What is driving the global decline of human fertility? Need for a multidisciplinary approach to the underlying mechanisms.

An intense period of human population expansion over the past 250 years is about to cease. Total fertility rates are falling dramatically all over the world such that highly industrialized nations, including China and the tiger economies of SE Asia, will see their populations decline significantly in the coming decades. The socioeconomic, geopolitical and environmental ramifications of this change are considerable and invite a multidisciplinary consideration of the underlying mechanisms. In the short-term, socioeconomic factors, particularly urbanization and delayed childbearing are powerful drivers of reduced fertility. In parallel, lifestyle factors such as obesity and the presence of numerous reproductive toxicants in the environment, including air-borne pollutants, nanoplastics and electromagnetic radiation, are seriously compromising reproductive health. In the longer term, it is hypothesized that the reduction in family size that accompanies the demographic transition will decrease selection pressure on high fertility genes leading to a progressive loss of human fecundity. Paradoxically, the uptake of assisted reproductive technologies at scale, may also contribute to such fecundity loss by encouraging the retention of poor fertility genotypes within the population. Since the decline in fertility rate that accompanies the demographic transition appears to be ubiquitous, the public health implications for our species are potentially devastating.

Racial and Temporal Differences in Fertility-Education Trade-Offs Reveal the Effect of Economic Opportunities on Optimum Family Size in the United States.

Contemporary trends in low fertility can in part be explained by increasing incentives to invest in offspring's embodied capital over offspring quantity in environments where education is a salient source of social mobility. However, studies on this subject have often neglected to empirically examine heterogeneity, missing out on the opportunity to investigate how this relationship is impacted when individuals are excluded from meaningful participation in economic spheres. Using General Social Survey data from the United States, I examine changes in the relationship between number of siblings and college attendance for White and Black respondents throughout the 1900s. Results show that in the early 1900s, White individuals from larger families had a lower chance of completing four years of college education than those from smaller families, whereas the likelihood for Black individuals was more uniform across family sizes. These racial differences mostly converged in the later part of the century. These results may help explain variations in the timing of demographic transitions within different racial groups in the United States and suggest that the benefits of decreasing family size on educational outcomes may be conditional on the specific economic opportunities afforded to a family.

On the Timing of Marriage and Childbearing: Family Formation Pathways Among Immigrants in Switzerland.

This paper examines childbearing in and outside of marriage as a manifestation of the Second Demographic Transition among immigrant populations in Switzerland. Based on full-population register data, we simultaneously analyse fertility and partnership changes at different stages of the migration process. Results from a multistate event history model show that most of the differences in family formation patterns between migrant groups and natives are in the sequencing of marriage and first birth among childless unmarried women. Out of wedlock family trajectories prove to be a common experience for European migrants, but a sustainable family pathway only among natives, as well as among immigrants from France, and Sub-Saharan Africa. Among married women, it is the risk of a third birth that marks the differences between groups; first and second birth rates are relatively similar across migrant groups. Distinguishing between the transition patterns of newly arrived immigrants and settled immigrants (characterised by various residence durations) support the disruption hypothesis among EU migrants and the interrelated life events hypothesis among non-EU groups. Family size and the partnership context of fertility highlight which family regime prevails in different population subgroups and the role that immigrants play in the Second Demographic Transition and family transformation in Europe.

The Global Decline in Human Fertility: The Post-Transition Trap Hypothesis.

Over the past half a century many countries have witnessed a rapid fall in total fertility rates, particularly in the world's most advanced economies including the industrial powerhouses of Eastern Asia and Europe. Such nations have now passed through the first and second demographic transitions and are currently exhibiting fertility rates well below the replacement threshold of 2.1, with no sign of recovery. This paper examines the factors responsible for driving these demographic transitions and considers their impact on both fertility and fecundity (our fundamental capacity to reproduce). I argue that because the first demographic transition was extremely rapid and largely driven by socioeconomic factors, it has had no lasting impact on the genetic/epigenetic underpinnings of human fecundity. However, the second demographic transition will be different. A series of conditions associated with low fertility societies, including relaxed selection pressure for high-fertility genotypes, the indiscriminate use of assisted reproductive technologies to treat human infertility, and environmental contamination with reproductive toxicants, may impact our genetic constitution in ways that compromise the future fecundity of our species. Since any fundamental change in the genetic foundations of human reproduction will be difficult to reverse, we should actively pursue methods to monitor human fecundity, as sub-replacement fertility levels become established across the globe.

