Ecological determinants of divorce: a structural approach to the explanation of Japanese divorce.

This paper examines the ecological determinants of contemporary Japanese divorce rates on the prefectural level. LISREL and computer-generated graphics are the analytic methods used. The aggregate level of analysis demands the use of the ecological model which posits that demographic changes, economic activities, migration patterns, and the level of urbanization are significant predictors of divorce rate. Our analysis demonstrates that sex ratio, female labor force participation, female in-migration patterns, population increase, and net household income all play a significant role in affecting the divorce rate. Our findings also confirm the well-supported hypothesis that both population density and modernization positively influence modern Japan's divorce rates. The residual analysis also points out that in order to account for the large proportion of the unexplained variance of Japanese divorce, behavioral-related variables and island- or prefecture-specific dimensions need to be included in the ecological model of divorce.     

Ecological determinants of divorce: A structural approach to the explanation of Japanese divorce

Abstract

This paper examines the ecological determinants of contemporary Japanese divorce rates on the prefectural level. LISREL and computer‐generated graphics are the analytic methods used. The aggregate level of analysis demands the use of the ecological model which posits that demographic changes, economic activities, migration patterns, and the level of urbanization are significant predictors of divorce rate. Our analysis demonstrates that sex ratio, female labor force participation, female in‐migration patterns, population increase, and net household income all play a significant role in affecting the divorce rate. Our findings also confirm the well‐supported hypothesis that both population density and modernization positively influence modern Japan's divorce rates. The residual analysis also points out that in order to account for the large proportion of the unexplained variance of Japanese divorce, behavioral‐related variables and island‐ or prefecture‐specific dimensions need to be included in the ecological model of divorce.     

Fitness consequences of divorce in the oystercatcher, Haematopus ostralegus

We investigated the fitness consequences of divorce in oystercatchers. We made a distinction between two types of divorce: in desertions the disruption of the pair bond is initiated by one of the pair members, and in usurpations by a conspecific individual. Survival and reproduction prospects for oystercatchers are largely determined by their social status (nonbreeder or breeding bird at a site of a specific quality). Changes in social status in relation to divorce showed that birds taking the initiative to leave their mate increased in fitness, relative to birds that were forced to leave their partner. Status of individuals that remained in their territory after divorce was unaffected if their mate was expelled, but declined if their mate deserted. Survival after divorce was significantly lower for birds that were expelled than for those deserting. Divorce rate, and especially desertion rate, was higher among occupants of low- than high-quality territories. In general, divorce rate increased following elevated mortality. In high-quality territories usurpations increased with increasing breeder mortality, but at low-quality territories this relation was absent. Desertion rates were similarly related to mortality in both territory types. Divorce participants thus differed strongly in their fitness prospects, depending on the type of divorce, the role played in the divorce and the quality of the territory where divorce took place. Studies that do not observe the birds during divorce cannot determine the type of divorce and the role played by the individuals, and this may lead to misleading conclusions on the costs and benefits of divorce. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Gift-giving in romantic couples serves as a commitment signal: Relational mobility is associated with more frequent gift-giving

The present study explored why married couples periodically exchange gifts. Based on the commitment signal hypothesis, we tested whether relational mobility, which was operationalized as divorce rate in Study 1 and relational opportunities in Study 2, is positively correlated with the frequency of gift exchanges among married couples. In Study 1, we found that married couples in the U.S., which is associated with a relatively high divorce rate, were more likely to give and receive gifts to and from their partners than those in Japan, which is associated with a relatively low divorce rate. This societal difference, in contrast, was not observed among unmarried couples, who were still developing their relationship (and thus, partner changes could frequently happen regardless of the country-level divorce rate). Study 2, a secondary analysis of extant survey data, revealed that Japanese married couples who have more relational opportunities more frequently engage in gift exchanges than those who do not. Together, these results support our hypothesis that periodical gift exchanges work as commitment signals among married couples.     

Psychiatry and Psychotherapy: Is a Divorce Imminent?

Despite the long tradition of psychiatrists practicing psychotherapy, many psychiatric and medical leaders are predicting and urging a reorientation of psychiatry toward the medical model. They would leave psychotherapy to psychologists, social workers and the like. Many social, governmental and institutional factors favor such a change. The marriage of psychiatry and psychotherapy has always been an uneasy one, and the push for divorce may be irresistible. The author cautions that a divorce could be detrimental to medicine by substituting, in the name of “science,” a dehumanized, technological psychiatry for the current “moral” treatment. One alternative to divorce is a broader approach to psychiatry, combining biological, neuromedical, socioenvironmental and psychodynamic factors. The divorce, though imminent, should be resisted.     

