Birth spacing in Pakistan

Life table analysis was applied to data from the 1975 Pakistan Fertility Survey to identify child spacing differentials between population subgroups. Women in urban areas had shorter birth intervals than their rural counterparts from parities 1-6; only after parity 7 was this differential reversed. Similarly, women with some education had shorter birth intervals at the earlier parities than uneducated women. While overall family size is relatively homogeneous in Pakistan, women of more modern backgrounds seem to space their children more closely than traditional women. Age at marriage appears to play an important role not only in determining the length of the 1st interval, but also that of subsequent intervals. An unexpected finding was that ever users of contraception had distinctly more rapid spacing of their births than never users. The median interval to 1st birth was shortest in North West Frontier Province, but similar in Punjab and Sind. Multiple classification analysis revealed that some differentials in child spacing by education, residence, and province persisted even after other variables were controlled. Cohort of mother had an independent effect, with younger cohorts having shorter birth intervals. However, the variable that had the strongest effect on length of interval (aside from the 1st interval) was breastfeeding duration. It is likely that increasing urbanization and improved levels of education among women will lead to high levels of marital fertility associated with shorter birth intervals. Even though these trends tend to increase the age at marriage, they are associated with shorter durations of breastfeeding. In the longer term, greater use of contraception among women in the modern sector may partially counteract the fertility increasing effect of reduced birth intervals.     

Concordance between partners in desired waiting time to birth for newlyweds in India

Examining waiting time to birth among newlywed couples is likely to provide insights into the desire for spacing births among newlywed husbands and wives. Data from the Indian National Family Health Survey of 2005-06 are used to examine the desired waiting time (DWT) to birth among newlywed couples. The dependent variable is spousal concordance on desired waiting times. Overall 65% of couples have concordant desired waiting times. Among discordant couples, wives were more likely to want to wait longer than their husbands. Couples from richer wealth quintiles were more likely than couples from the poorest quintile to have concordant desired waiting times. Muslims were less likely than Hindus to have concordant desires. There is a need for spacing contraceptive methods among newlyweds in India. This may have implications for the Indian Family Planning Programme, which to date has largely focused on sterilization. Programmes need to include newlywed husbands to promote use of spacing methods.     

Why do women stop reproducing before menopause? A life-history approach to age at last birth

Evolutionary biologists have long considered menopause to be a fundamental puzzle in understanding human fertility behaviour, as post-menopausal women are no longer physiologically capable of direct reproduction. Menopause typically occurs between 45 and 55 years of age, but across cultures and history, women often stop reproducing many years before menopause. Unlike age at first reproduction or even birth spacing, a woman nearing the end of her reproductive cycle is able to reflect upon the offspring she already has—their numbers and phenotypic qualities, including sexes. This paper reviews demographic data on age at last birth both across and within societies, and also presents a case study of age at last birth in rural Bangladeshi women. In this Bangladeshi sample, age at last birth preceded age at menopause by an average of 11 years, with marked variation around that mean, even during a period of high fertility. Moreover, age at last birth was not strongly related to age at menopause. Our literature review and case study provide evidence that stopping behaviour needs to be more closely examined as an important part of human reproductive strategies and life-history theory. Menopause may be a final marker of permanent reproductive cessation, but it is only one piece of the evolutionary puzzle.     

Maternal factors and infant and child mortality in Bangladesh

Using data from The World Fertility Survey, this study shows that the length of the preceding birth interval was the most important maternal factor influencing infant and child mortality risks in Bangladesh. This was such a crucial factor that its effects remain unaltered whether or not the influences of mother's age at birth and birth order are controlled. Infant and child mortality in Bangladesh can be expected to decline considerably if successive births can be spaced by an interval of at least 1.5 years. Child spacing seems to be the major factor requiring program attention. The effects of mother's education and place of residence on infant and child mortality are independent of the effects of maternal age at birth, birth order, and the preceding birth interval. The higher survival chances of children of educated mothers resulted neither through the age at which childbearing started nor through birth spacing but are likely to be related to their smaller family size and to other non-maternal proximate determinants of early mortality.     

