Birth order and prosociality in the early adolescent brain.

Birth order is a crucial environmental factor for child development. For example, later-born children are relatively unlikely to feel secure due to sibling competition or diluted parental resources. The positive effect of being earlier-born on cognitive intelligence is well-established. However, whether birth order is linked to social behavior remains controversial, and the neural correlates of birth order effects in adolescence when social cognition develops remain unknown. Here, we explored the birth order effect on prosociality using a large-scale population-based adolescent cohort. Next, since the amygdala is a key region for sociality and environmental stress, we examined amygdala substrates of the association between birth order and prosociality using a subset neuroimaging cohort. We found enhanced prosociality in later-born adolescents (N = 3160), and observed the mediating role of larger amygdala volume (N = 208) and amygdala-prefrontal functional connectivity with sex-selective effects (N = 183). We found that birth order, a non-genetic environmental factor, affects adolescent social development via different neural substrates. Our findings may indicate the later-born people's adaptive survival strategy in stressful environments.

Analysis of Maternal Postnatal Depression, Socioeconomic Factors, and Offspring Internalizing Symptoms in a Longitudinal Cohort in South Africa.

Importance: Few studies from low-and-middle income countries have investigated long-term associations between maternal postnatal depression and offspring internalizing (ie, depressive and anxiety) symptoms, and none have investigated interactions in this association. Objective: To investigate the association between maternal postnatal depression and offspring internalizing symptoms from adolescence to adulthood and the interaction with exposure to socioeconomic adversity and with the child's sex. Design, Setting, and Participants: This secondary analysis used data from Birth to Twenty Plus (BT20+), a prospective birth cohort study of children born in Soweto, South Africa, and followed up until age 28 years. Data were collected from 1990 to 2018, and data were analyzed for this study from February 16 through December 15, 2020. Exposures: Maternal postnatal depression self-reported by mothers 6 months after childbirth. Main Outcomes and Measures: The main outcome was offspring internalizing symptoms, assessed at offspring ages 14 years, 22 years, and 28 years and modeled longitudinally. Participants with the highest probability of experiencing high internalizing symptoms (ie, those in the top 20% of the distribution) from age 14 to 28 years were categorized as belonging to the high internalizing symptoms trajectory (vs the low trajectory). Socioeconomic adversity was measured with an index (continuous variable) including low maternal education, household crowding, low assets, and low maternal age. This variable was further stratified into more than 1 SD above the mean index, more than 1 SD below the mean index, and from 1 SD below to 1 SD above the mean index to conduct subgroup analyses. Associations were investigated using multivariable regression models. Results: Among 1087 participants born in Soweto, South Africa (543 [50.0%] male participants; 544 [50.0%] female participants), 118 individuals (10.8%) showed a high trajectory of internalizing symptoms from age 14 to 28 years vs 969 individuals (89.1%) with a low trajectory. Children exposed to maternal postnatal depression had statistically significantly increased odds of following the high trajectory (adjusted odds ratio [aOR] per 1-SD increase in maternal postnatal depression, 1.20; 95% CI, 1.02-1.41). This increase in odds differed by exposure to socioeconomic adversity and by child sex: for male participants, the increase in odds was greater in a context of higher vs lower socioeconomic adversity (eg, for >1 SD above the mean: aOR, 3.28; 95% CI, 1.06-10.14 vs for >1 SD below the mean: aOR, 0.98; 95% CI, 0.64-1.50; P for interaction = .12), while for female participants, the increase in odds was greater in a context of lower vs higher socioeconomic adversity (eg, for >1 SD below the mean: aOR, 1.82; 95 % CI, 1.12-2.98 vs for >1 SD above the mean: aOR, 0.59; 95 % CI, 0.30-1.17; P for interaction = .002) (P for 3-way interaction = .003). Conclusions and Relevance: This study found that postnatal depression was associated with higher odds of persistently increased internalizing symptoms among offspring from adolescence to adulthood in a middle-income country, with variation by socioeconomic adversity and sex. These findings suggest that better understanding of these associations is needed to implement targeted interventions and maximize the impact of public health initiatives aimed at breaking the intergenerational transmission of mental health problems.

Meta-Analyses of Fraternal and Sororal Birth Order Effects in Homosexual Pedophiles, Hebephiles, and Teleiophiles.