Social life factors affecting the mortality, longevity, and birth rate of total Japanese population: effects of rapid industrialization and urbanization

To expand upon the findings that lower mortality was found in Japanese urban areas in contrast to the Western model where in the US and Britain the risk of death was higher in metropolitan areas and conurbations, 22 social life indicators are examined among 46 prefectures in Japan in terms of their effect on age specific mortality, life expectancy, and age adjusted marriage, divorce, and birth rates. The effects of these factors on age adjusted mortality for 8 major working and nonworking male populations, where also analyzed. The 22 social life factors were selected from among 227 indicators in the system of Statistical Indicators on Life. Factor analysis was used to classify the indicators into 8 groups of factors for 1970 and 7 for 1975. Factors 1-3 for both years were rural or urban residence, low income and unemployment, and prefectural age distribution. The 4th for 1970 was home help for the elderly and for 1975, social mobility. The social life indicators were classified form 1 to 8 as rural residence in 1970 and 1975, urban residence, low income, high employment, old age, young age, social mobility, and home help for the elderly which moved from 8th place in 1970 to 1st in 1975. Between 1960-75, rapid urbanization took place with the proportion of farmers, fishermen, and workers declining from 43% in 1960 to 19% in 1975. The results of stepwise regression analysis indicate a positive relationship of urban residence with mortality of men and women except school-aged and middle-aged women, and the working populations, as well as life expectancy at birth for males and females and ages 20 and 40 years for males. Rural residence was positively associated with the male marriage rate, whereas the marriage rate for females was affected by industrialization and urbanization. High employment and social mobility were positively related to the female marriage rate. Low income was positively related to the divorce rate for males and females. Rural residence and high employment were positively related to the birth rate. The birth rate is higher in rural areas. Mortality of professional, engineering, and administrative workers was slightly lower than the total working population, while sales workers, those in farming, fishing, and forestry, and in personal and domestic service had significantly higher mortality. The mortality of the nonworking population was 6-8 times higher than sales, transportation, and communication, and personal and domestic service as well as the total population.     

Influence of reproductive output on divorce rates in polar seabirds

The high occurrence of social monogamy in birds has led to questions about partner fidelity, or the perennial nature of monogamy from one breeding season to another. Despite the evolutionary advantages of partner fidelity, divorce occurs among 95% of bird species. We aimed to describe patterns of divorce and partner fidelity in five seabird species breeding in Arctic and Antarctic regions and investigated the influence of breeding status on pair bond maintenance. For four out of the five species considered, we observed low divorce rates (respectively 1.9%, 3.3%, 2.5%, and 0.0% for Brünnich''s guillemot, glaucous gull, Antarctic petrel, and south polar skua), while the divorce rate was much higher (19.1%) for the black‐legged kittiwake. For kittiwakes, the divorce rate was lower for pairs that managed to raise their chick to 15 days of age, while the effect of breeding success on divorce in the four other species could not be tested due to the rareness of divorce events. Our results emphasize the potentially large temporal (interannual) variations that should be taken into account in understanding divorce and partner fidelity in seabirds.     

Divorce in the early years of marriage in England and Wales: results from a prospective study using linked records

A representative sample of over 1000 couples who married during 1979 in England and Wales was followed from the date of marriage until mid-1984 to investigate the characteristics of couples who divorce soon after marriage. Results of this 5 year study show that couples who apparently lived together before marriage had a below average chance of early divorce, whereas couples where the addresses of the partners before marriage were very close had a significantly high rate of early breakdown. The chance of early divorce was significantly above average for spouses marrying in their teens and for both husbands and wives who, at their marriage, belonged to social class 5 (work in unskilled manual occupations). Couples who married with a civil ceremony had an above average (and those marrying with a religious ceremony a below average) risk of early divorce, but such differences were found to be negligible on analyzing the results from a matched case-control study in which each "case" marriage (one which did end in early divorce) was matched with a "control" marriage (one which did not end in early divorce). There is substantial evidence that age at marriage and previous marital status of the marriage partners have a decided influence upon the propensity to divorce. 2 conclusions concerning fertility are more likely than the average married couple to have had a pre-maritally conceived child, and 2) that couples who divorce relatively quickly tend on average to have larger family sizes, even if children who were pre-martitally conceived are exluded.     