Variations in within-group inter-individual distances between birth- and non-birth seasons in wild female patas monkeys

Individual spatial positioning plays an important role in mediating the costs and benefits of group living, and thus shapes different aspects of animal social systems including group structure and cohesiveness. I aimed to quantify variation in individual spacing behavior and its correlates in a group of wild patas monkeys (Erythrocebus patas) living in north Cameroon. I collected data on inter-individual distances during group scans when following subject females. Individuals had longer inter-individual distances during the non-birth season than during the birth season. Dominance relationships had little effect on inter-individual distances between females during both the non-birth and birth seasons. The results suggest that group cohesion was higher during the birth season than the non-birth season. Thus I conclude that higher group cohesion during the birth season may reduce the predation risk of infants.     

Spousal agreement on preferred waiting time to next birth in sub-Saharan Africa

This study investigates how various social, demographic and economic factors affect spousal agreement on preferred waiting time to next birth. Data for matched cohabiting couples from ten Demographic and Health Surveys in sub-Saharan Africa (Benin, Burkina Faso, Ghana, Guinea, Mali, Ethiopia, Kenya, Mozambique, Zambia and Zimbabwe), conducted between 2003 and 2006, were analysed to compare reported waiting time to next birth by the husband and the wife. Couples where the reported waiting time to next birth was the same for both partners (difference is 0 months) were defined as having agreement on waiting time to next birth. In sub-Saharan Africa, spousal agreement on waiting time to next birth was found to be associated with wanting the next child sooner. When the spouses disagree on waiting time to next birth, the wives want to wait longer than their husbands in most cases. Additionally, the study found that demographic factors are the primary determinants of spousal agreement on waiting time to next birth, not socioeconomic factors. The strongest predictors of spousal agreement on waiting time to next birth were number of living children, difference between the number of ideal and living children and wife's age. Couples with fewer children, a younger wife and those with a difference of five or more children between ideal and living number of children were more likely to agree on waiting time to next birth. Effects of socioeconomic factors, such as education and wealth status, on spousal agreement on waiting time to next birth were generally weak and inconsistent. The findings highlight some of the challenges in developing programmes to promote spousal communication and birth spacing and underscore the need for programmes to be gender-sensitive.     

Fertility at low and high altitude in central Nepal

Abstract

Data are reported on ages of menarche, first marriage and first childbirth, migration, venereal disease, birth control, birth spacing and on completed fertility rate in populations of Central Nepal living at low (8,500 feet) and high altitude (12,400 feet). The high‐altitude population reported a significantly lower completed fertility rate which could be partly accounted for by later age at marriage and first childbirth and increased birth spacing. Longer post‐partum ammenorhea and breast feeding did not account for the increased average pregnancy gap.     

半干旱生态条件下春小麦群体生态场的空间分布

在冠幅半径只有株距一半的三叶期,群体重庆场呈以每株立地点为峰顶的相对独立的小凸起,随着个体生长,拔节期群体的生态场成为一个稍见起伏的大凸峰,将行距加倍后,场强在行间出现明显的低谷;株距也加们后,在株间出现同样的低谷。群体的相对密度对其场强分布趋势起重要作用。由于边行效应使群体在发育后期边行的场强增高从而使群体强分布呈近似平顶凸起状。     

Positive Effect of Large Birth Intervals on Early Childhood Hemoglobin Levels in Africa Is Limited to Girls: Cross-Sectional DHS Study

Background

Short birth intervals are independently associated with increased risk of adverse maternal, perinatal, infant and child outcomes. Anemia in children, which is highly prevalent in Africa, is associated with an increased risk of morbidity and mortality. Birth spacing is advocated as a tool to reduce anemia in preschool African children, but the role of gender differences and contextual factors has been neglected. The present study aims to determine to what extent the length of preceding birth interval influences the hemoglobin levels of African preschool children in general, as well as for boys and girls separately, and which contextual factors thereby play a crucial role.

