This study analyzes sex ratios garnered from one hundred and one years of baptismal records from the south-western French town of Villeneuve-sur-Lot, between 1610 and 1711. It is the continuation of a larger project attempting to divine infanticide among married couples in early modern Western Europe. By comparing observed sex ratios (OSRs) in baptisms with the Universal Sex Ratio at Birth (USRB) established by Visaria (1967) it has been suggested a number of times that significant and patterned deviations represent sex-selective infanticide. In the case of Villeneuve, swift shifts between preponderances of girl children and boy children during crises suggest compensatory practice, purposefully engaged in to even out potentially imbalanced sex ratios among adults later. In this way it may be suggested that the preference for boys or girls in Villeneuve over time was balanced, based on circumstance, rather than some inherent perceived value of boys over girls.

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The concept of temperature dependent sex determination (TSD) has been somewhat of an evolutionary enigma for many decades and has had increased attention with the growing predictions of a changing climate, particularly in species that are already threatened or endangered. TSD taxa of concern include marine turtles, which go through various life stages covering a range of regions. This, in turn, creates difficulties in addressing basic demographic questions. Secondary sex ratios (from life stages post-hatchling) were investigated by capturing juvenile green turtles (Chelonia mydas), 22.6-60.9 cm in straight carapace length (SCL), from three developmental areas along the east coast of Florida (a region known to have important juvenile aggregations) by analyzing circulating testosterone levels. All three aggregations exhibited significant female biases with an overall ratio of 3.2:1 (female: male). The probability of a turtle being female increased as the size of the individual decreased. Ratios obtained in this study were slightly less female-biased, but not significantly different, than those observed in the late 1990s. However, they were significantly more biased than those found in a late 1980s pilot study. The shift to significantly female-biased ratios may be beneficial to a recovering population, an evolutionary adaptation, and is common among juvenile aggregations. A more skewed female bias in smaller size classes may be indicative of recent, warmer periods during incubation on the nesting beaches. This female bias could become more exaggerated if temperatures meet future climate warming predictions.

Survivorship of children is unsurprisingly dependent upon numerous variables, not least of which is the role that preferential treatment plays in biasing the birth and survival of sons and daughters across cultures. This study draws upon an evolutionary approach by examining the "Trivers-Willard hypothesis" concerning condition-dependent sex allocation and differential parental investment. The central idea is that within a polygynous social mating structure - where reproductive variance is higher for males than for females as an intrinsic function of polygyny - mothers in optimal condition (defined by high status, good health, and abundant resources) are more likely to produce and invest in male offspring whereas mothers in poor condition (defined by low status, poor health, and resource deprivation) are more likely to produce and invest in female offspring so as to maximize potential lifetime reproductive success. Previous research on humans concerning this hypothesis tends to be restricted to one cultural group and thereby limited in sample size. For this study, nationally representative household survey data collected by the Demographic and Health Surveys (DHS+) program across 35 countries was used to test biological, resource-oriented, and behavioral aspects affecting maternal condition, sex allocation, and parental investment in humans. Country samples ranged from 732 to 21,839 women interviewed within South Asia, Sub-Saharan Africa, the Caribbean/Latin America, and the Near East/North Africa. The units of analysis were the mothers and their lastborn child (N = 128,039 woman-child pairs). A sequence of hierarchical regressions theoretically pre-specified a causal model concerning four constructed scales measuring maternal socioeconomic resources, maternal biological condition, prenatal care for the lastborn child, and health-seeking for the lastborn child. In startling contrast to the predictions of the original hypothesis, analysis of the overall model revealed small, yet stable, cross-regional main effects suggesting that - for all four regions – maternal biology predicts lastborn daughters while maternal resources predict lastborn daughters for each region, with the exception of Sub-Saharan Africa. Moreover, protective/preventative health-related behaviors predict lastborn sons within South Asia and the Near East/North Africa, while prenatal care and health-seeking are differentially attributed to the prediction of sons and daughters within Sub-Saharan Africa and the Caribbean/Latin America.

