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Traditionally it has been suggested that sexual selection can cause sexual size dimorphism (SSD). However, a recent review in gastropods shows that SSD itself can also cause sexual selection (Ng et al., 2019. Animal Behaviour, 148, 53–62). This may be the case if mate choice exists, with males preferring to mate with females similar in body size but somewhat larger than themselves (female-biased preference). We formally investigated this verbal explanation by computer simulations using a Gaussian mating preference function. Parameters of that function were also estimated from empirical data. Our results suggest that sexual selection (estimated as selection differential) is strong when mate choice is high and exerted by only one of the sexes, being influenced by SSD and the magnitude of the female-biased preference. All these factors cause a negative relationship between SSD and the (sexual) selection differential, similar to that observed in Ng et al.‘s review on gastropods. Empirical estimates of male mate choice from wild-captured mating pairs of different gastropod species confirm that mate choice by males is biased towards females slightly larger than themselves. Our results also illustrate that if mate choice is truly involved in determining SSD, present-day sexual selection cannot be used to estimate the past magnitude of mate choice, as SSD influences present-day patterns of sexual selection.

Protandry occurs when males mature prior to females in the breeding season. There may be a fitness benefit for males if they are able to copulate and defend virgin and more fecund females. Therefore, fitness benefits can be investigated by studying assortative mating during mate guarding of virgin females before and after female sexual maturation. The asynchrony of female development in the protandrous spider Manogea porracea (Araneidae) provides an opportunity to investigate how female sexual maturity (subadult and adult females) influence size-assortative pairing. We investigated size differences between couples composed of males and subadult females, and of males and adult females. We hypothesized that size-assortative pairing is stronger in couples with adult females. Adult females were larger than subadults, but the size of males paired with females from both groups was similar. We found assortative pairing within all couples involving an adult female. However, this pattern was not observed among couples with subadult females. It is possible that the production of sexual pheromones by adult females after their last molt intensifies male intrasexual competition, promoting positive assortative pairing. We discuss the potential mechanisms affecting male mate choice and mate competition during pairings in M. porracea.

Melanin is a common pigment that can indicate individual quality to potential mates and social dominance to competitors. For many avian species, plumage melanism varies within both males and females. If predictive of individual quality, sexual selection may drive contrasting expressions of melanism for each sex, reflecting their different reproductive roles. For an alpine population of horned larks, Eremophila alpestris, we investigated whether plumage ornament size and darkness predicted morphometric traits, parental care and fitness correlates, and we evaluated support for assortative pairing. Males with darker crowns and larger masks were associated with greater wing length and mass, respectively. Males with darker ornaments were paired with females that provisioned nestlings at a higher rate, began nesting earlier in the season, had larger clutch sizes and ultimately had greater nest success. For females, plumage ornaments did not predict morphometric traits (i.e. wing length, mass), provisioning rate of the male partner, clutch initiation date or reproductive success. Instead, females with darker crowns provisioned nestlings more frequently and had larger clutches. Overall darker males tended to pair with darker females, but plumage ornament size did not correlate within mated pairs. We demonstrate that: (1) the darkness of plumage ornaments is a better predictor of fitness than ornament size and (2) darker males are associated with greater individual quality and reproductive investment of the female mate, while female darkness primarily predicts reproductive investment. These results indicate the potential for sex-specific selection pressures and mate choice based on the predictive value of plumage melanism.

As many long-lived seabirds are biparental and monogamous, individuals need to choose their mates wisely. While assortative mating based on physical traits is widely studied, mate choice in sexually monomorphic species based on behavioural traits remains poorly understood. We propose that personality is a possible factor on which mate choice is based and that certain personality traits within a behavioural syndrome confer a greater fitness. Here we measure boldness, a commonly explored behavioural syndrome, in black-legged kittiwakes, Rissa tridactyla, nesting at Middleton Island, Alaska, U.S.A. We measured boldness by presenting subjects with a novel object and recording the response. We considered the first principal component scores from the analysis of these responses to represent an individual's boldness. Some kittiwakes exhibited the strategy of assortative mating based on boldness, and bold birds that mated assortatively exhibited the greatest reproductive success. Within a breeding season, individuals became bolder as they reached the most critical point in the breeding season (chick hatching), which supports our finding that bolder individuals have greater reproductive success. We conclude that personality should be considered when investigating mate choice because individual personality may have an important influence on reproductive success.

We examine the causal relationship between the educational attainment of parents and that of their children using quasi-experimental variation from changes in parents' access to university generated by the geographical expansion of the Finnish university system between the late 1950s and early 1970s. Our results suggest that, for the children of parents affected by the changes in university accessibility, there is a strong positive spillover effect of around 0.5 from parent's to child's attained years of education. Our analyses using alternative parental and child outcomes suggest that the effect of parental education is partly driven by assortative mating and may also be related to children's improved school performance.

Speciation is often thought of as a slow process due to the waiting times for mutations that cause incompatibilities, and permit ecological differentiation or assortative mating. Cases of rapid speciation and particularly cases of rapid adaptive radiation into multiple sympatric species have remained somewhat mysterious. We review recent findings from speciation genomics that reveal an emerging commonality among such cases: reassembly of old genetic variation into new combinations facilitating rapid speciation and adaptive radiation. The polymorphisms in old variants frequently originated from hybridization at some point in the past. We discuss why old variants are particularly good fuel for rapid speciation, and hypothesize that variation in access to such old variants might contribute to the large variation in speciation rates observed in nature.

