Lisa Cameron et al.
We document that China's One-Child Policy, one of the most radical approaches to limiting population growth, has produced significantly less trusting, less trustworthy, more risk-averse, less competitive, more pessimistic, and less conscientious individuals. Our data were collected from economics experiments conducted with 421 individuals born just before and just after the One-Child Policy's introduction in 1979. Surveys to elicit personality traits were also used. We use the exogenous imposition of the One-Child Policy to identify the causal impact of being an only child, net of family background effects. The One-Child Policy thus has significant ramifications for Chinese society.
Anthony Volk & Jeremy Atkinson
Evolution and Human Behavior, forthcoming
The precise quantitative nature of the Environment of Evolutionary Adaptedness (EEA) is difficult to reconstruct. The EEA represents a multitude of different geographic and temporal environments, of which a large number often need to be surveyed in order to draw sound conclusions. We examine a large number of both hunter-gatherer (N = 20) and historical (N = 43) infant and child mortality rates to generate a reliable quantitative estimate of their levels in the EEA. Using data drawn from a wide range of geographic locations, cultures, and times, we estimate that approximately 27% of infants failed to survive their first year of life, while approximately 47.5% of children failed to survive to puberty across in the EEA. These rates represent a serious selective pressure faced by humanity that may be underappreciated by many evolutionary psychologists. Additionally, a cross-species comparison found that human child mortality rates are roughly equivalent to Old World monkeys, higher than orangutan or bonobo rates and potentially higher than those of chimpanzees and gorillas. These findings are briefly discussed in relation to life history theory and evolved adaptations designed to lower high childhood mortality.
Population and Development Review, December 2012, Pages 685-705
Over the second half of the twentieth century rapid population growth in the less developed countries has redrawn the global demographic map. Many once-poor countries have also experienced strong economic growth, which in combination with the demographic change has yielded marked shifts in the world's economic balance, with far-reaching geopolitical implications. At the same time, low fertility in much of the developed world presages a future of population shrinkage, accompanied by pronounced population aging. In per capita terms, the economic advantages of the developed countries will likely persist for many years, but their actual and potential falls in population may accentuate their loss of relative economic power and eventually lead to marginalization of their international standing and influence. Preventing population shrinkage will be an urgent task for them, requiring either large-scale immigration (likely to be ruled out) or raising the birth rate. Existing pro-family policies have had at best modest effects on fertility levels. Two novel approaches are described that would plausibly have greater impact. One would counteract the disproportionate influence of older voters in the electorate by granting voting rights to all citizens, allowing custodial parents to vote on behalf of their children. The second would reform the public pension system to reestablish the link between the financial security of retired persons and the number of children they have raised to productive adulthood.
Lena Edlund & Chulhee Lee
NBER Working Paper, January 2013
Sex ratios at birth in South Korea reached 116.5 boys per 100 girls in 1990, but have since declined. In 2007, sex ratios were almost normal, a development heralded as a sign that son preference and sex choice have vanished. However, normal sex ratios imply neither. We show that over the last 60 years, the relationship between sex ratios and parental status changed from negative to positive. This pattern, we argue, is consistent with a model where parents prefer sons and sex select - ultrasound and economic development accounting for the change in who chooses sons.
M. Rolland et al.
Human Reproduction, February 2013, Pages 462-470
Study question: Are temporal trends and values of semen quality parameters in France identifiable in partners of totally infertile women?
Summary answer: Among a sample of 26 609 partners of totally infertile women undergoing an assisted reproductive technology (ART) procedures in the whole of France over a 17-year period, there was a continuous decrease in semen concentration of about 1.9% per year and a significant decrease in the percentage with morphologically normal forms but no global trend for motility.
Study design, size, duration: This was a retrospective and descriptive study using data registered by Fivnat, the professional association in charge of statistics for ART in France during the 1989-2005 study period. Data were provided by 126 main ART centres over the whole metropolitan territory. The source population included 154 712 men, aged 18-70, who were partners of couples undergoing their first ART cycle and for whom semen quality indicators (concentration, total motility and percentage of morphologically normal forms), measured on fresh ejaculated semen, were available.
Participants/materials, setting, methods: The study population was 26 609 partners of women who had both tubes either absent or blocked. The temporal trends for each indicator of semen quality were modelled using a generalized additive model that allowed for nonlinear relationships between variables and were adjusted for season and age. In-depth sensitivity analyses included the reiteration of the analysis on data from a second spermiogram available for each man and on another subsample of men diagnosed as fertile. Variables such as centre, technique (standard in vitro fertilization or intra-cytoplasmic sperm injection) and an interaction factor between technique and time were also included in the model.