Are Rural Areas Holdouts in the Second Demographic Transition? Evidence From Canada and the United States.

A central premise of the first demographic transition theory is that demographic change would occur more slowly in rural than urban areas. Few studies, however, have investigated whether rural areas remain holdouts during the second demographic transition. To address this gap, this study (1) examines trends among rural and urban families in Canada and the United States over a 30-year period and (2) determines whether compositional differences in demographic, socioeconomic, and religious factors explain current differences between rural and urban families. We find that rural Canadian women continue to have, on average, 0.6 more children than urban women. However, rural families do not trail behind urban families on any other indicator of family change. In fact, rural women in both countries are now significantly more likely to cohabit and roughly 10 percentage points more likely to have children outside of marriage than urban women. These differences are largely explained by lower levels of education and income among rural American women and fewer immigrants in rural Canada. Examining family change through a rural-urban lens fills important empirical gaps and yields novel insights into current debates on the fundamental causes of ongoing family change in high-income countries.

Energy and social factor decomposition to identify drivers impeding sustainable environmental transition in emerging countries: SDGs-2030 progress assessment using LMDI analysis.

The balance between human growth, economic prosperity, and the consumption of hydrocarbon energy factors has become a prerequisite for environmental sustainability. However, the complexities of these factors force researchers to work for more viable combinations of such a balance. Therefore, this study attempted to determine the factors driving environmental sustainability in leading populated economies. For this purpose, the Logarithmic Mean Division Index (LMDI) utilized to decompose critical factors such as activity, economy, real density, energy intensity, and suburban effects for the period 1999-2022. Both population and its consequences (economic activity) have been found to be the leading factors behind environmental fluctuations, and energy has a negative impact on hydrocarbon forms, while contributing positively to environmental sustainability with high efficiency and low intensity. Therefore, sustainable demographic and energy transitions can be leading pathways for environmental sustainability in developing economies.

Women's subsistence strategies predict fertility across cultures, but context matters.

While it is commonly assumed that farmers have higher, and foragers lower, fertility compared to populations practicing other forms of subsistence, robust supportive evidence is lacking. We tested whether subsistence activities-incorporating market integration-are associated with fertility in 10,250 women from 27 small-scale societies and found considerable variation in fertility. This variation did not align with group-level subsistence typologies. Societies labeled as "farmers" did not have higher fertility than others, while "foragers" did not have lower fertility. However, at the individual level, we found strong evidence that fertility was positively associated with farming and moderate evidence of a negative relationship between foraging and fertility. Markers of market integration were strongly negatively correlated with fertility. Despite strong cross-cultural evidence, these relationships were not consistent in all populations, highlighting the importance of the socioecological context, which likely influences the diverse mechanisms driving the relationship between fertility and subsistence.

Comorbidity Profiling in Rural and Urban Population of West Bengal, India: Report From a Community-Based Primary Healthcare System.

Introduction The burden of non-communicable diseases (NCDs) is fast changing across the world, especially in the context of rapid urbanization, adoption of Western lifestyles, and an aging multi-morbid population. Over the last three decades, India has undergone a significant demographic and socioeconomic transition. For effective targeting of health system resources and services, it is essential to understand how the prevalence of NCDs varies among population groups across India. We set out to understand the distribution of NCDs and co-morbidities in urban and rural West Bengal. Methods As part of a service improvement project, data was collected from four urban and four rural community-based clinics across West Bengal, India. The reason for visiting the healthcare center was recorded as the primary diagnosis and co-morbidities were recorded per the Elixhauser comorbidity scoring criteria. Associations between all the demographic variables and NCDs were studied using the Poisson regression model and multivariate analysis. Demographic profile, co-morbidities, and Elixhauser comorbidity index were expressed as frequency (%), mean (standard deviation, SD), or median (interquartile range, IQR) as appropriate. Results We obtained data from 1244 patients of which 886 (71%) were from urban areas and 358 (29%) were from rural areas. Patients were mostly female (61%) and had a mean (SD) age of 53 (11) years. There was a positive correlation between living in an urban residence and age, body mass index (BMI), hypertension, cardiovascular disease (CVD), and respiratory disease. There was a positive correlation between CVD and age, male sex, living in an urban residence, and hypertension but did not correlate positively with diabetes. BMI positively correlated with living in an urban residence, hypertension, diabetes, and musculoskeletal disorders. We observed a significantly higher prevalence of musculoskeletal (p=0.002) and psychological diseases (p<0.001) in the rural population, while the prevalence of hypertension (p<0.001) and respiratory diseases among the participants living in urban areas was higher (p<0.001). There was no statistically significant difference in the prevalence of diabetes between urban and rural areas (p=0.38). In the multivariable analyses, we observed that increased age, being overweight, and living in urban areas were associated with hypertension (prevalence ratio (PR): 1.40, 1.30, and 1.30, respectively; all p-values <0.05). An interaction between sex and living area was associated with a lower prevalence of musculoskeletal diseases (PR: 0.34; 95%CI: 0.18-0.66), i.e., musculoskeletal diseases were less prevalent in males living in urban areas (p=0.002). Conclusion There is a rise in multimorbidity with changing demographic patterns and a narrowing of the urban-rural gap in disease distribution. More investment is required in risk factor prevention, screening, and treatment, with greater accessibility of healthcare resources for those in rural areas. Further work needs to be done to study the trends and distribution of NCDs in West Bengal to inform healthcare policy.

