Euclidean distances discriminatively predict short-term and long-term attraction to potential mates

We tested the ability of a Euclidean algorithm to predict attraction to potential mates—a relatively upstream domain in the temporal sequence of the mating process. Participants in two studies reported their ideal mate preferences using a 23-item preference instrument. Separately, they rated their attraction to profiles of potential mates that varied on those 23 dimensions. Study 1 (N = 522) found that Euclidean distances predicted attraction to potential mates both in terms of (1) overall mate value and (2) unique mate value. Study 2 (N = 411) replicated these effects and further found that Euclidean mate values discriminatively predict between short- and long-term attraction. Across both studies, a Euclidean model outperformed a variety of alternative models for predicting attraction to potential mates. These results suggest that a Euclidean algorithm is a good model for how multiple preferences are integrated in mate choice.     

Sex differences in friendship preferences

Friendships can help us solve a number of challenges, increasing our welfare and fitness. Across evolutionary time, some of the many challenges that friendships helped to solve may have differed between men and women. By considering the specific and potentially distinct recurrent problems men's and women's friendships helped them solve, we can derive predictions about the qualities that would have made men's and women's same-sex friends ideal partners. This logic leads to several predictions about the specific friend preferences that may be differentially prized by men and women. Across three studies (N = 745) with U.S. participants—assessing ideal hypothetical friends, actual friends, and using a paradigm adapted from behavioral economics—we find that men, compared to women, more highly value same-sex friends who are physically formidable, possess high status, possess wealth, and afford access to potential mates. In contrast, women, compared to men, more highly value friends who provide emotional support, intimacy, and useful social information. Findings suggest that the specific friendship qualities men and women preferred differed by sex in ways consistent with a functional account of friendship.     

Attractiveness and Rivalry in Women’s Friendships with Women

Past research suggests that young women perceive their same-sex friends as both facilitating the pursuit of desirable mates and competing for access to desirable mates. We propose that similar levels of physical attractiveness between young adult female friends might be one explanation for the opposing forces in their friendships. Forty-six female friendship pairs completed questionnaires about themselves, their friend, and their friendship; in addition, each woman’s picture was rated by a set of nine naive judges. Friends were similar in both self-rated and other-rated level of attractiveness. Within-pair analyses revealed that women agreed on which friend was more attractive, and the less attractive members of each friendship pair (by pair consensus as well as outside judges’ ratings) perceived more mating rivalry in their friendship than did the more attractive members of each friendship pair. We offer directions for research on women’s friendships over the lifespan.     

Sex (similarities and) differences in friendship jealousy

Friendships provide material benefits, bolster health, and may help solve adaptive challenges. However, a recurrent obstacle to sustaining those friendships—and thus enjoying many friendship-mediated fitness benefits—is interference from other people. Friendship jealousy may be well-designed for helping both men and women meet the recurrent, adaptive challenge of retaining friends in the face of such third-party interference. Although we thus expect several sex similarities in the general cognitive architecture of friendship jealousy (e.g., it is attuned to friend value), there are also sex differences in friendship structures and historical functions, which might influence the inputs of friendship jealousy (e.g., the value of any one friendship). If so, we should also expect some sex differences in friendship jealousy. Findings from a reanalysis of previously-published data and a new experiment, including both U.S. student and adult community participants (N = 993), provide initial support for three predicted sex differences: women (versus men) report greater friendship jealousy at the prospective loss of best friends to others, men (versus women) report greater friendship jealousy at the prospective loss of acquaintances to others, and men's (but not women's) friendship jealousy is enhanced in the context of intergroup contests.     

Friends and Symptom Dimensions in Patients with Psychosis: A Pooled Analysis

Background

Having friends is associated with more favourable clinical outcomes and a higher quality of life in mental disorders. Patients with schizophrenia have fewer friends than other mentally ill patients. No large scale studies have evaluated so far what symptom dimensions of schizophrenia are associated with the lack of friendships.

Methods

Data from four multi-centre studies on outpatients with schizophrenia and related disorders (ICD F20-29) were included in a pooled analysis (N = 1396). We established whether patients had close friends and contact with friends by using the equivalent items on friendships of the Manchester Short Assessment of Quality of Life or of the Lancashire Quality of Life Profile. Symptoms were measured by the Brief Psychiatric Rating Scale or by the identical items included in the Positive and Negative Syndrome Scale.

