Does sex of children matter? Implications for fertility in Pakistan

Preference for children of either sex is considered a constraint on fertility decline as it induces many couples to keep adding on surviving children in the hope of having a desired sex composition of children. However, preferences for children of a particular sex may differ in relation to demographic and socioeconomic characteristics of women, traditional values and cultural practices, such as propagating a family name, providing economic advantages, and obtaining a medium of social and economic security in times of illness, unemployment and old age. Utilizing the Pakistan Integrated Household Survey (2001-02), this paper aims at investigating the existence of sex preference and examines sex preference differentials by different attributes of women in Pakistan. The results reveal that there is a desire to have another child in the presence of all children of one sex, either sons or daughters. The desire to have a son with only or mostly daughters, however, is stronger than the desire to have a daughter with only or mostly sons. This behaviour will retard fertility decline unless there is a shift in the desire to have children of both sexes in Pakistan.     

The relation of son preference and religion to induced abortion: the case of South Korea

This paper explores the factors that influence the practice of induced abortion in a very low fertility society, with particular emphasis on son preference and three distinct religions: Confucianism, Buddhism and Christianity. Using multivariate logistic regression models fitted by the generalized estimating equation (GEE) method, this paper analysed the data collected by the 2000 Korea National Fertility and Family Health Survey of 6348 married women aged 15-49 years with a total of 1217 pregnancy outcomes. The results showed that the likelihood of induced abortions in women with two or more children, compared with those with one child, was significantly influenced by the sex composition of the previous children: odds ratio (OR)=12.71 (95% CI=5.49, 29.42) for women with only son(s), and OR=3.91 (95% CI=1.67, 9.14) for women with only daughter(s). At parity two, women with two sons were much more likely to have induced abortions than women with two daughters (OR=5.88, 95% CI=2.70, 12.85). Although Buddhist women were not significantly different from Confucian women in induced abortion practice, Christian women were much less likely than Confucian women to have an induced abortion (OR=0.39, 95% CI=0.18, 0.88 for women with only sons and OR=0.44, 95% CI=0.24, 0.81 for women with two children). This suggests that even in this very low fertility society, son preference and religious affiliation are significant predictors of women's practice of induced abortion.     

Two sons and a daughter: sex composition and women's reproductive behaviour in madhya pradesh, India

Summary This article examines how the sex composition of women's current children at the start of a pregnancy interval influences both fertility desires and the full range of reproductive actions women may take to realize them, including temporary contraception, abortion and sterilization, in Madhya Pradesh, India, where popular notions of ideal family size and sex composition are dominated by son preference. The analysis is conducted using a dataset of 9127 individual pregnancy intervals from a 2002 statewide representative survey of 2444 women aged 15-39 with at least one child. The results indicate that women's preferences go beyond a singular preference for male children, with the preferred composition of children being two boys and one girl. Women with this composition are 90% less likely to report having wanted another pregnancy (OR 0.097, p<0.01) relative to those with two girls. These preferences have significant implications for reproductive actions. While sex composition has no statistically significant effect on the use of temporary contraception, those with the preferred sex composition are twice as likely to attempt abortion (OR 2.436, p<0.01) and twelve times more likely to be sterilized (OR 12.297, p<0.01) relative to those with two girls only.     

Preferences for sex of children: a multivariate analysis

Data from the 1973-74 Growth of Alberta Family Study were used to determine whether women who express a preference for sons versus daughters differ from each other in terms of selected characteristics. 67% of the 599 women surveyed indicated a preference for at least 1 child of each sex. However, the majority of those who wanted 3 children desired 2 sons and 1 daughter, indicating a slight son preference. Discriminant function analysis indicated the pull toward son preference was greater the higher the woman's education, the more sisters the wife has, and the higher the current family size and number of additional children expected. While the number of wife's sisters makes the greatest contribution to daughter preference among adolescent mothers, birth place (Canada) was most important among older women. Finally, it was shown that acceptance of traditional female roles was a significant discriminator among women with a strong sex preference and those with no sex preference at all. These findings suggest that sex preference may become an important factor in fertility decisions as family size continues to decrease. If sex predetermination were to become possible, an imbalance in the sex ratio is a likely result.     

