New Kids on the Block
Selection against small males in utero: A test of the Wells hypothesis
R. Catalano et al.
Human Reproduction, April 2012, Pages 1202-1208
Background: The argument that women in stressful environments spontaneously abort their least fit fetuses enjoys wide dissemination despite the fact that several of its most intuitive predictions remain untested. The literature includes no tests, for example, of the hypothesis that these mechanisms select against small for gestational age (SGA) males.
Methods: We apply time-series modeling to 4.9 million California male term births to test the hypothesis that the rate of SGA infants in 1096 weekly birth cohorts varies inversely with labor market contraction, a known stressor of contemporary populations.
Results: We find support for the hypothesis that small size becomes less frequent among term male infants when the labor market contracts.
Conclusions: Our findings contribute to the evidence supporting selection in utero. They also suggest that research into the association between maternal stress and adverse birth outcomes should acknowledge the possibility that fetal loss may affect findings and their interpretation. Strengths of our analyses include the large number and size of our birth cohorts and our control for autocorrelation. Weaknesses include that we, like nearly all researchers in the field, have no direct measure of fetal loss.
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Why is the Teen Birth Rate in the United States so High and Why Does it Matter?
Melissa Schettini Kearney & Phillip Levine
NBER Working Paper, March 2012
Abstract:
This paper examines two aspects of teen childbearing in the United States. First, it reviews and synthesizes the evidence on the reasons why teen birth rates are so uniquely high in the United States and especially in some states. Second, it considers why and how it matters. We argue that economists' typical explanations are unable to account for any sizable share of the geographic variation. We describe some recent analysis indicating that the combination of being poor and living in a more unequal (and less mobile) location, like the United States, leads young women to choose early, non-marital childbearing at elevated rates, potentially because of their lower expectations of future economic success. Consistent with this view, the most rigorous studies on the topic find that teen childbearing has very little, if any, direct negative economic consequence. If it is explained by the low economic trajectory that some young women face, then it makes sense that having a child as a teen would not be an additional cause of poor economic outcomes. These findings lead us to conclude that the high rate of teen childbearing in the United States matters mostly because it is a marker of larger, underlying social problems.
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World War II, Missing Men, and Out-Of-Wedlock Childbearing
Dirk Bethmann & Michael Kvasnicka
Economic Journal, forthcoming
Abstract:
Drawing upon county-level census data for the German state of Bavaria in 1939 and 1946, we use World War II as a natural experiment to study the effects of changes in the adult sex ratio on out- of-wedlock fertility. Our findings show that war-induced shortfalls of men significantly increased the nonmarital fertility ratio in the middle of the century. Furthermore, we find that the regional magnitude of this effect varies with the county-level share of prisoners of war in an inverse manner. Unlike military casualties and soldiers missing in action, prisoners of war had a sizeable positive probability of returning home from the war. It appears therefore that both current marriage market conditions and foreseeable improvements in the future marriage market prospects of women influenced fertility behavior in the immediate aftermath of World War II.
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Facial attractiveness and fertility in populations with low levels of modern birth control
Antonio Silva et al.
Evolution and Human Behavior, forthcoming
Abstract:
Evolutionary models of human mate choice generally assume that physical attractiveness has evolved through sexual selection, i.e., it has been associated with higher mating opportunities and subsequent reproductive success across our evolutionary history. Here we investigate whether facial attractiveness is related to fertility in order to understand the extent to which selection can operate on attractive traits in modern populations. We used data from two populations where the prevalence of modern birth control methods is low and thus unlikely to disconnect mating opportunities from reproductive success: men and women from contemporary rural Senegal and men from the West Point Military Academy in the USA who graduated in 1950. We found that facial attractiveness negatively predicts age-specific reproduction in both sexes in Senegal and is independent from lifetime reproductive success in men from the USA. Overall, the results suggest that facial attractiveness is not under positive selection and raise questions about methodological approaches currently used to assess attractiveness.
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Seasonal Distribution of Psychiatric Births in England
Giulio Disanto et al.