Results

Seven hundred and sixty-nine patients (55.1%) had seen a friend in the previous week and 917 (65.7%) had someone they regarded as a close friend. Low levels of negative symptoms and hostility were significantly associated with having a close friend and contact with a friend. Overall, almost twice as many patients with absent or mild negative symptoms had met a friend in the last week, compared with those with moderate negative symptoms.

Conclusions

Higher levels of negative symptoms and hostility are specifically associated with the lack of friendships in patients with psychotic disorders. These findings suggest the importance of developing effective treatments for negative symptoms and hostility in order to improve the probability of patients with schizophrenia to have friends.     

Generation,ethnic and religious diversity in friendship choice: exploring interethnic close ties in Britain

Abstract

Interethnic friendships can reflect intergroup relations and immigrants' integration into host societies. Using pooled 2007–09 Citizenship Surveys, this study investigates interethnic friendship patterns and determinants of friendship choice in Britain. The paper focuses on generational, ethnic and religious diversity in forming interethnic close ties. The most common friendship pattern is having co-ethnic close friends. This ethnic boundary in interethnic ties, however, weakens across generations whereby those born in or migrated to Britain at young ages have a higher chance of having close friends from other ethnic groups. We find that interethnic friendships are formed in a ‘pan-ethnic’ pattern by which those with similar ethnic/racial and religious background such as Muslim Indians and Pakistanis, or mixed white and black Caribbean and black Caribbean, are more likely to nominate one another as close friends.     

Sexual selection and assortative mating: an experimental test

Mate choice and mate competition can both influence the evolution of sexual isolation between populations. Assortative mating may arise if traits and preferences diverge in step, and, alternatively, mate competition may counteract mating preferences and decrease assortative mating. Here, we examine potential assortative mating between populations of Drosophila pseudoobscura that have experimentally evolved under either increased (‘polyandry’) or decreased (‘monogamy’) sexual selection intensity for 100 generations. These populations have evolved differences in numerous traits, including a male signal and female preference traits. We use a two males: one female design, allowing both mate choice and competition to influence mating outcomes, to test for assortative mating between our populations. Mating latency shows subtle effects of male and female interactions, with females from the monogamous populations appearing reluctant to mate with males from the polyandrous populations. However, males from the polyandrous populations have a significantly higher probability of mating regardless of the female's population. Our results suggest that if populations differ in the intensity of sexual selection, effects on mate competition may overcome mate choice.     

Friendship,bitching, and the making of ethical selves: what it means to be a good friend among girls in a London school

This article explores the relationship between friendship, personhood, and ethics among girls in a London school. While a Western ideal of friendship is posited as a personal, private, and spontaneous relationship between autonomous individuals, I argue that girls’ friendships are a complex entanglement and interaction between forensic and mimetic dimensions of the self. Girls’ ideals of friendship, and practices of making friends, suggest forensic pre‐constituted selves acting with volition in order to become closer to other selves. However, bitching, exclusion, and breaking friendships foreground mimetic dimensions as girls shape each other and themselves according to gendered ethical criteria. Examining these analytical strands offers insight into how individuality is produced through sociality in everyday life.     

Within‐Species Mate Preferences Do Not Contribute to the Maintenance of Sexually Monomorphic Mating Signals in Green Lacewings

We know much less about the evolutionary forces and constraints that maintain similar mating displays in females and males than we do about sexually dimorphic mating displays. Both female and male green lacewings have sexually monomorphic vibrational mating signals and are equally choosy against heterospecific mating signals. This similarity in between‐species sex roles may explain a large part of the presence of species‐specific female signals in these species, but does not necessarily predict why female and male signals are similar. We tested for within‐species sex‐specific similarities in mate preferences in Chrysoperla lucasina that may contribute to the maintenance of sexually monomorphic mating signals in this species. We found weak preferences and low levels of discrimination for signals with varying fine‐scale temporal features (volley duration, period, and volley‐duty cycle). The longer signals that both sexes produced in response to playback were sexually monomorphic, but some females and most males also produced shorter signals with significantly reduced volley durations and periods. Notably, all of these signals had indistinguishable volley‐duty cycles, the ratio of volley duration to volley period. We propose that mating signals in C. lucasina are maintained in both sexes because of similar between‐species mate preferences, but the sexually monomorphic mating signals cannot be attributed to significant within‐species mate preferences. What differences are present in within‐species sex roles may be resolved by a male‐biased signal polymorphism, in long and short signals that are hypothesized to have distinct functions during mate calling and courtship.     

