Teenage fertility, socioeconomic status and infant mortality

This paper examines the relationship between infant mortality and a complex measure of socioeconomic status for evidence of diminution. In data on counties in the US with a minimum of 20 infant deaths over the 5-year period 1971-75, no evidence of a declining relationship between socioeconomic status and infant mortality was found. Both level of community affluence and racial composition of the population exerted direct effects on levels of infant deaths. In addition, both socioeconomic status and racial composition exhibited indirect effects which operated through teenage childbearing. When total infant mortality was subdivided, teenage fertility serves as a mediating variable in the link between socioeconomic status and neonatal mortality, but not for the postneonatal components. Given the nearly equivalent total effect of socioeconomic status on infant mortality, it is concluded that the classic division into neonatal (supposedly a function of biological and genetic agents) and postneonatal (traditionally attributed to social and environmental agents), may be too crude to allow the contemporary effects of the socioenvironmental milieu to be evaluated effectively.     

Farm background, socioeconomic status, and fertility: the two-generation hypothesis

This paper examines whether the effects of farm background on socioeconomic differentials in fertility are diminished among nonfarm couples. The data are for a sample of white ever-married women belonging to the 1901-1910 birth cohorts. The research provides another test of the 2 generation-urbanite hypothesis 1st advanced by the Goldberg studies of Detroit and Indianapolis. Unlike a number of other studies, the findings do not support the hypothesis. Thus, a number of questions arise concerning the results obtained by previous investigators in support of this hypothesis. Different types of samples measuring farm background and socioeconomic status may be plausible explanations for the differing results. It is also important to note that both the Detroit and Indianapolis samples can hardly be considered representative of US urban populations in the 1940s and 1950s. A further difficulty with the Detroit study was that Goldberg aggregated the data of a relatively large number of cohorts. The Indianapolis sample was constrained by the eligibility requirements of the original study. The difficulties of adequately testing Goldberg's hypothesis may have been compounded by the extension of the hypothesis to nationally representative samples. Moreover, The hypothesis was not supported when education was used as a measure of socioeconomic status in the Detroit study. Until other studies can be carefully replicated, definitive answers to such questions as to whether fertility differentials by socioeconomic status will disappear or have become attenuated must remain an unanswered question.     

Influence of macro and micro minerals in the peri-parturient period on fertility in dairy cattle

Infertility in dairy cattle is a complex, multi-factorial problem that cannot be evaluated in isolation of other diseases and disorders. Clearly there is a role for the prevention of problems in the peri-parturient period, in particular hypocalcaemia, mastitis, lameness and retained placenta (RP), that all have a negative impact on the subsequent fertility of the cow. Minerals, trace elements and vitamins play a vital role in the prevention of these disorders at this time. Macro minerals are involved in the acid base status of the dairy cow and influence calcium metabolism. The use of anionic salts in combination with adequate calcium and magnesium supplementation may help to improve dry matter intakes and reduce negative energy balance in the post-calving period as well as prevent hypocalcaemia. Vitamin E and zinc are effective in prevention of mastitis that occurs predominantly in the first weeks of lactation, through enhanced antioxidant function and keratinisation of the teat canal. Lameness in dairy cattle also occurs mainly in lactation though most of the original insults to the hoof can occur prior to calving. Zinc and biotin are implicated in improving keratinisation of the hoof and prevention of this disease. Organic forms of zinc are retained better than inorganic sources and may provide greater benefit in disease prevention. Retained placenta can be reduced by prevention of hypocalcaemia and also adequate selenium status of the dairy cow. Selenium yeast is known to have higher retention in tissues and may play an important role in ensuring sufficient selenium is available to the cow for reduction of disease.     

Low fertility increases descendant socioeconomic position but reduces long-term fitness in a modern post-industrial society

Adaptive accounts of modern low human fertility argue that small family size maximizes the inheritance of socioeconomic resources across generations and may consequently increase long-term fitness. This study explores the long-term impacts of fertility and socioeconomic position (SEP) on multiple dimensions of descendant success in a unique Swedish cohort of 14 000 individuals born during 1915–1929. We show that low fertility and high SEP predict increased descendant socioeconomic success across four generations. Furthermore, these effects are multiplicative, with the greatest benefits of low fertility observed when SEP is high. Low fertility and high SEP do not, however, predict increased descendant reproductive success. Our results are therefore consistent with the idea that modern fertility limitation represents a strategic response to the local costs of rearing socioeconomically competitive offspring, but contradict adaptive models suggesting that it maximizes long-term fitness. This indicates a conflict in modern societies between behaviours promoting socioeconomic versus biological success. This study also makes a methodological contribution, demonstrating that the number of offspring strongly predicts long-term fitness and thereby validating use of fertility data to estimate current selective pressures in modern populations. Finally, our findings highlight that differences in fertility and SEP can have important long-term effects on the persistence of social inequalities across generations.     