Son preference in Bangladesh: an emerging barrier to fertility regulation

This study investigates the effect of son preference on contraceptive use and desire for additional children using national level survey data from Bangladesh for the years 1969 and 1979. National probability samples of ever married women between the ages of 10 and 50 were selected and stratified by urban-rural residence. Specifically, the study focuses on contraceptive use and desire for additional children and separates the effect of sex preference from that of high parity on fertility control. Son preference has a negative effect on contraceptive use and a positive effect on the desire for additional children regardless of socioeconomic and demographic characteristics. This advese effect of son preference on fertility regulation seemed to have persisted over the years. Relevent socioeconomic conditions in Bangladesh are described. In 1979, the effect of sex composition on contraceptive use or desire for additional children varied by parity. The negative effect of fewer living sons on contraceptive use and its positive effect on desire for additional children was higher in parities between 2 and 4 than in other parities. The effect of sex composition was stronger on desire for additional children than on contraceptive usage. In 1969, however, there was no consistent positive relationship between sex composition and contraceptive use. The relationship between sex composition and desire for more children was positive. Among women of parities 2 to 4, an excess of daughters continued to have a major positive effect on desire for additional children, and a negative effect on contraceptive use, after controlling for other sociodemographic variables. For parities 1 and 5 or above, the effect was either weak or inconsistent.     

Children of homosexuals and transsexuals more apt to be homosexual

Do the sexual inclinations of parents influence those of their children? Of 77 adult children of homosexual parents who volunteered for three different investigations, at least 23 (30%) were currently homosexual: twelve (55%) of 22 daughters and three (21%) of fourteen sons of lesbians; five (29%) of seventeen daughters and three (17%) of eighteen sons of gays; none of six sons with both a gay and a lesbian parent. At least 25 (32%) were currently heterosexual. Of the ten with transsexual parents, one of nine daughters was currently lesbian, one was currently heterosexual, and one was transsexual. The son's sexual preference was not reported. These findings suggest that parents' sexual inclinations influence their children's.     

Beautiful parents have more daughters: a further implication of the generalized Trivers-Willard hypothesis (gTWH)

The generalized Trivers-Willard hypothesis (gTWH) [Kanazawa, S., 2005. Big and tall parents have more sons: further generalizations of the Trivers-Willard hypothesis. J. Theor. Biol. 235, 583-590) proposes that parents who possess any heritable trait which increases the male reproductive success at a greater rate than female reproductive success in a given environment will have a higher-than-expected offspring sex ratio, and parents who possess any heritable trait which increases the female reproductive success at a greater rate than male reproductive success in a given environment will have a lower-than-expected offspring sex ratio. One heritable trait which increases the reproductive success of daughters much more than that of sons is physical attractiveness. I therefore predict that physically attractive parents have a lower-than-expected offspring sex ratio (more daughters). Further, if beautiful parents have more daughters and physical attractiveness is heritable, then, over evolutionary history, women should gradually become more attractive than men. The analysis of the National Longitudinal Study of Adolescent Health (Add Health) confirm both of these hypotheses. Very attractive individuals are 26% less likely to have a son, and women are significantly more physically attractive than men in the representative American sample.     

Intention versus behaviour in parental sex preferences among the Mukogodo of Kenya

The relationship between parents' stated sex preferences for children and actual parental behaviour towards sons and daughters is examined among the Mukogodo, a group of traditional pastoralists in rural Kenya. Although their cultural values are male-centered and they tend to express a preference for sons, Mukogodo parents actually appear to be more solicitous of daughters, and the Mukogodo have a strongly female-biased childhood sex ratio. Studies of stated sex preferences should therefore be coupled with attempts to assess actual parental investment in sons and daughters.     

Reproductive costs of sons and daughters in Rocky Mountain bighorn sheep

Differential maternal investment theory predicts that in sexuallydimorphic and polygynous species mothers should invest morein sons than in daughters. We tested the hypothesis that bighornewes that raise sons incur greater reproductive costs than ewesthat raise daughters. Although ewe mass gain during lactationand subsequent winter body mass loss were independent of lambsex, lambs born the year following the weaning of a son hadlower survival than lambs born after a daughter. The effectsof lamb sex on subsequent reproductive success of ewes becamemore evident at high population density. Lamb sex did not affectmaternal survival. Population density, weather, and ewe agedid not alter the relationship between lamb sex and subsequentreproductive success of the ewe. The year after weaning a son,ewes were more likely to have a daughter than a son, while ewesthat had previously weaned a daughter had similar numbers ofsons and daughters. Our results show that for bighorn sheepewes, sons have a greater life-history cost than daughters,suggesting a differential maternal investment in the sexes.     