Methods and Findings

This cross-sectional study uses data from Demographic and Health Surveys (DHS) conducted between 2003 and 2011 in 20 African countries. All preschool children aged 6–59 months with a valid hemoglobin measurement and a preceding birth interval of 7–72 months as well as their corresponding multigravida mothers aged 21–49 years were included in the study. Hemoglobin levels of children and mothers were measured in g/l, while birth intervals were calculated as months difference between consecutive births. Multivariate analyses were done to examine the relationship between length of preceding birth interval and child hemoglobin levels, adjusted for factors at the individual, household, community, district, and country level. A positive linear relationship was observed between birth interval and the 49,260 included children’s hemoglobin level, whereby age and sex of the child, hemoglobin level of the mother, household wealth, mother’s education and urbanization of place of residence also showed positive associations. In the interaction models, the effect of a month increase in birth interval is associated with an average increase of 0.025 g/l in hemoglobin level (P = 0.001) in girls, while for boys the effect was not significant. In addition, for girls, the effect of length of preceding birth interval was highest in young mothers and mothers with higher hemoglobin levels, while for boys, the highest effect was noticed for those living in more highly educated regions. Finally, significantly higher hemoglobin levels of girls compared to boys were observed at birth but with increasing age, the sex difference in hemoglobin level gradually becomes smaller.

Conclusions

A longer birth interval has a modest positive effect on early childhood hemoglobin levels of girls, and this effect is strongest when their mothers are in their early twenties and have a high hemoglobin level. Remarkably, although the physiological iron requirement is higher for boys than girls, birth spacing has little influence on hemoglobin levels of preschool boys. We speculate that the preference for male offspring in large parts of Africa significantly influences nutritional patterns of African preschool boys and girls, and as such also determines the different effect of birth spacing. Finally, gender aspects should be considered in intervention programs that aim to improve anemia in African children.     

Weaning behaviour in human evolution

Human life history incorporates early weaning, a prolonged period of post-weaning dependency and slow somatic growth, late onset of female reproduction, reduced birth spacing and a significant post-reproductive female lifespan, combined with rapid early brain growth. Weaned human offspring lack the cognitive skills and physical capacity required to locate, procure and prepare foods that are appropriate for their immature state and sufficient for their high energy requirements. During the weaning process and throughout childhood human offspring are supported by the provision of energy dense and easily digestible foods. Changes in weaning behaviour during human evolution imply a shift in the balance between maternal costs of lactation and the risk of poor offspring outcome, and may have been driven by an increase in infant nutritional and metabolic requirements, a reduction reproductive lifespan resulting in selection for reduced birth spacing or a change in other factors affecting offspring survival and fitness.     

Birth spacing in langur monkeys (Presbytis entellus)

This paper presents 10 years of reproductive data on birth interval length and 5 years of data on reproductive behavior postpartum from a captive colony of gray langur monkeys (Presbytis entellus)housed in Berkeley, California. Birth intervals of females following different pregnancy and nursing schedules are compared. Females whose infants survive to the age of 9 months have a median birth interval of 15.4 months. The experimental separation of mothers from infants for a period of 2 weeks, 6 to 9 months postpartum, had no significant effect on the median birth interval length. Females experiencing a pregnancy failure or the loss of a neonate had median birth intervals of 9.6 and 10.7 months, respectively. These intervals were significantly shorter than the birth intervals of females whose infants survived to 9 months, showing that the presence of a nursing infant delays the female’s time to next conception by approximately 5 to 6 months. Females experienced a median of three estrous periods (two estrous cycles) before conceiving postpartum, regardless of pregnancy outcome or length of infant survival, and females rarely conceived during their first estrous period postpartum. Weaning did not occur until after the mother’s next conception. These data indicate that, in populations of langurs characterized by average birth intervals of 15 to 16 months, the loss of an infant after the age of 5 to 6 months will not accelerate a female’s ability to conceive or shorten the birth interval length. The available data on birth spacing from populations of free-ranging langurs are reviewed. It could not be demonstrated that non-Himalayan populations are characterized by birth intervals which are as long as 20 to 24 months. Rather, it is suggested that female langurs inhabiting seasonally arid sites, such as Jodhpur, Abu, and Dharwar, may be capable of producing infants on the average of every 15 to 16 months. Flexibility in the timing of births and the lack of well-defined birth seasons at these sites may be explained by this species’ dietary and digestive adaptations. Additionally, data on birth spacing and the age of missing infants from the above field sites, where it has been suggested that infanticide following changes in male leadership occurs habitually, do not lend support to the sexual selection hypothesis of infanticide as proposed by S. Hrdy (1974, 1977).     

