On the Origin of Species

Kevin Lewis

February 11, 2010

Gender and Racial Biases: Evidence from Child Adoption

Mariagiovanna Baccara, Allan Collard-Wexler, Leonardo Felli & Leeat Yariv
NYU Working Paper, January 2010

This paper uses a new data set on domestic child adoption to document the preferences of potential adoptive parents over born and unborn babies relinquished for adoption by their birth mothers. We show that adoptive parents exhibit significant biases in favor of girls and against African-American babies. A non-African-American baby relinquished for adoption attracts the interest of potential adoptive parents with probability 11.5% if it is a girl and 7.9% if it is a boy. As for race, a non-African-American baby has a probability of attracting the interest of an adopting parent at least seven times as high as the corresponding probability for an African-American baby. In addition, we show that a child's desirability in the adoption process depends significantly on time to birth (increasing over the pregnancy, but decreasing after birth) and on adoption costs. We also document the attitudes toward babies' characteristics across different categories of adoptive parents - heterosexual and same-sex couples, as well as single women and foreign couples. Finally, we consider several recently discussed policies excluding same-sex and foreign couples from the adoption process. In our data, such policies would reduce the number of adopted babies by 6% and 33%, respectively.


Selection in utero: A biological response to mass layoffs

Ralph Catalano, Claire Margerison Zilko, Katherine Saxton & Tim Bruckner
American Journal of Human Biology, forthcoming

Most research describing the biological response to unemployment appears appropriately motivated by clinical or public health concerns and focuses on death, disease, and medical care. We argue that expanding the work to include other outcomes could contribute to basic science. As an example, we use the response to mass layoffs to discriminate between two explanations of low ratios of male to female live births in stressed populations. One explanation asserts that ambient stressors reduce the ratio of males to females conceived. The other argues that the maternal stress response selects against males in utero. We show that selection in utero better explains the observed data. We conclude that human adaptation to the economic environment deserves scrutiny from a wider array of scientists than it now receives.


Education Differences in Intended and Unintended Fertility

Kelly Musick, Paula England, Sarah Edgington & Nicole Kangas
Social Forces, December 2009, Pages 543-572

Using a hazards framework and panel data from the National Longitudinal Survey of Youth (1979-2004), we analyze the fertility patterns of a recent cohort of white and black women in the United States. We examine how completed fertility varies by women's education, differentiating between intended and unintended births. We find that the education gradient on fertility comes largely from unintended childbearing, and it is not explained by child-bearing desires or opportunity costs, the two most common explanations in previous research. Less-educated women want no more children than the more educated, so this factor explains none of their higher completed fertility. Less-educated women have lower wages, but wages have little of the negative effect on fertility predicted by economic theories of opportunity cost. We propose three other potential mechanisms linking low education and unintended childbearing, focusing on access to contraception and abortion, relational and economic uncertainty, and consistency in the behaviors necessary to avoid unintended pregnancies. Our work highlights the need to incorporate these mechanisms into future research.


Mothers' Antenatal Depression and Their Children's Antisocial Outcomes

Dale Hay, Susan Pawlby, Cerith Waters, Oliver Perra & Deborah Sharp
Child Development, January/February 2010, Pages 149-165

Interviews of 120 British adolescents and their parents (80% of a random sample of antenatal patients drawn from a representative urban population and followed longitudinally) revealed that 40 (33%) had been arrested and/or had a diagnosis of DSM-IV conduct disorder by 16 years of age; of those, 18 (45%) had committed violent acts. Depression in pregnancy significantly predicted violence in adolescence, even after controlling for the family environment, the child's later exposure to maternal depression, the mother's smoking and drinking during pregnancy, and parents' antisocial behavior. Mothers with a history of conduct problems were at elevated risk to become depressed in pregnancy, and the offspring of depressed women had a greater chance of becoming violent by age 16.