Main results and the role of chance: There was a significant and continuous decrease in sperm concentration of 32.2% [26.3-36.3] during the study period. Projections indicate that concentration for a 35-year-old man went from an average of 73.6 million/ml [69.0-78.4] in 1989 to 49.9 million/ml [43.5-54.7] in 2005. A significant, but not quantifiable, decrease in the percentage of sperm with morphologically normal forms along the 17-year period was also observed. There was no global trend but a slight, significant increase in total motility between 1994 and 1998 was observed. The results were robust after sensitivity analysis.
Scandinavian Journal of Public Health, December 2012, Pages 761-764
Background: The gender ratio at birth (M/F: male births divided by total births) is expected to approximate 0.515. This has shown to be declining in industrialised countries and to display a latitude gradient in Europe, with more males born in southern climates.
Methods: Annual national data for Scandinavian countries for male and female live births were obtained from the World Health Organisation and analysed with contingency tables.
Results: This study analysed 18,250,193 live births. A significant decreasing trend in M/F was noted in all countries except Norway, and overall. There was no latitude gradient. M/F was less than 0.515 for almost all countries, with a resultant male deficit of 19,517 live births.
Conclusions: M/F is decreasing in Scandinavia and M/F overall is <0.515. The interaction of several poorly comprehended factors is likely.
Jim Mossman et al.
Asian Journal of Andrology, January 2013, Pages 152-154
Recent studies investigating possible causes of male subfertility have largely focused on how lifestyle or environmental factors impact on the process of spermatogenesis. Markedly, fewer studies have investigated those risk factors that result in reduced sperm quality, such as poor sperm motility. The speed at which sperm swim is a major predictor of fertility and is extremely variable in human populations. It has been hypothesized that offspring sex may be adaptively manipulated to maximize the offspring's reproductive fitness (e.g., parents with genes for good male fertility traits, such as high sperm speed, would produce primarily sons and fewer daughters because the offspring will inherit advantageous male fertility genes). Conversely, parents with poor male fertility genes would produce primarily daughters. We tested whether there was an association between how fast a man's sperm swam and the sex bias of his siblings in a sample of men attending clinic for fertility investigations with their partner and with a wide range of semen characteristics, including sperm speed. We found that the sex bias of a man's siblings is associated with his sperm speed; men with female-biased siblings had significantly slower sperm (judged using computer-assisted sperm analysis (CASA)) than men from male-biased sibships. This observation suggests family composition is an important factor that needs to be considered in future epidemiological and clinical studies of human fertility.
Bioethics, February 2013, Pages 59-64
A number of authors have objected to potential parents' use of reproductive genetic technologies on the grounds that the use of these technologies reflects a morally problematic attitude toward parenting. More specifically, proponents of this view have argued that such a choice is inconsistent with the unconditional acceptance that lies at the heart of praiseworthy parental attitudes. This paper offers a rebuttal of this view by arguing that it is possible for a parent to exhibit unconditional acceptance of the child herself without accepting each of that child's traits. If this is true, the use of reproductive genetic technologies does not inherently undermine appropriate parental attitudes. Further, by working to change some of a child's specific traits, a parent may instead exemplify an aspirational aspect of praiseworthy parenting and so demonstrate appropriate parental attitudes.
American Economic Journal: Economic Policy, forthcoming
I study the impact of a universal child benefit on fertility and family well-being. I exploit the unanticipated introduction of a new, sizeable, unconditional child benefit in Spain in 2007, granted to all mothers giving birth on or after July 1, 2007. The regression discontinuity-type design allows for a credible identification of the causal effects. I find that the benefit did lead to a significant increase in fertility, as intended, part of it coming from an immediate reduction in abortions. On the unintended side, I find that families who received the benefit did not increase their overall expenditure or their consumption of directly child-related goods and services. Instead, eligible mothers stayed out of the labor force significantly longer after giving birth, which in turn led to their children spending less time in formal child care and more time with their mother during their first year of life. I also find that couples who received the benefit were less likely to break up the year after having the child, although this effect was only short-term. Taken together, the results suggest that child benefits of this kind may successfully increase fertility, as well as affecting family well-being through their impact on maternal time at home and family stability.
