Fertility Research
Promiscuity and the evolutionary transition to complex societies
Charlie Cornwallis, Stuart West, Katie Davis & Ashleigh Griffin
Nature, 19 August 2010, Pages 969-972
Abstract:
Theory predicts that the evolution of cooperative behaviour is favoured by low levels of promiscuity leading to high within-group relatedness. However, in vertebrates, cooperation often occurs between non-relatives and promiscuity rates are among the highest recorded. Here we resolve this apparent inconsistency with a phylogenetic analysis of 267 bird species, demonstrating that cooperative breeding is associated with low promiscuity; that in cooperative species, helping is more common when promiscuity is low; and that intermediate levels of promiscuity favour kin discrimination. Overall, these results suggest that promiscuity is a unifying feature across taxa in explaining transitions to and from cooperative societies.
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Maternal Health and the Baby Boom
Stefania Albanesi & Claudia Olivetti
NBER Working Paper, July 2010
Abstract:
U.S. fertility rose from a low of 2.27 children for women born in 1908 to a peak of 3.21 children for women born in 1932. It dropped to a new low of 1.74 children for women born in 1949, before stabilizing for subsequent cohorts. We propose a novel explanation for this boom-bust pattern, linking it to the huge improvements in maternal health that started in the mid 1930s. Our hypothesis is that the improvements in maternal health contributed to the mid-twentieth century baby boom and generated a rise in women's human capital, ultimately leading to a decline in desired fertility for subsequent cohorts. To examine this link empirically, we exploit the large cross-state variation in the magnitude of the decline in pregnancy-related mortality and the differential exposure by cohort. We find that the decline in maternal mortality is associated with a rise in fertility for women born between 1921 and 1940, with a rise in college and high school graduation rates for women born in 1933-1950, and with a decline in fertility for women born in 1941-1950. These findings are consistent with a theory of fertility featuring a trade-off between the quality and quantity of children. The analysis provides new insights on the determinants of fertility in the U.S. and other countries that experienced similar improvements in maternal health.
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Male Scientists Want To Be Fathers
Anne Lincoln & Elaine Howard Ecklund
Southern Methodist University Working Paper, August 2010
Abstract:
Prior to the 1980s, scholars assumed that work-family balance was a problem only for women and that men integrated the "separate spheres" with little trouble. More recently, research finds that satisfaction with work and career is related to satisfaction with life for both men and women while conflict between paid work and family responsibilities leads to lower productivity in paid labor and a decrease in family functioning for both men and women and spillover between the two spheres leads to feelings of imbalance. Importantly, researchers call for distinguishing between specific job characteristics that are presumed to be stressful and the subjective experience of these conditions. Using data from the Perceptions of Women in Academic Science study, we examine gender differences in satisfaction with work and life outside work among biologists and physicists, fields with strikingly different proportions of men and women. We find many similarities between biologists and physicists and between men and women, but also some striking gender differences. While women have fewer children than men and nearly half report that career is the culprit for having fewer children than they had wanted, men are hit harder by having fewer children than desired. Having smaller families appears to affect men more negatively than women. We discuss implications for social policy.
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Characteristics of the first child predict the parents' probability of having another child
Markus Jokela
Developmental Psychology, July 2010, Pages 915-926
Abstract:
In a sample of 7,695 families in the prospective, nationally representative British Millennium Cohort Study, this study examined whether characteristics of the 1st-born child predicted parents' timing and probability of having another child within 5 years after the 1st child's birth. Infant temperament was assessed with the Carey Infant Temperament Scale (Carey, 1972; Carey & McDevitt, 1978) at age 9 months, childhood socioemotional and behavioral characteristics with the Strengths and Difficulties Questionnaire (Goodman, 2001), and childhood cognitive ability with the Bracken School Readiness Assessment (Bracken, 2002) test at age 3 years. Survival analysis modeling indicated that the 1st child's low reactivity to novelty in infancy, high prosociality, low conduct problems, and high cognitive ability in childhood were associated with increased probability of parents having another child. Except for reactivity to novelty, these associations became stronger with time. High emotional symptoms were also positively associated with childbearing, but this was likely to reflect reverse causality-that is, the effect of sibling birth on the 1st child's adjustment. The results suggest that child effects, particularly those related to the child's cognitive ability, adaptability to novelty, and prosocial behavior, may be relevant to parents' future childbearing.