Psychologists using quantitative studies of the trait intelligence have established with much confidence that the impact of genes on intelligence increases with age, while the environmental effect of the family of origin declines. We examined the conjecture that a similar trend of increasing effect of genes/declining family environmental effect characterizes other status-related outcomes when arranged in typical age-graded sequence over adolescence and early adulthood. We used DeFries-Fulker (1985) (DF) analysis with longitudinal data on 1,576 pairs of variously-related young adult siblings (MZ twins; DZ twins; full siblings; half siblings; cousins; and nonrelated siblings; mean age 28) to estimate univariate quantitative genetic decompositions for fifteen status-related outcomes roughly ordered along the early life course: Verbal IQ, High school GPA, College plans, High school graduation, Some college, College graduation, Graduate school, Educational attainment, Occupational education, Occupational wages, Personal earnings, Household income, Household assets, Home ownership, and Subjective social status, with and without covariate controls for Age, Female gender, and Race/ethnicity (black, Hispanic, other; reference white). Results for successive outcomes did not support the conjecture of increasing heritability with maturity. Rather, the impacts of both the genes and the family environment tended to decline over the life course, resulting in a downward trend in family influences from all sources. There was some evidence of a recrudescence in relative influence of the family environment for outcomes related to the household that are often shared with a spouse, such as home ownership, suggesting a role of assortative mating in status reproduction. Other findings and limitations of the study are discussed.

People can estimate their own and their romantic partner's intelligence (IQ) with some level of accuracy, which may facilitate the observation of assortative mating for IQ. However, the degree to which people may overestimate their own (IQ), as well as overestimate their romantic partner's IQ, is less well established. In the current study, we investigated four outstanding issues in this area. First, in a sample of 218 couples, we examined the degree to which people overestimate their own and their partner's IQ, on the basis of comparisons between self-estimated intelligence (SEI) and objectively measured IQ (Advanced Progressive Matrices). Secondly, we evaluated whether assortative mating for intelligence was driven principally by women (the males-compete/females choose model of sexual selection) or both women and men (the mutual mate model of sexual selection). Thirdly, we tested the hypothesis that assortative mating for intelligence may occur for both SEI and objective IQ. Finally, the possibility that degree of intellectual compatibility may relate positively to relationship satisfaction was examined. We found that people overestimated their own IQ (women and men ≈ 30 IQ points) and their partner's IQ (women = 38 IQ points; men = 36 IQ points). Furthermore, both women and men predicted their partner's IQ with some degree of accuracy (women: r = 0.30; men: r = 0.19). However, the numerical difference in the correlations was not found to be significant statistically. Finally, the degree of intellectual compatibility (objectively and subjectively assessed) failed to correlate significantly with relationship satisfaction for both sexes. It would appear that women and men participate in the process of mate selection, with respect to evaluating IQ, consistent with the mutual mate model of sexual selection. However, the personal benefits of intellectual compatibility seem less obvious.

Size-assortative mating (SAM) is usually explained by the mate-choice hypothesis. However, this hypothesis does not consider the effects of variations in the intensity of mating competition on mate choice and SAM. For example, in populations with male-biased operational sex ratios (OSR) and high densities, large males will have more advantages during mating competition and will have access to the most mating opportunities with large, preferred females (i.e. mating competition hypothesis). In this study, we investigated the effects of mating competition and mate choice on the strength of SAM in Edessa contermina (Hemiptera: Pentatomidae). We also described sexual size dimorphism and the mating system of this Neotropical stink bug in a conservation area of the Brazilian savanna. We used density as a proxy for mating competition intensity because it was positively correlated with OSR. Size-assortative mating was more consistent under intense mating competition. However, males copulated with relatively larger females as population density increased. Males assortatively mated based on size in the first and second copulation events observed, while both female matings were random. Thus, male mate choice may promote SAM in E. contermina, but its strength is affected by variations in the intensity of mating competition. Hence, we provided empirical support for mating competition as a potential mechanism promoting subtle changes in SAM. We discussed potential implications of this mechanism on the mating patterns of pentatomids.

Although schizotypy has received much research interest, studies have largely ignored attractiveness and assortative mating for this trait. In an on-line study, participants (N = 170) rated high and low schizotypy vignettes for long and short term attractiveness. They also filled in the O-LIFE measure of schizotypy (Mason et al., 2005). For Unusual Experiences, and Cognitive Disorganisation, high vignettes received significantly lower ratings than the low vignettes in both short and long term mating context. In comparison to the low vignettes, high Impulsive Nonconformity vignettes had higher ratings as short term partners. We also found assortative preferences for Introvertive Anhedonia and Unusual Experiences. The findings support the idea that some of the schizotypy sub-traits could be part of an adaptive fast life history strategy.

As the Dark Triad (DT) has been rarely examined from different rater perspectives, there is a lack of insight about important questions on assessment and understanding of these traits. The present study explores real similarity (assortment), reciprocity, assumed similarity and self-other agreement for the DT traits on 188 heterosexual romantic partners using self-reports and partner- reports. By using variable-centered and couple- centered approach and various analytic tools, moderate to high positive assortment was found for all DT traits, the highest for Machiavellianism. The levels of assumed similarity and self-partner agreement were similar or somewhat higher than those usually obtained for other personality traits. We discussed the implications of the results obtained concerning measurement and interpersonal relevance of the DT traits.

We study the relationship between segregation and preferences for redistribution in Europe. We measure segregation as the incidence of assortative mating in terms of education and occupation. Assortative mating is measured at the regional level for 10 European countries using the IPUMS data. We combine these data with eight waves of the European Social Survey (2002-2016). We find that increased socioeconomic segregation in most forms of assortative mating leads affluent individuals to support less redistribution. Results suggest that affluent individuals are less socially attached when there are high levels of segregation.