Ecology and signal evolution in lizards

Current models of signal evolution explain diversity by invoking a variety of social, perceptual and environmental factors. Social systems and spacing patterns determine the active space of signals and their function. Receiver sensory systems and habitat characteristics interact to constrain signal design. These factors are traditionally implicated in promoting directional evolutionary change, leading to increases or decreases in signal complexity. We examine macro-evolutionary trends in signal design, as reflected by display modifier repertoire size, for 124 species of iguanian lizards to identify the importance of ecological factors in display evolution. Possessing a small home range, being arboreal and feeding on moving prey are all correlated with the evolution of large repertoires. However, living in closed habitats is associated with increased evolutionary change in repertoire size, producing greater signal diversity. Ecological factors can thus act either directionally or to promote evolutionary lability.   © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 127–148.     

论转基因林木的潜在生态风险性

基因工程技术为加快林木遗传改良进程开辟了一条崭新的途径．由于林木栽培环境复杂、生产周期长、经营管理粗放,且主要为风媒传粉植物等原因,与集约化程度较高的农作物相比,转基因林木环境释放及推广的潜在生态风险性更大．如转基因林木大量种植可加速该树种遗传多样性水平降低,导致遗传脆弱性;转基因林木的长期持续强选择压力作用导致害虫、病菌协同进化;外源基因逃逸有可能使非转基因植物的生态适合度增强或降低,进而影响到自然界的物种多样性等。     

Coexistence of nearly neutral species

Aims The neutral theory of biodiversity provides a powerful framework for modeling macroecological patterns and interpreting species assemblages. However, there remain several unsolved problems, including the effect of relaxing the assumption of strict neutrality to allow for empirically observed variation in vital rates and the 'problem of time'—empirically measured coexistence times are much shorter than the prediction of the strictly neutral drift model. Here, we develop a nearly neutral model that allows for differential birth and death rates of species. This model provides an approach to study species coexistence away from strict neutrality.Methods Based on Moran's neutral model, which assumes all species in a community have the same competitive ability and have identical birth and death rates, we developed a model that includes birth–death trade-off but excludes speciation. This model describes a wide range of asymmetry from strictly neutral to nearly neutral to far from neutral and is useful for analyzing the effect of drift on species coexistence. Specifically, we analyzed the effects of the birth–death trade-off on the time and probability of species coexistence and quantified the loss of biodiversity (as measured by Simpson's diversity) due to drift by varying species birth and death rates.Important findings We found (i) a birth–death trade-off operating as an equalizing force driven by demographic stochasticity promotes the coexistence of nearly neutral species. Species near demographic trade-offs (i.e. fitness equivalence) can coexist even longer than that predicted by the strictly neutral model; (ii) the effect of birth rates on species coexistence is very similar to that of death rates, but their compensatory effects are not completely symmetric; (iii) ecological drift over time produces a march to fixation. Trade-off-based neutral communities lose diversity more slowly than the strictly neutral community, while non-neutral communities lose diversity much more rapidly; and (iv) nearly neutral systems have substantially shorter time of coexistence than that of neutral systems. This reduced time provides a promising solution to the problem of time.     