This study investigated the relations between numbers of older brothers, numbers of older sisters, and the odds of homosexuality in later-born males, including males who are most attracted sexually to prepubescent or early pubescent children (pedohebephiles) and males who are most attracted sexually to adults (teleiophiles). The authors meta-analyzed data from 24 samples of homosexual and heterosexual men, originally reported in 18 studies, and totaling 18,213 subjects. The results confirmed that older brothers increase the odds of same-sex preference in pedohebephiles as they do in teleiophiles. They also replicated the recent finding that older sisters have a similar but weaker statistical association with the odds of homosexuality. These findings have two theoretical implications. First, the findings for older brothers and older sisters indicate some commonality in the factors that influence sexual preference in teleiophiles and those that influence sexual preference in pedohebephiles. Second, the finding for older sisters confirms a prediction stemming from the hypothesis that male fetuses stimulate maternal antibodies that increase the odds of homosexuality in later-born males. Such immunization could result from miscarried as well as full-term fetuses, and number of older sisters should correlate with number of male fetuses miscarried before gestation of the subject.

Reassessing the Effect of Older Sisters on Sexual Orientation in Men.

This research reanalyzed questionnaire data from 8279 homosexual and 79,519 heterosexual men who participated in 2005 in an internet-based research project sponsored by the British Broadcasting Corporation. It focused on parameters of sibship composition (older brothers, older sisters, younger siblings) previously shown or hypothesized to influence sexual orientation in males. The results included the usual finding that older brothers increase the odds of homosexuality in later-born males. As predicted, older sisters also increase those odds, although by a lesser amount than older brothers. Other results confirmed that the odds of homosexuality are increased in only-children, the amount of increase being equal to that produced by one older brother and greater than that produced by one older sister. Finally, the results indicated that younger siblings have no effect on the odds of homosexuality in males. These results might be explained by the hypothesis that two different types of immune responses in pregnant women can affect the future sexual orientation of their male fetuses. One type of response affects fetuses in first pregnancies and reduces subsequent fertility. The other type affects fetuses in later pregnancies and has little or no effect on fertility. Finally, we conducted an estimate of combined sibship effects. Men who were exposed to any of the influences that we identified (being an only-child or having an older sibling) had 27% greater odds of homosexuality than did subjects who were exposed to none of these influences (i.e., the first-born of two or more children).

Handedness and Birth Order Among Heterosexual Men, Gay Men, and Sao Praphet Song in Northern Thailand.

Previous research has examined handedness and birth order to inform sexual orientation and gender identity/role expression development; however, sexual orientation and gender identity/role expression have rarely been disentangled to provide a more nuanced perspective. In Thailand, we investigated sexual orientation and gender identity simultaneously via comparison of 282 heterosexual men, 201 gay men, and 178 sao praphet song-i.e., androphilic, markedly feminine males recognized as a "third" gender. Handedness was examined as: extremely left-handed, moderately left-handed, ambidextrous, moderately right-handed, or extremely right-handed. Birth order was examined as numbers of older and younger brothers and sisters, by using Berglin's, fraternal, and sororal indices, and by examining the older brother odds ratio and sibling sex ratio. Compared with heterosexual men, gay men and sao praphet song were more likely to be extremely right-handed. Sao praphet song were also more likely to be extremely left-handed than heterosexual and gay men. Heterosexual men and sao praphet song had later sororal birth order compared with the expected Thai population value, suggesting stopping rules influenced when probands' mothers ceased having children. These findings provide new insights and replicate previous findings in a non-Western sample. Regarding handedness, in males, mechanisms related to extreme right-handedness likely influence the development of androphilia, whereas mechanisms related to both extreme right- and extreme left-handedness likely explain the combination of androphilia and feminine gender identity/role expression. Regarding birth order, similar to the conclusions of some prior research, stopping rules pose a challenge for testing the fraternal birth order effect.

Blessed are the first: The long-term effect of birth order on trust.

Acknowledging childhood as a crucial period for the formation of social preferences, we investigate whether the order of birth predicts trust in adult life. We find that laterborns trust on average 5% less than their older siblings, independently from personality traits, family ties, risk aversion and parental inputs. Family random- and fixed-effects estimates suggest that the variation in trust is mostly explained by within- rather than between-family characteristics. The effect of birth order is mediated by education outcomes only for women, while it is moderated by mother's education for the entire sample, thereby leading to relevant policy implications.