Increases in parental investment and child health as a result of an early intervention

Daphne Blunt Bugental, David Beaulieu & Amelia Silbert-Geiger
Journal of Experimental Child Psychology, forthcoming

Parental investment (involving time or money invested in 3-year-olds) and child health were assessed as an outcome of (a) children's risk status (preterm vs. full-term birth) and (b) maternal resources (defined here in terms of their problem-solving skills in resolving caregiving challenges). Resources were varied systematically as a function of maternal participation in a traditional home visitation program versus a novel cognitively enhanced program that facilitated parenting skills more successfully. As predicted, mothers in the traditional home visitation condition invested preferentially in low-risk children, whereas mothers in the cognitively enhanced condition invested preferentially in high-risk children (who, in turn, showed maximal health benefits). Maternal investment of time in care provision mediated the relationship between predictor variables and children's health. This pattern supports an evolutionary model of parental investment in which parents show discriminative solicitude based on the reproductive potential of the child and parents' access to relevant resources.


Who Owns Children and Does it Matter?

Alice Schoonbroodt & Michèle Tertilt
NBER Working Paper, January 2010

Is there an economic rationale for pronatalist policies? In this paper we propose and analyze a particular market failure that may lead to inefficiently low equilibrium fertility and therefore to a need for government intervention. The friction we investigate is related to the ownership of children. If parents have no claim on their children's income, then the private benefit from producing a child may be smaller than the social benefit. We present an overlapping-generations (OLG) model with fertility choice and altruism, and model ownership by introducing a minimum constraint on transfers from parents to children. Using the efficiency concepts proposed in Golosov, Jones, and Tertilt (2007), we find that whenever the transfer floor is binding, fertility choices are inefficient. We show how this inefficiency relates to dynamic inefficiency in standard OLG models with exogenous fertility and Millian efficiency in models with endogenous fertility. In particular, we show that the usual conditions for efficiency are no longer sufficient. Further, we analyze several government policies in this context. We find that, in contrast to settings with exogenous fertility, a PAYG social security system cannot be used to implement the efficient allocation. To achieve the efficient outcome, government transfers need to be tied to a person's fertility choice in order to provide incentives for child-bearing.


Natural Selection In Utero Contributes to the Male Longevity Deficit in Contemporary Human Populations

Ralph Catalano
University Of California Working Paper, October 2009

Much literature invokes natural selection to explain the pervasive deficit in the average lifespan of men compared to women. The explanation assumes that mothers, not fathers, provisioned children over much of human existence, and that women who lived long enough to help their children and grand children survive to reproductive age had more grandchildren and great-grandchildren than did shorter-lived women. Although this argument implies that natural selection would conserve mutations that conferred longevity on mothers but not fathers, it offers no explanation of the considerable changes over historic time in the male longevity deficit thereby implying that these arise solely from culture. I show, however, that natural selection in utero empirically predicts variability over time in the deficit. This mechanism spontaneously aborts less fit fetuses during stressful times and reportedly selects more against males than females. My finding suggests that natural selection interacts with culture to predictably affect both the life span and sex ratio of contemporary human populations.


Reproductive development and parental investment during pregnancy: Moderating influence of mother's early environment

David Coall & James Chisholm
American Journal of Human Biology, March/April 2010, Pages 143-153

The association between a woman's age at menarche and the birth weight of her children is highly variable across human populations. Life history theory proposes that a woman's early environment may moderate this association and thus account for some of the variation between populations. According to one life history theory model, for individuals who develop in a childhood environment of high local mortality rates (experienced subjectively as psychosocial stress), it can be adaptive to mature earlier, have more offspring during their reproductive lifetime, and reduce investment in each offspring. In an environment of low psychosocial stress, however, it may be adaptive to mature later, have fewer offspring, and invest more in each. In this study, birth weight and proportionate birth weight (neonate's birth weight as a percentage of its mother's prepregnancy weight) were used as measures of parental investment during pregnancy. In a sample of 580 first-time mothers, we tested the hypothesis that the psychosocial stress experienced as a child would moderate the association between age at menarche and investment during pregnancy. We found that earlier menarche in those women who experienced stressful life events before 15 years of age was associated with a lower birth weight and proportionate birth weight. Conversely, in those who reported no childhood stressors, earlier menarche was associated with increased birth weight and proportionate birth weight. Our data suggest that the moderating influence of the childhood psychosocial environment on the association between age at menarche and parental investment throughout gestation operates in a dose-dependent manner.