From maternal tending to adolescent befriending: The adolescent transition of social support

Attachment theory holds that parental relationships have lifelong effects on offspring social lives. The tend-and-befriend hypothesis posits that female friendships among humans evolved as part of a primate-wide coping mechanism to mediate stress by relying on social support. Here we bridge developmental and evolutionary frameworks to examine adolescent girls’ perception of their reliance on female friendship for social support, how perceptions of parental relationships affect peer relationships, and the extent to which parent and peer relationships buffer depressive symptoms. We predict perceived maternal relationship quality will be positively associated with close female friendships, and maternal relationships, paternal relationships, and female friendship will buffer depressive symptoms. Participants were adolescent girls from a summer science camp (N = 95). Participants filled out demographic information, social network surveys, the Parent-Adolescent Communication Scale, and the Center for Epidemiology Depression Scale. Data was analyzed with Pearson's correlations, t tests, and path analysis. Adolescent girls with few female friends, compared with girls who had more than two very close female friends, experienced more depressive symptoms (t = 3.382, p = .001, D = 0.784). Adolescent girls with few female friends experienced more depressive symptoms compared to girls with two or more very close female friends (t = 3.382, p = .001, D = 0.784). Stronger maternal and paternal relationships were associated with having more female friends (maternal: t = −3.213, p = .003, D = 0.837; paternal: t = −2.432; p = .017). In the path analysis model, only maternal relationship quality significantly predicted female friendship category (β = .33, CR = 2.770, p < .006). Furthermore, participants with two or more very close female friends and higher paternal relationship quality had significantly fewer depressive symptoms (friends; β = −.19, CR = −2.112, p = .035; paternal: β = −.33, CR = −3.220, p < .001), and older participants had more depressive symptoms (β = .17, CR = −1.931, p = .036). These results provide additional support for the tend-and-befriend hypothesis, suggesting that maternal tending sets the stage for close female friendships.     

What is a mate preference? Probing the computational format of mate preferences using couple simulation

What is the computational format of mate preferences? Different researchers hold a range of assumptions: weights, thresholds, ranges, ideal templates, or combinations thereof. These varying assumptions have important implications for theory and methods in studying human mating; however, this inconsistency has scarcely been acknowledged or empirically addressed. Here, we use two samples of U.S. romantic dyads (ns = 1052, 590), a newly developed mate preference questionnaire, and a new computational modeling technique, “couple simulation,” to empirically compare alternative models of the format of ideal romantic partner preferences. We find evidence that preferences are best understood as representing ideal trait values integrated into mate value evaluations using distance metrics.     

Female Mate Preferences Among Pan troglodytes schweinfurthii of Kanyawara, Kibale National Park, Uganda

Studies of reproduction among chimpanzees traditionally have focused on the mating strategies of males. However, less is known about the mating strategies of female chimpanzees and whether they demonstrate mate choice. I investigated sexual behavior and female mate preference in the chimpanzees of the Kanyawara community. To estimate mate preferences, I analyzed female proceptivity and resistance rates of 6 estrous females toward a total of 13 males as well as male solicitation and aggression rates toward females. Males solicited some females more often than others for mating and preferred them throughout estrus, not only during the periovulatory period (POP), when conception was most likely. In contrast, though females had strong mate preferences in both non-POP and POP, their mate preferences were not consistent between the 2 phases. The shift in mate preferences is evidence of a promiscuous yet tactical mating strategy to confuse paternity. Further, females were more proceptive and generally less resistant toward eschewed males in non-POP and more proceptive and less resistant toward preferred males in POP. Hence, the results indicate that females attempted to mate selectively during the fertile phase. Kanyawara female chimpanzees appear to change their mating strategies and selectivity during estrus and thus may pursue a mixed reproductive strategy. The tactic may allow females to deceive males, indicating that promiscuity among chimpanzee females may be more strategic than previously thought.     

Friends without benefits: When we react negatively to helpful and generous friends

Being able to identify reliable friends and allies is key to surviving and thriving in the social world. Many cooperative accounts of friendship argue that people select friends based on how helpful and generous they are. While people certainly like helpful and generous others, here we explore a context in which people might respond negatively to a friend being prosocial: When one's friend is more helpful or generous toward another friend. We argue that such preferential prosociality prompts negative reactions, even when the alternative is a friend being less prosocial overall, because giving preferentially to another friend may be viewed as a threat of potential displacement of one's own friendship. In four studies (N?=?702), we predict and find that people respond negatively to a friend who was more helpful (Studies 1–2) and generous (Studies 3–4), preferring instead that a friend be less helpful and generous overall. Importantly, this preferential prosociality was viewed as particularly negative when the recipient was another friend and was seen as much less negative when the recipient was a relative (Study 1 and 4) or a romantic partner (Study 2). We discuss the implications of these results for cooperation and alliance-based accounts of friendship.     

