Opposite-sex Siblings Research Articles

Genetic and environmental effects on blood pressure in a Norwegian sample.

Systolic (SBP) and diastolic (DBP) blood pressures were measured in a health screening of the adult population in Nord-Trøndelag, Norway. Correlations were computed for 23,936 pairs of spouses, 43,586 pairs of parent and offspring, 19,151 pairs of siblings, 1,251 pairs of grandparents-grandchildren, 1,146 pairs of biological uncles/aunts-nephews/nieces (avuncular), 801 non-biological avuncular pairs, 169 pairs of same-sex twins, and smaller groups of other types of relationships. Spouse correlations of 0.08 and 0.09 were approximately constant or slightly decreasing with marital duration. The correlation values for SBP and DBP were approximately 0.16 for parents-offspring, 0.19 to 0.23 for same-sex siblings with similar values for DZ twins, 0.19 and 0.16 for opposite-sex siblings, 0.52 and 0.43 for MZ twins, and close to zero for most of the second-order relationships. Genetic additive variance was estimated at 0.29 and genetic dominance variance at 0.18 with the best model for SBP. The corresponding estimates from the best models for DBP were 0.29 or lower and 0.22 or lower, the sum not exceeding 0.35. There was evidence of a moderate effect of environmental factors shared by same-sex siblings and twins (for DBP), but no cultural transmission, and whether or not adult relatives live together does not affect familial resemblance for BP. The data did not permit a very precise resolution of the relative magnitude of genetic dominance and sibling effects. The correlation structure did not show sex-specific genetic effects.

Nemaline myopathy: a report of two siblings as evidence of autosomal recessive inheritance of the infantile type

We report two opposite-sex siblings with the severe infantile form of nemaline myopathy; diagnoses were made on muscle biopsy. Neither parent showed clinical or electromyographic evidence of myopathy, and both had negative muscle biopsies. Autosomal recessive inheritance seems likely.

Adolescent sexual activity in the family context: The impact of older siblings

Using approximately 2,000 sibling pairs from the National Longitudinal Survey of Labor Market Experience of Youth, we examine the influence of an older sibling's age at first sexual intercourse on the sexual initiation of a younger sibling. Hypotheses about differences by gender composition of the pair are tested, using a framework derived from social comparison theory and a two-stage failure-time model. Results provide evidence of a direct but modest-sized older sibling effect for white but not black youth. This effect is approximately equal in magnitude for same- and opposite-sex siblings. Little support is offered for the greater salience and association of sexual activity for brother-brother as compared with sister-sister pairs.

Siblings of opposite sex as a risk factor for child mortality.

To examine whether contracting an infection from a sibling of the opposite sex affects child mortality. Retrospective study of twins and case-control study of randomly selected children conducted within a prospective cohort study. Urban and rural areas of Guinea-Bissau. 251 Pairs of twins (65 male pairs, 72 female pairs, and 114 mixed pairs), and 39 children who died and 78 controls identified in a cohort of 853 children aged less than 4, comprising 772 randomly selected children, all twins, and all children who had measles living in Bandim 2. Death of a child and sex of cotwin or older sibling nearest in age. The mortality among children from mixed pairs of twins was higher than that among pairs of the same sex (relative risk 1.47, 95% confidence interval 1.14 to 1.90). Boys had a slightly higher mortality especially in the older groups. In the case-control study the older sibling nearest in age was of the opposite sex for 29 (74%) of the children compared with 36 (46%) of the controls matched for age, sex, and area. Mortality was higher among both boys and girls with older siblings of the opposite sex than among those with siblings of the same sex (odds ratio 1.90, 0.78 to 4.61 v 7.5, 1.59 to 35.30), but the difference was more pronounced among girls. Children whose older sibling nearest in age is of the opposite sex or who have cotwins of the opposite sex have a higher mortality from infectious diseases. Further investigation is needed to determine the nature of this relation.

Social preference of zebra finches for siblings, cousins and non-kin

Adult zebra finches, Taeniopygia guttata, were tested for their tendency to perch selectively near relatives in two experiments. In the first experiment, males and females were allowed to choose between opposite-sex siblings ( r=1/2) and non-kin ( r≤1/16); males were also tested with male siblings and non-kin. The second experiment was similar to the first, except that stimulus sets consisted of first cousins ( r=1/8) and non-kin of test birds. Neither sex discriminated between siblings and non-kin in heterosexual tests, but males preferred to associate with siblings in isosexual tests. Females preferred male first cousins over non-kin; this result is believed to reflect a mating preference. For both female heterosexual preferences and male isosexual preferences, discrimination of kin was not dependent on shared prior experience.