Religion, fertility and genes: a dual inheritance model

Religious people nowadays have more children on average than their secular counterparts. This paper uses a simple model to explore the evolutionary implications of this difference. It assumes that fertility is determined entirely by culture, whereas subjective predisposition towards religion is influenced by genetic endowment. People who carry a certain 'religiosity' gene are more likely than average to become or remain religious. The paper considers the effect of religious defections and exogamy on the religious and genetic composition of society. Defections reduce the ultimate share of the population with religious allegiance and slow down the spread of the religiosity gene. However, provided the fertility differential persists, and people with a religious allegiance mate mainly with people like themselves, the religiosity gene will eventually predominate despite a high rate of defection. This is an example of 'cultural hitch-hiking', whereby a gene spreads because it is able to hitch a ride with a high-fitness cultural practice. The theoretical arguments are supported by numerical simulations.     

Stable aggregate fertility in a time of family change: a decomposition of trends in American fertility, 1970-1999

Population-level birth rates in the United States were largely stable between 1970 and 1999. This stability contrasts with rapid change in marriage rates and fertility timing during the same period. In this article, I use decomposition techniques to analyze this seeming paradox. I decompose the general fertility rate into four components: age distribution, marital status, age-specific nonmarital fertility, and age-specific marital fertility. Absent other changes, declining time spent married would have led to substantial decline in fertility. Several factors combined to counterbalance these changes in marital behavior. Among white women in the 1970s and 1980s, marital fertility rates increased at older ages, consistent with a scenario in which women postponed both marriage and childbearing; increased nonmarital birth rates during this period were not a driving factor in overall fertility trends. Increased nonmarital fertility was more important in compensating for declining time spent married among African American women and among white women in the 1990s.     

Variation and change in fertility in West Central Nepal

This article employs temporal and intracultural frames of reference to examine patterns of variation in fertility among the caste-Hindus of West Central Nepal. Before the onset of major socioeconomic development in the region, three groups, the large-farm high castes, the small-farm high castes, and the low castes, exhibited distinct patterns of reproductive behavior which have been traced over the course of 25 years. Analysis of age-specific fertility rates suggests that one group, the small farm high-caste, maintained relatively low fertility before major development of the region occurred, and, over time, began using modern contraception in order to keep fertility low. Evidence from the low castes suggests that they are beginning deliberately to reduce fertility, but the large-farm high castes continue to have high fertility.     

Recent trends and components of change in fertility in Nepal

The objectives of this article are, first, to provide improved estimates of recent fertility levels and trends in Nepal and, second, to analyse the components of fertility change. The analysis is based on data from Nepal's 1996 and 2001 Demographic and Health Surveys. Total fertility rates (TFR) are derived by the own-children method. They incorporate additional adjustments to compensate for displacement of births, and they are compared with estimates derived by the birth-history method. Fertility is estimated not only for the whole country but also by urban/rural residence and by woman's education. The own-children estimates for the whole country indicate that the TFR declined from 4.96 to 4.69 births per woman between the 3-year period preceding the 1996 survey and the 3-year period preceding the 2001 survey. About three-quarters of the decline stems from reductions in age-specific marital fertility rates and about one-quarter from changes in age-specific proportions currently married. Further decomposition of the decline in marital fertility, as measured by births per currently married woman during the 5-year period before each survey, indicates that almost half of the decline in marital fertility is accounted for by changes in population composition by ecological region, development region, urban/rural residence, education, age at first cohabitation with husband, time elapsed since first cohabitation, number of living children at the start of the 5-year period and media exposure. With these variables controlled, another one-third of the decline is accounted for by increase in the proportion sterilized at the start of the 5-year period before each survey.     

Relationships in a simple harmonic mean two-sex fertility model

A continuous time two-sex stable population model that does not recognize age is examined under the “harmonic mean” consistency condition of equation (2). Solutions for the stable population intrinsic growth rate r and the sex composition 5 are presented in equations (5) and (6). The process of stabilization is examined, and it is shown that, given two basic constraints, any initial population sex composition will eventually converge to the stable population value. An algebraic solution for the discrete case where the sex ratio at birth is unity is presented and used to describe the trajectory to stability of several hypothetical populations. A closed form algebraic expression for the trajectory to stability is presented for the continuous model in the special case of no mortality.     