Stratified pathways to Italy's "latest-late" transition to adulthood.

During the last few decades, Western societies have undergone substantial social and demographic changes, and the transition to adulthood progressively moved from an early, contracted, and simple pattern to a late, protracted, and complex one. These trends have been extensively analyzed under the Second Demographic Transition framework, emphasizing the role of individual agency and ideational change. A growing parallel literature underlines social stratification, the gender revolution, and contextual opportunities as driving forces. This paper builds on this emerging literature to analyze trends of the transition to adulthood in Italy, a salient social and demographic context among the "lowest-low" fertility countries. Drawing from the European Social Survey 2018 data, I use Sequence Analysis to compute a taxonomy of ideal types of transition to adulthood and analyze their evolution across cohorts. These analyses show that the emergence of a late and protracted transition to adulthood, associated with "lowest-low" fertility levels, is stratified by gender and socioeconomic background. This study contributes to the growing literature on the social stratification of life course trajectories and the relevance of contextual opportunities and constraints by analyzing the transition to adulthood in a low-opportunity context from a longitudinal, stratified perspective.

The Impact of Childhood Mortality on Fertility in Rural Tanzania: Evidence From the Ifakara and Rufiji Health and Demographic Surveillance Systems.

This manuscript examines the relationship between child mortality and subsequent fertility using longitudinal data on births and childhood deaths occurring among 15,291 Tanzanian mothers between 2000 and 2015. Generalized hazard regression analyses assess the effect of child loss on the hazard of conception, adjusting for child-level, mother-level, and contextual covariates. Results show that time to conception is most reduced if an index child dies during the subsequent birth interval, representing the combined effect of biological and volitional replacement. Deaths occurring during prior birth intervals were associated with accelerated time to conception during future intervals, consistent with hypothesized insurance effects of anticipating future child loss, but this effect is smaller than replacement effects. The analysis reveals that residence in areas of relatively high child mortality is associated with hastened parity progression, again consistent with the insurance hypothesis. Investigation of high-order interactions suggests that insurance effects tend to be greater in low-mortality communities, replacement effects tend to be stronger in high-mortality community contexts, and wealthier families tend to exhibit a weaker insurance response but a stronger replacement response to childhood mortality relative to poorer families.

Ageing and shrinking population: The looming demographic challenges of super-aged and super-low fertility society starting from Asia.

The world is generally getting more prosperous and healthier, and people live longer. Japan, with the world's most advanced population ageing, has made various efforts over the past half-century to prepare for the ageing society. Globally, many countries observe today's rapid demographic changes accompanied by low birth rate and start acknowledging population shrinkage as a looming challenge beyond that of population ageing. The world will face dual challenges of population ageing and shrinkage, but these two issues have been considered in isolation. In addition, the progression differs from region to region and country to country, preventing policymakers from taking a future-back approach to address the core challenges. This issue of Global Health & Medicine carries two valuable articles on population ageing and related policies reported by staff members of the WHO Western Pacific Regional Office (WPRO) and the United Nations Population Fund (UNFPA). This paper will consider the importance of ageing and low fertility rate (declining birthrate) as global issues by placing the WHO and UNFPA articles in a broader context. Population ageing and shrinkage overlap and significantly impact society through health issues. Still, the impact on countries, regions, and the world will become obvious with a time lag. Therefore, this paper advocates analyzing and critically reviewing the experience of countries in which demographic changes are already well advanced, and sharing them with the world. This will contribute significantly to those regions and countries that will walk the same path in the future.