Sexual segregation in the left and right horns of the gerbil uterus: “The male embryo is usually on the right, the female on the left” (Hippocrates)

We examined reproductive tracts of 253 female Mongolian gerbils (Meriones unguiculatus) and recorded the uterine locations (relative to siblings of opposite sex) in which 812 male and 823 female fetuses were found. Within-litter comparisons revealed that sexes were not distributed randomly across uterine horns. The percentage of males in right horns (55.0%) was greater than the percentage of males in left horns (41.8%) and the percentage of females in right horns (45.0%) was significantly less than the percentage of females (58.2%) in left horns. We did not find differences in the total number of fetuses in left and right uterine horns or a sex bias in the total sample of 1635 fetuses. Results were discussed in terms of: (a) effects of sexual segregation of fetuses on expected probabilities of fetuses developing adjacent to 0, 1, or 2 fetuses of opposite sex and (b) consequent alterations in expected frequencies of behavioral phenotypes in populations of gerbils.

Familial factors related to lung function in children aged 6-10 years. Results from the PAARC epidemiologic study.

Familial factors related to lung function between six and 10 years of age have been studied among 1,160 children whose both parents were examined in 1975 in the French PAARC (Pollution Atmosphérique et Affections Respiratoires Chroniques) Cooperative Study. The three indices FVC (forced vital capacity), FEV1 (forced expiratory volume in one second), and FEF25-75 (forced expiratory flow between 25 and 75 per cent of the vital capacity) were studied after adjustment for sex, town, age, and height (and weight for children's FVC and FEV1). Maternal (but not paternal) smoking was associated with a significant decrease in FEV1 and FEF25-75, but not in FVC. Familial resemblance was observed for all indices between children and parents and between siblings. None of the environmental factors considered (i.e., parental smoking or education) or body habitus explained the familial resemblance observed. Conversely, after taking into account the aggregation between siblings, associations between children's lung function and parental characteristics (smoking, lung function) remained significant. Parental-children correlations exhibited an increasing temporal trend with increasing age of the children. All but one correlation for FVC, FEV1, and FEF25-75 residuals of children with mothers' residuals were higher in the oldest age group compared with the youngest age group at the 0.10 level. Furthermore, correlations between siblings of opposite sex were significantly lower than correlations between siblings of like sex, especially for FEV1/FVC and FEF25-75/FVC. Results suggest that different growth patterns between boys and girls may be a critical factor in the study of lung function familial resemblance.

Sexual Behavior in the Home

To the Editor.—In an effort to discriminate "how typical families rear their children" from "abnormal sexual behavior in the home," Dr Rosenfeld et al got a large sample of parents to anonymously report their bathing practices.1 They found that " . . . parents give little coherent explanation of why they . . . stop bathing with the child of the opposite sex or stop siblings of different sexes from bathing together after they reach a certain age."

Sex-of-Sibling Effects on Opposite- and Same-Sex Friendships

This study did not replicate a 1981 finding by Burker, et al. that opposite-sex siblings have a positive effect on women's opposite-sex friendships and a negative effect on men's opposite-sex friendships; extrapolation of their finding to romantic relationships was also not supported. The present study also investigated effects of sex-of-sibling on same-sex friendships; data for 71 women and 49 men ( M age = 18.8 yr.) showed that effects of sex-of-sibling were not specific to friendships with members of one sex. Finally, while Burker, et al.'s results are consistent with a process of sibling deidentification, the current study, in suggesting a positive effect of sisters on same-sex friendships, is consistent with a process of sibling identification.

Familial influences on television viewing and aggression: A sibling study

Familial influences on aggressive behavior and TV viewing were investigated in a survey of adolescent siblings. Same-sex siblings resembled one another in aggression (brothers, r = 0.59; sisters, r = 0.52) and in their exposure to violent TV programs; opposite-sex siblings were dissimilar. Within individuals, the frequency of watching crime and action programs correlated nonsignificantly with aggression. Two other variables, however, were associated with aggression: identification with aggression and aggression consequences. These relationships also held up between families (BF, covariance of sibling' averages) and within families (WF, covariance of sibling' differences). The latter WF relationship indicated that one sibling was typically the more extreme on both aggression and its correlate than a brother or sister. These results were interpreted in light of behavioral genetic data that suggest substantial genetic influences, few common environmental influences, and large within-family environmental influences on personality development.

