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Women Favour Dyadic Relationships, just Men Adopt Clubs: Cantankerous-Cultural Evidence from Social Networking

• Tamas David-Barrett,
• Anna Rotkirch,
• James Carney,
• Isabel Behncke Izquierdo,
• Jaimie A. Krems,
• Dylan Townley,
• Elinor McDaniell,
• Anna Byrne-Smith,
• Robin I. M. Dunbar

x

• Published: March sixteen, 2015
• https://doi.org/10.1371/journal.pone.0118329

Figures

Abstruse

The ability to create lasting, trust-based friendships makes it possible for humans to grade large and coherent groups. The recent literature on the evolution of sociality and on the network dynamics of human societies suggests that large homo groups have a layered construction generated past emotionally supported social relationships. At that place are also gender differences in adult social style which may involve unlike merchandise-offs between the quantity and quality of friendships. Although many accept suggested that females tend to focus on intimate relations with a few other females, while males build larger, more hierarchical coalitions, the existence of such gender differences is disputed and data from adults is deficient. Here, we nowadays cross-cultural prove for gender differences in the preference for close friendships. We use a sample of ∼112,000 profile pictures from nine earth regions posted on a pop social networking site to show that, in self-selected displays of social relationships, women favour dyadic relations, whereas men favour larger, all-male cliques. These apparently dissimilar solutions to quality-quantity merchandise-offs suggest a universal and central difference in the function of shut friendships for the two sexes.

Citation: David-Barrett T, Rotkirch A, Carney J, Behncke Izquierdo I, Krems JA, Townley D, et al. (2015) Women Favour Dyadic Relationships, merely Men Prefer Clubs: Cross-Cultural Testify from Social Networking. PLoS Ane ten(three): e0118329. https://doi.org/10.1371/periodical.pone.0118329

Academic Editor: Luo-Luo Jiang, Wenzhou Academy, CHINA

Received: April 12, 2014; Accepted: Jan 3, 2015; Published: March xvi, 2015

Copyright: © 2015 David-Barrett et al. This is an open admission article distributed under the terms of the Creative Eatables Attribution License, which permits unrestricted employ, distribution, and reproduction in whatever medium, provided the original writer and source are credited

Data Availability: All relevant data are within the paper and its Supporting Information files.

Funding: This report was supported past European union FP7 EINS grant understanding No 288021 to TDB, European Research Council Advanced grant to RD, EU Marie Curie Fellowship, grant understanding No 297854 to JC. The funders had no role in study design, data collection and analysis, conclusion to publish, or preparation of the manuscript.

Competing interests: The authors take alleged that no competing interests be.

Introduction

The recent literature on both the development of sociality and the network dynamics of man and fauna societies [ane–8] suggests that large social groups cannot be fully connected: they accept a layered structure that is generated by emotionally supported social relationships [nine–fifteen]. Although there are structural aspects to social organisation, private behaviour is crucially shaped past dyadic relationships. Information technology may be that preferred patterns of relationships vary past gender in a manner that typically reflects sex differences in reproductive strategies [16–19].

For instance, friendships or close and prolonged amalgamation with not-kin are characterised by homophily, so that people typically cull friends of the aforementioned historic period and gender (for recent reviews see [twenty–22]). Sex differences in reproductive strategies also shape adult social behaviour [20,23–26] and may reflect dissimilar trade-offs betwixt the quantity and quality of friendships. Thus, it has been suggested that females invest more than heavily in a few, high-quality and time-consuming friendships, while males prefer groups with less investment per member, and college grouping cohesion [27–30].

There is reason to believe these gender differences have evolutionary roots. Offset, sex differences in friendship emerge early [31], are quite apparent already in small children and appear to increase with age [21,32,33]. 2nd, similar gender patterns exist in some not-human being primates [13,34]. One obvious explanation is that male person peer sociality evolved to enable hunting, coalitionary back up for within-group potency, and/or defence in larger groups, while women'south peer sociality is to a greater extent shaped by their college investment in reproduction and child rearing, also as their historically more frequent feel of out-migration and the demand to integrate into a patrilocal gild with few, if any, kin [eighteen,xx,25]. Patrilocality is likewise the norm for chimpanzees and bonobos, lending further support to female person transfer being the norm throughout hominin evolution [35,36].