PLoS ONE, April 2012
Abstract:
There is general consensus that season of birth influences the risk of developing psychiatric conditions later in life. We aimed to investigate whether the risk of schizophrenia (SC), bipolar affective disorder (BAD) and recurrent depressive disorder (RDD) is influenced by month of birth in England to a similar extent as other countries using the largest cohort of English patients collected to date (n=57,971). When cases were compared to the general English population (n=29,183,034) all diseases showed a seasonal distribution of births (SC p=2.48E-05; BAD p=0.019; RDD p=0.015). This data has implications for future strategies of disease prevention.
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Gert Stulp et al.
American Journal of Human Biology, forthcoming
Objective: In this article we examine the association between female height and reproductive success in a US sample and present a review of previous studies on this association. We also outline possible biological explanations for our findings.
Methods: We used data from a long-term study of 5,326 female Wisconsin high school graduates to examine the association between female height and reproductive success. Twenty-one samples on this association were covered by our literature review.
Results: Shorter women had more children surviving to age 18 than taller women, despite increased child mortality in shorter women. Taller women had a higher age at first birth and age at first marriage and reached a higher social status, but the negative effect of height on reproductive success persisted after controlling for these variables. However, while these effects were quite consistent in Western populations, they were not consistently present in non-Western populations. Our review also indicated that child mortality was almost universally higher among shorter women.
Conclusions: We conclude that shorter women have a higher number of live births but that final reproductive success depends on the positive effect of height on child survival.
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Orlando Sotomayor
Economics & Human Biology, forthcoming
Abstract:
A natural experiment is employed to analyze the relationship between living standards, diabetes, and cardiovascular disease. Results show that shocks generated by two powerful tropical storms striking Puerto Rico during the late 1920s and early 1930s had long-term consequences consistent with the fetal origins hypothesis. Individuals in the womb or early infancy in the aftermath of the storms are more likely to report a diagnosis of hypertension, high cholesterol, diabetes, and are considerably more likely to have no formal schooling.
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Explaining Recent Trends in the U.S. Teen Birth Rate
Melissa Schettini Kearney & Phillip Levine
NBER Working Paper, March 2012
Abstract:
We investigate possible explanations for the large decline in U.S. teen childbearing that occurred in the twenty years following the 1991 peak. Our review of previous evidence and the results of new analyses presented here leads to the following main set of observations. First, the observed decline in teen childbearing is even more surprising given the increasing share of Hispanic teens, who have higher birth rates. Second, we find that a reduction in sexual activity and an increase in contraceptive use contributed to the decline roughly equally. Third, we are able to identify a statistically discernible impact of declining welfare benefits and expanded access to family planning services through Medicaid, but combined they can only account for 12 percent of the observed decline in teen childbearing between 1991 and 2008. We are unable to find any impact of other policies (including abstinence only or mandatory sex education) or labor market conditions. In the end we conclude that the standard factors which are claimed to be related to the rate at which teens give birth appear to explain little of the recent trend.
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Hormonal evidence supports the theory of selection in utero
R.A. Catalano et al.
American Journal of Human Biology, forthcoming
Objectives: Antagonists in the debate over whether the maternal stress response during pregnancy damages or culls fetuses have invoked the theory of selection in utero to support opposing positions. We describe how these opposing arguments arise from the same theory and offer a novel test to discriminate between them. Our test, rooted in reports from population endocrinology that human chorionic gonadotropin (hCG) signals fetal fitness, contributes not only to the debate over the fetal origins of illness, but also to the more basic literature concerned with whether and how natural selection in utero affects contemporary human populations.
Methods: We linked maternal serum hCG measurements from prenatal screening tests with data from the California Department of Public Health birth registry for the years 2001-2007. We used time series analysis to test the association between the number of live-born male singletons and median hCG concentration among males in monthly gestational cohorts.
Results: Among the 1.56 million gestations in our analysis, we find that median hCG levels among male survivors of monthly conception cohorts rise as the number of male survivors falls.
Conclusions: Elevated median hCG among relatively small male birth cohorts supports the theory of selection in utero and suggests that the maternal stress response culls cohorts in gestation by raising the fitness criterion for survival to birth.