Testing a covariotide model of DNA substitution

The concomitantly variable codons hypothesis of DNA substitution argues that at any time only a fraction of the codons in a gene are capable of accepting a mutation. However, as mutations are fixed at some positions in a gene, the sites that are potentially variable also change because of changed functional constraints. This hypothesis has been termed the "covarion" hypothesis or when the model is applied to nucleotides, the "covariotide" hypothesis. The covarion-covariotide model has proven to be remarkably difficult to test. Here I examine a covariotide hypothesis for 11 genes using a likelihood ratio test. I show that in nine of the genes examined a covariotide model provides a better explanation of the data than a model that does not allow constraints to change over time.     

Spouses' socioeconomic characteristics and fertility differences in sub-Saharan Africa: does spouse's education matter?

Although the general objective of this study is to examine the extent to which spouses' socioeconomic characteristics determine whether modern contraception is used and whether family limitation (the demand for no more children) is desired, its central goal is to evaluate the degree to which the net effect of a woman's education on those fertility decisions is altered once a control is made for the level of schooling of the husband. Individual characteristics of spouses included as controls in this analysis are on the one hand women's attributes relating to employment, age, parity, ethnic identity, and urban residence and, on the other hand, the occupation of the husband. Data used in this research are provided by DHS surveys conducted in fourteen sub-Saharan countries: Mali. Burkina Faso, Niger, Nigeria, Cameroon, Benin, Senegal. Ghana, Central African Republic, Kenya, Zambia, Zimbabwe, Namibia and Rwanda. With two dichotomous outcome variables, logistic regression was used to estimate two nested models for each dependent variable and for each country covered by the study. DHS respondents used as units of analysis in this study are women who were married (any kind of union) and non-pregnant at the time when each national survey was conducted. The findings suggest that, while an educated wife needs the support of an educated husband to state a preference for family limitation in contemporary sub-Saharan Africa, controlling for husband's education and other relevant covariates does little to undermine the evidence that woman's advanced education and the adoption of modern family planning are positively related in the developing world.     

A combined macro and microvascular model for whole limb heat transfer

A new prototype model for whole limb heat transfer is proposed wherein the countercurrent heat exchange from the large central arteries and veins in the core of the limb is coupled to microvascular models for the surrounding muscle and the cutaneous tissue layers. The local microvascular temperature field in the muscle tissue is described by the bioheat equation of Weinbaum and Jiji. The new model allows for an arbitrary axial variation of cross-sectional area and blood distribution between the muscle and cutaneous tissue, accounts for the blood flow to and heat loss from the hand and treats the venous return temperature and surface temperature distribution as unknowns that are determined as part of the solution to the overall boundary value problem. Representative solutions are presented for a wide range of environmental conditions for a limb in both the resting state and during exercise.     

Environmental change and predator diversity drive alpha and beta diversity in freshwater macro and microorganisms

Global biodiversity is eroding due to anthropogenic causes, such as climate change, habitat loss, and trophic simplification of biological communities. Most studies address only isolated causes within a single group of organisms; however, biological groups of different trophic levels may respond in particular ways to different environmental impacts. Our study used natural microcosms to investigate the predicted individual and interactive effects of warming, changes in top predator diversity, and habitat size on the alpha and beta diversity of macrofauna, microfauna, and bacteria. Alpha diversity (i.e., richness within each bromeliad) generally explained a larger proportion of the gamma diversity (partitioned in alpha and beta diversity). Overall, dissimilarity between communities occurred due to species turnover and not species loss (nestedness). Nevertheless, the three biological groups responded differently to each environmental stressor. Microfauna were the most sensitive group, with alpha and beta diversity being affected by environmental changes (warming and habitat size) and trophic structure (diversity of top predators). Macrofauna alpha and beta diversity was sensitive to changes in predator diversity and habitat size, but not warming. In contrast, the bacterial community was not influenced by the treatments. The community of each biological group was not mutually concordant with the environmental and trophic changes. Our results demonstrate that distinct anthropogenic impacts differentially affect the components of macro and microorganism diversity through direct and indirect effects (i.e., bottom‐up and top‐down effects). Therefore, a multitrophic and multispecies approach is necessary to assess the effects of different anthropogenic impacts on biodiversity.