Social norms have been put forward as prominent explanations for the changing labour supply decisions of women. This paper studies the intergenerational formation of these norms, examining how they affect subsequent female labour supply decisions, taking into account not only the early socialization of women but also that of their partner. Using large representative panel data sets from West Germany, results suggest that women with partners who grew up with a working mother are more likely to participate in the labour force, work longer hours, and earn higher labour income. Our study can assess a variety of potential mechanisms for this intergenerational link. It cannot be explained by other confounding patterns. We find no evidence that this finding reflects assortative mating; rather, analysis suggests that the partner’s preferences play a decisive role for the labour supply decision of partnered women. Our results suggest that policy measures supporting the labour force participation of today’s mothers will increase the female labour force participation of the next generation.

In Western nations, the simultaneous increases in interracial relationships and the use of dating apps such as Tinder have raised questions regarding the influence of dating apps on partner choice. This study examines whether principles of assortative mating – people's tendency to select partners similar to them – apply to dating apps, or whether the reduced cue environment used on these apps leads users to choose more heterogeneous partners. Young (age

Mate choice through direct assortment on heritable traits, assortative mating (AM), is predicted in theory to inflate the genetic variance in a population and the correlation between relatives. Here, we revisit the theory of AM, first established in the landmark 1918 paper from RA Fisher, and provide new theory and analytical results. In particular, we shed light on inconsistencies in the literature regarding the correlation between double first cousins under AM and provide a solution. We derive new theory for AM due to X-chromosome loci. We show in the latter case that the inflation of genetic variance induced under AM is twice as large in females compared to males. These two theoretical contributions are verified and illustrated through simulations. We also provide a more general unified framework for the correlation between relatives in a non-inbred population.

Using data from the Panel Study of Income Dynamics (PSID) and the Medical Expenditure Panel Survey (MEPS), we analyze the health gap between married and unmarried individuals of working-age. Controlling for observables, we find a gap that peaks at 10% points at ages 55–59 years. The marriage health gap is similar for men and women. If we allow for unobserved heterogeneity in innate health (permanent and age-dependent), potentially correlated with timing and likelihood of marriage, we find that the effect of marriage on health disappears below age 40 years, while about 5% points difference between married and unmarried individuals remains at older ages (55–59 years). This indicates that the observed gap is mainly driven by selection into marriage at younger ages, but there might be a protective effect of marriage at older ages. Exploring the mechanisms behind this result, we find that better innate health is associated with a higher probability of marriage and a lower probability of divorce, and there is strong assortative mating among couples by innate health. We also find that married individuals are more likely to have a healthier behavior compared to unmarried ones. Finally, we find that health insurance is critical for the beneficial effect of marriage.

In species with sexual reproduction, the mating pattern is a meaningful element for understanding evolutionary and speciation processes. Given a mating pool where individuals can encounter each other randomly, the individual mating preferences would define the mating frequencies in the population. However, in every mating process we can distinguish two different steps. First, the encounter between partners. Second, the actual mating once the encounter has occurred. Yet, we cannot always assume that the observed population patterns accurately reflect the individual’s preferences. In some scenarios the individuals may have difficulties to achieve their preferred matings, such as in monogamous species with low population size, where the mating process is similar to a sampling without replacement. In the latter, the encounter process will introduce some noise that may disconnect the individual preferences from the obtained mating pattern. Actually, the difference between the mating pattern observed in a population and the mating preferences of the individuals have been shown by different modeling scenarios.Here I present a program that simulates the mating process for both discrete and continuous traits, under different encounter models and individual preferences, including effects as time dependence and aging. The utility of the software is demonstrated by replicating and extending, a recent study that showed how patterns of positive assortative mating, or marriage in human societies, may arise from non-assortative individual preferences. The previous result is confirmed and is shown to be caused by the marriage among the “ugliest” and oldest individuals, who after many attempts were finally able to mate among themselves. In fact, I show that the assortative pattern vanishes if an aging process prevents these individuals from mating altogether. The software MateSim is available jointly with the user’s manual, at http://acraaj.webs.uvigo.es/MateSim/matesim.htm

Color polymorphisms are widespread in nature and can be maintained by several evolutionary processes. We used the coconut crab (Birgus latro) red/blue color polymorphism as a test case to explore the functional significance of intraspecific variation in crab coloration. Across our study sites on Pemba and Chumbe Islands, Tanzania, and Christmas Island, Australian Territory, red:blue morph ratios were 76.5%, 66.7% and 72.0% respectively, or approximately 3:1 in each case. To investigate whether coloration is sex or size dependent, signals strength or behavior, or is a physiological pleiotropic effect, we measured body weights, linear dimensions, pinch-force, behavioral dispositions and took crude environmental variables in the field. Except for a slight tendency for red crabs to be found in more open situations, we found no differences between color morphs for any of these variables. Other factors associated with color polymorphisms in other species, including frequency-dependent predation seems unlikely in such a large species with few natural predators, while niche separation in space seems improbable as morphs are typically found together. Assortative mating is plausible but mating is rapid, suggesting little choice is involved. Our findings suggest that neither morphological nor behavioral factors can explain color polymorphism in this species and that explanations must be found elsewhere.