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Brennan Peterson et al.
Human Reproduction, May 2012, Pages 1375-1382
Background: In the USA, the postponement of childbearing reflects contemporary social norms of delaying marriage, pursing educational goals and securing economic stability prior to attempting conception. Although university students are more likely to delay childbearing, it is unclear to what extent they are aware of age-related fertility decline. The current study is the first of its kind to assess fertility awareness and parenting attitudes of American undergraduate university students.
Methods: Two-hundred forty-six randomly selected undergraduate university students (138 females and 108 males) completed an online self-report survey adapted from the Swedish Fertility Awareness Questionnaire. Students were evenly distributed between the freshman, sophomore, junior and senior classes with a mean age of 20.4 years.
Results: Participants wanted to have their first and last child within the window of a woman's fertility. However, participants demonstrated a lack of fertility awareness by vastly overestimating the age at which women experience declines in fertility, the likelihood of pregnancy following unprotected intercourse and the chances that IVF treatments would be successful in the case of infertility. Nearly 9 in 10 participants want to have children in the future and viewed parenthood as a highly important aspect of their future lives.
Conclusions: Delaying childbearing based on incorrect perceptions of female fertility could lead to involuntary childlessness. Education regarding fertility issues is necessary to help men and women make informed reproductive decisions that are based on accurate information rather than incorrect perceptions.
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Piotr Sorokowski, Agnieszka Sorokowska & Dariusz Danel
Economics & Human Biology, forthcoming
Abstract:
Many studies have investigated how different variables influence the reproductive success (RS) in the populations of natural birth control. Here, we tested hypotheses about positive relationship between wealth, height and several measures of RS in an indigenous, traditional society from West Papua. The study was conducted among the Yali tribe in a few small, isolated mountain villages. In this tribe, a man's wealth is measured by the number of pigs he possesses. We found that wealth was related to fertility and number of living children, but not to child mortality in both men and women. Additionally, child mortality increased with the number of children in a family. Finally, we did not observe any relationship between height and reproductive success measures or wealth. We provide several possible explanations of our results and also put forward hypothetical background for further studies of indigenous populations.
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Prepared social learning about dangerous animals in children
Clark Barrett & James Broesch
Evolution and Human Behavior, forthcoming
Abstract:
Natural selection is likely to have shaped developmental systems for rapid acquisition of knowledge about environmental dangers, including dangerous animals. However, learning about dangerous animals through direct encounters can be costly and potentially fatal. In social species such as humans, the presence of stored information about danger in the minds of conspecifics might favor the evolution of prepared social learning mechanisms that cause children to preferentially attend to and remember culturally transmitted information about danger. Here we use an experimental learning task to show that children from two very different cultures exhibit prepared social learning about dangerous animals: city-dwelling children from Los Angeles, who face relatively little danger from animals, and Shuar children from the Amazon region of Ecuador, to whom dangerous animals pose a much greater threat. Both populations exhibited similar prepared learning effects. Danger information was learned in a single trial without feedback, immediately entered long-term memory, and was recalled with only minor attenuation a week later, while other information presented at the same time (animal names and diets) was immediately forgotten. We discuss the significance of these design features of prepared learning in light of the phylogeny and function of danger learning systems.
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Ability transmission, endogenous fertility and educational subsidy
Kazumasa Oguro, Takashi Oshio & Junichiro Takahata
Applied Economics, Spring 2012, Pages 2469-2479
Abstract:
In this study, we attempt to investigate how educational subsidy, childcare allowance and family allowance affect economic growth and income distribution on the basis of simulation models which incorporate intergenerational ability transmission and endogenous fertility. The simulation results show that financial support for higher education can both increase economic growth and reduce income inequality, especially if the abilities of parent and child are closely correlated. In contrast with educational subsidy, raising childcare allowance or family allowance has limited impacts on growth and income inequality.
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Advancing Maternal Age Is Associated With Increasing Risk for Autism: A Review and Meta-Analysis
Sven Sandin et al.