The rarity of multiple mating by females in the social Hymenoptera

Summary: Interest in how often female social insects mate is particularly intense because of its impact on sociality and because of the well-known extreme multiple mating in honeybees. With multiple mating, worker to brood relatedness decreases but worker versus queen interests often converge. The overwhelming majority of species of social ants, bees, and wasps mate only once. Even those species where some females mate multiply typically have effective mate numbers close to one. Ants have effective mate numbers of 1.43, which drops to 1.15 if the advanced fungus growers (2.14) and harvester ants (6.76) are excluded. Honeybees have effective mate numbers of 12.48. Stingless bees and bumblebees have effective mate numbers of only 1.06 and 1.02 respectively. Polistine wasps have effective mate numbers of 1.01. Vespine wasps have effective mate numbers of 1.12 excluding only Vespula which has effective mate numbers of 3.68. Favoring the very low mate numbers we observe for nearly all female social insects is the narrow time window for mating, lack of material gain from males, lack of male ability to harass females (who must move their sting aside to mate in most species), and lack of paternal care. Single mating may be further favored by the apparent lack of any post-copulatory sperm discrimination mechanisms. Leks and male territories, which are common in social insects, make it easier for females to choose the single best mate, further contributing to low mate numbers. Multiple mating is a rare, derived trait in a generally single-mating group. Single mating may have facilitated the origins of sociality in the Hymenoptera because it confers higher relatedness among potential workers and the brood they care for. The rare exceptions to low mate numbers all come from highly social species with single queens, morphological castes, and many workers. Multiple mating might be stable in highly social species because their highly specialized workers have few selfish responses to lowered relatedness. The unusual cases of multiple mating are most likely to be selected for because they increase genetic diversity in the brood, though empirical support for specific genetic diversity hypotheses has proved to be elusive. What is clear is that single mating is predominant in this large, evolutionarily and ecologically successful group.     

Effect of egg cannibalism on mating preferences and reproductive fitness of Menochilus sexmaculatus Fabricius (Coleoptera: Coccinellidae)

Cannibalism has been reported in a large proportion of coccinellids in fields as well as in laboratories but studies involving mate preferences and potential benefits of cannibalism on reproduction in Menochilus sexmaculatus Fabricius (Coleoptera: Coccinellidae) have yet not been done. Thus, we assessed the effect of conspecific egg cannibalism on mate preferences and reproductive outputs including offspring development. Higher mate preferences were recorded for non-cannibalistic mates (fed on A. craccivora) than cannibalistic ones (fed on conspecific eggs). Mating parameters were significantly influenced by cannibalism. Time to commence mating lasted less for homogeneous diet pairs than heterogeneous diet pairs. Longer copulation duration and higher fecundity were recorded when one of the individuals in mating pair or both was a non-cannibal. Egg viability did not differ significantly in all the reciprocal crosses. In addition, the total developmental durations of offspring were similar for all mating pairs.     

Inheritance of female mating preference in a sympatric sibling species pair of Lake Victoria cichlids: implications for speciation

Female mate choice has often been proposed to play an important role in cases of rapid speciation, in particular in the explosively evolved haplochromine cichlid species flocks of the Great Lakes of East Africa. Little, if anything, is known in cichlid radiations about the heritability of female mating preferences. Entirely sympatric distribution, large ecological overlap and conspicuous differences in male nuptial coloration, and female preferences for these, make the sister species Pundamilia pundamilia and P. nyererei from Lake Victoria an ideally suited species pair to test assumptions on the genetics of mating preferences made in models of sympatric speciation. Female mate choice is necessary and sufficient to maintain reproductive isolation between these species, and it is perhaps not unlikely therefore, that female mate choice has been important during speciation. A prerequisite for this, which had remained untested in African cichlid fish, is that variation in female mating preferences is heritable. We investigated mating preferences of females of these sister species and their hybrids to test this assumption of most sympatric speciation models, and to further test the assumption of some models of sympatric speciation by sexual selection that female preference is a single-gene trait. We find that the differences in female mating preferences between the sister species are heritable, possibly with quite high heritabilities, and that few but probably more than one genetic loci contribute to this behavioural speciation trait with no apparent dominance. We discuss these results in the light of speciation models and the debate about the explosive radiation of cichlid fishes in Lake Victoria.     