Romantic relationships with a large age difference between partners are judged to be less acceptable, more disgusting, and less likely to succeed than age-similar relationships. We investigated the role of strategic moralization in condemnation of man-older age-discrepant relationships. We hypothesized that (1) this condemnation promotes self-serving interests of those who stand to lose from violation of age-based assortative mating, and (2) endorsement of prostitution mediates the association between participant's age and condemnation of man-older age-discrepant relationships because these relationships make the exchange of sex for resources explicit and acceptable. Using self-reports from 430 participants, we documented that endorsement of prostitution mediates the association between age and condemnation of man-older age-discrepant relationships for women but not men.

Temperature plays a critical role in survival and reproduction, especially in ectotherms. Therefore, it is important to understand the mechanisms influencing life history traits and reproductive behaviours in order to predict climate change impacts on species’ occurrence and performance. Here, we used the crustacean Artemia franciscana to investigate the potential impacts of temperature on life history traits, mating patterns and intensity of sexual selection. We reared A. franciscana at three temperatures 20 °C, 25 °C, and 30 °C and measured life history traits such as growth, mortality or development of sexual traits. Our observations confirmed a clear link between life history traits and temperature, with advanced sexual maturity and increased mortality rates following temperature rises. Also, we found that mating is size assortative close to the ideal developmental temperature. Nevertheless, when temperatures deviate from the optimum, mating patterns were altered. Although selection intensity for females remained similar at all tested temperatures, as males preferentially mated with the larger females, size assortative mating disappeared at the highest temperature. Overall, our results highlight the potential for a temperature-dependent disruption of A. franciscana mating patterns. This disruption is especially pronounced under high temperatures as reproduction becomes progressively more random, thus entailing a relaxation of sexual selection intensity.

We investigate the spread from ancestors to descendants, under a model of sexual reproduction, of hereditary elements distinguishing individuals from their fellow human beings. These hereditary elements, termed labels, are either symbolic, implying a socio-cultural or ethnic self-determined category, or biological, i.e. a DNA sequence (for example founder mutations). The impact of various modes of preferential (assortative) mating on the dissemination of a known ancestral label was studied for both kinds of labels, the symbolic and the biological. For the socio-cultural based labeling, both mathematical modeling and simulation studies were carried out, and disclosed a marked delay in the spread of the labels in future generations, compared to the case where mating was random. The transmission of biological labels (founder mutations) from an ancestor to descendants under various modes and degrees of assortative mating was investigated by simulations and supplemented by an in-depth analysis of allele frequencies of Familial Mediterranean Fever (FMF) in an Israeli Muslim Arab village. The high carrier frequency of FMF in this village was satisfactorily explained solely by the presence of a founder effect and a pronounced high factor of selective mating, causing segregation and consanguinity among its inhabitants. Contribution of further evolutionary mechanisms such as heterozygote advantage, drift, differential reproductive success or selection pressure was not essential to explain these results.

Seasonal journeys between breeding and non-breeding habitat are undertaken by a diverse array of animals. Parallel developments in tracking and genomic methods are enabling finer resolution of these movements and their role in the evolutionary process. Evidence from allopatric and co-occurring breeding populations indicates that variation in migratory behavior is often associated with genetic differentiation. While assortative mating and selection against hybrids due to divergent migratory phenotypes can contribute to reproductive isolation, the details of these mechanisms remain unclear. Here we identify gaps in our understanding of the role of seasonal migration in the speciation process and propose a framework to test the relative significance of reproductive barriers associated with variation in migratory behavior that might underlie population differentiation.

Body constitution plays an important role in human mate choice. Cross-cultural research reports that women on average prefer men with muscular physique. It is still unclear, however, what mechanisms influence the inter-individual variation in mate preferences and choices of partner's physique. In this study, we tested the mechanisms of an imprinting-like effect (similarity between father and an ideal and actual partner) and of homogamy (similarity between self and an ideal and actual partner) for male physique in heterosexual women and homosexual men. To assess the variation in male physique, we employed somatotype paradigm which characterizes body constitution using three components: endomorphic (heavy-set), mesomorphic (muscular), and ectomorphic (lean). In total, 149 homosexual men and 769 heterosexual women from the Czech Republic indicated the somatotype of their father, ideal and actual partner, and in homosexual men also their own somatotype. In line with previous research, the somatotype most preferred by both men and women was the mesomorphic, followed by the ectomorphic and the endomorphic one. Women's preferences for an ideal partner somatotype weakly correlated with their fathers' somatotype, especially in women who reported a positive relationship with their fathers during childhood. Among homosexual men, we found imprinting-like preferences only for the ectomorphic somatotype component and no significant association with the quality of their relationships with their fathers. We also found no significant relationship between the fathers' and actual partners' somatotype in either heterosexual women or homosexual men. Our research indicates that fathers have a rather weak influence on mate preference for somatotypes and no influence on actual mate choice.

Ever since the Chinese Communist Party took power in 1949, China has endured multiple political mobilizations that shattered traditional norms and reshuffled social hierarchies. Its reversal to market liberalization since the late 1970s has been no less remarkable in disrupting previously established social structures. Using data compiled from the 2000 Census, this study explores the influences of these institutional transformations on educational assortative mating. The results indicate that early political mobilizations have reduced the strength of educational association moderately and continuously whereas the onset of market reforms sharply reverses the trend to increasing association. Additional analyses further reveal that couples with sent-down wives have no or weaker advantages in homogamy whereas educational association among couples who are both sent-down is significantly weaker than others. In sum, the results show that whilst the effects of economic reforms on assortative mating are massive and pervasive, early political disruptions significantly affected only certain groups, mostly women.