However, the scope of human gender differences is disputed. Several studies found few sexual practice differences in the number of shut non-related friends that an individual turns to for help and aid [four,37–42] while others observe crucial differences in the quantity and intensity of male and female peer ties [16,23,24,30,32,43–45]. Sexual activity differences also depend on which component of friendship is beingness studied, as well equally the historic period and civilization of the subjects. For example, the review by Rose and Rudolph [21] establish that girls have a greater preference for extended dyadic interactions and prosocial behaviour, while boys collaborate more than in peer groups with a loftier network density and clear potency hierarchy. But gender differences are negligible concerning the expectations males and females have of friends and in the symmetrical reciprocity they expect from them [22]. In any instance, documented sex differences tend to be pocket-sized or medium-size rather than big [22,46].

All reviews stress the need for more friendship inquiry on adults and on people from other than 'WEIRD' [47] societies [21,22,46]. About research on friendships has involved children or teenagers, and in that location is to date only limited and mixed evidence for gender differences in adult homo friendships [20,38,48–50]. Here, we use data from a social media site to explore gender differences in close peer relations. Nosotros hypothesised that social relations amid aforementioned-aged adults would exhibit gender homophily and would vary by gender, such that men would exhibit higher numbers of friends compared to women.

Methods and Data

To investigate close friendships in the ii sexes, we used Facebook Profile Pictures following the instance of contempo literature that deals with social networking data [51–54]. Facebook is the most popular global social networking site, the main part of which is to fulfil psychosocial needs for belonging and cocky-presentation [55]. Upon signing up, each user may cull a Profile Film, which represents the user to the rest of the Facebook community, is public, and appears at the top of the user's contour and as the icon adjacent to the user's proper name wherever he or she posts on the site. Each user tin have only one Profile Picture at a fourth dimension. Usually the picture features the user only. When the picture displays peers they tend to exist the user with friends or acquaintances [51]. The choice of profile pictures is related to the user's desired impression formation [55]. This impression is not, however, likewise detached from the real world: Facebook user profiles have been found to reflect actual rather than idealised identities [56]. We thus assume that Profile photographs of peers are probable to align with behavioural inclinations, and thus provide a reliable proxy for relationship preferences.

Data collection

We used random search terms to select 309 users (seeds) of Facebook who shared their batch of friends publicly. (The 309 users had on average 362 friends.) In the first wave of data drove, nosotros located the Contour Pictures of all the friends of each of these users (111,863 Profile Pictures in total); each photo was categorised with respect to the type of the picture, and the number and gender of the persons displayed (come across Table one). Data collection took place between July 2011 and January 2012.

Boosted data was collected in two farther waves. In the commencement of these (wave two), geographical data based on geographical location was collected to control for cultural differences. The coders were provided with a list of geographic regions: Europe (56 seeds), Central and South asia (16), Latin America (9), Eye Eastward and North Africa (14), North America (fourteen), South E Asia (43), Sub-Saharan Africa (vii), Commonwealth of australia (9), E Asia (nineteen), or 'tin can't tell region' (21). In the second (moving ridge three), we used a finer classification of the number of people shown in Profile Pictures: the first two waves classified all pictures with four or more individuals equally a single category, merely in wave iii this was extended to specify individual numbers upwardly to 20.

The coding was done by viii coders, all but two of whom were research administration at the University of Oxford. All coders bar i (the pb author) were blind during the coding phase, knowing just that the project was to written report gender differences on social networking sites. Coders were instructed to avoid whatever word of the project amidst themselves during the coding phase. All results presented in this paper are robust to the elimination of each of the coders, each of the regions, and the type of Profile Pictures displayed past the seeds.