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Explaining Cross-National Differences in Fertility: A Comparative Approach to the Demographic Shift
Nigel Barber
Cross-Cultural Research, February 2010, Pages 3-22
Abstract:
Low fertility in modern societies challenges evolutionary social scientists. A comparative analysis of less developed countries investigated various possible predictors of low fertility including urbanization, monogamous marriage, level of participation in the monetary economy (GDP), and low infant mortality. Using a sample of 45 countries broken out by urban and rural location, each of these predictors of total fertility was significant in a regression analysis (r 2 = .76) that controlled for survey year, geographic latitude, sex ratio, and geographic hemisphere. Multivariate prediction estimated that the demographic shift (TFR < 2.6) occurs when infant mortality falls below 33 per thousand, when polygyny reaches zero, and when GDP per capita rises above US$20,508. (The low fertility at high latitudes, reported by Barber, was further found explainable in terms of monogamous marriage). Declining fertility in modern societies evidently constitutes an adaptive response to ecological conditions and is largely predictable from them.
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Household Investment Decisions and Offspring Gender: Parental Accounting
Vicki Bogan
Cornell Working Paper, June 2010
Abstract:
Numerous behavioral factors have been identified as having an impact on household stockholding decisions. Given there is both theoretical and empirical evidence to support the premise that offspring gender can influence specific types of parental preferences, I model and test the theory that offspring gender has an effect on parental investment decision making. I find that having only female offspring increases the probability of stock market participation. Specifically, I find that for male respondents, having only female offspring increases the probability of stockholding by over 6 percent.
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Family planning and fertility decline in rural Iran: The impact of rural health clinics
Djavad Salehi-Isfahani, Jalal Abbasi-Shavazi & Meimanat Hosseini-Chavoshi
Health Economics, forthcoming
Abstract:
During the first few years of the Islamic Revolution of 1979, and aided by pro-natal government policies, Iranian fertility was on the rise. In a reversal of its population policy, in 1989, the government launched an ambitious and innovative family planning program aimed at rural families. By 2005, the program had covered more than 90% of the rural population and the average number of births per rural woman had declined to replacement level from about 8 births in the mid 1980s. In this paper, we evaluate the impact of a particular feature of the program - health houses - on rural fertility, taking advantage of the variation in the timing of their construction across the country. We use three different methods to obtain a range of estimates for the impact of health houses on village-level fertility: difference-in-differences (DID), matching DID, and length of exposure. We find estimates of impact ranging from 4 to 20% of the decline in fertility during 1986-1996.
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Thomas Eich
Culture, Health & Sexuality, October 2010, Pages 755-769
Abstract:
In the Sunni Arab world, hymen repair has become a subject of considerable controversy due to a public statement of Egypt's Mufti Guma˛a in 2007. This paper analyses Guma˛a's position and the ensuing public debate about it as a means to study the larger conceptions of virginity and the hymen in Middle Eastern societies. In line with critical feminist studies it is shown that supporters as well as critics of the operation rely heavily on patriarchal arguments, views and rhetoric. Both share the societal vision that sexuality can only be lived out licitly in the framework of marriage and both agree that this ideal is in crisis. Where the two sides disagree is over the way in which this ideal should be protected, which derives from their conceptualisation of creation in general and female nature in particular. As a result, debate about hymen repair is not only not transforming social structures but is perpetuating them.
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Natural versus Assisted Reproduction: In Search of Fairness
Daniela Cutas & Lisa Bortolotti
Studies in Ethics, Law, and Technology, 2010
Abstract:
In this paper, we are concerned with the ethical implications of the distinction between natural reproduction (via sexual intercourse) and reproduction that requires assistance (either medical or social). We argue that the current practice of enforcing regulations on the latter but not on the former means of reproduction is ethically unjustified. It is not defensible to tolerate parental ignorance or abuse in natural reproduction and subsequently in natural parenting, whilst submitting assisted reproduction and parenting to invasive scrutiny. Our proposal is to guarantee equal (ethical and legal) treatment to people engaging in either form of reproduction or parenting.
