Global-scale changes in the area of atoll islands during the 21st century: Since 2000, land area on 221 atolls examined had increased by 61.74 km2 (6.1 %); most of the increase in land area occurred in the Maldives & South China Sea

Global-scale changes in the area of atoll islands during the 21st century. Andrew Holdaway, Murray Ford, Susan Owen. Anthropocene, Volume 33, March 2021, 100282. https://doi.org/10.1016/j.ancene.2021.100282

Highlights

• Since 2000, land area on 221 atolls examined had increased by 61.74 km2 (6.1 %).

• 153 atolls increased in size and 68 decreased in size between 2000 and 2017.

• Most of the increase in land area occurred in the Maldives and South China Sea.

• Land reclamation was primarily responsible for land area increases on atolls.

Abstract: The long-term persistence of atoll islands is under threat due to continued sea level rise driven by anthropogenic climate change. One widely discussed potential impact of sea level rise is the widespread, chronic erosion of atoll islands. Despite concerns of erosion driven by sea level rise, no published evidence exists of pervasive erosion of atoll islands at a global scale. Existing studies of atoll island change have been based on small, temporally sparse samples of islands on a limited number of atolls. As a result, the global response of atoll islands coincident with sea level rise remains uncertain. Using rich collections of Landsat imagery, this study analyses changes in land area on 221 atolls in the Indian and Pacific Oceans. Results show that, between 2000 and 2017, the total land area on these atolls has increased by 61.74 km2 (6.1 %) from 1007.60 km2 to 1069.35 km2. Most of the change in land area resulted from island building within the Maldives and on atolls in the South China Sea. Since 2000, the Maldives have added 37.50 km2 of land area, while 16.57 km2 of new islands have appeared within the South China Seas Spratly and Paracel chains. Understanding the extent of land area change at the global scale improves insights into the variation in responses, and how the manipulation of land is shaping the potential habitability trajectory for some atoll communities. Results highlight the anthropogenic imprint on the size of atoll islands, thereby providing a better understanding of variations in the future trajectories of human settlement and adaptation within atoll settings.

Keywords: Atoll islandsErosionSea level riseIsland buildingLand reclamation

5. Discussion

5.1. Global scale island change

This study has examined, for the first time, land area change on atolls at a global-scale. The study measures land area change in the major atoll nations including the Maldives, Marshall Islands, Kiribati and Tuvalu, as well as large numbers of atolls in Micronesia and French Polynesia. This examination of island change covers a spatial extent far greater than previous efforts to monitor land area change on atolls, which have not exceeded ten atolls in any given study (Table 1). Likewise, by utilising Landsat imagery, we resolved land area changes occurring at larger time intervals than in previous studies.

Results from this study showed that, at a global-scale, no major reduction has occurred in total landmass on atolls in the Pacific and Indian Oceans. To the contrary, due primarily to the construction of artificial islands, considerably more land on atolls is present now than in the year 2000, an increase of 61.74 km2. This increase represents an area over twice as large as the entire land area of the nation of Tuvalu. Most of the increase in land area resulted from the construction of islands on a small number of atolls in the Maldives and South China Sea (SCS) (Figs. 4 & 5). When we exclude the ten atolls with the largest land area increases, all of which are in the South China Sea and Maldives and showed evidence of island building, we noted only a 19.59 km2 increase in land area. Of those 211 atolls, the average increase in land area was 0.09 km2, with a median value of 0.03 km2 per atoll. When we excluded the atolls in the South China Sea and considered all other atolls in the Pacific Ocean, we saw a 6.00 km2 increase, with a per atoll average increase of just 0.04 km2 with a median value of 0.01 km2. Our results showed that, aside from atolls that are heavily engineered, the land area on most atolls has been stable with no evidence of loss over the study period. This observation is consistent with recent studies that have also shown a predominantly stable or accretionary trend in the area of atoll islands worldwide (McLean and Kench, 2015; Duvat, 2019).

5.2. Reclamation and Island building

The most significant total changes to the planform area of atoll islands have resulted from local-scale land reclamation and island building in the Maldives and South China Sea, which we observed before, during and after construction in our record. The observations of island building on atolls is consistent with remotely sensed observations of coastal cities worldwide, where land reclamation has been widely adopted as an approach to increase land availability relatively efficiently (Sengupta et al., 2018; Tian et al., 2016; Chee et al., 2017), underpinned by extensive investment to economic and political agendas.