Nosotros used just publicly available pictures. No pictures or other information associated with this research was either separately downloaded or stored. The inquiry projection was approved by the Central Academy Research Ethics Commission of University of Oxford, and each coder received a full inquiry ideals briefing before joining the coding team.

Data exclusion

As adult interpersonal processes were our focus hither, we excluded all Profile Pictures that contained a not-human figure, a infant or child, people of markedly different ages (every bit judged past the coders), pictorial collages (i.e. pictures composed of multiple, distinct or coloured photos), a person or people whose gender(south) were unidentifiable or that did non incorporate a person. 81,246 Contour Pictures remained, of which 19,984 (26%) contained more than than ane person. For an overview of the data see Fig. 1.

Fig i. The ratio of men in Contour Pictures (with same age adults only) every bit a function the number of persons in the moving picture.

The value corresponding to each n adds up to 1. The size of the disks denotes the share in the ratio at that item bin. Crossing points on the grid are the only possible points given the detached nature of the data.

https://doi.org/ten.1371/journal.pone.0118329.g001

Results

Gender homophily

First, we studied gender homophily in profile pictures. Every bit expected, if the Profile Pictures displayed three or more than persons (7.6% of Profile Pictures displaying adults), they tended to exist the same gender, confirming our gender homophily hypothesis (Fig. 1).

The gender ratio on Profile Pictures persons exhibited a tri-modal distribution (see Fig. two). In Profile Pictures with 5–12 persons, the frequencies for women-only, men-merely, and equal gender ratios are 15.5%, xl.6%, 15.7%. (Annotation that for n<5 the trimodality cannot exist, while for very large n the male person groups dominate to such an extent that merely one modality is left.) These are in a higher place the frequencies for all other combinations: pictures with both genders but unequally represented (such as i woman and two men) were significantly less mutual. Given that the population mean is approximately balanced, this finding suggests a strong gender homophily.

Fig 2. Relative frequencies of different gender ratios for groups where 5< = n< = 12.

The distribution shows a trimodal pattern with women-merely, gender-equal and men-only gender ratios significantly in a higher place naught.

https://doi.org/10.1371/journal.pone.0118329.g002

This preference for same-sex friends was further supported by the subsample that contains Contour Pictures displaying fewer than 5 people. While pictures with 2 persons showed a higher mixed than same gender frequency (sample average (2F+2M)/1F1M-one = -0.123 (bootstrapping mean -0.122 and due south.d. 0.044), likely indicative of pictures of romantic couples, both the 3-person pictures (sample average 2(3F+3M)/(1F2M+2F1M)-i = 4.34 (bootstrapping mean 4.36 and due south.d. 0.39) and the 4-person pictures (sample average 3(4F+4M)/(1F3M+2F2M+3F1M)-i = four.78 (bootstrapping hateful 4.75 and southward.d. 0.51) had a much higher aforementioned-gender frequency compared to mixed-gender frequency (Fig. 3A).

Fig 3. Bootstrap histograms.

Panel (a): the ratio of aforementioned gender Contour Pictures compared to mixed gender profile pictures (probability corrected); green, crimson, and blue lines correspond to n = ii, three, and 4. Panel (b): the number of people on a Profile Picture men (carmine) or women (blue) appear on; straight lines: aforementioned gender with due north between 2 and 4, dashed lines: mixed gender with n between 2 and four, dotted lines: mixed gender with n between 2 and xx. Panel (c): the ratio of the frequency of aforementioned-gender pictures between the genders; green: pictures with one person, red: two persons, dark-brown: 3 persons, and blue: 4 persons. (100,000 bootstrapping repeats.)

https://doi.org/10.1371/journal.pone.0118329.g003

Male propensity towards displaying more people

Studying the gender limerick of peer groups indicated that, when Contour Pictures display a big group of people, they tend to exist all male, which was in line with our expectations. In groups of three or 4 persons, men and women had the aforementioned propensity to announced in same-gender Profile Pictures (Table 1). Still, larger groups were predominantly male person, and increasingly so as the group size grows (Fig. 4).

