Natural selection in utero induced by mass layoffs: the hCG evidence

Cohort Selection In Utero against Male Twins and Childhood Cancers: A Population-Based Register Study

BACKGROUND

Cancer ranks as the second leading cause of death among children ages 1 to 14 years in the United States. Previous research finds that strong cohort selection in utero against males precedes a reduction in live-born males considered frail. We examine whether such cohort selection in utero may similarly affect the frequency of childhood cancers among male live births.

METHODS

We examined 1,368 childhood cancers among males born in Sweden over 144 months, from January 1990 to December 2001, and followed to age 15 in the Swedish Cancer Registry. We retrieved the count of male twins by birth month from the Swedish Birth Registry. We applied autoregressive, integrated, moving average time-series methods to identify and control for temporal patterns in monthly childhood cancers and to evaluate robustness of results.

RESULTS

Fewer childhood cancers occur among monthly male birth cohorts with elevated selection in utero (i.e., a low count of live-born male twins). This association appears in the concurrent month (coef = 0.04; 95% CI, 0.001-0.079) as well as in the following month in which most births from the twin's conception cohort are "scheduled" to be born (coef = 0.055; 95% CI, 0.017-0.094).

CONCLUSIONS

Elevated cohort selection in utero may reduce the number of frail male gestations that would otherwise have survived to birth and received a cancer diagnosis during childhood.

IMPACT

This novel result warrants further investigation of prenatal exposures, including those at the population level, that may induce cohort selection in utero for some cancer types but not others.

Maternal Diabetes and Infant Sex Ratio

PURPOSE OF REVIEW

Evolutionary hypotheses on the ratio of males to females at birth posit that women terminate pregnancies with low likelihood of surviving and producing grandchildren. Thus, females are preferred to males under unfavorable conditions. Much of this literature has focused on catastrophic disruptions that induce maternal stress and result in fewer males. Diabetes may similarly affect the sex ratio.

RECENT FINDINGS

A male bias at birth among infants born to women with GDM is widely recognized; mild hyperglycemia experienced early in pregnancy may signal favorable conditions and warrant investment in males. There are sparse data on women with pregestational diabetes, but some evidence for a female bias born to those with type 1 diabetes and severe hyperglycemia (i.e., requiring insulin). Disease-related maternal stress in these women may lead to the selective termination of male fetuses. Further examination of pregestational diabetes stands to contribute to scientific understanding of the sex ratio.

A toolkit for the application of placental-fetal molecular biomarkers in epidemiologic studies of the fetal origins of chronic disease

Purpose of review

In this review, we provide essential background knowledge and an analytical framework for the application of placental-fetal molecular biomarkers in fetal origins chronic disease epidemiology. The widely available and highly quantitative placental hormone human chorionic gonadotropin (hCG) is used as an example. hCG is currently used for diagnosing fetal genetic disorders; yet it can and should be expanded to understanding the fetal origins of chronic diseases. We provide justification and methods to do this.

Recent findings

Ten papers published in the last 5 years were identified with supportive findings relevant to the application of biomarkers of hCG in epidemiologic studies on the developmental origins of health and disease (DOHaD).

Summary

There is increasing and consistent evidence that placental-fetal biomarkers may be highly informative in observational studies, as exemplified by hCG, with the correct approaches for measurement and data analysis.

Cyclical unemployment and infant health

This study provides evidence on the effect of cyclical unemployment on infant health. We match individual-level data from a detailed survey of mothers and their children in Memphis, TN, with 5-year average census-tract unemployment rates from the American Community Survey. Our findings indicate that a one percentage point increase in the local unemployment rate is associated with a statistically significant increase in the probability of having a low birthweight baby (a baby weighing less than 2500 grams). We also find evidence of a statistically significant decrease in gestational age. These effects are concentrated among infants born to mothers without a college education and into households earning less than $25,000 a year.

A review of the established and suspected causes of variations in human sex ratio at birth

The human sex ratio (proportion male) at birth (SRB) varies with many variables. Some of this variation has an established proximate cause. For instance, low SRB (more females) at birth are associated with various forms of stressful events or circumstances during or prior to pregnancy. These low SRB are almost certainly mainly caused by maternal-stress-induced male foetal loss. Other types of SRB variation are thought to be caused by hormonal variation in either or both parents around the time of conception. One or other of these two types of proximate cause seems to be responsible for most of the established variation of SRB. This will be illustrated here in respect of some selected forms of SRB variation. It seems likely that a clarification of the hormonal causes of SRB variation will also help explain the striking (apparent) inconsistencies in the results of reported tests of the influential Trivers-Willard hypothesis. It is further proposed that an appreciation of the evidence that parental hormones influence SRB may enhance understanding of several important pathologies (hepatitis B, toxoplasmosis, testicular cancer, prostate cancer and autism).

Household Financial Distress and Initial Endowments: Evidence from the 2008 Financial Crisis

This paper studies in utero exposure to the 2008 financial crisis. Exploiting the sudden and unexpected collapse of the Icelandic economy, I find that first-trimester exposure to the crisis led to a sizable and significant reduction in birth weight, increased the probability of a low birth weight ( < 2500 g), and decreased the probability of a high birth weight ( > 4000 g). I also find evidence that the collapse reduced the sex ratio, indicating selection in utero due to maternal prenatal stress exposure. My results imply large welfare losses from financial distress that have hitherto been ignored - because children with worse health at birth can expect substantially lower lifetime earnings - and suggest that economic hardships may in general exacerbate income inequalities in the long run as low-income households are typically more exposed to financial distress. Copyright © 2016 John Wiley & Sons, Ltd.

