From 2016... Establishing a link between sex-related differences in the structural connectome and behaviour

From 2016... Tunç B et al. 2016. Establishing a link between sex-related differences in the structural connectome and behaviour. Phil. Trans. R. Soc. B 371:20150111. http://dx.doi.org/10.1098/rstb.2015.0111

Recent years have witnessed an increased attention to studies of sex differences, partly because such differences offer important considerations for personalized medicine. While the presence of sex differences in human behaviour is well documented, our knowledge of their anatomical foundations in the brain is still relatively limited. As a natural gateway to fathom the human mind and behaviour, studies concentrating on the human brain network constitute an important segment of the research effort to investigate sex differences. Using a large sample of healthy young individuals, each assessed with diffusion MRI and a computerized neurocognitive battery, we conducted a comprehensive set of experiments examining sex-related differences in the meso-scale structures of the human connectome and elucidated how these differences may relate to sex differences at the level of behaviour. Our results suggest that behavioural sex differences, which indicate complementarity of males and females, are accompanied by related differences in brain structure across development. When using subnetworks that are defined over functional and behavioural domains, we observed increased structural connectivity related to the motor, sensory and executive function subnetworks in males. In females, subnetworks associated with social motivation, attention and memory tasks had higher connectivity. Males showed higher modularity compared to females, with females having higher inter-modular connectivity. Applying multivariate analysis, we showed an increasing separation between males and females in the course of development, not only in behavioural patterns but also in brain structure. We also showed that these behavioural and structural patterns correlate with each other, establishing a reliable link between brain and behaviour.



Check also Multifaceted origins of sex differences in the brain. Margaret M. McCarthy. Phil. Trans. R. Soc. B Vol. 371, Issue 1688, February 19 2016. https://doi.org/10.1098/rstb.2015.0106

Abstract: Studies of sex differences in the brain range from reductionistic cell and molecular analyses in animal models to functional imaging in awake human subjects, with many other levels in between. Interpretations and conclusions about the importance of particular differences often vary with differing levels of analyses and can lead to discord and dissent. In the past two decades, the range of neurobiological, psychological and psychiatric endpoints found to differ between males and females has expanded beyond reproduction into every aspect of the healthy and diseased brain, and thereby demands our attention. A greater understanding of all aspects of neural functioning will only be achieved by incorporating sex as a biological variable. The goal of this review is to highlight the current state of the art of the discipline of sex differences research with an emphasis on the brain and to contextualize the articles appearing in the accompanying special issue.

But there is another window into the human brain and that is through the minds of boys and girls. Hines has discovered a robust sex difference in toy preference between boys and girls and has convincingly demonstrated over many studies that girls prenatally exposed to androgen owing to a genetic anomaly (congenital adrenal hyperplasia (CAH) girls) have a boy-like toy preference [30,31]. In this issue, Hines [32] makes another major leap forward in illuminating how androgens impact the developing human brain with evidence that CAH girls are less sensitive than unaffected girls to extraneous socialization cues about gender-appropriate toy-choices. Thus, rather than concluding that there is some undiscovered ‘prefers-dolls-nucleus' in the brain, her recent work demonstrates how children are differentially sensitive to socializing cues, so that girls become even more girl-like by modelling the behaviour of other females. In this way, the nature versus nurture conundrum is broken down with the realization that nature determines the response to nurture. Whether the converse is true for boys is not yet known.

Jinping Xi : Swift shift from collective leadership to strongman rule was the result of a widely shared consensus among China’s ruling elite that the regime was facing a severe crisis that necessitated a return to such rule

A Strong Leader for A Time of Crisis: Xi Jinping’s Strongman Politics as A Collective Response to Regime Weakness. Nimrod Baranovitch. Journal of Contemporary China, Jul 13 2020. https://doi.org/10.1080/10670564.2020.1790901

ABSTRACT: Seeking to explain the reasons for the swift shift from collective leadership to strongman rule during Xi Jinping’s early years in office, this article argues that it was the result of a widely shared consensus among China’s ruling elite that the regime was facing a severe crisis that necessitated a return to such rule. This argument challenges the widely held view that the dramatic centralization of power in Xi’s hands was the result mainly of his individual personality, motives, and actions. While many of the factual details that this article presents are not new, it is the first to systematically integrate many of these facts to create a coherent explanation of China’s surprising abandonment of the collective leadership model that goes beyond Xi’s individual role.