Fig four. The ratio of same-gender women-only to men-only frequencies (nF/nM as function of n).

Greyness lines denote a one-standard-deviation band from bootstrapping. In a higher place n>4, men-only groups dominate, while women-only groups get extremely rare. The linear OLS coefficient of nF/nM as a function of n is negative, with R² = 0.86, and p<0.01

https://doi.org/10.1371/journal.pone.0118329.g004

The male propensity to be function of larger groups was further supported by the fact that men appear together with more people than practice women (Fig. 3B). For groups with two–iv peers of the same gender, men appeared in pictures with 2.47 people on (bootstrapping mean ii.47, due south.d. 0.01), equally opposed to two.35 of women (bootstrapping hateful 2.35, south.d. 0.01), which are significantly dissimilar from each other (p<0.0001). For groups with ii–20 peers of any gender, men appeared with two.xc (bootstrapping mean 2.ninety, s.d. 0.07), every bit opposed to two.54 of women (bootstrapping hateful 2.54, s.d. 0.05) which are also significantly unlike from each other (p<<0.0001). This suggests that independently of gender combinations and group size, men tend to appear with a larger number of people displayed in Profile Pictures.

Women focus on dyadic relationships

Finally, we detected an unexpectedly strong female person focus on same gender dyads. Women not only tended to appear in Profile Pictures displaying a smaller number of people, equally expected in the second research hypothesis, only there was also a strong preference towards pictures containing two women (Fig. 3C). There were 50.viii% more than pictures with two female person peers than pictures with two male peers (bootstrapping mean 51.v, s.d. xiv.8). This is especially remarkable given that same-gender pictures with one, 3, or four or more people had an well-nigh perfect gender balance: at that place were just six.4% more pictures with one woman just in our dataset than with one human being just (bootstrapping mean 7.2, with s.d. 14.ane), only 1.ane% more pictures with three women than with three men (bootstrapping mean 1.vii, s.d. x.8), and i.0% fewer pictures with four women compared to four men (bootstrapping mean 0.five, s.d. 12.5).

Cultural variation

Although in that location was substantial variation across the different world regions, the principal patterns of our findings were present in each of them(Fig. 5A-C), with only the magnitude of the effect varying. While a selection bias may theoretically have affected the relatively small local variation of our results, we discover this unlikely: the seeds were randomly selected and at the fourth dimension of the information collection 17% of the global adult population was using Facebook. Furthermore, measures for other than our three main findings reported above were less uniform among the earth regions (Fig. 5D).

Fig 5. Cultural variation in the main finding.

Panel (a): the ratio between same-gender and mixed gender pictures of unlike group size (corrected by the probability of appearance, meet text). Panel (b): number of close friends (aforementioned gender, with groups size 2 to four). Panel (c): the ratio between same-gender Profile Pictures every bit a function of group size (1F/1M normalised to 0). Panel (d): cultural variation in the proportion of unmarried person pictures within all Profile Pictures in a given global region. (Region codes of Panels a-c: green: Central and Due south Asia, blue: Europe, dashed blue: Latin America, dashed greenish: Middle East and North Africa, dotted blue: N America, dotted light-green: South-East Asia, reddish: Sub-Saharan Africa, black: Australia, dashed black: Eastern asia.)

https://doi.org/10.1371/periodical.pone.0118329.g005

Follow-Up Studies

It is possible that the relative prevalence of female-female person Profile Pictures in comparing to male-male ones may non reflect friendship behaviour simply either (a) a female person preference for putting upward pictures of 2 people of any gender, or (b) a reluctance among men to brandish pictures with two male friends, especially in regions where homophobia is mutual. We tested both of these alternative explanations.