The levels and trends of contraceptive use before first birth in India (2015-16): a cross-sectional analysis.

BACKGROUND: Indian women are more prone to first birth at a relatively younger age after marriage. Also, we do not have sufficient literature available that focuses on contraceptive use before first birth. The analysis of the present study was done using data from the fourth round of National Family Health Survey (2015-16), India. The objectives of the present study were to measure the levels and trends of contraceptive use before first birth among Indian ever married women, aged 15-34 years. METHODS: The study includes 279,896 ever married women aged 15-34 years at the time of the NFHS-4 survey. To identify the socio-demographic determinants governing the pioneering study behavior, multivariable techniques have been used in the analysis. The statistical significance of the relationship between socio-demographic factors and contraceptive use prior to first birth was tested using a chi-squared test for association. Hosmer Lemeshow statistics and Nagelkerke R square have been used to check how well the logistic regression model fits the data. Map of India showing different zonal classification is made using the ArcGIS software version 10.3. RESULT: The trends of contraceptive usage show a decline in use before first birth and the various socio-demographic factors affecting the use of contraceptive before first birth are religion, caste, education, wealth index, media exposure, age at marriage and the zonal classifications. CONCLUSION: The noticeable result in this study is the comparative decline in contraceptive use by women in India before first birth in NFHS-4 with respect to previous NFHS done in India. The likelihood of using contraception before first birth is significantly affected by factors like place of residence, religion, caste, current age of women, age at marriage, education level of women, wealth index, media exposure and zonal classification.

Time trends in and factors associated with repeat adolescent birth in Uganda: Analysis of six demographic and health surveys.

BACKGROUND: Information on repeat adolescent birth remains scarce in sub-Sahara Africa. We investigated the prevalence and time trends in repeat adolescent birth in Uganda, and associated factors. METHODS: We analyzed Uganda Demographic and Health Survey data of women age 20-24 years collected on 6 surveys (1988/89-2016) to estimate repeat adolescent birth (first live birth <18 years of age followed by another live birth(s) <20 years). Further, we estimated the wantedness of the second order birth and the prevalence of short birth intervals birth (<13 months) between the first and second such birth. On the 2016 survey, we examined factors associated with repeat adolescent birth using bivariate and multivariate modified Poisson regression. RESULTS: At the 1988/89 survey, 58.9% of women with first birth <18 years reported a repeat adolescent birth. This percentage increased to 66.8% in 2006 (+7.9 percentage points [pp], p = 0.010) and thereafter declined to 55.6% by 2016 (-11.2 pp, p<0.001), nevertheless, no change occurred between 1988/89 and 2016 (-3.3pp, p = 0.251). Among women with repeat adolescent births, the mean number of live births by exact age 20 years (2.2 births) and prevalence of short birth intervals (3.5% in 1988/89, 5.4% in 2016) (+1.9pp, p = 0.245) did not change. Increasingly more women with repeat adolescent births preferred to have had the second child later, 22.5% in 1995 and 43.1% in 2016 (+20.6pp, p = <0.001). On the 2016 survey, women from poorer households and those of younger age at first birth were significantly more likely to report repeat adolescent birth. CONCLUSION: Following a first birth <18 years, more than half of the women report a repeat adolescent birth (<20 years), with no decline observed in 30 years. Increasingly more women wanted the second adolescent pregnancy later, highlighting the need to support adolescents with improved family planning services at each contact.

Developmental changes in parental authority legitimacy and over-time associations with adjustment: Differences in parent, first-born, and second-born perspectives.

Discrepancies in first- (M = 14.97 years, SD = 1.82) and second-born adolescents' (M = 12.20 years, SD = 1.90 years) and their parents' perceptions of parental authority legitimacy (PAL) were examined in a longitudinal sample of 145 predominantly White, middle-class, U.S. families. Utilizing a growth curve modeling approach, changes in the discrepancies between parents' and both first- and second-born adolescents' ratings of PAL over the course of 4 years were examined separately by the social-cognitive domain of the issues (social domain theory; Smetana, 2011; Turiel, 2002). We found that discrepancies between parents and first-borns increased over time for personal and multifaceted issues, whereas discrepancies for second-born adolescents increased over socially regulated issues. Additionally, larger initial discrepancies between parents and both adolescents over socially regulated issues (i.e., moral and conventional) were associated with greater depressive symptoms, while decreases in discrepancies over time were generally associated with better adjustment outcomes but with some domain and birth order differentiation. Discussion focuses on the developmental appropriateness (or inappropriateness) of family member perception differences in authority legitimacy over the course of adolescence. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Men's age at first birth and alcohol-related morbidity and mortality among siblings.