GENDER SALIENCE AND SOCIAL IDENTITY: THE IMPACT OF SEX OF SIBLINGS ON EDUCATIONAL AND OCCUPATIONAL ASPIRATIONS

Summary. It is proposed that an understanding of sex differences in educational and occupational aspirations of adolescents would benefit from a perspective which stresses gender identification. The social identification approach (Turner, 1982) hypothesises that these differences are a function of the degree of gender identification, which in turn is a function of the salience of sex. According to McGuire and McGuire's (1981) distinctiveness postulate, gender becomes more salient as the number of opposite sex siblings increases. In order to explore these gender salience effects 81 male and female sixth form pupils completed a questionnaire concerning their self‐perceptions, examination performance, occupational choice, and comparisons with members of each sex. Large sex differences were obtained, showing that educational and occupational ambitions were inhibited among females. Correlational analyses revealed that number of opposite sex siblings was more closely related to responses than were number of same sex, or total number of, siblings. In particular, females' choice of science O‐levels decreased as number of brothers increased. The results are taken to suggest that sex of sibling effects have an intergroup dimension which should be the focus of further research.

Galton's data a century later.

A century ago, Francis Galton obtained data from thousands of individuals on a variety of sensory, psychomotor, and physical attributes. A sub- stantial portion of these data has remained unana- tyzed. In this article, we report on the reliability of the measures, developmental trends in mean scores, correlations of the measures with age, correlations among measures, occupational differences in scores, and sibling correlations. Test-retest correlations gen- erally were very substantial Growth continued some individuals, especially those from lower eco- nomic strata, until they were in their mid-2Os. De- velopmental trends during later childhood, adoles- cence, and early maturity were found to be similar to those described in contemporary developmental psychological literature, except that the tempo of development appears to have been slightly slower then than now. Persons from lower economic strata were smaller and weaker and showed less sensory efficiency. In addition, analyses of variance indicated that persons from lower economic strata continued their physical growth longer than persons from more advantaged environments. Sibling resemblances were substantial on most of the measures; opposite-sex siblings resembled one another less than did same- sex siblings. In 1884, Francis Galton established an anthropo- metric laboratory at the International Health Exhi- bition in South Kensington, London, for the mea- surement in various ways of Human Form and Faculty (quoted in Pearson, 1924, p. 359). In about one year, data were collected on 9,337 individuals. A similar laboratory, which operated several years, was established in the Science Galleries of the South Kensington Museum in 1888. The purposes of these laboratories were described in a handbill as follows: 1. For the use of those who desire to be accurately measured in many ways, either to obtain timely warning of remediable faults in development, or to learn their powers.

Family resemblance for normal pulmonary function

Family resemblance for normal pulmonary function as measured by forced vital capacity and one second forced expiration volume is assessed using a path analysis model which incorporates sex differences in transmissibility of the phenotype from parents to offspring as well as in the effect of a correlated shared-sibling environment. Application of this model, called XTAU, to familial correlations indicates that transmissible factors, which may be genetic or cultural, accounts for 20-30% of the variation in these measures. Further, a pronounced same-sex-specific effect of the sibling environment is indicated which enhanced the observed correlation between same-sex siblings and diminished the observed correlation between opposite-sex siblings. These results are consistent with findings of twin studies of pulmonary function indicating high heritability for both FVC and FEV1.0. In addition, the complex multifactorial model of family resemblance for normal pulmonary function is shown to have implications for specifying causal models of pulmonary disorders such as asthma, bronchitis, allergic rhinitis, and chronic obstructive pulmonary disease.

Birth Order and Children's Socialization into Sport

The purpose of this study was to examine the comparative influence of socia lizing agents in the social systems, employing multiple regression analysis with birth order and sex as the control variable. A fixed-alternative questionnaire was conducted with 623 boys and 559 girls. Subjects were categorized into first- born, intermediate-born, youngest-born, and only-child. The data indicated the differential function and role of individual-family-member influence. First-borns and only-children were demonstrated to have higher dependency on parents than later-borns. The father was fundamentally the primary socializing agent, and then was dethroned on the most significant socializing role model by entrustment his role to older like-sex siblings. There were two prominent features of in teraction patterns between siblings that younger borns had reinforcing functions for their sport involvement of older borns, while older borns served as rote models for later-borns' socialization into sport in the family. Such tendencies were saliently demonstrated between like-sex siblings rather than opposite-sex siblings. As one of the important predictors, siblings particularly operated as the smoothing function to facilitate children's participation into peer groups. The more children were stimulated by significant interaction patterns with siblings, the more in tensely they were involved in peer group activities. These findings suggest future researchers should focus primarily on the family constellation variables such as birth order, family size, the spacing interval between children, and the sex of older and younger siblings on children's socialization into sport.