Journal of the American Academy of Child & Adolescent Psychiatry, May 2012, Pages 477-486
Objective: We conducted a meta-analysis of epidemiological studies investigating the association between maternal age and autism.
Method: Using recommended guidelines for performing meta-analyses, we systematically selected, and extracted results from, epidemiological scientific studies reported before January 2012. We calculated pooled risk estimates comparing categories of advancing maternal age with and without adjusting for possible confounding factors. We investigated the influence of gender ratio among cases, ratio of infantile autism to autism spectrum disorder (ASD), and median year of diagnosis as effect moderators in mixed-effect meta-regression.
Results: We found 16 epidemiological papers fulfilling the a priori search criteria. The meta-analysis included 25,687 ASD cases and 8,655,576 control subjects. Comparing mothers ≥35 years with mothers 25 to 29 years old, the crude relative risk (RR) for autism in the offspring was 1.52 (95% confidence interval [CI] = 1.12-1.92). Comparing mothers ≥35 with mothers 25 to 29, the adjusted relative risk (RR) for autism in the offspring was 1.52 (95% CI = 1.12-1.92). For mothers <20 compared with mothers 25 to 29 years old, there was a statistically significant decrease in risk (RR = 0.76; 95% confidence interval = 0.60-0.97). Almost all studies showed a dose-response effect of maternal age on risk of autism. The meta-regression suggested a stronger maternal age effect in the studies with more male offspring and for children diagnosed in later years.
Conclusions: The results of this meta-analysis support an association between advancing maternal age and risk of autism. The RR increased monotonically with increasing maternal age. The association persisted after the effects of paternal age and other potential confounders had been considered, supporting an independent relation between higher maternal age and autism.
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Saving Babies: The Contribution of Sheppard-Towner to the Decline in Infant Mortality in the 1920s
Carolyn Moehling & Melissa Thomasson
NBER Working Paper, April 2012
Abstract:
From 1922 to 1929, the Sheppard-Towner Act provided matching grants to states to fund maternal and infant care education initiatives. We examine the effects of this public health program on infant mortality. States engaged in different types of activities, allowing us to examine whether different interventions had differential effects on mortality. Interventions that provided one-on-one contact and opportunities for follow-up care, such as home visits by public health nurses, reduced infant deaths more than classes and conferences. Overall, we estimate that Sheppard-Towner activities can account for 9 to 21 percent of the decline in infant mortality over the period.
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Ethnic differences in growth in early childhood: An investigation of two potential mechanisms
Amanda Sacker & Yvonne Kelly
European Journal of Public Health, April 2012, Pages 197-203
Background: There are clear ethnic differences in birthweight. This study examines whether and how these disparities are replicated in a later marker of physical development, height at 5 years.
Methods: Observational data from the UK Millennium Cohort Study, constructed to over-represent ethnic minority (Indian, Pakistani, Bangladeshi, Black African, Black Caribbean and Other) children.
Results: Mean birthweight of ethnic minority children was lower than that of the ethnic majority (3.06-3.34 kg vs. 3.41 kg), but ethnic minority children were not shorter at 5 years. Pakistani, Caribbean and African children were actually taller on average (by 0.5 cm, 1.4 cm and 3.5 cm). Controlling for parental height and birthweight did not affect height differentials. Two mechanisms were hypothesized: (i) a cramped intrauterine environment given the short stature of some minority children's mothers resulted in catch-up growth; and (ii) conditions during the parents' childhood led to a reduced capacity to reach their height potential. A reparameterization of parent heights showed that mother's height contributed more to predicting child height than joint parental height alone. Birthweight was positively related to height and attenuated the extra contribution from mothers' heights. Decomposing the effects into their constituent parts found some support for both hypotheses.
Conclusions: These results suggest that children from ethnic minority backgrounds are not disadvantaged with respect to height growth compared with the ethnic majority. However, if adiposity is more likely when children are tall for their age, then ethnic inequalities in adult health could increase as the current generation of children mature.
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Claudia Buss et al.