Within the South China Sea, widespread and rapid island building has occurred to support the construction of military bases (Barnes and Hu, 2016; Asner et al., 2017). Examination of two separate island chains within the South China Sea (Spratly Islands and Paracel Islands) showed that the Spratly Islands underwent a rapid increase in area between 2014 and 2016, with 14.70 km2 land added over this period. The increase largely resulted from the construction centred on Mischief, Fiery Cross and Subi Reefs, where 6.14 km2, 2.82 km2 and 4.29 km2 of land has been added respectively. The land area in the Paracel Islands increased steadily between 2000 and 2017, with planform land area increasing from 8.00 km2 to 9.86 km2. Much of this growth has been the result of >1km2 of reclamation on Woody Island. Island building in the Maldives, which eclipses the amount constructed in the South China Sea by 37.50 km2 to 16.57 km2, has been to provide additional land for the local population and to expand tourism facilities and associated infrastructure, such as airports (Fallati et al., 2017). More recent observations, outside of our study period, show large islands under construction on South Malé atoll, which appear likely to add >2 km2 of land.

5.3. Implications of island building

The majority of atolls examined in this study are sparsely or unpopulated atolls. They have little existing or likely future large-scale construction similar to that observed in the Maldives and South China Sea. That atoll nations have demonstrated the desire and ability to manipulate densely populated urban atoll islands is evident, however, to foster economic growth and in cases adapt to sea level rise. For example, island building in the Maldives has, in places, been designed not only to increase the planform area of the islands, but also to raise the land levels to potentially mitigate future impacts of sea level rise (Brown et al., 2020). In the case of Hulhumalé, an artificial island in the Maldives with a population of ∼17,000, incorporating future sea level rise as a design criterion was deemed economically viable, with revenue generated from sales of real estate likely to cover the costs of construction (Bisaro et al., 2019). Similar planning to expand an island and build vertically are underway on Tarawa Atoll, the most populated atoll in Kiribati, with a proposal to building a raised section of island, ∼300 ha in size, to accommodate 35,000 residents and withstand two meters of sea level rise (Walters, 2019). Raising existing islands equally poses unique challenges and additional costs, however, relative to constructing new islands (Brown et al., 2020), and may result in unanticipated maladaptive trajectories.

5.4. Monitoring future islands using remote sensing

We showed that freely available imagery and processing and classification techniques within a cloud-based analytical platform can detect massive changes of atoll island planform area over the 21st century. We caution, however, that small-scale changes in atoll area, the styles of which are often detected using local-scale assessments, are unlikely detectable accurately using this approach. Consequently, our approach does not replace existing island-scale assessments of changes needed to inform local-scale coastal management and climate adaptation strategies. Rather, findings of this study represent a promising avenue for a systematic global-scale program for monitoring changes in atoll islands that can better inform where high-resolution monitoring might be necessary. Our approach is highly automated and uses freely available imagery and analytical toolsets. Similar efforts using Landsat imagery have been employed at a global scale to monitor changes in global surface water, forest cover and shoreline change (Hansen et al., 2013; Pekel et al., 2016; Luijendijk et al., 2018). The accuracy of our classification is quite high, however, given the pronounced difference between land and sub-tidal land cover classes. This accuracy arises because, with the 30 m resolution, even a small number of misclassified pixels can greatly affect the relative changes in atoll landmass, particularly on smaller atolls. Our approach is consistent across space and time, enabling comparison between the rates of change within different atoll chains, which at present is problematic due to the fragmentary nature of small-scale high-resolution studies.

Higher self-perceived attractiveness & fewer minor ailments predicted lower scores of Somatization, Obsessive–Compulsive, Interpersonal Sensitivity, Depression, Anxiety, Phobic Anxiety, Paranoid Ideation, Psychoticism

Self-Perceived Facial Attractiveness, Fluctuating Asymmetry, and Minor Ailments Predict Mental Health Outcomes. Javier I. Borráz-León, Markus J. Rantala, Severi Luoto, Indrikis A. Krams, Jorge Contreras-Garduño, Tatjana Krama & Ana Lilia Cerda-Molina. Adaptive Human Behavior and Physiology, Aug 31 2021. https://rd.springer.com/article/10.1007/s40750-021-00172-6

Abstract

Objective  Phenotypic markers associated with developmental stability such as fluctuating asymmetry, facial attractiveness, and reports of minor ailments can also act as indicators of overall physical health. However, few studies have assessed whether these markers might also be cues of mental health. We tested whether self- and other-perceived facial attractiveness, fluctuating asymmetry, and minor ailments are associated with psychopathological symptoms in a mixed sample of 358 college students, controlling for the effects of body mass index, age, and sex.

Methods  We applied the Symptom Checklist-90-Revised (SCL-90-R) questionnaire to assess psychopathological symptoms, a battery of questionnaires about self-perceptions of facial attractiveness, and gathered information about the number of previous minor ailments as well as demographic data. Other-perceived attractiveness was assessed by an independent mixed sample of 109 subjects. Subjects’ facial fluctuating asymmetry was determined by geometric morphometrics.