Studies of homogamy in personality in heterosexual couples have arrived at inconsistent results and research of this issue in same-sex couples is almost non-existent. Moreover, homogamy in actual couples can differ from preferred homogamy in ideal partners. In Study 1, preferences for personality homogamy and perceived homogamy in actual relationships as measured by a Ten-Item Personality Inventory were assessed in heterosexual and homosexual men from Brazil and the Czech Republic. In men of both sexual orientations, we found preferences for homogamy in all personality characteristics except for Emotional Stability, while perceived homogamy in actual couples was limited to Extraversion in heterosexual couples. The results were nearly identical for both studied populations. In Study 2, resemblance in the Big Five personality traits measured by a 60-item NEO-FFI was tested in 49 actual heterosexual and 40 male same-sex long-term couples from the Czech Republic. Heterosexual partners resembled each other in Extraversion, Openness, and Conscientiousness, whereas homosexuals only in Extraversion. Our results thus indicate that while preferences for personality homogamy exist in both heterosexual and homosexual men, they translate only partially into actual mate choice, especially in homosexual men.

11 pages; International audience; In monogamous species that provide biparental care, partners with similar behavioural types generally have a better reproductive success than dissimilar ones. The pattern of assortative mating for behavioural type is thus often interpreted as resulting from a mate choice process. However, an alternative process is also possible when the partners become similar through postpairing adjustments (behavioural convergence). The disentanglement of these two nonexclusive mechanisms is an important evolutionary question. Only sexual selection based on behavioural similarity before pairing can explain the maintenance of the behavioural type variability. In a previous study, we reported the existence of behavioural convergence for aggressiveness between partners in convict cichlids Amatitlania siquia, a monogamous tropical fish. We tested herein the assumption of mate choice based on behavioural similarity for aggressiveness using either short-term binary choice or long-term group level pairing. Pairing was not based on behavioural similarity between potential partners. Choosing a behaviourally compatible partner is a complex task because it requires profiling the potential mates. Individuals would thus achieve higher fitness benefits from choosing a partner on more conspicuous criteria (such as size for instance) and then attempt to increase partner similarity by convergence after pairing. Sexual selection does not appear to drive the maintenance of aggressiveness type variability in convict cichlids.

This paper focuses on the long-term impacts of the termination of universal primary education (UPE) in the Republic of Kenya in 1988. We exploit this sudden change as a policy experiment to investigate whether female educational attainment affects total fertility and leads to improved educational outcomes for their children. In the Republic of Kenya, UPE was introduced in 1974 and terminated in 1988. We apply a fuzzy regression discontinuity design to assess the effect on female education at the threshold. The termination of UPE immediately reduced the length of female education by an average of 1.3 years. We find that each additional year of education reduced the average number of children per woman by 0.27 by the age of 26 and by 0.44 by the age of 37. Furthermore, additional maternal education reduces the likelihood of their children not being enrolled in school at the ages of 6 and 7 years by 20 percent. We examine three possible pathways: female labor outcomes, contraception, and assortative mating. Additional schooling significantly enhances knowledge of contraception and preventive measures against sexually transmitted diseases. Also, women with longer education tended to match with more educated partners, indicative of assortative mating, whereas the female labor outcomes channel seemed to be silent.

The extent to which like-with like marry is particularly important for inequality as well as for the outcomes of children that result from the union. In this paper we discuss approaches to the measurement of changes in assortative mating. We derive two key conditions that a well-defined measure should satisfy. We argue that changes in assortativeness should be interpreted through a structural model of the marriage market; in particular, a crucial issue is how they relate to variations in the economic surplus generated by marriage. We propose a very general criterion of increase in assortativeness, and show that almost all indices used in the literature are implied by our criterion with one notable exception, that moreover violates one of our conditions. Finally, we use our approach to evaluate the evolution of assortative matching in the US over the last decades, and conclude that assortative matching has increased, particularly at the top of the education distribution. Institutional subscribers to the NBER working paper series, and residents of developing countries may download this paper without additional charge at www.nber.org.

This paper examines how unilateral divorce affects assortative mating, and household income inequality across newly married couples as a result of changes in the matching patterns. I exploit variation in the adoption and timing of unilateral divorce laws using three estimators---the two-way fixed effects, DID_M, and synthetic control estimators. I find that unilateral divorce increases income inequality by 6–20%. This is likely driven by increased assortative mating---unilateral divorce moderately increases educational sorting and substantially increases income sorting. This is partially driven by reduced marriage entry and changes in women’s labor force participation at the time of marriage.

The extent to which like-with like marry is important for inequality as well as for the outcomes of children that result from the union. In this paper we present evidence on changes in assortative mating and its implications for household inequality in the UK. Our approach contrasts with others in the literature in that it is consistent with an underlying model of the marriage market. We argue that a key advantage of this approach is that it creates a direct connection between changes in assortativeness in marriage and changes in the value of marriage for the various possible matches by education group. Our empirical results do not show a clear direction in the change in assortativeness in the UK, between the birth cohorts of 1945-54 and 1965-74. We find that changes in assortativeness pushed income inequality up slightly, but that the strong changes in education attainment across the two cohorts contributed to scale down inequality. Institutional subscribers to the NBER working paper series, and residents of developing countries may download this paper without additional charge at www.nber.org.

While intermarriage with non-indigenous people has been identified as a significant predictor of the economic assimilation of Native people, the explanation for this effect is less understood. In this paper, I examine whether the economic assimilation from marrying a Native person with white ancestry is driven by productivity advantages or by selection into intermarriage. The data come from panel data on farm households on the Eastern Cherokee Reservation from 1894 to 1906 linked to information on the racial ancestry of each household head contained in the Eastern Cherokee applications to the U.S. Court of Claims. I estimate an endogenous switching model and find evidence of positive selection into marriages with males with white ancestry. After accounting for selection, I find no evidence of an intermarriage premium. These findings are additionally supported by the results from sibling-fixed effects models.