Estimating relative parental investment in sons versus daughters

Fisher proposed that natural selection would adjust the population sex ratio so that parental expenditure on sons equals expenditure on daughters. Thus if two daughters can be produced for every son, the Fisherian equilibrium is ? sons and ? daughters. The relative cost of a son versus a daughter is necessarily manifested in the trade-off between family size and sex ratio, and we offer a method to estimate this trade-off from data on family compositions. Simulation studies indicate that the method works well in some cases but not others. Application of the method to data on a polychaete suggests that sons are much costlier than daughters; the observed sex ratio in fact significantly favored daughters, but not to the extreme predicted by our measure of differential cost.     

Who suppresses female sexuality? An examination of support for Islamic veiling in a secular Muslim democracy as a function of sex and offspring sex

Whether it is men or women who suppress female sexuality has important implications for understanding gendered relations, ultimately providing insight into one widespread cause of female disadvantage. The question of which sex suppresses female sexuality more avidly, however, neglects that our interests are never unambiguously masculine or feminine; each of us has a combination of male and female kin which alters how much of our future fitness derive from each sex. Here we exploit a nationally representative sample of 600 Tunisians to test whether support for Islamic veiling—a proxy for female sexual suppression—is more common amongst one sex than the other, and is affected by the relative sex of one's offspring (i.e., the number of sons relative to daughters). We find that men are more supportive of Islamic veiling than women, but women with more sons are more supportive of veiling and more likely to wear veils than women with fewer sons. All effects were robust to the inclusion of religiosity, which was weaker amongst men and unrelated to the number of sons a woman had. The number of daughters affected neither religiosity nor support for veiling, but did increase women's likelihood of wearing contemporary, fashionable Tunisian veils compared with no head covering. We further found that men were more religious if they had more sons. Overall, these findings highlight that far from being the fixed strategy of one sex or the other, female sexual suppression manifests facultatively to promote one's reproductive interests directly or indirectly by creating conditions beneficial to one's descendent kin. These results show that both men and women can suppress female sexuality, although the function in either case appears more closely aligned with male rather than female interests.     

No evidence for adjustment of sex allocation in relation to paternal ornamentation and paternity in barn swallows

Sex allocation theory predicts that parents should adjust investment in sons and daughters according to relative fitness of differently sexed offspring. In species with female preference for highly ornamented males, one advantage potentially accruing to parents from investing more in sons of the most ornamented males is that male offspring will inherit characters ensuring sexual attractiveness or high-quality genes, if ornaments honestly reveal male genetic quality. Furthermore, in species where extra-pair fertilizations occur, offspring sired by an extra-pair male are expected to more frequently be male than those of the legitimate male if the latter is of lower quality than the extra-pair male. We investigated adjustment of sex ratio of offspring in relation to ornamentation of the extra-pair and the social mate of females by direct manipulation of tails of male barn swallows Hirundo rustica . Molecular sexing of the offspring was performed using the W chromosome-linked avian chromo-helicase-DNA-binding protein (CHD) gene while paternity assessment was conducted by typing of hypervariable microsatellite loci. Extra-pair offspring sex ratio was not affected by ornamentation of their biological fathers relative to the experimental ornamentation of the parental male. Experimental ornamentation of the parental males did not affect the sex ratio of nestlings in their broods. Female barn swallows might be unable to bias offspring sex ratio at hatching according to the quality of the biological father. Alternatively, fitness benefits in terms of sexual attractiveness of sons might be balanced by the cost of compensating for little parental care provided by highly ornamented parental males, if sons are more costly to rear than daughters, or the advantage of producing more daughters, if males with large ornaments contribute differentially more to the viability of daughters than sons.     

Lack of Sex-Biased Maternal Investment in spite of a Skewed Birth Sex Ratio in White-Headed Langurs (Trachypithecus leucocephalus)