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Pair‐Bonding Modifies the Age‐Specific Intensities of Natural Selection on Human Female Fecundity
Duncan Gillespie, Mirkka Lahdenperä, Andrew Russell & Virpi Lummaa
American Naturalist, August 2010, Pages 159-169
Abstract:
In many animals, including humans, the ability of females to reproduce depends not only on their survival to each age but also on being pair‐bonded to a mate. Exposure of the genetic variation underlying fecundity to natural selection should therefore depend on the proportion of females both alive and pair‐bonded. In spite of this, female "marital" status is seldom considered to impact the strength of selection on age‐specific fecundity. We used marriage‐history data of preindustrial Finns who experienced conditions of natural mortality and fertility to investigate how assortative mating by age and socioeconomic status affected female fitness and underlay age‐specific female marriage patterns. The probability that a female was married peaked at age 30-40 years; females who married in their early 20s to high‐socioeconomic‐status husbands had the highest levels of lifetime reproductive success. Greater age difference between the pair, which is typical for females who are married to high‐socioeconomic‐status husbands, increased the likelihood of widowhood occurring premenopause, adding to declines in the proportion of genetic variation exposed to selection with age. Using the age schedule of female marriage, we present an indicator of selection intensity on within‐pair‐bond fecundity. Our results suggest that the decline in selection intensity after age 30 years is a factor in the evolutionary maintenance of female reproductive senescence and menopause.
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Effect of Teenage Parenthood on Mental Health Trajectories: Does Sex Matter?
Katie Brooks Biello, Heather Sipsma & Trace Kershaw
American Journal of Epidemiology, 1 Aug 2010, Pages Pages 279-287
Abstract:
Rates of teenage pregnancy and parenthood in the United States remain high. Although many consequences of teenage parenthood have been well studied, little prospective research has examined its effect on mental health. This study aims to better understand the impact of teenage parenthood on mental health and to determine whether sex modifies this relation. Using data from the National Longitudinal Survey of Youth, 1997 (1997-2006), and a matched cohort design, the authors compared changes in the mental health of parenting teenagers and nonparenting teenagers over 6 years of follow-up with mixed-effects regression. The results indicate that mental health improved for all teenagers over 6 years of follow-up. Furthermore, overall, teenage parenthood was not associated with changes in mental health; however, sex modified this relation. Although the mental health of teenage fathers improved at a faster rate compared with nonparenting teenage males, teenage mothers improved at a slower rate compared with nonparenting teenage females. Psychological health has important implications for both the teenage parent and the child. Future studies should aim to better understand the mechanisms through which teenage parenthood impacts mental health among both males and females, and interventions should be developed to ensure mental health among young parents.
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Ren Mu & Xiaobo Zhang
Economics & Human Biology, forthcoming
Abstract:
Evidence shows that exposure to nutritional adversity in early life has larger long-term impacts on women than on men. Consistent with these findings, our paper shows a higher incidence of disability and illiteracy among female survivors of the Great Chinese Famine (1959-1961). Moreover we find that the better health of male survivors most plausibly reflects higher male excess mortality during the famine, whereas the observed gender difference in illiteracy rate is probably better explained by the culture of son preference.
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Lei Jin, Felix Elwert, Jeremy Freese & Nicholas Christakis
Demography, August 2010, Pages 579-586
Abstract:
In human populations, variation in mate availability has been linked to various biological and social outcomes, but the possible effect of mate availability on health or survival has not been studied. Unbalanced sex ratios are a concern in many parts of the world, and their implications for the health and survival of the constituent individuals warrant careful investigation. We indexed mate availability with contextual sex ratios and investigated the hypothesis that the sex ratio at sexual maturity might be associated with long-term survival for men. Using two unique data sets of 7,683,462 and 4,183 men who were followed for more than 50 years, we found that men who reached their sexual maturity in an environment with higher sex ratios (i.e., higher proportions of reproductively ready men) appeared to suffer higher long-term mortality risks than those in an environment with lower sex ratios. Mate availability at sexual maturity may be linked via several biological and social mechanisms to long-term survival in men.