Results  The results revealed that in both men and women, higher self-perceived attractiveness and fewer minor ailments predicted lower scores of Somatization, Obsessive–Compulsive, Interpersonal Sensitivity, Depression, Anxiety, Phobic Anxiety, Paranoid Ideation, Psychoticism, and a General Psychopathology Index. Higher facial fluctuating asymmetry was associated with higher Interpersonal Sensitivity, but did not contribute to its prediction when controlling for the other studied variables.

Conclusions  The observed strong associations between self-perceived attractiveness, minor ailments, and psychopathology indicate common developmental pathways between physiological and psychological symptomatology which may reflect broader life history (co)variation between genetics, developmental environment, and psychophysiological functioning.

Discussion

This research assessed whether facial FA measurements, perceptions of attractiveness, and reports of minor ailments are associated with mental health through a lower occurrence of psychopathological symptoms in a mixed sample of young adults. The results indicated that in both men and women, higher self-perceptions of facial attractiveness and fewer minor ailments predicted lower scores of Somatization, Obsessive–Compulsive, Interpersonal Sensitivity, Depression, Anxiety, Phobic Anxiety, Paranoid Ideation, Psychoticism, and the General Psychopathology Index. Higher facial fluctuating asymmetry was associated only with higher Interpersonal Sensitivity, but did not contribute to its prediction when controlling for the other studied variables.

The observed strong associations between self-perceived attractiveness, reports of minor ailments, and mental health outcomes in both sexes support and extend previous results on the relationship between phenotypic indicators of attractiveness and developmental psychopathologies (e.g., Ehlinger & Bashill, 2016). According to previous literature, perceived high attractiveness is associated with higher physical fitness (Hönekopp et al., 2004), greater reproductive success (Singh, 1993), better social competence (Eagly et al., 1991), better immune function (Luoto et al., 2021), and good self-esteem (Bale & Archer, 2013; but see Mares et al., 2010). This would explain why, in the present study, higher self-perceptions of attractiveness contributed to the expression of lower psychopathological symptoms.

Although the relationships between minor ailments and mental health have not been tested in these previous studies, our results suggest that both self-perceived attractiveness (as a result of genetics, developmental environment, and previous sociobiological interactions) and minor ailments (as indicators of general health) could be cues of mental health in men and women. Thus, the present findings build on previous literature by going beyond the use of questionnaires to evaluate mental health by integrating phenotypic traits and markers of general health. This approach allows establishing a more holistic understanding of the variables that play a role in the development of psychopathological symptoms that might also be involved in the development of mental disorders. Moreover, even though our study did not aim to test the association between LH strategies and mental health outcomes, our results suggest that LH dynamics might be associated with the expression of physically attractive traits and mental health outcomes through environmental disturbances that affect resource allocation during the development of an individual (cf. Kahl et al., 2020; Kavanagh & Kahl, 2018; Luoto et al., 2021). Further research may benefit from integrating phenotypic indicators of attractiveness and markers of general and mental health with LH theory to test how these variables are predicted by LH strategies and/or experienced harshness/unpredictability.

The impact of innate attractiveness on social interactions during development is evident very early in life, even before other traits like musculature, sports ability, or dominant behavior (Bobadilla et al., 2013). For example, Langlois et al. (1995) observed that mothers of attractive infants were more prone to be emotional and playful with them. In contrast, the opposite effect was observed with less attractive infants. Likewise, Cash (1980) reported that observers and parents gave better ratings on behavior, health, and intelligence to attractive infants than less attractive ones. Other studies have found that less attractive children had higher probabilities of being physically abused and treated less favorably by teachers than more attractive ones in preschool years (Sweeting & West, 2001). Thus, lower self-perceived attractiveness could be associated with stressful social situations in the early stages of life, a risk factor that contributes to the development of psychopathological symptoms in later years (e.g., Doom & Cicchetti, 2018; Eisenbarth et al., 2019). However, based on these studies, it is not possible to disentangle correlation from causation, and other latent variables—some of which may be endogenous rather than exogenous—may be driving the association between attractiveness and the nature of social experiences.