Risk for referral to the child welfare system following parental relationship transitions in Norway.

BACKGROUND: There is a lack of knowledge concerning how changes in family structures are associated with involvement in child welfare systems. Particularly little attention has been paid to the role of parental relationship transitions, which may involve major changes in the lives of children and parents in terms of housing, finances, and relationship boundaries between family members. OBJECTIVE: To investigate how transitions in parental relationship status are linked to referrals to the child welfare system. PARTICIPANTS AND SETTING: All children born in Norway in 1995 (N = 60,218) and 2005 (N = 56,644) and their parents. METHODS: This retrospective birth cohort study consisted of child welfare statistics merged with various registers from Statistics Norway. Logistic panel-data models were used to examine the relationship between the occurrence of a parental relationship transition and referral to the child welfare system. Four types of relationship transitions were analyzed: (1) couple to a single mother, (2) couple to a single father, (3) single mother to a couple, and (4) single father to a couple. RESULTS: The occurrence of any type of relationship transition increased the likelihood of referral to the child welfare system in the year that the transition occurred, with the transitions to single motherhood, to single fatherhood, and from single fatherhood to a couple associated with greater odds of referral than the transition from single motherhood to a couple. CONCLUSIONS: Understanding how parental relationship transitions are associated with referrals to the child welfare system is important to appropriately facilitate help to families in need.

Demographic and epidemiological transitions and burden of adolescent healthcare in sub-Saharan Africa: A review.

This review's main objective is to discuss how demographic and epidemiological transitions relate to the burden of adolescent healthcare in sub-Saharan Africa (SSA). The review explicitly discussed the burden of adolescent healthcare, the current African policies on adolescent healthcare, and gaps in the African policies compared with Europe and North America. We also examined how adolescent healthcare policies evolve and documented the recommended essential part of the policy for enhancing its sustainability. The burden of adolescent health is high in SSA with diseases and reproductive health-related problems prevailing among adolescents. However, variations exist in the burden of adolescent healthcare across countries in the region. While some SSA countries are currently undergoing demographic and epidemiological transition processes concerning adolescent health care, the majority are either at an early stage of the transition or yet to commence the process. Policy-makers should consider effective ways to improve adolescents' health in SSA through preventive mechanisms and a multi-dimensional approach.

Implications of the Theory of Basic Human Values for the Second Demographic Transition: Interdependence and Individualism in the Era of Self-Fulfillment.

I examine the implications of a modern psychological theory of values for the Second Demographic Transition (SDT). The SDT derives its values theory and measurement from Maslow, who noted that resource-rich environments cause value shifts towards personal-focused growth values. However, Maslow has been replaced by the theory of basic human values (TBHV) which distinguishes person and social-focused growth values. This distinction has two important implications for the SDT. First, some individualistic and self-expressive values identified by the SDT are not growth but basic need motivated and therefore functions of resource-poor environments. Second, the TBHV values on interdependence and independence are strongly influenced by gender and reflect preferences for family and care or career. Therefore, these values can be used to address critiques of the SDT based on the stalled gender revolution. I show that distinguishing values as described in the TBHV can be useful for the SDT. I find that benevolence (interdependence) is positively and openness to change (autonomy/stimulation) is negatively related to marriage in the Netherlands using longitudinal panel data and discrete event history models.

Sustained and Universal Fertility Recuperation in Kazakhstan.

The fertility rates of Kazakhstan have reversed to levels not seen for several decades. The striking fertility increase poses questions regarding the extent to which this new development is shared across socio-demographic groups and the nature of fertility recuperation. The current study employs UNICEF Multiple Indicator Cluster Survey data and event-history modelling to analyse parity progressions to one, two, three, and four children. The results suggest a sustained fertility increase that is not merely associated with the recuperation of delayed first births, but a genuine increase across all birth orders. This pattern is evident for both main ethnicities in Kazakhstan and across educational groups. The gradual increase of higher-order births, especially among ethnic Kazakhs, indicates a reversed fertility transition and also that the previous fertility decline in the 1990s was not part of a general transition towards below-replacement fertility but rather a reflection of economic crisis after the collapse of the Soviet Union.