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How Strong Leaders are Made: A Combination of Structure and Agency

For many years, some Western experts and liberal Chinese intellectuals and reformist leaders have
urged China to adopt significant political reforms and promote democratization, arguing that this
was the only way that the country would be able to continue to develop and flourish and overcome
the many structural problems that it faced.70 However, as China’s politics under Xi Jinping demonstrates, for many Chinese and particularly among the majority of China’s top-level leaders, this option has obviously not been a desirable one. In fact, as one China observer has put it, the return to
strongman politics under Xi Jinping was actually a ‘return to a more normal political reality in
China’.71 Indeed, ironically, even many of the more liberal and reformist leaders in China of recent
decades have supported the notion of strong, authoritarian leadership, arguing that such leadership
is necessary to advance reform.72 Thus, the choice of the Chinese ruling elite to return to strongman
politics in a time of crisis should come as no surprise. After all, the tendency to centralize political
power in times of crisis is a well-known phenomenon and is certainly not unique to China. Many
dictators and less totalitarian strong leaders in world history have emerged and continue to emerge
in situations of national crisis. Moreover, as history has shown multiple times, in states of emergency,
even in democracies it is a norm, often anchored in the law, to concentrate more power in the hands
of the regime at the expense of citizens’ individual rights and liberties. In light of these general
tendencies, it should come as no surprise that the centralization of political power in a time of crisis
manifests itself in a more radical form in a non-democratic country like China that has always
preferred authoritative forms of government.
As the shift to personalistic rule under Xi Jinping seems to demonstrate, China’s ruling elite still
considered a strongman leader as the best mechanism to overcome the many challenges that their
country currently confronts. From the perspective of China’s political culture, a strong leader can
unite quarreling factions within the political elite by imposing his unchallenged authority. Very much
aware of this role, since he came to power, Xi has repeatedly criticized the cliques and factions within
the Party, and the continuing campaign against corruption that has been implemented under his
command has dealt powerful blows to both factions, signaling that he is above factional politics.73 As an all-powerful leader, Xi can also take decisive and drastic actions to radically transform
a problematic reality without the need to compromise or appease competing sources of power
and interest groups. Furthermore, a strong leader can also create a sense of security among an
anxious society and restore the legitimacy of the regime in the eyes of the public when this
legitimacy is challenged or eroded. Indeed, in authoritarian regimes, the charisma and popularity
of the top leader often serve as one of the regime’s main sources of legitimacy,74 especially in times
when other resources of legitimation are exhausted. In addition to all of these advantages, strong leaders can also project their personal power outward to deter external powers that already pose or
are about to pose a serious threat to their country.
The tendency in China to centralize political power seems to have been strengthened in recent
decades and even more so in recent years as a result of global events. As many of the sources cited in
this article illustrate, China’s leaders consider the collapse of the Soviet Union a disaster that took
place not only because the regime lost its legitimacy, but also because of political reforms and
because the leadership lost its faith in the dominant ideology and the political system. In a similar
vein, many Chinese look at the gloomy outcome of the Arab Spring in Syria, Libya, Egypt, and other
countries and see political chaos, civil war, mass death, and rising poverty, and they find nothing
attractive in this path of failed democratization.
It is quite possible that the return of strongman leadership to China would have taken place long
before Xi Jinping came to power. Favorable conditions for such a return were already in existence
during the years that followed the Tian’anmen crisis of 1989, when the Party’s legitimacy was at its
lowest point since the Cultural Revolution. Indeed, the ‘Mao Craze’ (毛热) that swept China in the
wake of the violent crackdown, during which the country saw a surge of popular nostalgia for the
deceased leader, reflected the yearning of the public and many conservative members of the ruling
elite for an all-powerful leader who would restore a sense of stability, order, and security.75 The
yearning for strong leadership was not confined to popular fads but was also manifested in several
policy changes. Indeed, in the early 1990s the Party retreated from all of former general secretary
Zhao Ziyang’s political reforms, and contrary to the practice that Deng Xiaoping promoted of
decentralizing power in the higher ranks of the Party, all of the three highest political positions
(Party general secretary, chairman of the CMC, and president) were given to Jiang Zemin. Moreover,
after promoting collective leadership for almost a decade, as an immediate reaction to the
Tian’anmen crisis, Deng himself seems to have realized that this model of leadership had its
limitations. Thus, although he did not eliminate collective leadership, already in June 1989 he
came up with the new concept of the ‘core leader’ in a clear attempt to consolidate the authority
of Jiang Zemin and thereby ensure elite cohesion.76
These changes notwithstanding, several conditions prevented the return of strongman leadership
at that time. These factors included the memory of the disastrous Cultural Revolution, which was
still too fresh, Deng’s resistance to such a renaissance and his insistence on proceeding with reforms,
and no less importantly, the fact that the new Party general secretary, Jiang Zemin, did not possess
the personal qualities that are needed to make a strongman leader. However, contrary to the
situation in the post-Tian’anmen years, in 2012/2013 all of the factors that prevented the return of
a strong leader two decades earlier had disappeared. The Cultural Revolution had practically been
forgotten, Deng Xiaoping was not around anymore, China was richer and more confident that
material prosperity could be achieved without political reform, and Xi Jinping had more charisma
than Jiang Zemin and Hu Jintao, as well as the other necessary personal qualities that are needed to
make a strong leader and which were mentioned in the beginning of this article. Xi was the right man
at the right time, and once he had the support of enough members of China’s ruling elite due to the
severe crisis that the regime was facing, the way was paved for China’s return to one-man rule.
However, while provisional elite support certainly helped empower Xi Jinping in his early years in
office, his moves and actions in recent years suggest that he has taken this opportunity and
consolidated and developed his strongman leadership to a degree that is perhaps beyond the
intentions even of those who supported him. It remains to be seen for how much longer Xi will be
able to hold so much power and still maintain his legitimacy and the broad elite support that he has
enjoyed until recently.