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
Stress-related variation in the intrauterine milieu may impact brain development and emergent function, with long-term implications in terms of susceptibility for affective disorders. Studies in animals suggest limbic regions in the developing brain are particularly sensitive to exposure to the stress hormone cortisol. However, the nature, magnitude, and time course of these effects have not yet been adequately characterized in humans. A prospective, longitudinal study was conducted in 65 normal, healthy mother-child dyads to examine the association of maternal cortisol in early, mid-, and late gestation with subsequent measures at approximately 7 y age of child amygdala and hippocampus volume and affective problems. After accounting for the effects of potential confounding pre- and postnatal factors, higher maternal cortisol levels in earlier but not later gestation was associated with a larger right amygdala volume in girls (a 1 SD increase in cortisol was associated with a 6.4% increase in right amygdala volume), but not in boys. Moreover, higher maternal cortisol levels in early gestation was associated with more affective problems in girls, and this association was mediated, in part, by amygdala volume. No association between maternal cortisol in pregnancy and child hippocampus volume was observed in either sex. The current findings represent, to the best of our knowledge, the first report linking maternal stress hormone levels in human pregnancy with subsequent child amygdala volume and affect. The results underscore the importance of the intrauterine environment and suggest the origins of neuropsychiatric disorders may have their foundations early in life.
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A possible link between the pubertal growth of girls and prostate cancer in their sons
David Barker et al.
American Journal of Human Biology, forthcoming
Objectives: Among women attending antenatal clinics during 1934-1944 a large intercristal diameter, the maximum distance between the pelvic iliac crests, was associated with a raised incidence of breast and ovarian cancer in the daughters in later life. At puberty, the intercristal diameter of girls enlarges rapidly under the influence of estrogen. We speculated that high maternal estrogen concentrations during pregnancy initiate hormonal cancers in their daughters. Here, we examine the association between the mothers' intercristal diameters and prostate cancer in their sons.
Methods: Using the national cancer registry we identified 221 cases of prostate cancer among 6,975 men born during 1934-1944 in Helsinki, Finland. Four thousand four hundred and one of these men had their mother's bony pelvic measurements recorded: there were 149 cases among them.
Results: Hazard ratios for prostate cancer rose as the mother's intercristal diameter increased; but this association was restricted to men who were born before 40 weeks of gestation. Among these men the hazard ratio was 1.27 (95% CI 1.09-1.48; P = 0.002). The hazard ratio was 2.2 (1.3-3.7; P < 0.001) in men whose mothers weighed more than 80 kg in late pregnancy compared with those whose mothers weighed 60 kg or less.
Conclusions: These findings are consistent with a conceptual framework for the origins of hormonally dependent cancers that invokes exposure of embryonic tissue to maternal sex hormones followed by resetting of the fetal hypothalamic-gonadotropin axis in late gestation. We hypothesize that compensatory prepubertal growth among girls is associated with hormonal cancers in the next generation.
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Early-Life Socioeconomic Status and the Prevalence of Breast Cancer in Later Life
Tetyana Pudrovska, Andriy Anishkin & Yifang Shen
Research on Aging, May 2012, Pages 302-320
Abstract:
Knowledge of mechanisms linking early-life social environment and breast cancer remains limited. The authors explore direct and indirect effects of early-life socioeconomic status (SES) on breast cancer prevalence in later life. Using 50-year data from the Wisconsin Longitudinal Study (N = 4,275) and structural equation modeling, the authors found a negative direct effect of early-life SES, indicating that women from higher SES family backgrounds had lower breast cancer prevalence than women from lower SES families. Additionally, early-life SES has a positive indirect effect on breast cancer via women's adult SES and age at first birth. Were it not for their higher SES in adulthood and delayed childbearing, women from higher SES families of origin would have had lower breast cancer prevalence than women from lower SES families. Yet early-life SES is associated positively with adult SES and age at first birth, and women's higher adult SES and delayed childbearing are related to higher breast cancer prevalence.