Stressful life events and limited resource availability contribute to impaired health and immune function in children and adolescents (Dunkel et al., 2020; Kim et al., 2020; Schmeer et al., 2019; Wickrama et al., 2005; Yiğit et al., 2018). For example, children born in socioeconomically disadvantaged families had higher probabilities to have developmental impairments due to the inability to provide proper nutrition, vaccination, and adequate access to health care (Krams et al., 2019; Lauringson et al., 2020; Rubika et al., 2020). Likewise, children from unstable family environments are more likely to develop fast LH strategies which can contribute to the development of higher psychopathological symptoms (Hurst & Kavanagh, 2017; Kahl et al., 2020). Chronically stressful life experiences and/or lack of resources may exert deleterious effects on biological functioning (Luoto et al., 2021) that could be translated into a higher number of minor ailments and fast LH strategies that, based on our results, would contribute to the prediction of psychopathological symptoms (Hurst & Kavanagh, 2017; Schmeer et al., 2019; Wickrama et al., 2005). Thus, this previous literature supports the view of self-perceived attractiveness and minor ailments as outcomes of mental health, rather than the other way around. However, it is also possible that perceptions of attractiveness, minor ailments, and mental health can be mutually influenced and/or be connected by a latent variable, such as genetic heritability and covariation between those traits. As another possibility, previous studies have reported that some mental disorders such as depression and bipolar disorder are associated with low-grade neuroinflammation (Rantala et al., 2018, 2021). This low-grade neuroinflammation and the increase of proinflammatory cytokines may reduce the bioavailability of neurotransmitters such as serotonin, norepinephrine, and dopamine (Miller, 2009), leading to low mood and sickness behavior that may promote a warped self-image and, probably, lower self-perceptions of attractiveness (Rantala et al., 2019).

On the other hand, even though we found that facial FA—a physical trait related to apparent health and developmental stability (Stephen & Luoto, 2021)—was positively correlated with Interpersonal Sensitivity scores, the effect size was low (r = 0.105) as most of the previous studies have reported (e.g., Borráz-León & Cerda-Molina, 2015; Pound et al., 2007). Facial FA was not correlated with any of the other psychopathological dimensions. Thus, it is possible that facial FA is more related to indicating an optimal developmental environment rather than mental health both in humans and non-human animals (Borráz-León et al., 2017b; De Anna et al., 2013; Luoto et al., 2021). However, it is noteworthy that the present research partially replicates and extends previous results (e.g., Shackelford & Larsen, 1997; Thornhill & Møller, 1997) on the relationship between facial FA and psychophysiological stress, with the advantage of using statistical analyses beyond a bivariate correlational approach, a more reliable technique for calculating facial FA (Fink et al., 2005), and a higher sample size (i.e., three times higher) than in previous research (e.g., Shackelford & Larsen, 1997).

It is also possible that insults from poor developmental environments may contribute to a dysregulation of physiological systems (e.g., the hypothalamic–pituitary–adrenal axis) affecting the development of symmetrical traits and contributing to altered cortisol responses and higher stress perceptions (Borráz-León et al., 2017b), which, in turn, would affect mate value, attractiveness, and health indicators (Borráz-León et al., 2017a; Rantala et al., 2019). In contrast, self-perceived attractiveness could be more directly related to mental health. This hypothesis is in line with the multiple fitness model (Cunningham et al., 1995) which proposes that perceived physical attractiveness results from the evaluation of multiple features rather than a single one, signaling different aspects of mate value (Little et al., 2006; Luoto, 2019; Miller & Todd, 1998; Stephen & Luoto, 2021). Thus, our results suggest that self-perceived attractiveness and number of previous ailments may not only signal general health, thereby affecting sexual selection processes, but that they may also covary with mental health outcomes.

Limitations

It is possible that our findings arose from response bias covariance since SCL-90-R is a self-rating instrument and its accuracy relies on correct interpretation of questions, which is susceptible to denial, minimization, and bias mechanisms (Eisen et al. 1999). Nevertheless, a moderate-to-high reliability and internal consistency of the SCL-90-R have been reported in the literature (e.g., Otte et al., 2017), including in this study. The αs of the psychopathological symptoms range from 0.76 to 0.81, which reduced the probability of bias in the responses.

Another possible limitation of this study is that we did not measure self-esteem in our sample. Since self-esteem tends to be associated with positive social outcomes (e.g., Borráz-León et al., 2018, 2019b; Harris & Orth, 2020), and since higher self-perceived attractiveness predicted lower psychopathological symptoms in our sample, it is possible that mechanisms such as low self-esteem, warped self-image, and adverse childhood experiences, which could be driven by psychopathology, could lead to lower self-perceived attractiveness and impaired mental health (cf. Rantala et al., 2019).

As this study was conducted only on university students, further studies with more heterogeneous samples are needed to increase the generalizability of the results, as well as to investigate the role of self-esteem as a mediator in the associations between self-perceived attractiveness and psychopathological symptoms. Based on these data, we are unable to verify the direction of causality between self-perceived attractiveness, minor ailments, and psychopathological symptoms, or whether latent variables underlie these associations.

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.