The Washington Consensus, 1970-2015: Despite the unpopularity of the Washington Consensus, its policies reliably raise average incomes; countries that had sustained reform were 16% richer 10 years later

The Washington Consensus Works: Causal Effects of Reform, 1970-2015. Kevin B. Grier, Robin M. Grier. Journal of Comparative Economics, September 8 2020. https://doi.org/10.1016/j.jce.2020.09.001

Highlights
• Sustained economic reform significantly raises real GDP per capita over a 5- to 10-year horizon.
• Despite the unpopularity of the Washington Consensus, its policies reliably raise average incomes.
• Countries that had sustained reform were 16% richer 10 years later.

Abstract: Traditional policy reforms of the type embodied in the Washington Consensus have been out of academic fashion for decades. However, we are not aware of a paper that convincingly rejects the efficacy of these reforms. In this paper, we define generalized reform as a discrete, sustained jump in an index of economic freedom, whose components map well onto the points of the old consensus. We identify 49 cases of generalized reform in our dataset that spans 141 countries from 1970 to 2015. The average treatment effect associated with these reforms is positive, sizeable, and significant over 5- and 10- year windows. The result is robust to different thresholds for defining reform and different estimation methods. We argue that the policy reform baby was prematurely thrown out with the neoliberal bathwater.