Hierarchical structures which lie hidden between human complex conditions and reproductivity cannot be simple, and trends of each population component does not necessarily pertain to evolutionary theories. As an illustration, the fitness of individuals with heritable extreme conditions can be low across continuing generations in observational data. Autism and schizophrenia are characterized by such evolutionary paradox of survival and hypo-reproductivity in the complex human diversity. Theoretical mechanisms for the observational fact were evaluated using a simple formula which was established to simulate stochastic epistasis-mediated phenotypic diversity. The survival of the hypo-reproductive extreme tail could be imitated just by the predominant presence of stochastic epistasis mechanism, suggesting that stochastic epistasis might be a genetic prerequisite for the evolutionary paradox. As supplemental cofactors of stochastic epistasis, a random link of the extreme tail to both un- and hyper-reproductivity and group assortative mating were shown to be effective for the paradox. Especially, the mixed localization of un- and hyper-reproductivity in the tail of a generational population evidently induced the continuous survival of outliers and extremes. These hypothetical considerations and mathematical simulations may suggest the significance of stochastic epistasis as the essential genetic background of complex human diversity.

Mating success is an important issue in modern societies. One in two adults reports poor mating performance. One solution to this problem is to know as much as possible about human mating preferences. In this research, we investigated if women (N = 223) high on the Dark Triad Traits are attracted to males with high levels of narcissism and tested the moderation effect of women's mating orientation and experience with unfaithful men. We showed that women high on all the Dark Triad traits were attracted to males with high narcissism levels. Women with high levels of Machiavellianism, narcissism, or psychopathy that were oriented to long term mating were more attracted to males high on narcissism. Women high on psychopathy who had many experiences with unfaithful men are less attracted by males with high narcissism levels. Experiences with infidelity did not affect the relationships between women's Machiavellianism and narcissism on the one hand and attraction to males high on narcissism, on the other hand. Our research supports the idea of positive assortative mating of women high on the Dark Triad traits, which is conditional on mating orientation and experience with infidelity.

The compatibility between partners in romantic relationships has been found for various characteristics, including intelligence. Theoretically, this phenomenon implies that people are able to discern the intelligence of themselves and others. In practice, however, the accuracy of such estimations is influenced by various factors, such as personality traits. Grandiose narcissism has been found to be the strongest personality predictor of self-overestimated intelligence, however, it remains to be determined whether the self-perceived bias generalises to people close to the narcissist, such as their romantic partners. In the current study, in a sample of 150 heterosexual couples, we examined whether grandiose narcissism was associated with self and partner's estimation of intelligence. Additionally, we measured participants' objective intelligence (Raven's test) and relationship satisfaction. First, we found that narcissism was associated with the overestimation of intelligence. Second, narcissistic women overestimated the intelligence of their partners. Furthermore, narcissistic women were perceived as highly intelligent by their partners, even after controlling for objective intelligence. Finally, we found support for assortative mating for narcissism. Thus, intelligence seems to be an important attribute in the way how narcissistic women perceive their partners, as well as how partners view the intelligence of narcissistic women.

9 pages; International audience; In monogamous species, partner compatibility is a key factor influencing pairing and reproductive success. In pairs with biparental care, studies have mostly focused on behavioral compatibility because it is likely to encourage the coordination of parental care within pairs, leading to a better reproductive success. Behavior modulation, throughout the breeding season and as a function of the social context, is under the regulatory feedback control of endocrine mechanisms. From this link, the idea of hormonal partner compatibility as a key component of pair cohesion and maintenance has recently emerged. Here, we investigated the link between partner behavioral assortment and their hormonal response to the pairing context. We formed assortative and disassortative pairs of convict cichlids based on their behavioral type (proactive or reactive) and took hormone and fitness measurements. Testosterone, 11-ketotestosterone, 17β-estradiol and cortisol levels were measured from fish-holding water before and after pair formation. We found no relationship between the behavioral type of individuals and their pre-pairing hormone levels. Only the level of cortisol was affected by the partner but independently of its behavioral type. Reproductive success was not affected by the level of hormonal similarity within pairs, but we found that the variation in 11-ketotestosterone similarity between the isolated context and the pairing context was related to spawning size, and the variation in cortisol similarity to the number of fry. Behavioral compatibility does not reflect hormonal compatibility in the convict cichlid, but the relationship between reproductive success and the flexibility of hormonal similarity between partners suggests hormonal adjustment within pairs in this species.

The Internet has now become a habitual channel for finding a partner, but little is known about the impact of this recent partnership market on mate selection patterns. This study revisits the supply side perspective on assortative mating by exploring the role played by online venues in breeding educational, racial/ethnic and religious endogamy. It compares couples that met online (through either online dating platforms, Internet social networking, Internet gaming website, Internet chat, Internet community, etc.) to those that met through various offline contexts of interaction. Using unique data from the U.S. for the year 2009 and data from Germany collected between 2008 and 2014, I run log-multiplicative models that allow for the strength of partners’ association to vary along meeting settings. Results reveal that the Internet promotes weaker couple endogamy compared to conventional contexts typically known to foster endogamy, such as school, family, friends, or religious venues.