Daniel Kruger & Sarah Vanas
Letters on Evolutionary Behavioral Science, Fall 2012
Because the reproductive strategies of men and women are somewhat divergent, influences of the sex ratio on the intensity of mating competition and selectivity for partners produce different outcomes in female biased and male biased populations. Male mating opportunities are enhanced by scarcity and incentives for long-term commitment are diminished, encouraging serial and simultaneous polygyny. Paternal investment is lower in these populations, as indicated by higher divorce rates, more out-of-wedlock births, and a greater proportion of single mother households. Scarce females are able to more effectively secure commitment from partners as well as demand higher levels of resource investment. Women marry earlier in these populations. Although single father households are relatively uncommon, we expect to see higher proportions of households with children headed by single fathers where women are scarce. We also expect to see higher fertility among married couples, both because women may have greater bargaining power in reproductive decision-making and the role of woman in childbearing may be more salient to and valued by men. Data from the 2000 U.S. Census across 318 Metropolitan Statistical Areas supported these hypotheses.
D. Walsh & G. McCartney
Public Health, forthcoming
Background: Research published in 2010 showed that premature mortality in Glasgow over the period 2003-2007 was 30% higher than that in Liverpool and Manchester, despite the three cities sharing almost identical levels and patterns of socio-economic deprivation. A number of theories have been proposed to explain this discrepancy, including [in the light of US research linking variations in the termination of pregnancy (ToP) rate to differences in social and health outcomes] the suggestion that variations in current levels of mortality across the cities could be influenced by differences in earlier ToP rates.
Objectives: To undertake further analyses of mortality data for Glasgow, Liverpool and Manchester to assess the likelihood of differences in ToP rates influencing rates of excess mortality in Glasgow; to analyse long-term trends in numbers and ToP rates in the three cities (and, for comparison, between Scotland and England); and to investigate potential explanations for any differences in ToP rates.
Study design and methods: Mortality analyses were based on the same age-, sex- and deprivation-standardized data that were used in the previous research on the three cities. ToP data (and population denominator data) covering the period 1980-2009 were obtained from Scottish and English national organizations. Historical national ToP data for the years 1969-1979 were obtained from an additional published source. Rates were calculated per female aged 15-44 years and, for analyses of ToP among teenagers, per female aged 15-19 years. Potential explanations for differences in rates were investigated by means of literature searches and discussions with key informants.
Results: The ToP rate in Glasgow was lower than the ToP rates in Liverpool and Manchester over the total period analysed (as was the case for Scotland compared with England and Wales), although the gap has narrowed considerably, especially among females aged <20 years. This is due to a greater increase in the ToP rate in Glasgow (and Scotland), attributed, in part, to better access to ToP services. The differences in ToP rates do not appear to have been influenced by women travelling to England from Ireland for access to ToP facilities, nor by Glaswegian women travelling outside Scotland for the same reason. However, 90% of ‘excess' deaths that took place in Glasgow compared with Liverpool and Manchester between 2003 and 2007 related to individuals born prior to the 1967 Abortion Act; these excess deaths, therefore, are not influenced by earlier variations in ToP rates.
Conclusions: Differences in ToP rates between the cities are unlikely to impact on variations in later mortality rates. Thus, while the topic of ToP is important, investigation into the reasons behind Glasgow's excess mortality levels should focus on other hypotheses.
Kristin Snopkowski & Rebecca Sear
Evolution and Human Behavior, forthcoming
It has been suggested that human mothers are cooperative breeders, as they need help from others to successfully raise offspring. Studies working under this framework have found correlations between the presence of kin and both child survival and female fertility rates. This study seeks to understand the proximate mechanisms by which kin influence fertility using data from the 1987 Thailand Demographic and Health Survey (DHS), a nationally representative sample of 6775 women. Kin influence is measured by the length of time couples live with the husband's or wife's parents after marriage. Event history analysis, multilevel modeling and structural equation modeling are used to investigate both fertility outcomes and potential pathways through which postnuptial residence may influence fertility outcomes, including employment status, maternal and child outcomes, contraceptive use, breastfeeding duration, and age at marriage. We show that living virilocally (with husband's kin after marriage) increases total fertility by shortening time from marriage to first birth, and increasing the likelihood of progression to each subsequent birth. These effects are mediated through correlations between virilocal residence and earlier age at marriage as well as delayed initiation of contraceptive use. We find no influence of husband's kin on maternal or child outcomes. Living uxorilocally (with wife's kin after marriage) also reduces age at marriage, shortens time from marriage to first birth and (marginally) improves child survivorship, but has no effect on other child and maternal outcomes or progression to subsequent births and results in a similar number of living children as women living neolocally.