Keywords: ReformWashington ConsensusRule of lawProperty rightsEconomic development

Effects of the Black Death: Growth of Europe relative to the rest of the world, demise of serfdom in Western Europe, decline in the authority of religious institutions, and emergence of stronger states

Jedwab, Remi and Johnson, Noel D. and Koyama, Mark, The Economic Impact of the Black Death (August 18, 2020). SSRN, Aug 18 2020. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3689980

Abstract: The Black Death was the largest demographic shock in European history. We review the evidence for the origins, spread, and mortality of the disease. We document that it was a plausibly exogenous shock to the European economy and trace out its aggregate and local impacts in both the short-run and the long-run. The initial effect of the plague was highly disruptive. Wages and per capita income rose. But, in the long-run, this rise was only sustained in some parts of Europe. The other indirect long-run effects of the Black Death are associated with the growth of Europe relative to the rest of the world, especially Asia and the Middle East (the Great Divergence), a shift in the economic geography of Europe towards the Northwest (the Little Divergence), the demise of serfdom in Western Europe, a decline in the authority of religious institutions, and the emergence of stronger states. Finally, avenues for future research are laid out.

Keywords: Pandemics; Black Death; Institutions; Cities; Urbanization; Malthusian Theory; Demography; Long-Run Growth; Middle Ages; Europe; Asia
JEL Classification: N00; N13; I15; I14; J11; O10; O43

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Numerous scholars are interested in the emergence of the rule of law and “inclusive institutions” (e.g. Acemoglu and Robinson, 2012, 2019). One aspect of this is the protection of minorities. Finley and Koyama (2018) study the Black Death pogroms in the Holy Roman Empire and show that political decentralization and fragmentation was dangerous for minority groups: the fact that no one ruler had an encompassing interest in protecting Jews made violence more likely. Specifically, using data from Germania Judaica for the entirety of the Holy Roman Empire and covering 340 Jewish communities, Finley and Koyama (2018) construct an ordinal measure of pogrom intensity. They find that the persecution of Jews was more violent in communities governed by bishoprics, archbishoprics, and imperial free cities. Specifically, they had a 20-25% higher “intensity score” meaning that Jews in those cities were more likely to be “wiped out” or “killed in large numbers”. In contrast, Jews were less vulnerable in territories ruled either by the emperor or by one of the major secular electors. These findings suggest that in the absence of the rule of law, minority groups are better protected under an autocrat and that they are especially vulnerable when power is contested.

In addition to reported genetic and hormonal effects, there are cell type–specific sex differences in tissue composition

The impact of sex on gene expression across human tissues. Meritxell Oliva et al. Science  Sep 11 2020:Vol. 369, Issue 6509, eaba3066. https://science.sciencemag.org/content/369/6509/eaba3066

The role of sex in the human transcriptome
In humans, the inheritance of the XX or XY set of sex chromosomes is responsible for most individuals developing into adults expressing male or female sex-specific traits. However, the degree to which sex-biased gene expression occurs in tissues, especially those that do not contribute to characteristic sexually dimorphic traits. is unknown. Oliva et al. examined Genotype-Tissue Expression (GTEx) project data and found that 37% of genes in at least one of the 44 tissues studied exhibit a tissue-specific, sex-biased gene expression. They also identified a sex-specific variation in cellular composition across tissues. Overall, the effects of sex on gene expression were small, but they were genome-wide and mostly mediated through transcription factor binding. With sex-biased gene expression associated with loci identified in genome-wide association studies, this study lays the groundwork for identifying the molecular basis of male- and female-based diseases.

Structured Abstract
INTRODUCTION
Many complex human phenotypes, including diseases, exhibit sex-differentiated characteristics. These sex differences have been variously attributed to hormones, sex chromosomes, genotype × sex effects, differences in behavior, and differences in environmental exposures; however, their mechanisms and underlying biology remain largely unknown. The Genotype-Tissue Expression (GTEx) project provides an opportunity to investigate the prevalence and genetic mechanisms of sex differences in the human transcriptome by surveying many tissues that have not previously been characterized in this manner.

RATIONALE
To characterize sex differences in the human transcriptome and its regulation, and to discover how sex and genetics interact to influence complex traits and disease, we generated a catalog of sex differences in gene expression and its genetic regulation across 44 human tissue sources surveyed by the GTEx project (v8 data release), analyzing 16,245 RNA-sequencing samples and genotypes of 838 adult individuals. We report sex differences in gene expression levels, tissue cell type composition, and cis expression quantitative trait loci (cis-eQTLs). To assess their impact, we integrated these results with gene function, transcription factor binding annotation, and genome-wide association study (GWAS) summary statistics of 87 GWASs.