BACKGROUND: Men's age at first birth may negatively or positively affect alcohol-related morbidity and mortality, although little evidence is available. METHODS: We used register data of over 22,000 brothers to analyze the associations between age at first birth and alcohol-related morbidity and mortality from the age of 35 until the age of 60 or 72. We employed conventional Cox models and inter-sibling models, which allowed adjustment for unobserved social and genetic characteristics shared by brothers. RESULTS: The findings show that men's age at first birth was inversely associated with alcohol-related morbidity and mortality, independent of unobserved characteristics shared by brothers and of observed demographic confounders. Men who had their first child late at 35-45 years experienced lower alcohol-related morbidity and mortality (hazard ratio (HR) = 0.57, 95 % confidence interval (CI) = 0.43, 0.75) than men who had their first child at 25-29. Men who had their first child before age 20 had the highest morbidity and mortality among all fathers (HR = 1.36, 95 % CI = 1.09, 1.69), followed by men who had their child at 20-24 (HR = 1.12, 95 % CI = 1.00, 1.25). CONCLUSIONS: The results imply that the inverse association between men's age at first birth and alcohol-related morbidity and mortality is not driven by familial characteristics.

A short review of biological research on the development of sexual orientation.

We review research supporting biological mechanisms in the development of sexual orientation. This research includes studies on neural correlates, prenatal hormones and related physical/behavioral correlates, genetics, and the fraternal birth order effect (FBOE). These studies, taken together, have provided substantial support for biological influences underlying the development of sexual orientation, but questions remain unanswered, including how biological mechanisms may differ in contributing to men's and women's sexual orientation development.

Youngest versus oldest child: why does mothers' snack choice differ?

Young children frequently consume energy dense snacks, which is one of the factors contributing to childhood overweight. The consumption of more healthy snacks could help in meeting the dietary intake requirements of children. Previous research suggested that mothers of first children showed more health-conscious food behavior compared to mothers of not-first children. However, what is missing from earlier research is an in-depth exploration of differences in considerations to choose a snack and the reasons connected. Therefore, this study aims to characterize differences in mothers' snack choice for their youngest child at 2-3 years and their oldest child when he/she was of the same age. Moreover, this study aims to identify reasons for these differences. A grounded theory approach was used for data collection and analysis. Semi-structured interviews were carried out with 17 Dutch mothers with two or three children. All mothers indicated differences between snacks provided to their youngest child (2-3 years) and their oldest child when it was of the same age. Most frequently mentioned differences were youngest children receive unhealthy snacks at a younger age, the structure regarding snack providing is more fixed, and that youngest children receive less age-specific snacks. Most frequently mentioned reasons for these differences were role-modelling, novelty of the first-born, availability of other types of snacks at home, and school hours of the oldest child. The study provided insights into the possible role of siblings in shaping snack consumption. Results might be relevant for the development of intervention strategies to increase mothers' awareness and to help to meet children's dietary requirements.

Depression, negative relating with the oldest child, and the mediating role of resilience in community elders' psychological well-being: a pilot study in Greece.

AIM: This study examined the role of both positive and negative aspects of social relationships with partners, friends, and children on the psychological well-being of Greek elders, as well as the potential mediating role of resilience. METHODS: The sample included 100 Greek older community-dwellings recruited from three care centres. They completed questionnaires consisted of the Scales of Psychological Well-Being, the shortened Family Members' Interrelating Questionnaire, the Significant Others Scale, the Brief Symptom Inventory, and the Brief Resilience Scale. RESULTS: The findings suggested that mental health (i.e. depression), rather than physical frailty, and a negative relationship with the oldest child, rather than a lack of social support from family or friends in general, have detrimental effects in elders' well-being. In contrast, resilience has a positive effect on well-being that mediates the association between negative relating with the oldest child and well-being. Elderly parents perceived their child's relating more negatively than their own relating towards the child, and it was the child's negative relating to them, rather than their relating toward the child, that predicted their psychological well-being. An interdisciplinary approach to the care of the geriatric population is highlighted. CONCLUSIONS: To improve elders' well-being and enhance successful ageing, the determinants of well-being should be key targets of ageing research. Policy, prevention, and intervention actions should address the modifiable variables of any underlying emotional and social issues among elderly people (i.e. depression, negative relating with children, and resilience).