Start, we tested whether there is a gender difference in the preference for Profile Pictures containing two people only. We randomly selected 960 new profiles on Facebook with two same-aged individuals on them. Out of the 960, we were unable to determine the gender of the account user in xi cases. Out of the remaining 949 cases, 493 pictures belonged to a man and 456 belonged to a woman. Given the fact that the overall Facebook participation gender ratio is almost counterbalanced, this upshot suggests that the probability of women having a strong preference to put upwards pictures of 2 people of any gender is negligible.

Second, nosotros tested if homophobia in the state where the seed owner of the Facebook account lived would affect the ratio between female person and male same-gender ii-person pictures. (To correct for the fact that unlike countries have different gender ratios amidst Facebook users, we used the (2F/1F)/(2M/1M)-1 mensurate.) As a measure of homophobia, we used the country level geographical codes of our data, and the respective homophobia index for these countries every bit calculated by Pew Global [57]. As the homophobia index of Pew Global covers simply the largest 52 countries, we could non test this hypothesis on our entire database. For the remaining seeds, countries were coded to be depression on homophobia if they scored between 0 and twoscore for the question "Homosexuality is a manner of life that should be accepted by society" and to exist loftier homophobic countries if they scored between 60 and 100. This gave usa 66 seeds living in countries with low homophobia and 47 seeds in countries with high homophobia. The (2F/1F)/(2M/1M)-1 mean for the two groups were 0.63 and 0.52, respectively (Fig. 6). As the difference is non statistically meaning (p = 0.12), and is in the reverse management to that predicted by the hypothesis, we can conclude that male homophobia is non associated with the difference between 2F vs 2M frequencies in our dataset.

Fig 6. Homophobia is not related to the frequency of 2F Profile Pictures, bootstrapping distributions.

Blue line: highly homophobic countries; red line: countries with low homophobia (run into text for definitions). Dashed black line: the (2F/1F)/(2M/1M)-1 hateful of the unabridged database. (100,000 bootstrapping repeats.)

https://doi.org/10.1371/journal.pone.0118329.g006

Word

Man societies are complex, large-scale communities of multi-generational social networks. At base, all the same, these networks are congenital of the pocket-size personal networks of individuals. Our data shed light on the dynamics of these personal networks past providing stiff cross-cultural bear witness for the universality of a male person propensity to prefer a higher number friendships compared to women. While large women-only groups were almost non-existent in cocky-selected Profile Pictures, males were more likely to present themselves equally function of large all-male groups—arguably an essential element of male-male coalitional competition. Our results are broadly in line with many previous studies of homo friendship [27,30,58,59] which also found strong gender homophily and male preference for coalitions. This difference in the preferred number of friends may betoken different solutions to the quantity-quality trade-off in social ties. The emotional quality of a relationship is a positive function of the time invested in information technology [39,sixty], and the closer and more time-demanding a relationship 1 has, the less time can exist devoted to others [11,24]. At the aforementioned time, the amount of social upper-case letter available that individuals take to distribute among the members of their personal social networks is limited [61,62]. It thus appears as if women build a 'dumbo' network, while men make alliances based on 'loose' networks. We likewise establish gender similarity in the preferences for three and four friends, which may explain part of the inconclusive results in previous studies on sex differences in friendship numbers.

The male propensity to form coalitions could have emerged from the sexual division of labour in ancestral environments. It was a male responsibleness to defend the grouping against assault from outsiders, and to practice so successfully information technology was necessary that men ring together [20,24]. In males but not females, then, out-group defence called for coalitional cooperation and behaviour.