RESULTS
Sex effects on gene expression are ubiquitous (13,294 sex-biased genes across all tissues). However, these effects are small and largely tissue-specific. Genes with sex-differentiated expression are not primarily driven by tissue-specific gene expression and are involved in a diverse set of biological functions, such as drug and hormone response, embryonic development and tissue morphogenesis, fertilization, sexual reproduction and spermatogenesis, fat metabolism, cancer, and immune response. Whereas X-linked genes with higher expression in females suggest candidates for escape from X-chromosome inactivation, sex-biased expression of autosomal genes suggests hormone-related transcription factor regulation and a role for additional transcription factors, as well as sex-differentiated distribution of epigenetic marks, particularly histone H3 Lys27 trimethylation (H3K27me3).

Sex differences in the genetic regulation of gene expression are much less common (369 sex-biased eQTLs across all tissues) and are highly tissue-specific. We identified 58 gene-trait associations driven by genetic regulation of gene expression in a single sex. These include loci where sex-differentiated cell type abundances mediate genotype-phenotype associations, as well as loci where sex may play a more direct role in the underlying molecular mechanism of the association. For example, we identified a female-specific eQTL in liver for the hexokinase HKDC1 that influences glucose metabolism in pregnant females, which is subsequently reflected in the birth weight of the offspring.

CONCLUSION
By integrating sex-aware analyses of GTEx data with gene function and transcription factor binding annotations, we describe tissue-specific and tissue-shared drivers and mechanisms contributing to sex differences in the human transcriptome and eQTLs. We discovered multiple sex-differentiated genetic effects on gene expression that colocalize with complex trait genetic associations, thereby facilitating the mechanistic interpretation of GWAS signals. Because the causative tissue is unknown for many phenotypes, analysis of the diverse GTEx tissue collection can serve as a powerful resource for investigations into the basis of sex-biased traits. This work provides an extensive characterization of sex differences in the human transcriptome and its genetic regulation.


Check also Searching for sex differences. Melissa A. Wilson. Science  Sep 11 2020:Vol. 369, Issue 6509, pp. 1298-1299. DOI: 10.1126/science.abd8340

The behemoth effort, started a decade ago, known as the Genotype-Tissue Expression (GTEx) Consortium aims to discover how DNA variation affects gene expression across human tissues (1, 2). As part of this consortium, on page 1331 of this issue, Oliva et al. (3) find that more than one-third of genes show sex-biased expression in at least one tissue. Four other GTEx studies, on pages 1318, 1334, 1333, and 1332 of this issue, respectively, discuss the effects of gene regulation in human tissues (4), identify functional rare genetic variation (5), study predictors of telomere length (6), and report cell type–specific gene regulation (7). What is especially notable about Oliva et al. is the careful analysis, which revealed that in addition to reported genetic and hormonal effects (8), there are cell type–specific sex differences in tissue composition. Furthermore, their work highlights that rather than being strictly dimorphic, interindividual variation results in overlapping distributions of gene expression between the sexes.

Tattooed women perceive themselves as less attractive, & women's self-rated attractiveness impacts whether or not men's tattoos matter when judging attractiveness, trustworthiness, & potential as a father

Effects of gender, self-rated attractiveness, and mate value on perceptions tattoos. Karlyn Molloy, Danielle Wagstaff. Personality and Individual Differences, Volume 168, January 1 2021, 110382. https://doi.org/10.1016/j.paid.2020.110382

Abstract: Previous research has demonstrated that men's tattoos have an effect on viewer's perceptions, with tattooed men perceived as more attractive, masculine, aggressive, dominant, and healthy. However, little research has considered the effect of individual differences on perceptions of tattooed men, despite individual differences affecting mating efforts. In this study, we explored the effect of tattoo ownership on men's and women's perceptions of their own self-rated attractiveness and mate value, and explored the effect of tattoo ownership, self-rated attractiveness and mate value on the relationship between male stimuli tattoo level and eight character judgements. From a sample of 146 men and 299 women, we found that tattooed women perceive themselves as less attractive, and that women's self-rated attractiveness impacts whether or not men's tattoos matter when judging attractiveness, trustworthiness, and potential as a father. While some limitations are evident, this study expands on previous research, demonstrating that men's tattoo possession matters in the context of opposite-sex mating judgements, though may not be as important in judgements of same-sex rivals. Future research should explore the effect of varying tattoo size, style, and location, on perceptions of others.