The diploma thesis deals with the determination and expansion of numerical structures for Cloven-hoofed game ie. for roe deer (Capreolus capreolus), red deer (Cervus elaphus), fallow deer (Dama dama), sika deer (Cervus nippon), white-tailed deer (Odocoileus virginianus), mouflon (Ovis musimon), chamois (Rupicapra rupicapra) and wild boar (Sus scrofa). The social structures of female game numbers for different sex ratios have been developed and can be used in different types of breeding. Based on the model cases performed, it has been confirmed that, with a limited number of individuals in the population, the number of youngsters and the number of adults decreases in nature at the sex ratio in favor of females due to spontaneous game reduction. As a result, the average age of adults is reduced, and younger years are getting into reproduction. Another negative aspect of this unbalanced sex ratio is the increase in cloven-hoofed game and related damage and intraspecific stress. In addition, for some game reserves, if the sex ratio is increased for males, there are problems of a similar character, which are being overcome by greater losses in heat fights. This creates additional economic damage. Model cases have shown and confirmed that, with a limited number of game and around a balanced gender ratio of 1:1 to about 1.2:1 in favor for males and 1:1.2 in favor for females, there are no problems with population control because it is predictable. Once the gender ratio is wider, basic problems arise and that is poorly breeding. These wider gender ratios are on one side and the other unnatural in nature and therefore carry many problems.

Sexually transmitted infections (STIs) have important consequences for individuals and society. Extensive literature has shown that various individual factors impact STIs. However, much less is known about their structural causes and how they affect sexual behavior and sexual network formation. In the first two chapters of this dissertation, I investigate how sex ratios and ethnic divisions affect sexual activity and the spread of STIs. In the third chapter, I analyze the effect of ethnic-based romantic homophily on STIs. I provide a brief description of each chapter below. Chapter 1. We extend a theory of fidelity in a two-sided economy, and empirically discriminate between different rationales of sexual network formation by testing their implications for how sex ratios affect sexual activity, relationship stability, and the spread of sexually transmitted diseases in men versus women. We use a unique individual-level dataset in combination with census data from England and Wales, a setting where adult women outnumber adult men. Exploiting variation in cohort/ethnicity/region-specific sex ratios as a quasi-natural experiment, we find that a decrease in sex ratio imbalance decreases sexual infidelity and the number of serial partners, and increases the likelihood of safe sex. This in turn reduces the likelihood of acquiring a range of sexually transmitted infections and diseases, including chlamydia, gonorrhoea, genital warts, and herpes. Consistent with the rationale underlying the formation of egalitarian (in)fidelity networks, the effects of the sex ratio on sexual activity are larger for men compared to women, while its effects on sexual diseases are larger for women compared to men. The causality of these effects is established using classical and recent instrumental variables approaches and various robustness checks. For falsification, we show that sex ratios have no impact on several "atheoretical" health conditions, such as Parkinson's disease, chronic lung disease, heart attack, stroke, and diabetes, which do not arise from sexual interactions. Chapter 2. In societies organized around distinct racial and ethnic groups, limited communication between these groups might increase the search cost of sexual partners outside of own group, leading to racially segregated sexual networks and low risks of sexually transmitted diseases. At the same time, because sexual infidelity is more likely to be discovered when the cheated-upon individuals are co-ethnics, individuals in multiracial societies might find it cheaper to select sexual partners from diverse ethnic groups to hide their infidelity, which would lead to large interethnic sexual networks and high risks of STIs. We test these conflicting hypotheses by analyzing the causal effect of neighborhood-level racial diversity on sexual activity and STIs, using unique individual-level data from England, Wales, and Scotland. We find that individuals residing in multiracial neighborhoods have a greater number of sexual partners and are more likely to be infected with a wide range of STIs than their counterparts residing in more racially homogeneous neighborhoods. We use traditional and new instrumental variables approaches and various robustness checks to establish causation. Analyzing mechanisms, we find that within racially diverse neighborhoods, individuals who select sexual partners from diverse racial groups are more likely to be infected with STIs, holding the number of partners and other individual characteristics fixed. For falsification, we conduct a reverse-placebo test showing that racial diversity has no effect on a wide range of health conditions that do not arise from sexual interactions. From a policy perspective, our analysis implies that policies that promote racial and ethnic integration are likely to reduce unhealthy sexual activity and the spread of STIs in racially heterogeneous societies. Chapter 3. A classical hypothesis in social network theory holds that central individuals are more likely to receive and spread information than are their peripheral counterparts. We test this hypothesis in the context of sexual networks and sexually transmitted diseases, using data from the United Kingdom. Romantic homophily - the tendency to select sexual partners with similar ethnic background - is used as a measure of the extent to which an individual is peripheral in a sexual network. We find that more sexually homophilous individuals have a lower risk of sexual infections. This effect is causal, and larger for women, Whites, and heterosexuals.

