthood. Partial support for the evolutionary hypothesis was found as bullies had more children in NCDS and engaged in sexual intercourse earlier in TRAILS. In contrast, bullies reported worse health in NCDS and BCS70.

DISCUSSION

Bullying has played an important role in the developmental literature and in educational policy in the last few years. This surge in attention was fueled by a plethora of studies on maladjustment of victims. Negative outcomes have also been ascribed to perpetrators, but the scientific evidence here is thinner. In fact, some longitudinal studies leave doubt as to whether bullying others actually carries risk for maladjustment (Copeland et al., 2013; Wolke et al., 2013). Bullying research inspired by evolutionary theory has even suggested that bullies might reap benefits in the form of better health, access to partners, and reproductive opportunities. Here, we tested whether bullying was indeed linked to these outcomes in three cohorts.

Across the older cohorts (NCDS and BCS70), bullies showed worse health outcomes in middle adulthood. At first sight, this finding is not supportive of the hypothesis that bullying perpetrators are exposed to less stress given their rank in the social pecking order and thus should theoretically reap the benefits in form of better health (Volk et al., 2012). It appears that decreased stress among bullies is linked to better health in the short term—as supported by a study into differences by bullying status in increases in systemic inflammation levels from adolescence to early adulthood (Copeland et al., 2014)—but that this beneficial effect does not last for decades. In fact, bullying perpetrators engage in health-adverse behaviors (Ttofi et al., 2016) and experience more stress—though not necessarily worse health—as adults (Matthews et al., 2017). It is possible that negative health outcomes emerge later in life, which might explain why we did not observe this association in TRAILS. For instance, bullying perpetrators might continue to aggress against work colleagues and partners (Farrell & Vaillancourt, 2019; Matthiesen & Einarsen, 2007), thus jeopardize employment, friendships, and relationships and end up unhappy and unhealthy as adults. Bullying perpetration has also been associated with substance use later on (Vrijen et al., 2021), which has negative effects on physical health as well. Not detecting this association in TRAILS might mean that bullying perpetration in this cohort is still ongoing and health benefits resulting from lower social stress are continued to be reaped for the time being.

Notably, whereas health was worse among bullying perpetrators in NCDS and BCS70, NCDS participants had more offspring, the clearest indicator of evolutionary benefit. An association with a greater number of offspring was also observed among BCS70 when bullies and nonbullies were compared prior to matching. Bullies in the TRAILS sample engaged in sexual behavior earlier than nonbullies. Whereas early sex tends to be seen as risk behavior in developmental terms, it widens the span of years for reproduction and is thus considered beneficial from an evolutionary perspective. In this regard, the TRAILS results match those for NCDS and the unadjusted ones for BCS70.

It is worth keeping in mind that it might not be bullying in and of itself that conveys a reproductive advantage but that unexamined third variables explain both. Life-history theory, for instance, would suggest that traits and behaviors that represent fast life strategy and allocation of resources to reproduction increase someone’s likelihood to bully others as well as lower age at first sex and more offspring. A life-history perspective would also explain long-term links between bullying and the other outcomes examined in this study as individuals following a fast life-history strategy allocate resources to reproduction rather than somatic fitness. Bullies might forego good health in order to reap reproductive benefits, which is ultimately adaptive because transmission of genes is more important in an evolutionary sense than being healthy in old age. As such, negative health outcomes for bullying perpetrators would not necessarily mean that bullying is not at all adaptive because reproducing early and manifold is more important than preserving good health. A reproductive-versus-somatic trade-off would explain why bullying perpetrators enjoy greater reproductive success but suffer from worse health later on. Unfortunately, NCDS is the only cohort in our study where reproductive activity can be assumed to be more or less concluded, certainly among the female participants. If indeed the number of offspring is also higher among bullying perpetrators in BCS70 once this cohort has completed reproduction, that is, if NCDS results are replicated in another cohort, it would be interesting to study whether bullies who had more offspring are worse off in terms of health; thus whether short-term benefits in favor of long-term costs can be observed.