Male Reproductive Disorders and Fertility Trends: Influences of Environment and Genetic Susceptibility

It is predicted that Japan and European Union will soon experience appreciable decreases in their populations due to persistently low total fertility rates (TFR) below replacement level (2.1 child per woman). In the United States, where TFR has also declined, there are ethnic differences. Caucasians have rates below replacement, while TFRs among African-Americans and Hispanics are higher. We review possible links between TFR and trends in a range of male reproductive problems, including testicular cancer, disorders of sex development, cryptorchidism, hypospadias, low testosterone levels, poor semen quality, childlessness, changed sex ratio, and increasing demand for assisted reproductive techniques. We present evidence that several adult male reproductive problems arise in utero and are signs of testicular dysgenesis syndrome (TDS). Although TDS might result from genetic mutations, recent evidence suggests that it most often is related to environmental exposures of the fetal testis. However, environmental factors can also affect the adult endocrine system. Based on our review of genetic and environmental factors, we conclude that environmental exposures arising from modern lifestyle, rather than genetics, are the most important factors in the observed trends. These environmental factors might act either directly or via epigenetic mechanisms. In the latter case, the effects of exposures might have an impact for several generations post-exposure. In conclusion, there is an urgent need to prioritize research in reproductive physiology and pathophysiology, particularly in highly industrialized countries facing decreasing populations. We highlight a number of topics that need attention by researchers in human physiology, pathophysiology, environmental health sciences, and demography.

Studies of human sex ratios at birth may lead to the understanding of several forms of pathology

This article deals with the problem of the causes of the variation of sex ratio (proportion male) at birth. This problem is common to a number of areas in biology and medicine, for example, obstetrics, neurology/psychiatry, parasitology, virology, oncology, and teratology. It is established that there are signifi cantly biased, but unexplained, sex ratios in each of these fields. Yet workers in them (with the possible exception of virology) have regarded the problem as a minor loose end, irrelevant to the field's major problems. However, as far as I know, no one has previously noted that unexplained biased sex ratios occur, and thus pose (perhaps similar) problems, in all these fields. Here it is suggested that similar sorts of solutions apply in each. Further research is proposed for testing each solution. If the argument here is substantially correct across this range of topics, it may lead to an improved understanding not only of sex ratio but also of some of the pathologies in these specialties.

Twins less frequent than expected among male births in risk averse populations

Male twin gestations exhibit higher incidence of fetal morbidity and mortality than singleton gestations. From an evolutionary perspective, the relatively high rates of infant and child mortality among male twins born into threatening environments reduce the fitness of these gestations, making them more vulnerable to fetal loss. Women do not perceive choosing to spontaneously abort gestations although the outcome may result from estimates, made without awareness, of the risks of continuing a pregnancy. Here, we examine whether the non-conscious decisional biology of gestation can be linked to conscious risk aversion. We test this speculation by measuring the association between household surveys in Sweden that gauge financial risk aversion in the population and the frequency of twins among live male births. We used time-series regression methods to estimate our suspected associations and Box-Jenkins modeling to ensure that autocorrelation did not confound the estimation or reduce its efficiency. We found, consistent with theory, that financial risk aversion in the population correlates inversely with the odds of a twin among Swedish males born two months later. The odds of a twin among males fell by approximately 3.5% two months after unexpectedly great risk aversion in the population. This work implies that shocks that affect population risk aversion carry implications for fetal loss in vulnerable twin pregnancies.

Does "Out of work" get into the womb? Exploring the relationship between unemployment and adverse birth outcomes

This study uses Texas vital records from 1994 to 2003 to examine the relationship between self-reported maternal unemployment and birth outcomes, including birthweight and infant mortality. In the preferred specification, a sample containing 1,344, 605 sibling births to 604,649 mothers was used. Regression results indicated that within the same women, being unemployed was associated with lower average birthweights and higher rates of infant mortality than being engaged in market work, especially when unemployment preceded market work, and a range of hypothesized mediators did little to attenuate these relationships. Interaction models revealed that the poor average birth outcomes related to unemployment were driven by observations with at least one other indicator of health complication, such as presence of a medical risk factor. These results confirm that the relationship between unemployment and mother-child health varies across individuals, although further research is needed to understand the causal linkages connecting unemployment, health risks, and birth outcomes.

Very low birthweight: dysregulated gestation versus evolutionary adaptation

Much medical literature attributes persistently high rates of very low birthweight (VLBW) to "dysregulated" gestation. We offer the alternative view that natural selection conserved well-regulated, though nonconscious, decisional biology that protects the reproductive fitness of women by spontaneously aborting gestations that would otherwise yield frail infants, particularly small males. Modern obstetric practice, however, converts some fraction of these erstwhile spontaneous abortions into live births of very small infants. We further propose that the nonconscious decisional biology of gestation exhibits preferences also seen in consciously made decisions. We hypothesize that the incidence of VLBW among male infants should vary with the population's self-reported intentions to assume financial risk. We apply time-series modeling to monthly birth counts by sex and weight from the Swedish Medical Birth Registry between January 1993 and December 2010. We gauge risk aversion with monthly data from the Micro Index of the Swedish Consumer Tendency Survey (MISCT). Consistent with our argument that nonconscious decisional biology shares risk aversion with conscious decisions, we find that the incidence of VLBW among male infants in Sweden varies with the population's self-reported intentions to assume financial risk. We find increases above expected odds of a very low weight infant among males born 1 month after increases above expected levels of self-reported risk aversion in the Swedish population. We offer this finding as support for the argument that persistently high rates of VLBW arise, at least in part, from a combination of medical interventions and mechanisms conserved by natural selection to protect reproductive fitness.