No evidence of immediate fitness benefits of within-season divorce in monogamous birds

Individuals of socially monogamous species can correct for suboptimal partnerships via two secondary mating strategies: divorce and extra-pair mating, with the former potentially providing both genetic and social benefits. Divorcing between breeding seasons has been shown to be generally adaptive behaviour across monogamous birds. Interestingly, some pairs also divorce during the breeding season, when constraints on finding a new partner are stronger. Despite being important for a comprehensive understanding of the evolution of social monogamy, whether within-season divorce is adaptive and how it relates to extra-pair mating remains unknown. Here, we meta-analysed 90 effect sizes on within-season divorce and breeding success, extracted from 31 studies on 24 species. We found no evidence that within-season divorce is adaptive for breeding success. However, the large heterogeneity of effect sizes and strong phylogenetic signal suggest social and environmental factors—which have rarely been considered in empirical studies—may play an important role in explaining variation among populations and species. Furthermore, we found no evidence that within-season divorce and extra-pair mating are complementary strategies. We discuss our findings within the current evidence of the adaptiveness of secondary mating strategies and their interplay that ultimately shapes the evolution of social monogamy.     

A two-sex demographic model with single-dependent divorce rate

Divorce appears to be one of the least studied demographic processes, both empirically and in two-sex demographic models. In this paper, we study mathematical as well as biological implications of the assumption that the divorce rate is positively affected by the amount of single (i.e., unmarried/unpaired) individuals in the population. We do that by modifying the classical exponential two-sex model accounting for pair formation and separation. We model the divorce rate as an increasing function of the single population size and show that the single population pressure on the established couples alters the exponential behavior of the classical model in which the divorce rate is assumed constant. In particular, the total population size becomes bounded and a unique positive equilibrium exists. In addition, a Hopf bifurcation analysis around the positive equilibrium shows that the modified model may exhibit sustained oscillations.     

Carry-over effects of the social environment on future divorce probability in a wild bird population

Initial mate choice and re-mating strategies (infidelity and divorce) influence individual fitness. Both of these should be influenced by the social environment, which determines the number and availability of potential partners. While most studies looking at this relationship take a population-level approach, individual-level responses to variation in the social environment remain largely unstudied. Here, we explore carry-over effects on future mating decisions of the social environment in which the initial mating decision occurred. Using detailed data on the winter social networks of great tits, we tested whether the probability of subsequent divorce, a year later, could be predicted by measures of the social environment at the time of pairing. We found that males that had a lower proportion of female associates, and whose partner ranked lower among these, as well as inexperienced breeders, were more likely to divorce after breeding. We found no evidence that a female''s social environment influenced the probability of divorce. Our findings highlight the importance of the social environment that individuals experience during initial pair formation on later pairing outcomes, and demonstrate that such effects can be delayed. Exploring these extended effects of the social environment can yield valuable insights into processes and selective pressures acting upon the mating strategies that individuals adopt.     

Does competition for nests affect genetic monogamy in Cory's shearwater Calonectris diomedea?

Most bird species are socially monogamous. However, extra‐pair copulations (EPCs), resulting in extra‐pair paternity (EPP), commonly occur. EPCs should allow females to adjust social mate choice and allow males that fail to obtain a nest a chance to avoid missing a breeding season, especially when poor nest supply constrains social mate choice. Procellariiformes (albatrosses and petrels) are socially monogamous seabirds which seldom divorce, even when nest availability constrains social mate choice. In Cory's shearwater Calonectris diomedea, a burrow‐nesting petrel, two studies conducted in the Mediterranean, where competition for nests is weak, detected no EPP. EPP remains to be investigated at localities where competition for nests is much stronger, such as Vila islet, Azores archipelago, Atlantic Ocean. We conducted a genetic (microsatellites) study over two successive years on Vila, involving the breeding pairs of the same 65 nests each year and their single chick. EPPs occurred each year, the overall rate being 11.6%. Coupling genetic analyses to a 7‐year demographic survey provided additional data on pair bonds and competition for nests. Overall, cuckoldry was unrelated to divorce, nest density and inbreeding avoidance, but was more frequent when the social male was small. Nest changes were more costly for males than for females, and some apparently unpaired males attempted to dislodge social males during within‐pair copulations. These results are compatible with the existence of a link between poor nest availability and EPP and confirm that even species considered strongly monogamous can adopt flexible mating strategies.     