Keywords: AttractivenessMate selectionBody modificationIndividual differences

4. Discussion

Our study aimed to investigate the extent to which tattoos alter social perceptions of both the self and others, taking into consideration individual differences, and expanding on previous research by Galbarczyk and Ziomkiewicz (2017), and Galbarczyk et al. (2019). This previous research neglected to take into consideration individual variation in tattoo ownership of the participants, nor their self-rated attractiveness and mate value, factors that could influence the judgment of traits important in a mating context. Furthermore, they included only one, small, tattoo on their stimuli.

We hypothesised that tattooed males would rate themselves higher in attractiveness and tattooed females lower in attractiveness than non-tattooed individuals.2Interestingly, men with and without tattoos rated themselves equally attractive. Thus, our study failed to replicate previous research findings (e.g., Swami, 2011). However, tattooed women rated themselves significantly lower in attractiveness in comparison to non-tattooed women, in line with previous research (e.g., Hill, Ogletree, & McCrary, 2016). Women, more so than men, are expected to maintain certain standards of appearance, therefore body pressures are often seen as feminine issues (Coffey, 2013). Despite an increase in popularity, tattoos still breach mainstream appearance norms, especially when the bearer is unable or unwilling to hide their tattoo and/or has numerous large tattoos (Irwin, 2003). Tattoos have traditionally been considered to be a man's activity (Dickson, Dukes, Smith, & Strapko, 2014), therefore women who have tattoos could be regarded as being gender-role violators, and thus are more likely to endure social stigma related to tattoo ownership (Swami & Furnham, 2007). These social pressures could account for decreased self-rated attractiveness ratings by women in our study. Despite the historical stigma, tattooed men have enjoyed greater social acceptance in comparison to tattooed women (e.g., Braunberger, 2000) which could account for null findings in attractiveness rating between tattooed and non-tattooed men.

Based on previous research, we hypothesised that women would rate tattooed male stimuli as more masculine, dominant, aggressive, healthy, and less suitable as a potential father and partner, and that men would rate tattooed stimuli as more attractive, dominant, masculine and aggressive than non-tattooed stimuli. We only found partial support for this hypothesis. Women did rate male stimuli with a tattoo as more masculine, in line with predictions, although men rated male stimuli with a tattoo as less masculine, in contrast to previous research. This difference may have been because of the nature of our tattoo manipulation. In our study, we used a rather large tattoo as the modification, and included three levels of tattoo, rather than the one small tattoo as in Galbarczyk and Ziomkiewicz (2017), and Galbarczyk et al. (2019). It may be that there is an upper limit to the size of tattoo that is perceived as most masculine on a male. For women, the medium-sized tattoo was rated as most attractive, while for male raters, no tattoo was most attractive. Hill et al. (2016) found larger tattoos elicit more negative judgment than smaller tattoos. Individuals with greater tattoo coverage are more likely to experience negative judgment, as increased tattoo expression can be interpreted as more deliberate, and therefore tattoo modification is more likely to be perceived as reflecting a person's character. A medium-sized tattoo may strike the best balance between positive and negative characteristics for women when judging men, so they perceive a medium sized tattoo as most masculine. Men may ascribe less positive characteristics to rivals who possess a medium or large-size tattoo, and so perceive a smaller tattoo as most masculine; however, we did not measure the effects of small tattoos in this study. Further, the tattoos we used in our study were not symmetrical, and symmetry may have had an impact on perceptions. Given the variations in the way that the tattoos are presented, between the variety of studies on tattoos, future research should aim to compare a variety of tattoo types, sizes, and locations, and determine what impacts these factors have on perceptions of people with tattoos.