The Computational Mechanisms of Mate Choice

In many species, mating signals encode information important for both species recognition and mate quality assessment. I investigate how the computational mechanisms used by females to integrate the two sources of information can affect their mating decisions. First, I present a sequential analysis model of decision making based on a two‐component signal, in which the first component encodes information important for mate quality assessment and the second component for species recognition. When the components interact additively, the ability of females to discriminate between signals that differ in only the component important for mate‐quality assessment is the same independently of the value of the species‐recognition component. In contrast, when the components interact multiplicatively, discrimination in mate quality depends also on the species‐recognition component, which can either amplify or attenuate the perceived differences in mate quality. In the second part of the paper, I show results of a two‐choice phonotaxis experiment on female Italian treefrogs, Hyla intermedia, that confirm the model predictions by showing that directional preferences for call rate (important for mate‐quality assessment) are stronger when pulse‐rate and fundamental frequency (important for species recognition) are close to the preferred population mean than when they are either higher or lower than the mean.     

Variation in female mate choice within guppy populations: population divergence,multiple ornaments and the maintenance of polymorphism

The evolutionary significance of variation in mate choice behaviour is currently a subject of some debate and considerable empirical study. Here, I review recent work on variation within and among guppy (Poecilia reticulata) populations in female mate choice and mating preferences. Empirical results demonstrate that there is substantial variation within and among populations in female responsiveness and choosiness, and much of this variation is genetic. Evidence for variation in preference functions also exists, but this appears to be more equivocal and the relative importance of genetic variation is less clear cut. In the second half of this review I discuss the potential significance of this variation to three important evolutionary issues: the presence of multiple male ornaments, the maintenance of polymorphism and divergence in mate recognition among populations. Studies of genetic variation in mate choice within populations indicate that females have complex, multivariate preferences that are able to evolve independently to some extent. These findings suggest that the presence of multiple male ornaments may be due to multiple female mating preferences. The extreme polymorphism in male guppy colour patterns demands explanation, yet no single satisfactory explanation has yet emerged. I review several old ideas and a few new ones in order to identify the most promising potential explanations for future empirical testing. Among these are negative frequency dependent selection, environmental heterogeneity coupled with gene flow, and genetic constraints. Last, I review the relative extent of within and among-population variation in mate choice and mating preferences in order to assess why guppies have not speciated despite a history of isolation and divergence. I argue that variation within guppy populations in mate choice and enhanced mating success of new immigrants to a pool are major impediments to population divergence of the magnitude that would be required for speciation to occur.     

VARIATION IN THE STRENGTH OF MALE MATE CHOICE ALLOWS LONG‐TERM COEXISTENCE OF SPERM‐DEPENDENT ASEXUALS AND THEIR SEXUAL HOSTS

In several asexual taxa, reproduction requires mating with related sexual species to stimulate egg development, even though genetic material is not incorporated from the sexuals (gynogenesis). In cases in which gynogens do not invest in male function, they can potentially have a twofold competitive advantage over sexuals because the asexuals avoid the cost of producing males. If unmitigated, however, the competitive success of the asexuals would ultimately lead to their own demise, following the extinction of the sexual species that stimulate egg development. We have studied a model of mate choice among sexual individuals and asexual gynogens, where males of the sexual species preferentially mate with sexual females over gynogenetic females, to determine if such mating preferences can stably maintain both gynogenetic and sexual individuals within a community. Our model shows that stable coexistence of gynogens and their sexual hosts can occur when there is variation among males in the degree of preference for mating with sexual females and when pickier males pay a higher cost of preference.     

Reinforcement and learning

Evidence has been accumulating to support the process of reinforcement as a potential mechanism in speciation. In many species, mate choice decisions are influenced by cultural factors, including learned mating preferences (sexual imprinting) or learned mate attraction signals (e.g., bird song). It has been postulated that learning can have a strong impact on the likelihood of speciation and perhaps on the process of reinforcement, but no models have explicitly considered learning in a reinforcement context. We review the evidence that suggests that learning may be involved in speciation and reinforcement, and present a model of reinforcement via learned preferences. We show that not only can reinforcement occur when preferences are learned by imprinting, but that such preferences can maintain species differences easily in comparison with both autosomal and sex-linked genetically inherited preferences. We highlight the need for more explicit study of the connection between the behavioral process of learning and the evolutionary process of reinforcement in natural systems.