Perspectives on bullying that are not informed by evolutionary theory would suggest that bullying perpetration and earlier sex—for which we found a link in TRAILS—are both expressions of externalizing maladjustment, a view that in our data is supported by the higher levels of child psychopathology among bullies than nonbullies. Age at first sex and the bullying perpetration assessment will have been temporally closer to one another than bullying and some of the other outcomes in TRAILS, which underlines the possibility that both are concurrent expressions of an underlying construct such as externalizing behavior. It will be important to follow up on the BCS70 and TRAILS participants at an age similar to that of NCDS participants now to see whether divergent results across the samples used here indicate unstable, nonreplicable associations or have substantive meaning.

One might doubt whether are earlier age at first sex and number of partners and children are meaningful indicators of success and advantage in contemporary Western societies where slow life strategies dominate (Twenge & Park, 2019). At least within the developmental literature on adolescence and young adulthood, having many partners is considered an expression of maladjustment and risky sexual behavior and promiscuity in adulthood is often seen as a symptom of psychopathology. Contextual conditions might also be implicated in this link, such as norms in the peer group that favor both bullying and risky sexual behavior. Though this perspective suggests that it is not meaningful to study number of partners and children as solely positive outcomes, they still indicate reproductive success in an evolutionary sense. In other words, what is adaptive in an ultimate sense (maximized reproduction) might not be desirable in a proximate sense, given the stigma attached to families with greater number of offspring and societal norms surrounding numbers of sexual partners.

Limitations

Perhaps the most substantial limitation of this study is the bullying perpetration measurement. Though it is remarkable that researchers assessed bullying when child psychology had hardly picked up on the topic and its negative developmental outcomes, single-item assessments are clearly not optimal. Parents and teachers have a limited view on who engages in bullying (Ahn, Rodkin, & Gest, 2013) – and will have had so even more at a time when bullying did not receive the attention from educational policymakers and media as it does today. As a consequence, measures of bullying in NCDS and BCS70 might lack validity and will also not have included nonovert forms of bullying. Moreover, bullying by popular, high-status adolescents might not have been viewed by adults as the destructive behavior it is for victims and noninvolved peers and parents might generally be unaware of the behavior of their children at school unless informed and might have responded with other target of bullying in mind. Of note, however, the proportion of bullying perpetrators in NCDS and BCS70 is similar to that found in studies that used multi-item self-report measures (Espelage, Van Ryzin, & Holt, 2018). Moreover, whereas more recent studies provide participants with a definition of bullying that ideally encompasses its different dimensions (Kaufman, Huitsing, & Veenstra, 2020) such detail was not provided to the three samples on which our analyses are based. It might thus be that the outcomes only hold for perpetrators who engage in visible, direct forms of bullying behavior, such as physical and verbal bullying. Next to using bullying information from different reporters in TRAILS versus NCDS and BCS70, assessments were also done at a slightly younger age in TRAILS. Bullying is related to status more so in adolescence than in childhood which might have meant that associations with outcomes would be more pronounced in the cohorts where the assessment was conducted in mid- rather than early adolescence.

It could also be argued that what we conceptualized as bullying is actually general aggression, or understood by parents and teachers in NCDS and BCS70 as tapping into aggression more generally. Both bullying and aggression are used strategically to obtain social dominance to control resources (Hawley, 1999) and to increase reproductive success (Lindenfors & Tullberg, 2011; Vaillancourt, 2005). As such, the evolutionary propositions would to some extent be similar but lower health in adulthood would be expected for aggressive behavior and not necessarily, from an evolutionary perspective, for bullying perpetration, even though bad health might be acceptable in light of successful reproduction. We corrected for childhood psychopathology to account for this at least partly.

Next to the use of a single item to measure bullying, the present study should be interpreted in light of other methodological challenges: First, attrition was selective and, across samples, bullying perpetration predicted missing data on outcomes. Whereas multiple imputation provides a more advanced way to deal with missing data than case deletion or mean imputation, it would be important to see whether the results hold on more complete data.