Our finding that women prefer to picture themselves with fewer friends, and thus appear more than oft to focus their social capital letter on only one person at a time, suggests a strong female person preference for dyadic relations. The social benefits of such a female person dyadic social fashion are harder to pivot down, but three alternative hypotheses might be suggested. First, females may have developed a propensity to course dyadic same-sex friendships as a response to the challenges of their social environments. Given the likelihood of ancestral patrilocality [35,36,63,64], adolescent females would often take entered communities where they had few or no shut kin. For females specially, the presence of kin is fitness-enhancing, every bit has been repeatedly shown for both anthropoid primates [65,66] and humans [67,68]. Thus the formation of emotionally intense, exclusive and "sisterly" dyadic bonds may accept been a ways to essentially replace kin [25] and to defend against male and inter-female aggression in the new community where she did not have female kin [25,69,70]. This mirrors the case of patrilocal bonobos (Pan paniscus), where females enter foreign communities in adolescence and integrate into their new group through intense bond formation with another (typically older) female [71]. A second caption posits that, since females are the driving agents in human pair-bond formation, it may exist a female-specific sexual strategy to form exclusive dyadic relationships. In this framework, the high frequency of female-female person dyads in women's lives might be a by-product of a preference for pairbonding [12]. A third explanation focuses on females' unique chapters for intense empathic relationships, derived from the mother-baby bond. In this model, heightened female empathy creates an emphasis on private relationships as a effect of the psychological toolbox of mothering [72,73]. In comparison, males more often than not neither have nor crave this capacity, and hence they form less emotionally shut bonds, those of friendship included.

These 3 explanations for gender differences in social style—patrilocality, pair-bonding and maternal empathy—are difficult to tease autonomously. Not only is the evolutionary origin of all primate bonding likely to have arisen out of the mother-babe relationship [74], whatever forces shaped female friendship thereafter, unlike ultimate causes (e.k., defense confronting aggression in a patrilocal gild, or assistance among maternal kin) may take used similar proximate mechanisms (e.thou., high reliance on intimate disclosure) making it difficult to dissociate them. Furthermore, recent studies of shut friendship every bit a role of age suggests that women switch their primary focus from female person-female friendships to pairbonding and then to female parent-girl bonding at different stages of the life bike [75].

The importance for a female of maintaining close relationships once she has left her natal group sheds light on the strategies that women use during intrasexual aggression (notably exclusion and relationship-ending gossip [29,69]). If a female'southward bonds to friends and her spouse are crucial for accessing resources—from food to information—so breaking these bonds and/or excluding the female all together can radically affect that private's fitness, to the benefit of her competitors.

At that place are, inevitably, some potential limitations to our data. We cannot be sure that co-advent on Contour Pictures always reflects real-life social ties. Time to come research is needed in order to assess gender differences in offline sociality. However, no existing enquiry suggests that profile pictures would include imagined or random social relations to any significant extent (not least because the other person is likely to object) and our results are in line with other contempo findings from online social communities [50]. Displaying Profile Pictures with two or more people compared to only one person may also reflect some unknown personal psychological characteristics or specific life-events of account users; however, such possible characteristics should not affect our main results.

In summary, our results point to striking gender differences in intimate friendship strategies: women prefer shut dyadic bonds (with evolutionary origins in either pairbonding or social insurance purposes, or both), whereas men use their bonding capacity to build multimale groups (in effect, clubs). This concurs with work on chimpanzees, where females form tight, kin-based networks and males make loose, easy-to-pause alliances [76]. Since like gendered bonds are found in our closest primate relatives, they may long predate the evolution of our species. Amongst cercopithecine primates, females are disproportionately more probable to invest in core female 'friendships' with matrilineal relatives every bit group size gets larger, plain in gild to maximise the effectiveness with which these relationships office as social buffers [1,12,65]. By dissimilarity, chimpanzees [34] and humans may show a tendency to form close friendships with unrelated females in improver to those they might grade with close female relatives.

Supporting Information

Acknowledgments

Nosotros thank Elena Denaro, Joshua de Gastyne, Erin Simmons, and Cathal Power for aid in data collection.

Writer Contributions

Conceived and designed the experiments: TDB. Performed the experiments: TDB AR DT EM ABS. Analyzed the data: TDB. Wrote the paper: TDB AR JC IBI JK RD.

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