The Effects of Sibling Status on Sibling Interaction: Influence of Birth Order, Age Spacing, Sex of Child, and Sex of Sibling

MINNETT, ANN M.; VANDELL, DEBORAH LOWE; and SANTROCK, JOHN W. The Effects of Sibling Status on Sibling Interaction: Influence of Birth Order, Age Spacing, Sex of Child, and Sex of Sibling. CHILD DEVELOPMENT, 1983, 54, 1064-1072. 73 children 7-8 years old were videotaped as they interacted with a sibling in cooperative, competitive, and neutral situations. The effects of 4 factors-the children's birth order (firstor second-born), the age spacing of the dyad (1-2 or 3-4 years), the children's sex, and the siblings' sex--on the 7-8-year-olds' behavior were explored. Firstborn 7-8-year-olds were more likely to praise and teach their siblings, while their secondborn counterparts showed more joyful behavior and self-deprecation. The 7-8-year-olds were more aggressive with a closely spaced sibling and showed more positive behaviors and affection with a widely spaced sibling. Girls were more likely to praise and teach their sibling, while boys were more likely to engage in neutral behaviors. Cheating, aggression, and dominance were more characteristic of the children's behaviors with a same-sex sibling than with an opposite-sex sibling. It was concluded that children's experience of the sibling relationship varies systematically with sibling status.

A Biometrical Analysis of Perceptions of Family Environment: A Study of Twin and Singleton Sibling Kinships

Biometrical genetic analysis was applied to sibling and twin kinship data on 2 dimensions of perceived home environment. Correlations on 1 dimension, Restrictiveness-Permissiveness, were equal and significant for all kinships: MZ twins, DZ twins, same-sex siblings, and opposite-sex siblings significant for all 4 kinships: MZ twins, DZ twins, same-sex siblings, and opposite-sex siblings (r greater than .40). An E2-E1 biometrical model fitted Restrictiveness-Permissiveness, implying that treatments common to siblings create agreement about perceived environment. As intrapair differences were the same for all 4 kinships under this model, the equal environments assumption of the twin method was supported. In contrast, the Acceptance-Rejection dimension fitted a G-E1 model that makes the assumption that sibling similarity is the result of genetic factors and postulates an absence of shared environmental influences. This finding suggests that this aspect of home environment may depend as much on the child's inherited traits as on actual treatments and is in accord with the genetic analysis of individual traits in that developmentally effective environmental factors do not appear to be common to siblings.

On the social advantages of having an older, opposite-sex sibling: Birth order influences in mixed-sex dyads.

This study examined the influences of birth order on behavior occurring in the initial, unstructured interactions of 40 mixed-sex dyads composed of a man and a woman who each had a sibling of the opposite sex. The design contrasted four different dyad types: (a) a firstborn man paired with a firstborn woman, (b) a firstborn man paired with a last born woman, (c) a last born man paired with a firstborn woman and (d) a last born man paired with a last born woman. Results indicated that individuals with an older, opposite-sex sibling were particularly likely to have rewarding interactions with strangers of the opposite sex. Relative to firstborn men, last born men talked nearly twice as long, asked more questions, and evoked more gazes, verbal reinforcers, and self-reported liking from their female partners. Relative to firstborn women, last bora women were more likely to initiate the interaction and to exceed the rate at which their male partners smiled. These findings are inconsistent with Toman's (1961, 1976) family constellation theory but are consistent with the results of various empirical studies that have also documented the greater social skills of later borns.

On the social advantages of having an older, opposite-sex sibling: Birth order influences in mixed-sex dyads.

On the social advantages of having an older, opposite-sex sibling: Birth order influences in mixed-sex dyads.

Evidence for directional non-additivity in the genetics of finger ridge counts.

A genetical analysis of variation in finger ridge counts of 221 pairs of twins and 80 pairs of opposite sex siblings has been carried out. Negative regression of DZ and sibling pair variances on pair means suggests the action of non-additive genes or unequal gene frequencies tending to increase finger ridge counts. Negative skewness of the distributions supports this view. While models including dominance or epistasis are not a significant improvement over purely additive genetic models, it is regarded as important that large and positive values of non-additive genetic variance are estimated. The evolutionary importance of dominance and epistasis for greater finger ridge counts is discussed.

Gender Constancy and the Effects of Sex-typed Televised Toy Commercials

The present study represented a cognitive-developmental analysis of the effects of televised, sex-stereotypic information on children's behavior and attitudes toward toy play. The subjects were 50 male and 50 female 4-6-year-olds divided into high and low gender-constancy levels. As the children watched a cartoon, they either saw a commercial of a gender-neutral toy that showed 2 boys or 2 girls playing with the toy, or they saw no commercial (control). As predicted, only the high gender-constant children were differentially affected by the sex-role information in the different commercial conditions. Children at this stage who saw opposite-sex children playing with the toy avoided spending time with the toy and stated verbally that the toy was more appropriate for an opposite-sex sibling, relative to children in the 2 other conditions. The results are discussed in terms of their implications for theories of sex-role development and in terms of the role that television may play in maintaining sex stereotypes and sex-typed behavior.