Many monogamous species demonstrate size-assortative mating patterns within natural populations. To better understand the role of intersexual selection in this process, we examined the effect of male preference for female body size in the convict cichlid (Amatitlania siquia). We provided males with a choice between females that differed in size, relative to each other and in relation to the focal male. Based on previous work, we expected males to prefer the largest available female mates across all treatments. Surprisingly, males spent more time near the smaller of two available females, but only when the other female was larger than the male. Additionally, males spent little time with either of two potential female mates when both females were larger than the male. We hypothesized that while males might prefer the largest of available females, female behavior might limit males from acting on this preference. To test this, males were force paired with a smaller or larger female. Pair formation only occurred when the female was smaller than the male, and females that were larger than their male counterparts showed significantly more aggression when compared to smaller females. Together, these data suggest that in the absence of intrasexual competition, male mate preference for large females in convict cichlids might be limited by female aggression.

A tree based on the mitochondrial cyt b gene for 278 samples from throughout the range of the Eurasian Reed Warbler Acrocephalus scirpaceus ¿ African Reed Warbler A. baeticatus complex shows wellsupported geographically structured divergence for eight distinct lineages. The phylogenetic structuring together with the clarification of priority, provided by sequence data from seven type specimens, suggests that both taxonomy and distribution boundaries are in need of revision. The Iberian and Moroccan populations form a well-supported clade, and we propose that these are treated as taxonomically distinct, under the name ambiguus (Brehm, 1857). We propose that the names scirpaceus, fuscus, avicenniae, ambiguus, minor, cinnamomeus, hallae and baeticatus are used for the well supported clades in the complex, which we recommend to treat as one polytypic species, A. scirpaceus, pending studies of gene flow and assortative mating in the contact zones., We thank the Ministry of Environment and Tourism, Namibia for granting the necessary permits, and Ursula Franke-Bryson for kindly providing feathers for dna analyses from Namibia.

Somatolactin alpha (SLα) is a peptide hormone that regulates skin color, and SLα-deficient and SLα-excess strains have been established in medaka (Oryzias latipes). Their skin colors differ conspicuously and males prefer to mate with females from the same strain. Pre-mating sexual isolation in this model vertebrate provides an ideal platform for investigating the molecular mechanisms of mate choice. Thus, we studied the sensory cues utilized by these fish to discriminate the same and different strains. When males were given a choice under monochromatic light, where the skin colors differed only in terms of brightness but not in hue, mating occurred but it was not assortative. This suggests that: (1) a visual cue is essential for mate discrimination rather than odor or acoustic cues; (2) the visual cue is color and not shape, size, or motion; and (3) the color cue needs to be perceived as the relative balance of brightness at multiple wavelengths rather than the brightness at a specific wavelength. In addition, we introduced another skin-color mutation into the SLα-excess strain and found that this new strain and the original SLα-excess strain, which also overexpressed SLα but exhibited distinct skin colors, preferred different colors. This demonstrates that SLα is not a primary determinant of sexual preference. The symmetrically biased sexual preferences of the SLα-deficient and SLα-excess strains may be acquired postnatally depending on their individual skin color or that of tank mates.

Few studies have looked at assortative mating for the Dark Triad (i.e., Machiavellianism, psychopathy and narcissism), or assortative mating for facial characteristics related to personality. In two studies (n's = 302 and 262), we investigated whether women scoring high in the Dark Triad exhibited a preference for high and low Dark Triad male composite faces. In Study 1, using a two alternative forced-choice task and a short Dark Triad scale, there was little evidence for assortative mating. In Study 2, utilising a rating scale, longer personality measures, and controlling for perceptions of aggression, masculinity and dominance, we found positive assortative mating for narcissism in long-term relationships. Findings are discussed from evolutionary psychological perspective.

This paper employs recently developed marital matching models to examine empirically the role played by marital sorting in observed measures of marital production. Using the US Collaborative Perinatal Project (CPP), a large-scale study from the 1960s, and the National Longitudinal Survey of Youth 1979 (NLSY), we find that marital surplus is strongly correlated with indices of child quality, as measured by cognitive test scores, and with the durability of the marital union. At ages beyond infancy, the correlation between cognitive outcomes and marital surplus is robust to the inclusion of the parental characteristics that generate the match, suggesting that the correlation represents effects of the match itself. High marital surplus is associated with assortative mating on education and age, suggesting complementarity in parental inputs in child production. Our results suggest that marital surplus is an important input for child quality above and beyond its indirect effects on marital stability.

The differential allocation hypothesis (DAH) predicts that an individual should vary its reproductive\ud investment according to the attractiveness of its mate. A recently revised version of the DAH makes\ud explicit that investment can be positive, i.e. higher for the offspring of attractive males which should be\ud of higher quality, or negative, i.e. higher for offspring of unattractive males, for example compensating for\ud inheriting poor paternal genes. Moreover, investment can be made by the father and the mother. Here,\ud we tested whether experimental manipulation of male attractiveness affected parental investment at\ud different reproductive stages and thus influenced fitness-related traits in offspring. In two aviaries, all\ud male zebra finches, Taeniopygia guttata, were given red leg rings to increase attractiveness and in two\ud aviaries all males received green leg rings to decrease attractiveness. This controlled for assortative\ud mating between treatments. Ring colour was merely an experimental manipulation of male attractiveness,\ud not paternal quality, so we might expect additional investment to elevate offspring quality. Eggs\ud were cross-fostered between and within treatments to allow differentiation of effects of investment in\ud eggs and nestlings. Clutch and brood sizes were standardized. Both positive and negative investment\ud were observed: Eggs from red-ringed fathers had higher yolk to albumen ratios than eggs from greenringed\ud fathers. Nestlings from eggs laid and incubated by parents in the red-ringed group had higher\ud hatching masses than those in the green-ringed group. Both parents in the green-ringed group fed\ud nestlings more frequently than red-ringed parents. Offspring performance was influenced by the\ud treatment of both foster and biological parents, but combined effects of these different investment\ud patterns on fitness-related traits were ambiguous. Male attractiveness appeared to affect patterns of\ud reproductive investment but not consistently across all forms of reproductive investment suggesting that\ud the costs and benefits of differential allocation vary among individuals and across contexts.