Does Fraternal Birth Order Predict Male Homosexuality, Bisexuality, and Heterosexual Orientation with Same-Sex Attraction? Evidence from a Greek-Speaking Sample from Greece.

Studies have established that having older brothers is associated with an increased incidence of male homosexuality. This so-called fraternal birth order effect has been found in different times and cultural settings. The current study attempted to examine whether this effect was present in the Greek cultural context and whether it could also predict bisexuality or heterosexuality with occasional same-sex attractions. On the basis of an online sample of 1617 Greek-speaking participants, it was found that, for men, a higher number of older brothers were associated with an increased probability to be homosexual, but it had no effect on the probability to be bisexual or heterosexual with same-sex attractions. In women, the number of older brothers had not any effect on sexual orientation.

Fraternal Birth Order, Only-Child Status, and Sibling Sex Ratio Related to Sexual Orientation in the Add Health Data: A Re-analysis and Extended Findings.

The fraternal birth order (FBO) effect related to men's sexual orientation refers to the finding that the number of older brothers that a man has increases his chance of being androphilic. The FBO effect has generally been well replicated in diverse samples; one instance of non-replication was by Francis (2008) using Waves I and III of the Add Health data. We attempted to replicate the FBO effect in the Add Health data taking into account family size and other limitations of Francis' (2008) analyses. Also, we examined other sibling characteristics related to the FBO effect: sibling sex ratio and only-child status. We used two subsamples from Waves I (n = 20,745) and IV (n = 15,701) of the Add Health data, consisting of adolescents who were followed longitudinally from 1994 to 1995 until 2008. Wave I data were used to compute numbers of younger and older brothers and sisters from household roster information. Wave IV information about sexual orientation identity was used. Analyses were conducted within men and within women. We found modest support for the FBO effect in men, but not in women, using the older brother odds ratio, logistic regression analyses, and sibling sex ratio, which provided the strongest support for FBO. We found that gynephilic/biphilic women, but not androphilic/biphilic men, were more likely to be only-children compared to androphilic women and gynephilic men, respectively. We discuss limitations of the Add Health data and purported mechanisms for the FBO effect in men and the only-child effect in women.

On the Mathematics of the Fraternal Birth Order Effect and the Genetics of Homosexuality.

Mathematicians have always been attracted to the field of genetics. The mathematical aspects of research on homosexuality are especially interesting. Certain studies show that male homosexuality may have a genetic component that is correlated with female fertility. Other studies show the existence of the fraternal birth order effect, that is, the correlation of homosexuality with the number of older brothers. This article is devoted to the mathematical aspects of how these two phenomena are interconnected. In particular, we show that the fraternal birth order effect implies a correlation between homosexuality and maternal fecundity. Vice versa, we show that the correlation between homosexuality and female fecundity implies the increase in the probability of the younger brothers being homosexual.

Associations between birth order with mental wellbeing and psychological distress in midlife: Findings from the 1970 British Cohort Study (BCS70).

BACKGROUND: Previous research indicated that birth order was associated with physical health outcomes in adulthood. However, evidence on its association with mental health was lacking. The aim of this study was to investigate if birth order was associated with mental wellbeing and psychological distress at mid-life, stratified by gender, and taking into account confounding factors in childhood and adulthood. METHOD: The sample consisted of 9,354 participants of the 1970 British Cohort Study (BCS70). The Warwick Edinburgh Mental Wellbeing Scale (WEMWBS), the Malaise Index and attending a doctor's consultation in the past year for a mental health issue at age forty-two were used to assess mental wellbeing and psychological distress in midlife. Birth order was ascertained via a parental questionnaire and referred to the numerical birth position of the participants. The associations between birth order, mental wellbeing and psychological distress were tested using linear and logistic regression adjusting for birth characteristics: smoking during pregnancy, maternal age, mother's marital status, father's employment, region of birth, parental years of education and parental social class, and factors at age 42: years of education, employment status and partnership status. Potential mediating variables including breastfeeding and birthweight at birth and parental separation and conduct disorder measured at age ten were also taken into account. RESULTS: We find no evidence to support an association between birth order and midlife psychological distress or attending a doctor's consultation in both men and women. In unadjusted analysis, there was an association between birth order four and above and a reduced WEMWBS score of -0.79 (95% CI -1.57, -0.02) in men only. This association was attenuated after adjusting for birth characteristics and mediators at birth (0.86, 95% -1.78, 0.07) but was maintained once conduct disorder at age 10 was accounted for (-1.19, 95% CI -2.28, -0.09). However, this association was attenuated once again after adjusting for employment status, years in education and partnership status in adulthood (-1.04, 95% CI -2.11, 0.03). CONCLUSIONS: In this study, birth order was not associated with psychological distress or having a mental health issue at midlife. Accounting for employment status, years of education and partnership status in adulthood attenuated the relationship between birth order and mental wellbeing.