Journal of Comparative Economics, forthcoming
This paper explains how household formation rules affect the fertility and labour supply of women in the Former Soviet Union and neighbouring countries. Women who bear a male first child in countries dominated by traditional, patrilocal households are shown to have substantially lower subsequent fertility from those whose first child is female. Where households are generally nuclear, male first borns do not reduce subsequent fertility. Middle-aged women in more patrilocal contexts often work less if their first child is male, despite reduced fertility and being more likely to reside with a daughter-in-law. In more nuclear contexts, they tend to work more. These findings suggest that household formation rules are strongly related both to women's demand for sons and to the direction of intergenerational transfers.
Yaakov Bentov & Robert Casper
Fertility and Sterility, January 2013, Pages 18-22
In recent years, social and cultural trends have resulted in women delaying childbirth, thereby leading to reproductive senescence as a growing public health problem. We discuss potential etiologies for age-related female reproductive decline. We bring supportive evidence to the central role of mitochondrial dysfunction and oxygen radicals in the process of aging in general and reproductive senescence specifically. We also explore the role of coenzyme Q10 deficiency as a contributing factor and the effects of its administration.
Demography, November 2012, Pages 1433-1452
The unintended pregnancy rate in the United States remains high, and there are large race and education differences in unintended pregnancy and fertility. These differences make it important to study race and education differences in contraceptive behavior. Using nationally representative data from the 2002 National Survey of Family Growth, this study examines the effects of race and education on the likelihood that women have ever used particular types of hormonal contraception and have ever discontinued hormonal contraception because of dissatisfaction. The results show that blacks and Latinas were more likely to have used injectable contraceptives ("the shot") and less likely to have used oral contraceptives ("the pill") than were white women. Women with less education were more likely than college-educated women to have used the shot but there were no significant education differences in use of the pill. Among women who had ever used hormonal birth control, those with less than a college degree were more likely than college-educated women to discontinue the birth control because of dissatisfaction. However, net of education, this study found no significant racial/ethnic differences in discontinuation. The most commonly stated reason for discontinuation because of dissatisfaction was side effects.
Daniel Grossman et al.
American Journal of Public Health, January 2013, Pages 73-78
Objectives: We assessed the effect of a telemedicine model providing medical abortion on service delivery in a clinic system in Iowa.
Methods: We reviewed Iowa vital statistic data and billing data from the clinic system for all abortion encounters during the 2 years prior to and after the introduction of telemedicine in June 2008 (n = 17 956 encounters). We calculated the distance from the patient's residential zip code to the clinic and to the closest clinic providing surgical abortion.
Results: The abortion rate decreased in Iowa after telemedicine introduction, and the proportion of abortions in the clinics that were medical increased from 46% to 54%. After telemedicine was introduced, and with adjustment for other factors, clinic patients had increased odds of obtaining both medical abortion and abortion before 13 weeks' gestation. Although distance traveled to the clinic decreased only slightly, women living farther than 50 miles from the nearest clinic offering surgical abortion were more likely to obtain an abortion after telemedicine introduction.
Conclusions: Telemedicine could improve access to medical abortion, especially for women living in remote areas, and reduce second-trimester abortion.
Caitlin Gerdts, Divya Vohra & Jennifer Ahern
PLoS ONE, January 2013
Background: The WHO estimates that 13% of maternal mortality is due to unsafe abortion, but challenges with measurement and data quality persist. To our knowledge, no systematic assessment of the validity of studies reporting estimates of abortion-related mortality exists.
Study Design: To be included in this study, articles had to meet the following criteria: (1) published between September 1st, 2000-December 1st, 2011; (2) utilized data from a country where abortion is "considered unsafe"; (3) specified and enumerated causes of maternal death including "abortion"; (4) enumerated ≥100 maternal deaths; (5) a quantitative research study; (6) published in a peer-reviewed journal.
Results: 7,438 articles were initially identified. Thirty-six studies were ultimately included. Overall, studies rated "Very Good" found the highest estimates of abortion related mortality (median 16%, range 1-27.4%). Studies rated "Very Poor" found the lowest overall proportion of abortion related deaths (median: 2%, range 1.3-9.4%).
Conclusions: Improvements in the quality of data collection would facilitate better understanding global abortion-related mortality. Until improved data exist, better reporting of study procedures and standardization of the definition of abortion and abortion-related mortality should be encouraged.