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An exploration of secondary sex ratios among women diagnosed with anxiety disorders
M.S. Subbaraman, S.J. Goldman-Mellor, E.S. Anderson, K.Z. LeWinn, K.B. Saxton, M. Shumway & R. Catalano
Human Reproduction, August 2010, Pages 2084-2091
Background: Theory suggests that natural selection conserved reactivity in part because highly reactive women spontaneously abort less fit conceptuses, particularly small males. Other literature argues that high reactivity manifests clinically as anxiety disorders. If true, births to women diagnosed with anxiety disorders should exhibit a low secondary sex ratio (i.e. ratio of male to female births). We explored whether births to women diagnosed with anxiety disorders exhibit a lower sex ratio than births to women diagnosed with other psychiatric disorders, or to women without mental health diagnoses.
Methods: We performed a case-control comparison of the secondary sex ratios among groups of women categorized by mental health diagnosis using birth records linked to data from California County Mental Health system records. We compared sex ratios among 5994 deliveries to mothers diagnosed with anxiety disorders, 23 443 deliveries to mothers diagnosed with other psychiatric disorders and 1 099 198 ‘comparison' births.
Results: Although comparison births exhibited a higher sex ratio than births to women diagnosed with anxiety disorders or with other diagnoses, differences were not statistically significant. Births to African American women diagnosed with anxiety disorders, however, exhibited sex ratios significantly lower than comparison births among African Americans (OR = 0.89, P = 0.038) or births to African American women with other mental health diagnoses (OR = 0.88, P = 0.042).
Conclusions: We found that infants born to African American women diagnosed with anxiety disorders exhibited a significantly lower secondary sex ratio than reference groups. We urge confirmatory tests of our findings and discuss implications of the reactivity/anxiety hypothesis for psychiatry, obstetrics and public health.
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The Attention-Getting Capacity of Whines and Child-Directed Speech
Rosemarie Sokol Chang & Nicholas Thompson
Evolutionary Psychology, June 2010, Pages 260-274
Abstract:
The current study tested the ability of whines and child-directed speech to attract the attention of listeners involved in a story repetition task. Twenty non-parents and 17 parents were presented with two dull stories, each playing to a separate ear, and asked to repeat one of the stories verbatim. The story that participants were instructed to ignore was interrupted occasionally with the reader whining and using child-directed speech. While repeating the passage, participants were monitored for Galvanic skin response, heart rate, and blood pressure. Based on 4 measures, participants tuned in more to whining, and to a lesser extent child-directed speech, than neutral speech segments that served as a control. Participants, regardless of gender or parental status, made more mistakes when presented with the whine or child-directed speech, they recalled hearing those vocalizations, they recognized more words from the whining segment than the neutral control segment, and they exhibited higher Galvanic skin response during the presence of whines and child-directed speech than neutral speech segments. Whines and child-directed speech appear to be integral members of a suite of vocalizations designed to get the attention of attachment partners by playing to an auditory sensitivity among humans. Whines in particular may serve the function of eliciting care at a time when caregivers switch from primarily mothers to greater care from other caregivers.
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Rapid Transition towards the Division of Labor via Evolution of Developmental Plasticity
Sergey Gavrilets
PLoS Computational Biology, June 2010, e1000805
Abstract:
A crucial step in several major evolutionary transitions is the division of labor between components of the emerging higher-level evolutionary unit. Examples include the separation of germ and soma in simple multicellular organisms, appearance of multiple cell types and organs in more complex organisms, and emergence of casts in eusocial insects. How the division of labor was achieved in the face of selfishness of lower-level units is controversial. I present a simple mathematical model describing the evolutionary emergence of the division of labor via developmental plasticity starting with a colony of undifferentiated cells and ending with completely differentiated multicellular organisms. I explore how the plausibility and the dynamics of the division of labor depend on its fitness advantage, mutation rate, costs of developmental plasticity, and the colony size. The model shows that the transition to differentiated multicellularity, which has happened many times in the history of life, can be achieved relatively easily. My approach is expandable in a number of directions including the emergence of multiple cell types, complex organs, or casts of eusocial insects.