Mothers Have Lower Testosterone Than Non-Mothers: Evidence from the Philippines

Christopher Kuzawa, Lee Gettler, Yuan-yen Huang & Thomas McDade
Hormones and Behavior, forthcoming

Testosterone (T) is lower among fathers and men in committed relationships, suggesting that the hormone mediates the trade-off between mating and parenting effort. The function of T in women, and responses of the hormone to relationships or motherhood, are less well understood. Here we report relationships between T and pairbonding and motherhood in a random sample of 67 women (20.9 to 22.4 years old) participating in a population-based birth cohort study in the Philippines. Testosterone was measured in saliva collected at bedtime and at waking the following morning to capture circadian dynamics. Compared to non-mothers and non-pairbonded women, mothers and pairbonded women had 32% (p<0.0001) and 23% (p<0.004) lower waking T, respectively, but similar evening T. The lower waking T in mothers largely reflected reduced T in mothers of young offspring (<2 years), with mothers of older offspring (2+years) having intermediate T. These differences were independent of measures of breastfeeding, contraceptive pill use, menstrual cycle, sleep quality, education, employment and socioeconomic status. Our findings highlight a similar relationship between parenting and committed relationships and T in women as documented in men, and suggest that caregiving of dependent young may modulate female T. Future research should clarify whether this cross-sectional association reflects a suppressive effect of motherhood on T, whether these relationships vary across cultures, and the role of T within the endocrine architecture regulating female reproductive and caregiving strategies.


The Impact of Maternal Birth Month on Reproductive Performance: Controlling for Socio-Demographic Confounders

Ariane Kemkes
Journal of Biosocial Science, March 2010, Pages 177-194

Based on a 1900 census sample of 34,166 post-reproductive females (≥45 years), the birth month effect was put to the test, for both lifetime fertility as well as child survival, controlling for maternal birth cohort (1826-1835, 1836-1845, 1846-1855), Duncan's SEI, urbanity, nativity, literacy and marital duration. Testing for potential cohort effects did not indicate a temporal trend in fertility by maternal birth month (seasonal Mann-Kendall test, p=0.578), while a minute increase in offspring survival was detected (p<0.001, Sen's estimator of slope=0.02, 95% CI=0.02 to 0.03). Further analyses of the maternal birth month effect on child survival were therefore seized. For lifetime fertility, ANOVA results indicated that maternal birth month was a major predictor for total offspring count (F11, 33606_09.0, p<0.001), accounting for 37.2% of the total variability. In addition to main effects, a statistically significant interaction effect was observed (F538, 33606=2.2, p<0.001), with a corresponding effect size of η 2=0.40. Planned contrasts revealed that birth-month-specific differences in fertility achieved statistical significance (F11, 31798_12.9, p<0.001), while post-hoc multiple comparisons for literacy and nativity displayed an inverse relationship with fertility, which meets demographic expectations. Controlling for all factors of interest, models of cohort-specific offspring counts (independent ANOVAs for 1826-1835: F157, 3467&.3, p<0.001; 1836- 1845: F182, 10299u.5, p<0.001; 1846-1855: F199, 19859_7.9, p<0.001) indicated that women born in the first half of the year (particularly, January, February, April and May) achieved above-average parity, while those born in the latter half (namely, July, October, November and December) displayed markedly lower fertility averages. These monthly disparities are in line with previous observations and appear to be linked to seasonal optimal ripening of the oocyte or seasonal preovulatory over-ripeness ovopathy (Jongbloet, 1992).

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