Numerous hypotheses have been developed to explain sex allocation. In male-dispersing, female cooperatively breeding species, the local resource competition model predicts male-biased birth sex ratio, the local resource enhancement model predicts female-biased birth sex ratio, and the population adjustment model predicts that biased birth sex ratio should not be favored if the two sexes are equally costly to rear. The male quality model predicts that, in polygynous species, females in better physical condition will either produce more sons than daughters or invest more heavily in sons than in daughters. White-headed langurs are a female philopatry and female cooperatively breeding species. During a 11-yr study, a total of 133 births were recorded, among which birth sex ratio (M:F = 73:49) was significantly male-biased. This is consistent with the prediction of the local resource competition model. On the other hand, if mothers balanced their investment between the two sexes, according to Fisher's population adjustment model, males should be the less-costly-to-rear sex. However, we found no sex difference for infant mortality (12.3% in males and 12.2% in females), and sons induced slightly longer interbirth interval (son: 26.4 ± 1.1 mo, daughter: 24.1 ± 0.6 mo) and lactational period (son: 20.9 ± 1.0 mo, daughters: 19.6 ± 0.5 mo) for their mothers. Thus, the population adjustment model was not supported by this study. The local resource enhancement model was not supported because birth sex ratio did not bias to females who provided more reproductive assistance. On the individual level, probit regression showed no relation between birth sex ratio and group size. Because the group size was considered to be negatively related to female physical condition, our study did not support the male-quality model. We suggested several possibilities to explain these results.     

In poor families, mothers' milk is richer for daughters than sons: A test of Trivers-Willard hypothesis in agropastoral settlements in Northern Kenya

The Trivers–Willard hypothesis predicts the unequal parental investment between daughters and sons, depending on maternal condition and offspring reproductive potential. Specifically, in polygynous populations where males have higher reproductive variance than females, it predicts that mothers in good condition will invest more in sons, whereas mothers in poor condition will invest more in daughters. Previous studies testing this hypothesis focused on behavioral investment, whereas few examined biological investment. This study investigates the Trivers–Willard hypothesis on both behavioral and biological parental investment by examining breastfeeding frequencies and breast milk fat concentrations. Data from exclusively breastfeeding mothers in Northern Kenya were used to test hypotheses: Economically sufficient mothers will breastfeed sons more frequently than daughters, whereas poor mothers will breastfeed daughters more frequently than sons, and economically sufficient mothers will produce breast milk with higher fat concentration for sons than daughters, whereas poor mothers will produce breast milk with higher fat concentration for daughters than sons. Linear regression models were applied, using breastfeeding frequency or log‐transformed milk fat as the dependent variable, and offspring's sex (son = 1/daughter = 0), socioeconomic status (higher = 1/lower = 0), and the sex‐wealth interaction as the predictors, controlling for covariates. Our results only supported the milk fat hypothesis: infant's sex and socioeconomic status interacted (P = 0.014, n = 72) in their relation with milk fat concentration. The model estimated that economically sufficient mothers produced richer milk for sons than daughters (2.8 vs. 0.6 gm/dl) while poor mothers produced richer milk for daughters than sons (2.6 vs. 2.3 gm/dl). Further research on milk constituents in relation to offspring's sex is warranted. Am J Phys Anthropol , 2012. © 2012 Wiley Periodicals, Inc.     

Spending patterns of Chinese parents on children's backpacks support the Trivers-Willard hypothesis: Results based on transaction data from China's largest online retailer

Using the 2015 student backpack transaction data from the largest E-commerce business in China, this study takes a novel “big data” approach to test the patterns of parental sex preference by comparing the difference in cost between blue and pink backpacks at different quantiles of the backpack cost distribution. Unconditional quantile regression results show that, depending on the quantile of choice, the blue-pink difference in backpack cost can be positive, negative, or zero. This indicates the presence of son preference, daughter preference, and gender indifference in the same population. Treating backpack cost as a proxy measure of parental economic status, such results indicate that parents of high economic status invest more heavily in sons whereas parents of low economic status invest more heavily in daughters, as predicted by the Trivers-Willard hypothesis. The discovery of a third group, between the high- and low-status parents, who invest equally in sons and daughters further strengthens the argument.     

Male offspring production by asexual Potamopyrgus antipodarum, a New Zealand snail

As only females contribute directly to population growth, sexual females investing equally in sons and daughters experience a two-fold cost relative to asexuals producing only daughters. Typically, researchers have focused on benefits of sex that can counter this 'cost of males' and thus explain its predominance. Here, we instead ask whether asexuals might also pay a cost of males by quantifying the rate of son production in 45 experimental populations ('lineages') founded by obligately asexual female Potamopyrgus antipodarum. This New Zealand snail is a powerful model for studying sex because phenotypically similar sexual and asexual forms often coexist, allowing direct comparisons between sexuals and asexuals. After 2 years of culture, 23 of the 45 lineages had produced males, demonstrating that asexual P. antipodarum can make sons. We used maximum-likelihood analysis of a model of male production in which only some lineages can produce males to estimate that ~50% of lineages have the ability to produce males and that ~5% of the offspring of male-producing lineages are male. Lineages producing males in the first year of the experiment were more likely to make males in the second, suggesting that some asexual lineages might pay a cost of males relative to other asexual lineages. Finally, we used a simple deterministic model of population dynamics to evaluate how male production affects the rate of invasion of an asexual lineage into a sexual population, and found that the estimated rate of male production by asexual P. antipodarum is too low to influence invasion dynamics.     