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Contradictions of value: Between use and exchange in cord blood bioeconomy
Nik Brown
Sociology of Health & Illness, forthcoming
Abstract:
Umbilical cord blood (CB) has become established as an increasingly viable clinical alternative to bone marrow in the treatment of leukaemia leading to the construction of a global network of CB banks promoted through a moral ethos of gift. Additionally, some banks offer the opportunity to retain stem cells privately. CB is discursively presented as clinical ‘waste', a ‘by-product' of birthing. In this way CB units are made available to a global exchange-based bioeconomy. Crucially, CB collection has developed in parallel with several necessary obstetric practices, especially the immediate clamping of the cord following delivery, essential to high volume collection. However, this article strongly suggests the promotional basis of CB banking (such as by gift, waste or donation) is in tension with the growing preference of new parents to delay cord clamping. Based on focus groups with expectant parents, the promotion of CB banking can in fact be seen to feed into critical reflection on the value of CB for newborn infants, potentially reinvigorating a tradition of delayed umbilical cord clamping. Theoretically, these contradictory systems of valuing are conceptualised through recent literature on bioeconomy and Marx's writings on the contrasting tensions between use and exchange value.
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Alison Sanders et al.
PLoS ONE, March 2012
Abstract:
Exposure to toxic metals during the prenatal period carries the potential for adverse developmental effects to the fetus, yet such exposure remains largely unmonitored in the United States. The aim of this study was to assess maternal exposure to four toxic metals (arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb)) in a cohort of pregnant women in North Carolina. We analyzed blood samples submitted to the North Carolina Department of Health and Human Services for blood typing to assess toxic metal levels in pregnant women (n = 211) across six North Carolina counties. Whole blood metal concentrations were measured by inductively coupled plasma mass spectrometry. The association between maternal characteristics, including county of residence, age, and race, and metal exposure was analyzed using multiple linear regression analysis. A large fraction of the blood samples showed detectable levels for each of the four metals. Specifically, As (65.7%), Cd (57.3%), Hg (63.8%), and Pb (100%) were detected in blood samples. Moreover, compared with adult females participating in the Fourth National Report on Human Exposure to Environmental Chemicals and guidelines for pregnant women, some women in the sample population exceeded benchmark levels of Cd, Hg, and Pb. Evidence from this pilot study indicates that pregnant women in North Carolina are exposed to As, Cd, Hg, and Pb and suggests that factors related to maternal county of residence and race may impact maternal exposure levels. As increased levels of one or more of these metals in utero have been associated with detrimental developmental and reproductive outcomes, further study is clearly warranted to establish the impacts to newborns.
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Dante Cicchetti & Fred Rogosch
Development and Psychopathology, May 2012, Pages 411-427
Abstract:
In this investigation, gene-environment interaction effects in predicting resilience in adaptive functioning among maltreated and nonmaltreated low-income children (N = 595) were examined. A multicomponent index of resilient functioning was derived and levels of resilient functioning were identified. Variants in four genes (serotonin transporter linked polymorphic region, corticotropin releasing hormone receptor 1, dopamine receptor D4-521C/T, and oxytocin receptor) were investigated. In a series of analyses of covariance, child maltreatment demonstrated a strong negative main effect on children's resilient functioning, whereas no main effects for any of the genotypes of the respective genes were found. However, gene-environment interactions involving genotypes of each of the respective genes and maltreatment status were obtained. For each respective gene, among children with a specific genotype, the relative advantage in resilient functioning of nonmaltreated compared to maltreated children was stronger than was the case for nonmaltreated and maltreated children with other genotypes of the respective gene. Across the four genes, a composite of the genotypes that more strongly differentiated resilient functioning between nonmaltreated and maltreated children provided further evidence of genetic variations influencing resilient functioning in nonmaltreated children, whereas genetic variation had a negligible effect on promoting resilience among maltreated children. Additional effects were observed for children based on the number of subtypes of maltreatment children experienced, as well as for abuse and neglect subgroups. Finally, maltreated and nonmaltreated children with high levels of resilience differed in their average number of differentiating genotypes. These results suggest that differential resilient outcomes are based on the interaction between genes and developmental experiences.