The effect of divorce on infant mortality in a remote area of Bangladesh

The process of divorce is usually lengthy and hazardous, and can start quarrels that can lead to the abuse of women and their children. This study examines the effects of divorce on neonatal and postneonatal mortality of babies born before and after divorce in Teknaf, a remote area of Bangladesh. The longitudinal demographic surveillance system (DSS) followed 1,762 Muslim marriages in 1982-83 for 5 years to record divorce, deaths of spouse, emigration and births. It recorded 2,696 live births during the follow-up period, and their survival status during infancy. Logistic regression models were used to estimate the effect of divorce on neonatal and postneonatal mortality, controlling for maternal age at birth, parity, sex of the child and household economic status. The odds of neonatal and postneonatal deaths among babies born after divorce or less than 12 months before mothers were divorced were more than double the odds of those born to mothers of intact marriages. The odds of postneonatal deaths were two times higher among babies born more than 12 months before divorce happens than their peers. The high mortality of infants born before and after mothers were divorced may reflect how abusive marriage and divorce increase the vulnerability of women and children in rural Bangladesh. Divorce and abuse of women are difficult and intractable social and health problems that must be addressed.     

Is mate fidelity related to site fidelity? A comparative analysis in Ciconiiforms

We tested for an association between divorce rate and site fidelity in 42 avian species belonging to the order Ciconiiforms, using comparative methods that account for the influences of phylogenetic relationships on the data. Our methods enabled us to detect evidence of correlated evolution and provided information on the temporal ordering of evolutionary changes in these two variables. We found a significant correlation between divorce rate and site fidelity, indicating that species with little or no site fidelity are more likely to divorce. Our data suggest that the coupled evolution of divorce and site fidelity can be summarized by three major events. The first event corresponds to a transition from species showing high divorce rate and low or no site fidelity to species that tended to reuse the same nests over consecutive breeding seasons. This was followed by a transition towards higher mate fidelity, with the preservation of pair bonds over consecutive breeding attempts. In a third stage, divorce rate and the rate of site fidelity varied, independently of each other. We discuss our results within the context of the ancestor species and the past environments in which the traits originated, and address the importance of the potential for individual recognition in shaping the observed patterns of covariation between mate fidelity and site fidelity in Ciconiiforms. Copyright 2000 The Association for the Study of Animal Behaviour.     

Evolution of human serial pairbonding

Data on divorce taken for all available years between 1947 and 1981 from the Demographic Yearbooks of the United Nations on 58 peoples illustrate that divorce has a consistent pattern. Divorces exhibit a skewed distribution, characterized by the occurrence of the mode early in marriage (with a divorce peak on or around the fourth year) and a gradual, long-tailed decline following this peak. Divorce risk peaks in age category 25-29 for males and age categories 20-24 and 25-29 for females, the height of reproductive and parenting years, and divorce counts peak among couples with two or fewer children. These properties of divorce are unrelated to divorce rate; they occur in societies with both high and low divorce rates. Data on available horticultural and gathering/hunting societies illustrate that divorce also peaks among young couples early in marriage. Remarriage by divorced and widowed individuals of reproductive age is also common cross-culturally. It is proposed that the above four-year modal marriage duration among couples of reproductive age who divorce reflects a hominid reproductive strategy that probably evolved some time after the appearance of Homo in response to increased female "reproductive burden" and functioned to ensure the survival of the hominid infant through weaning. Serial pairbonding during the female's reproductive years had ancestral adaptive advantages, producing the modern cross-cultural pattern of serial pairbonding.     

Divorce among the Yoruba

Divorce rates among the northern Yoruba are not only higher than one might expect in patrilineal societies, but little different from those of the southern Yoruba, with cognatic descent groups. This initial observation challenges the hypothesis that divorce rates are directly correlated with the line of descent. Data on over 300 divorces were collected in four Yoruba towns—two with agnatic and two with cognatic descent groups. The divorces were classed by the length of the terminated marriage and its fertility, and the distribution of the types of divorce were then compared in the four towns. The results suggest that the rate of divorce is primarily correlated with the degree to which a woman is alienated by marriage from her own descent group. But a number of secondary factors seem to be important, and these may cumulatively raise or reduce the divorce rate to a marked degree.     