Cost-Effectiveness of Continuous Support From a Layperson During a Woman's First Two Births.

OBJECTIVE: To evaluate the cost-effectiveness and health outcomes related to continuous support from a layperson during a woman's first two births in a theoretical population. DESIGN: Cost-effectiveness analysis. PARTICIPANTS: A theoretical cohort of 1.2 million women based on an approximation of annual low-risk, nulliparous, term, singleton births in the United States with the assumption that these women have second births. This reflects the average number of births per woman in the United States. METHODS: We designed a cost-effectiveness model to compare outcomes in women with continuous support from relatives, friends, or community members with minimal to no training (excluding trained doulas) during labor and birth compared with outcomes for women with no continuous support. Outcomes included mode of birth, uterine rupture, hysterectomy, maternal death, cost, and quality-adjusted life years (QALYs). We derived probabilities from the literature and set a cost-effectiveness threshold at $100,000/QALY. RESULTS: In this theoretical model, continuous support by a layperson during the first birth resulted in fewer cesarean births, decreased costs, and increased QALYs for the first and subsequent births. Women with support from laypersons had 71,090 fewer cesarean births, 35 fewer uterine ruptures, 9 fewer hysterectomies, and 16 fewer maternal deaths, which saved $364 million with 2,673 increased QALYs. Sensitivity analyses showed that continuous support in the first birth was cost-effective even when varying the estimate of lost wages of the support person up to $708. CONCLUSION: Continuous labor support from a layperson leads to fewer cesarean births, improved outcomes, decreased costs, and increased QALYs. This highlights the need to increase women's access to continuous layperson support during labor and birth uninhibited by financial and institutional barriers.

The Relative Impacts of Sibling Relationships on Adolescent Body Perceptions.

The sibling relationship is the longest relationship of the life course and has been found to influence youth adjustment (Dunn, 2002 ). Given that adolescence is a time of increased body awareness, the authors examined the potential role of siblings' body conceptions and sibling relationship quality on adolescent body conceptions. In a sample of 101 predominantly White, middle-class adolescent sibling dyads, the authors found that positive sibling relationship quality was associated with higher physical self-worth in adolescents, but that this differed by sibling gender and sibling physical self-worth. Alternatively, negative sibling relationship quality was associated with lower physical self-worth for adolescents, but differed based on birth order, sibling physical self-worth, and adolescent gender.

Mother-infant interactions with firstborns and secondborns: A within-family study of European Americans.

Given the large numbers of families with more than one child, understanding similarities and differences in siblings' behaviors and in parents' interactions with their sibling infants is an important goal for advancing more representative developmental science. This study employed a within-family design to examine mean-level consistency and individual-order agreement in 5-month-old sibling behaviors and maternal parenting practices with their firstborns and secondborns (ns = 61 mothers and 122 infants). Each infant was seen independently with mother. Firstborn infants were more social with their mothers and engaged in more exploration with objects than secondborn infants; firstborn and secondborn infants' behaviors were correlated for smiling, distress communication, and efficiency of exploration. Mothers engaged in more physical encouragement, social exchange, didactic interaction, material provisioning, and language with their firstborns than with their secondborns. Notably, only maternal nurturing (e.g., feeding, holding) did not differ in mean level when mothers were with their two infants. However, mean differences in mothers' social exchange and material provisioning with their two children attenuated to nonsignificance when controlling for differences in siblings' behaviors. Individual-order agreement of mothers' behaviors with firstborn and secondborn infants (across an average of almost 3 years) was only moderate. These findings suggest that mother-firstborn interactions may differ from mother-secondborn interactions. Future research should move beyond studying mother-firstborn dyads to understand broader family and developmental processes.