Factors associated with exclusive breastfeeding at discharge during the COVID-19 pandemic in 17 WHO European Region countries

Both the consumption of breastmilk in infancy and a person’s season of birth influences his or her health, educational, professional, and behavioral outcomes. Further, season of birth effects differ by sex. However, current research, for the most part, neglects to examine if season of birth and breastfeeding are related. This paper examines the impact of sex-based variations in season of birth on breastfeeding likelihood and duration in the U.S. Using data from children born to female respondents of the National Longitudinal Survey of Youth 1979 (born between 1970 and 2012), this study examines with Probit, Negative Binomial, and Ordinary Least Squares (OLS) regressions if a child’s season of birth and sex are correlated with breastfeeding incidence and duration. The breastfeeding incidence and duration data are self-reported by the mother. Season of birth has a small but statistically significant impact on the incidence and duration of breastfeeding, which varies depending on the sex of the infant. Mothers giving birth to sons in the spring are 13.5% less likely to breastfeed than those giving birth to sons in the winter (with a p - value of 0.0269). Mothers with daughters born in the summer or fall (autumn) breastfeed slightly longer than mothers with daughters born in the spring. On average, mothers of summer-born daughters breastfeed 4.1% longer (with a 95% confidence interval of 0.3 - 7.8) and those with fall-born daughters 3.8% longer (with a 95% confidence interval of 0 - 7.5). Mothers giving birth to daughters in the spring are also significantly less likely to reach the breastfeeding six-week duration target (compared to fall and winter births) and the one-year duration target (compared to fall births). These findings suggest that the costs and benefits of breastfeeding an infant vary with the season of birth and the sex of the child. This finding could explain some of the season of birth effects previously identified in the literature. Further, policymakers seeking to increase breastfeeding rates should consider the reduced breastfeeding rates and durations for children born in the spring.     

Child mortality in Goa: A cross‐sectional analysis

Abstract

This paper is a study of the determinants of child mortality in the relatively developed Indian state of Goa. Data from the National Family Health Survey (NFHS, 1992–93) conducted in the state of Goa have been used to examine the child mortality experiences of 1,331 women who were within a marriage lasting 15 years. An aggregated index of child mortality, which summarizes the mortality experiences of a woman with exposure adjustment, is the study variable. Maternal education and longer birth spacing were found to lower child mortality risks significantly.     

Myofilament lattice spacing as a function of sarcomere length in isolated rat myocardium

The Frank-Starling relationship of the heart has, as its molecular basis, an increase in the activation of myofibrils by calcium as the sarcomere length increases. It has been suggested that this phenomenon may be due to myofilaments moving closer together at longer lengths, thereby enhancing the probability of favorable acto-myosin interaction, resulting in increased calcium sensitivity. Accordingly, we have developed an apparatus so as to obtain accurate measurements of myocardial interfilament spacing (by synchrotron X-ray diffraction) as a function of sarcomere length (by video microscopy) over the working range of the heart, using skinned as well as intact rat trabeculas as model systems. In both these systems, lattice spacing decreased significantly as sarcomere length was increased. Furthermore, lattice spacing in the intact muscle was significantly smaller than that in the skinned muscle at all sarcomere lengths studied. These observations are consistent with the hypothesis that lattice spacing underlies length-dependent activation in the myocardium.     

Giraffe birth locations in the South Luangwa National Park,Zambia: site fidelity or microhabitat selection?

Birth site location can have enormous implications for female reproductive success. Some ungulate species demonstrate consistent birth site fidelity, while others shift birth locations during their lifetimes as a function of ecological and social factors. We plotted 39 years of birth records from a wild population of Thornicroft's giraffe, Giraffa camelopardalis thornicrofti, to test the hypothesis that giraffe use consistent locations for birth. Data from 29 calves born to nine females revealed that birth seasonality was absent and that ecological zone had no significant impact on birth locations. Consecutive births by individual females were not limited to certain locations, with the distance between sequential birth sites tending to be greater if a calf failed to survive the first year of life. Our evidence conflicts with the suggestion that giraffe cows regularly return to special locations for bearing calves. We suggest that the choice of birth location is a function of nonseasonal breeding, predator pressure and extensive variation in microhabitat characteristics within ecological zones. Female giraffe have evolved a flexible reproductive strategy, whereby they regulate choice of birth site location based upon their past reproductive history, current ecological conditions (including both resource availability and predator pressure) and present social surroundings.