Degree of mutual ornamentation in birds is related to divorce rate

Many bird species have ornaments that are expressed equally in both sexes. I use comparative analysis to investigate why some monomorphic birds are highly ornamented, whereas others are drab. The results show a significant positive association between the degree of mutual ornamentation and divorce rate. This result is robust to the removal of the effects of phylogeny, site fidelity, residency, coloniality, nest type, mortality, body size and body-size dimorphism. The level of extra-pair paternity was not related to the degree of mutual ornamentation. I argue that these results are compatible with a process of mutual sexual selection, in which both sexes compete for access to mates. The coupled evolution of ornamentation and divorce rate, from the probable ancestral state of a high degree of ornamentation and a low divorce rate, appears to result mainly from a loss of ornamentation under mate fidelity.     

The coevolution of long‐term pair bonds and cooperation

The evolution of social traits may not only depend on but also change the social structure of the population. In particular, the evolution of pairwise cooperation, such as biparental care, depends on the pair‐matching distribution of the population, and the latter often emerges as a collective outcome of individual pair‐bonding traits, which are also under selection. Here, we develop an analytical model and individual‐based simulations to study the coevolution of long‐term pair bonds and cooperation in parental care, where partners play a Snowdrift game in each breeding season. We illustrate that long‐term pair bonds may coevolve with cooperation when bonding cost is below a threshold. As long‐term pair bonds lead to assortative interactions through pair‐matching dynamics, they may promote the prevalence of cooperation. In addition to the pay‐off matrix of a single game, the evolutionarily stable equilibrium also depends on bonding cost and accidental divorce rate, and it is determined by a form of balancing selection because the benefit from pair‐bond maintenance diminishes as the frequency of cooperators increases. Our findings highlight the importance of ecological factors affecting social bonding cost and stability in understanding the coevolution of social behaviour and social structures, which may lead to the diversity of biological social systems.     

Marriage: an evolutionary perspective

Marriage is universal, and pair bonding is found in other species too with highly dependent young. So marriage functions as a reproductive social arrangement that traditionally involved the extended family. The sexes are not identical in their biological contributions to children's survival, so they seek somewhat different attributes in a mate. Men seek a young, attractive, sexually faithful bride. Women seek a man who is older, taller, and (as in many other species) socially dominant. Both sexes prefer a kind, healthy, attractive, similar mate who is emotionally attached to them. A spouse who fails to maintain sufficiently high mate value is vulnerable to divorce. Infertility and sexual dissatisfaction predict divorce, as does death of a child, but the more children, the stabler the marriage. Cross-cultural data suggest that cruel or subdominant men (e.g., poor providers) and unfaithful women are prone to divorce. Marriages in which the wife dominates the husband in economic contributions, nonverbal behavior, and decision making tend to be less satisfying. In societies in which wives are economically independent of husbands, divorce rates are high. As women's economic power has risen with industrialization, divorce rates have climbed. Economic and fitness considerations also help explain cultural differences in polygyny, age at marriage, arranged marriage, concern with the bride's sexual chastity, and marriage ceremonies. Other factors also affect marital dynamics, such as state subsidies to families, the sex ratio, and influence of the couple's parents.     

Mating strategies in dominant meerkats: evidence for extra‐pair paternity in relation to genetic relatedness between pair mates

Rates of extra‐pair paternity (EPP) have frequently been associated with genetic relatedness between social mates in socially monogamous birds. However, evidence is limited in mammals. Here, we investigate whether dominant females use divorce or extra‐pair paternity as a strategy to avoid the negative effects of inbreeding when paired with a related male in meerkats Suricata suricatta, a species where inbreeding depression is evident for several traits. We show that dominant breeding pairs seldom divorce, but that rates of EPP are associated with genetic similarity between mates. Although extra‐pair males are no more distantly related to the female than social males, they are more heterozygous. Nevertheless, extra‐pair pups are not more heterozygous than within‐pair pups. Whether females benefit from EPP in terms of increased fitness of the offspring, such as enhanced survival or growth, requires further investigations.