A major challenge in biology is to understand the genetic basis of adaptation. One compelling idea is that groups of tightly linked genes (i.e., "supergenes" [1, 2]) facilitate adaptation in suites of traits that determine fitness. Despite their likely importance, little is known about how alternate supergene alleles arise and become differentiated, nor their ultimate fate within species. Herein we address these questions by investigating the evolutionary history of a supergene in white-throated sparrows, Zonotrichia albicollis. This species comprises two morphs, tan and white, that differ in pigmentation and components of social behavior [3-5]. Morph is determined by alternative alleles at a balanced >100-Mb inversion-based supergene, providing a unique system for studying gene-behavior relationships. Using over two decades of field data, we document near-perfect disassortative mating among morphs, as well as the fitness consequences of rare assortative mating. We use de novo whole-genome sequencing coupled with population- and phylogenomic data to show that alternate supergene alleles are highly divergent at over 1,000 genes and that these alleles originated prior to the split of Z. albicollis from its sister species and may be polymorphic in Z. albicollis due to a past hybridization event. We provide evidence that the "white" allele may be degrading, similar to neo-Y/W sex chromosomes. We further show that the "tan" allele has surprisingly low levels of genetic diversity yet does not show several canonical signatures of recurrent positive selection. We discuss these results in the context of the origin, molecular evolution, and possible fate of this remarkable polymorphism.

Individuals select mates adaptively, adjusting their ideal partner preferences in accordance with their own mate value, and prevailing environmental conditions. They may then select a mate that falls short of these preferences if they are unable to locate or attract someone who meets their ideals. In the current study we investigated the extent to which men and women of varying mate value compromise their mate choice decisions implicitly (by lowering their preferred ideals) or explicitly (by choosing a partner who falls short of their declared). Participants reported on their ideal trait preferences, the traits of an actual long-term partner, and their own mate value. We observed that both men and women engaged in substantial implicit compromise, with lower stated ideal preferences across all potential partner traits, as participant self-perceived mate value decreased. Explicit compromises were comparatively rare and unrelated to an individual's own mate value. We conclude that implicit compromise from both men and women plays a far greater role than does explicit compromise in either sex in driving assortative mating.

This study examines the association between individuals' educational assortative mating and time spent on child care and housework. Focus is put on hypogamous couples, or couples in which wives have more education than their husbands. Relative resources and gender revolution frameworks are considered as contexts to explain why hypogamous couples may share their time differently than other couples. A series of ordinary least squares regressions with population and sampling weights are employed using American Time Use Survey data from 2003 to 2018. Three, separate analyses using relative education, gender, and all educational pairings as the independent variables of interest are presented with child care and housework as the dependent variables. The current findings show that men in hypogamous marriages perform about 10 min more of child care per day on average than their peers in hypergamous and homogamous marriages, and that this comes primarily from basic care activities. This accounts for approximately 43% of the difference between men and women in the average amount of time spent on child care. No clear pattern of significance is apparent comparing individuals' time spent on housework by relative education, suggesting that housework and child care have evolved differently in the context of gendered domestic responsibilities. Men in hypogamous marriages are more egalitarian in their sharing of child care. However, this is only true for couples in which men have at least a high school diploma and women are highly educated.

This paper examines the consequences of political, economic and social change in mid-twentieth century China for patterns of assortative mating by both education and class. Traditionally in China, marriages were arranged by parents, and ideally matched families of similar socioeconomic status. However, the Marriage Law passed by the People’s Republic of China in 1950 promoted free choice and forbade arranged marriage and other interference by families in the marriage decisions of their children. Later, Land Reform, Collectivization and other movements had profound impacts on rural household organization and social relations. We investigate their effects on assortative mating by using novel linked administrative data compiled in rural Shanxi Province in North China in the mid-1960s. These data record the education and family class labels (jiating chushen) of spouses for 1459 couples in 30 villages. The class labels were assigned in the 1950s based on family landholding before the Land Reform and became hereditary. We find that class label had effects above and beyond those of education, suggesting that assortative mating studies that only consider education overlook an important dimension of social status in marriage patterns, and thereby overstate the overall permeability of boundaries between social groups. Furthermore, by comparing couples according to whether they married before or after 1949, we find that patterns of homogamy and hypergamy remained highly stable in the face of substantial social transformation after 1949.

Assortative mating has been found regarding personality traits, personal attitudes and values, and cognitive abilities, but so far no study has investigated assortative mating regarding multidimensional perfectionism. A total of 422 participants from a non-commercial panel (mean age = 36.0 years) completed measures of self-oriented, other-oriented, and socially prescribed perfectionism and rated the attractiveness of four potential dating partners (“dates”): a self-oriented, an other-oriented, a socially prescribed, and a non-perfectionist date. Results showed that all perfectionist dates were seen as less attractive than the non-perfectionist date. This effect, however, was moderated by self-oriented and other-oriented perfectionism. Participants high in self-oriented perfectionism found all three perfectionist dates more attractive than participants low in self-oriented perfections. Participants high in other-oriented perfectionism found the self-oriented perfectionist date more attractive, and the non-perfectionist date less attractive than participants low in other-oriented perfectionism. The findings are discussed with respect to assortative mating, the social disconnection model of perfectionism, and the heritability of perfectionism.