The study of sex allocation is one of the most successful areas in evolutionary biology: its theoretical predictions have been supported by experimental, observational and comparative approaches. Here, I develop sex allocation theory as follows: (1) I use fertility insurance theory to predict the sex ratio strategy of the malaria parasite, in response to human medical interventions that increase mortality and decrease fertility of the parasite’s various sexual stages; (2) Haplodiploidy has been suggested as a driver of the evolution of eusociality, as under this genetic system a female may be more related to her sister than to her own offspring. I examine a model considering queen versus worker control over the sex ratio of the colony and show that haplodiploidy alone does not explain the evolution of helping; (3) I follow up this study of the haplodiploidy hypothesis by examining the idea that split-sex ratios may favour the evolution of eusociality in haplodiploid species. I study the two mechanisms of split sex ratios, that are found in natural populations and may have been important in the transition to eusociality: queen virginity and queen replacement. I focus on the impact of worker reproduction by considering the effect of woker producing a fraction of the colony offspring and by considering variation in the workers’ offspring sex ratio. My analysis shows that worker reproduction does not promote the evolution of helping in haplodiploid species; (4) I examine the evolution and function of a sterile soldier caste in parasitoid wasps from the genus Encyrtidae. Two main functions have been hypothesized for the emergence of soldiers: spiteful mediation of a sex ratio conflict in mixed-sex broods, and altruistic protection and 7 facilitation of the development of relatives. I develop a model considering variation in the oviposition behaviour of females, that may produce single-sex or mixed-sex broods. I show that, in accordance with previous theory, females are expected to produce more soldiers than males, under the sex ratio conflict hypothesis. I also show that one of the consequences of this costly conflict is that females are favoured to produce single-sex broods over mixed-sex broods.

Abstract 1: A multi-level assessment of disproportionate population sex ratios and high-risk sexual behaviors among STD clinic patients Low male-to-female sex ratios in a population may influence high-risk sexual behaviors, such as multiple sex partners and inconsistent condom use, which facilitate the transmission of STDs. This study used multi-level modeling to assess whether population sex ratios were associated with these two individual-level behaviors. All analyses were stratified by gender. Interview data were collected from patients (N = 9,203, 48% male) attending participating STD clinics. Interviews included information on socio-demographics and sexual behavior, including number of sex partners in the previous 3 months and condom use at last sex. The sex ratio per census tract was obtained from the U.S. Census Bureau. There was no association between sex ratio and multiple sex partners or condom use for either men or women. That is, we found no evidence that a shortage of men in census tracts was associated with increased engagement in high-risk sexual behavior.   Abstract 2: A multi-level assessment of neighborhood vacancy rates and high-risk sexual behaviors among STD clinic patients The “broken windows” theory posits that physical neighborhood deterioration, and its association with reduced social cohesion, can lead to changes in individual behaviors. Thus individuals living in neighborhoods with high levels of deterioration may be more likely to engage in high-risk sexual behaviors. This study used multi-level modeling to evaluate the extent to which high residential vacancy rates increased the likelihood of individuals having multiple sex partners. Interview data, including data on patient demographics and sexual behaviors, were collected from patients (N = 6,347, 52% male) attending participating STD clinics in the Richmond, Virginia area from 2008-2010. Neighborhood vacancy rates were obtained from the U.S. Census Bureau. Fifty-one percent of men and 36% of women reported having 2 or more sex partners in the previous 3 months. Men who lived in census tracts with high vacancy rates were slightly more likely to report multiple sex partners (53.9%) compared to men who lived in low vacancy tracts (49.7%). In multi-level models, there was no association between high vacancy rates and having multiple sex partners among either women (OR = 0.98; 95% CI: 0.79, 1.20) or men (1.18; 95% CI: 0.99, 1.42). That is, we found no evidence that increased neighborhood deterioration, as measured by high residential vacancy rates, was associated with increased risk of having multiple sex partners among STD clinic patients.   Abstract 3: Residential segregation and gonorrhea rates in U.S. metropolitan statistical areas The residential segregation of black populations, often in areas of high economic disadvantage and low social status, may play a crucial role in the observed racial inequities in STD rates. An ecological analysis of 2005-2009 average gonorrhea rates was performed across 277 U.S. metropolitan statistical areas (MSAs). The black isolation index and Gini index of income inequality were used as proxy measures for racial and economic residential segregation respectively, derived from 2005-2009 U.S. Census estimates. We used logistic regression modeling to produce estimates of odds ratios (OR) and 95% confidence intervals (CI) for the association between a high black isolation index and Gini index, both independently and in combination, on gonorrhea rates in MSAs. Effect measure modification was assessed by calculating the relative excess risk due to interaction (RERI) between the two indices. Compared to MSAs with low levels of racial segregation, MSAs with high levels of racial segregation had increased odds of high gonorrhea rates (adjusted OR 5.54; 95% CI: 2.29-13.44). Adjustment for potential confounders did not noticeably impact the relationship between the Gini index and gonorrhea, with higher levels of income inequality predicting higher gonorrhea rates (adjusted OR = 2.47; 95% CI: 1.21-5.03). In combined models, the influence of racial residential segregation on gonorrhea rates was stronger than that of income inequality-based segregation; there was no evidence of additivity or a multiplicative interaction. Residential segregation by race or income equality may be a key component in the perpetuation of high rates of gonorrhea and other STDs among black populations in the U.S.