Second, we dichotomized ordinal bullying perpetration scores for NCDS and BCS and proportion scores for TRAILS. This was done to harmonize bullying perpetration measures as much as possible across samples, avoid skewed distributions, and to enable the matching procedure but also meant a loss of information. We chose cutoff scores for dichotomization in a way that would return reasonably comparable group sizes and applied this strategy also to victimization and popularity. It is not optimal that these cutoffs are therefore based on methodological rather than substantive considerations. One might ask whether results would have looked different if only those individuals with more extreme scores would have been included in the bully matching group. It is feasible that associations would be more pronounced (even worse health outcomes, more partners, more children) but this would have led to a vastly smaller group than its counterpart (nonbully), which would have increased the risk for model instability.

Third, the matching procedure allowed for a range of relatively subjective decisions, for instance between fixed and variable ratio matching and with respect to pruning (e.g., more pruning leads to better matching but to smaller samples). As developmental researchers increasingly use advanced methods, close collaboration between developers of such analyses packages and applied researchers is needed to ensure user friendliness and correct application.

Fourth, three samples from different periods were included which means that differences in effects might be explained by cohort effects. NCDS represents the first generation to grow up with the birth control pill being widely available but maybe not yet as accepted across all groups in the UK population. Tentatively, this might mean that number of children was less controlled by women in this cohort than in BCS70 and TRAILS. Similarly, covariates such as SES might have exerted a different influence on outcomes on those from the earlier compared to later-assessed cohorts and childhood psychopathology might have carried a greater stigma in the older cohorts.

Fifth, differences in measurement across the cohorts, and especially for TRAILS in comparison to NCDS and BCS70, might explain discrepancies in results. An example for this is the health assessment, which was kept broad in NCDS and BCS70 but referred explicitly to physical health in TRAILS. Another example concerns the number of partners, which reflects number of partners with whom the participant has cohabited for at least 1 month in NCDS and BCS70 whereas this variable refers to number of sexual partners in TRAILS. The former represents an imperfect assessment from an evolutionary standpoint, where number of sexual partners would have been the preferred measure. The value of the British cohorts in terms of length and inclusion of a bullying assessment long before the topic entered the mind of researchers, however, outweigh this limitation in our view.

Sixth, our central aim was to test Volk’s hypothesis of bullying as evolutionary adaptation (Volk et al., 2012) and we selected three cohorts where outcomes were assessed at different ages. Whereas we examined moderation by popularity and victimization – assessed at the same time as bullying perpetration, we did not explore potential mechanisms that might carry the effects of adolescent bullying into (late) adulthood. Our reasoning implicitly suggested that bullies retain a high status, but this remains to be tested. Another possibility might be that bullies who are successful in dating in adolescence and early adulthood build up and retain self-confidence when it comes to establishing sexual relationships and are able to build larger social networks which again adds opportunities to meet a potential (sexual) partner. Adolescents who frequently change their dating partners might settle down later and thus accumulate a greater number of partners even into adulthood. At present, the lack of longitudinal studies on stability of bullying status hinders any rigorous testing of such mechanisms. In a similar vein, it is difficult to derive immediate practical implications from the findings presented here. Naturally, bullying prevention needs to remain on the agenda even if only for victims, who carry the greatest plight. Reducing bullying in schools, however, will hardly eradicate evolutionary advantages for high-status individuals and high status among adolescents is linked to aggressive behavior. From a life-history strategy perspective, one might want to attempt to reduce antecedents for fast life strategies, such as growing up in harsh and unpredictable environments (Belsky, Schlomer, & Ellis, 2012), but it is somewhat doubtful that these are tasks for antibullying pre- and intervention programs. In that sense, the results of this study should be seen as furthering our understanding of long-term correlates of bullying but cannot immediately be translated into policy or practical implications.

Finally, we preregistered analyses but realized that not all premade analytic decisions were optimally suited. For instance, we intended to follow previous conceptualizations of bullying perpetration in TRAILS (Veenstra et al., 2005) but discovered that this would lead to too few bullying perpetrator cases to meaningfully use in matching. Moreover, we had not anticipated that so few children had been born to TRAILS participants yet, which made analyses with number of children as a count variable unreliable. These deviations from the preregistration highlight that some decisions are easier when the data are known.