The only other effect of tattoos had on perceptions of male stimuli was of the perceived ability to be a good father or partner, which decreased as tattoo size increased. Despite only predicting this would matter for women, we saw this change occur regardless of gender, implying men are also able to make value judgements of these characteristics in other men, which was not in line with Galbarczyk and Ziomkiewicz (2017).3 Again, this may have been due to the nature of the tattoo manipulation, implying that larger tattoos have a greater effect on viewer perceptions than a small tattoo. Given that health ratings also did not differ between stimuli, it is important to consider further the theory put forward that tattoos signal immunocompetence, which may not be relevant in the context of large tattoos. Future research should therefore explore the signalling value of various tattoo sizes in an opposite-sex mate attraction versus same-sex rival context.

When accounting for individual differences, we found no effects of stimulus tattoo level on men's ratings. Men who themselves had tattoos did rate the stimuli as more dominant, though no interactions with individual differences emerged, implying participant attributes had only a small effect on perceptions of potential rivals and the features of the rivals themselves had little to none. On the other hand, women's self-rated attractiveness interacted with stimulus tattoo level to affect ratings of attractiveness, trustworthiness, and potential as a father: three ratings that are important when judging a male as a potential romantic partner. Here, we found that as women's self-rated attractiveness increased, men's tattoos became more unappealing, with women rating male stimuli with larger tattoos as less attractive, and less capable as fathers. Further, women with low self-rated attractiveness showed a small but not significant preference for men with tattoos as more trustworthy. Human mate selection is mutual, with self-perceived attractiveness often used to estimate potential mate prospects (e.g, Todd et al., 2007). Given the sex difference in minimal parental investment, it is particularly important for women to weigh carefully the costs and benefits of engaging with any particular potential mate (Buss & Schmitt, 1993). Women who themselves rank high in the mating market (high attractiveness) can afford to be more choosy; whereas women lower in the mating market may have fewer options available (Conroy-Beam, 2018). In this case, mating with a male who potentially possesses more anti-social characteristics (as indicated by tattoo ownership) may be a preferable option. Interestingly, these results do not conform to the hypothesis put forward by Galbarczyk and Ziomkiewicz (2017) that men's tattoos serve as a signal that is more important in a rival context than a mate-attraction context. Here, we saw that male tattoo level had little impact on men's perceptions. On the other hand, women's self-evaluations influenced whether the stimulus features were important or not, which is in line with women's larger investment in offspring, and therefore reflect a cost-benefit analysis.

There are some limitations important to consider in this study. Firstly, we did not obtain as large a sample as Galbarczyk and Ziomkiewicz (2017), which may have limited the strength of the effects observed. That said, the researchers conceded that their effect sizes were small, and we were still able to observe differences in this study, though they were mostly between genders, rather than between tattoo sizes. We also performed a number of statistical analyses on this small sample, which inflates our chance of a Type I error, so we advise to take the results with caution. Secondly, we did not consider the impact of a small tattoo, and only looked at the difference between no tattoo and a medium or large tattoo. It may be that larger tattoos have qualitatively different effects on viewers' perceptions, and so research should explore the effect of varying tattoo sizes, as well as tattoo visibility, and their impact on perceptions. Some of the effects of tattoo size, and even the effects of tattoos in any study, may have more to do with the nature of the tattoo than of being tattooed, per se. Future research should endeavour to compare different tattoo sizes, styles, and symmetry/asymmetry, in order to reveal any nuances in the effect of tattoos on perceptions of others. One other thing which we did not consider in this study was the gendered nature of tattooing. Here, we proposed that tattoos serve a signal relevant in a male-signalling context, but women also possess tattoos. Future research should determine whether women's tattoos also serve a signal of immunocompetence, and what social signalling value women's tattoos possess, given tattoos appear to be associated with various masculine traits. With that said, this research was able to expand on the research of Galbarczyk and Ziomkiewicz, and Galbarczyk et al. (2019), demonstrating that women's individual differences affect their judgements of men with tattoos.