History of Childhood Abuse,Sensation Seeking,and Intimate Partner Violence under/Not under the Influence of a Substance: A Cross-Sectional Study in Russia

Objectives

To examine correlates of perpetration and victimization of intimate partner violence (IPV) under and not under the influence of a substance, we conducted a study among women in Russia.

Methods

In 2011, a cross-sectional survey was conducted among patients receiving services at a clinic for sexually transmitted infections in St. Petersburg, Russia. Multinomial logistic regression was used for analysis.

Results

Of 299 women, 104 (34.8%) and 113 (37.8%) reported a history of IPV perpetration and victimization, respectively. Nearly half (47.1%) of perpetrators and 61.1% of victims reported that the latest IPV event (perpetration and victimization, respectively) was experienced under the influence of a substance. Factors independently associated with IPV victimization under the influence of a substance were alcohol misuse and a higher number of lifetime sex partners, whereas only experience of childhood abuse (emotional and physical abuse) was independently associated with IPV victimization that did not occur under the influence of a substance. Childhood physical abuse, lower age of first sex, sensation seeking, and alcohol misuse were independently associated with IPV perpetration under the influence of a substance, while only childhood abuse (emotional and physical abuse) was independently associated with IPV perpetration that did not occur under the influence of a substance.

Conclusions

IPV under and not under the influence of a substance had different correlates (e.g., alcohol misuse and sensation seeking). Despite the strong association between substance use and IPV, experience of childhood abuse is an important predictor of IPV perpetration and victimization in Russia, above and beyond substance use.     

Paternal reproductive success drives sex allocation in a wild mammal

Parents should bias sex allocation toward offspring of the sex most likely to provide higher fitness returns. Trivers and Willard proposed that for polygynous mammals, females should adjust sex‐ratio at conception or bias allocation of resources toward the most profitable sex, according to their own body condition. However, the possibility that mammalian fathers may influence sex allocation has seldom been considered. Here, we show that the probability of having a son increased from 0.31 to 0.60 with sire reproductive success in wild bighorn sheep (Ovis canadensis). Furthermore, our results suggest that females fertilized by relatively unsuccessful sires allocated more energy during lactation to daughters than to sons, while the opposite occurred for females fertilized by successful sires. The pattern of sex‐biased offspring production appears adaptive because paternal reproductive success reduced the fitness of daughters and increased the average annual weaning success of sons, independently of maternal allocation to the offspring. Our results illustrate that sex allocation can be driven by paternal phenotype, with profound influences on the strength of sexual selection and on conflicts of interest between parents.     

Intralocus sexual conflict,adaptive sex allocation,and the heritability of fitness

Intralocus sexual conflict arises when selection favours alternative fitness optima in males and females. Unresolved conflict can create negative between‐sex genetic correlations for fitness, such that high‐fitness parents produce high‐fitness progeny of their same sex, but low‐fitness progeny of the opposite sex. This cost of sexual conflict could be mitigated if high‐fitness parents bias sex allocation to produce more offspring of their same sex. Previous studies of the brown anole lizard (Anolis sagrei) show that viability selection on body size is sexually antagonistic, favouring large males and smaller females. However, sexual conflict over body size may be partially mitigated by adaptive sex allocation: large males sire more sons than daughters, whereas small males sire more daughters than sons. We explored the evolutionary implications of these phenomena by assessing the additive genetic (co)variance of fitness within and between sexes in a wild population. We measured two components of fitness: viability of adults over the breeding season, and the number of their progeny that survived to sexual maturity, which includes components of parental reproductive success and offspring viability (RS^V). Viability of parents was not correlated with adult viability of their sons or daughters. RS^V was positively correlated between sires and their offspring, but not between dams and their offspring. Neither component of fitness was significantly heritable, and neither exhibited negative between‐sex genetic correlations that would indicate unresolved sexual conflict. Rather, our results are more consistent with predictions regarding adaptive sex allocation in that, as the number of sons produced by a sire increased, the adult viability of his male progeny increased.