This thesis examines demographic manifestations of son preference in three parts. Part I develops a simulation model that formalises the decision to practice prenatal sex selection through a "ready, willing and able" framework. The model is calibrated to South Korean and Indian sex ratio at birth (SRB) trajectories. Simulations reveal how SRB distortions in both countries have emerged despite declining son preference due to the rapid diusion of ultrasound combined with growing propensities to abort as a result of weakening norms for large families. Part II examines the potential role of big data to indirectly estimate the SRB at the subnational level in India. States with distorted SRBs tend to display a relatively high Google search activity for ultrasound. SRB "now-casts" generated using search volumes perform better than lagged variable models in high birth registration states. Part III examines the relationship between prenatal sex selection and postnatal excess female child mortality in two studies. The first applies lifetable techniques to decompose population changes in child sex ratios into a fertility component attributable to prenatal sex selection and a mortality component attributable to sex-differentials in postnatal survival. This study finds that although reductions in numbers of excess female deaths have accompanied increases in "missing" female births in all countries experiencing SRB distortions, excess female mortality has persisted in some but not in others. The second study uses birth histories of the Demographic and Health Surveys for six countries that have witnessed SRB distortions - India, Nepal, Pakistan, Azerbaijan, Armenia and Albania - to examine if differential mortality change by sex can be explained by the uptake of prenatal sex selection. This study finds that changes in prenatal sex selection only explain mortality change in India. Across all countries, although patterns of mortality disadvantage are concentrated amongst less educated mothers, prenatal sex selection is strongest among the better educated. Differential sorting into the two behaviours offers an explanation for why the effect for prenatal sex selection is generally weak.

This dissertation explores the mechanisms of the increasing female crime in China from the effect of the one-child policy, which is treated herein as a natural experiment. Data reveal that the women’s share of documented crime dramatically increased after the mid-1990s when the first one-child generation reached the age of legal responsibility. This change reflects the interplay of the behavioral change and the net-widening effect. The increasing criminality of the one-child generation is attributable to the gap between the equal gender expectations of the individual, which has been reshaped by the unique socialization practices under the influence of the policy, and a stubbornly unequal gender hierarchy in the society. As a result, the one-child-generation women who disproportionately suffer the resulting strains are more likely to become involved in property and occupational crime as the alternative means to fulfill their aspirations for economic success. Additionally, the effect of the policy affects not only the individual gender roles of the only children but also their peers who have siblings through the intermediary of a culture shift. Therefore, the policy has changed the behavior of a whole new generation through the process of socialization and the lag in the structural change. The net-widening effect is another pathway of the unequal gender structure and ideologies to the increasing female crime. Moral panic associated with the emergence of diverse forms of female offenses lead to an inordinate degree of adverse attention focused upon the one-child-generation women by criminal justice professionals. The increased criminalization of sexuality brought an increasing number of the one-child-generation women into conflict with the law, usually for prostituting themselves for easy money to fulfill their material satisfaction. Consequently, the one-child-generation female offenders are perceived as “doubly deviant” from the law and from the socially prescribed ideology of gender and are, therefore, punished more harshly than before by the criminal justice system. This dissertation not only explores an understudied country in criminological research but also seeks to apply the findings to a broad sphere to explain the increasing female crime that has been observed worldwide. It disentangles the theoretical controversy in explaining the increase in the share of crime committed by women in general by embedding the argument in a multidimensional gender role repertoire.