Demographic dividend-favorable policy environment in two pre-dividend African nations: review of national policies and prospects for policy amendments in Nigeria and Tanzania.

BACKGROUND: In collaboration with local partners, we reviewed 18 national policy documents across two sub-Saharan African countries identified as pre-dividend nations by the World Bank in 2017: Nigeria and Tanzania. Our aim was to assess national policies in pre-dividend countries and to determine whether national strategies were primed to capitalize on changing demographic structures, maximally attain the demographic dividend, and augment socio-economic growth. METHODS: We conducted policy reviews by focusing on five key sectors of the Gates Institute Demographic Dividend Framework: Family Planning, Maternal and Child Health, Education, Women's Empowerment, and Labor Market. This framework was developed as a tool for countries to apply targeted policies for accelerating the demographic dividend based on their demographic structure. For each component we used a comprehensive list of indicators, defined via a systematic literature review, through which we assessed national policies aimed at maximizing the demographic dividend. RESULTS: Between the two countries, we observed persistent gaps in policies targeting family planning. Although more comprehensive, policies addressing maternal and child health, education, women's empowerment, and labor market still lagged in their specificity and measurability. We identified specific policy amendments and alternatives that Nigeria and Tanzania could consider to mitigate these gaps. We also stress the importance of designing measurable policy initiatives across sectors. CONCLUSIONS: Based on these recommendations, as Nigeria, Tanzania, and other pre-dividend nations start experiencing rapid demographic changes, they may consider implementing routine policy reviews to strengthen policies across the five key sectors and harness the benefits of a demographic dividend.

Cultural niche construction with application to fertility control: A model for education and social transmission of contraceptive use.

The evolution of a cultural trait may be affected by niche construction, or changes in the selective environment of that trait due to the inheritance of other cultural traits that make up a cultural background. This study investigates the evolution of a cultural trait, such as the acceptance of the idea of contraception, that is both vertically and horizontally transmitted within a homogeneous social network. Individuals may conform to the norm, and adopters of the trait have fewer progeny than others. In addition, adoption of this trait is affected by a vertically transmitted aspect of the cultural background, such as the preference for high or low levels of education. Our model shows that such cultural niche construction can facilitate the spread of traits with low Darwinian fitness while providing an environment that counteracts conformity to norms. In addition, niche construction can facilitate the 'demographic transition' by making reduced fertility socially accepted.

The changing social gradient of marriage and cohabitation in seven Latin American countries.

While research shows that cohabitation has increased significantly among highly educated individuals in Latin America, much less is known about how the relationship between educational attainment and first union formation has changed over time and across the region's countries. Accordingly, this paper describes the changes across cohorts in the type of first union (marriage or cohabitation) entered by women from seven Latin American countries. It also analyzes trends in the relationship between women's education and the type of first union within and between these countries. Using Demographic and Health Survey (DHS) data, life tables, discrete-time event history models, and predicted probabilities were estimated to analyze the changing determinants of first-union formation. The results pointed to an overall increase in first-union cohabitation over time, with some important differences across countries. The multivariate analysis suggested that women's education influences the type and sequencing of the first union, with socioeconomically disadvantaged women increasingly likely to transition to early unions and enter cohabitation rather than marriage.

Trends and factors associated with declining lifetime fertility among married women in Kenya between 2003 and 2014: an analysis of Kenya demographic health surveys.

BACKGROUND: Globally, fertility has declined in the last three decades. In sub-Saharan Africa Including Kenya, this decline started more recent and at a slower pace compared to other regions. Despite a significant fertility decline in Kenya, there are disparities in intra- and interregional fertility. Reduction in lifetime fertility has health benefits for both the mother and child, thus it is important to improve women and children health outcomes associated with high fertility. The study, therefore evaluated the factors associate with change in lifetime fertility among married women of reproductive age in Kenya between 2003 and 2014. METHODS: The study used the Kenya Demographic and Health Survey (KDHS) datasets of 2003, 2008 and 2014. Analysis of variance (ANOVA) was used to calculate the mean number of children ever born and to assess the change in fertility across different factors. Poisson regression model with robust standard errors was used to study the relationship between number of children ever born (lifetime fertility) and independent variables. A Poisson-based multivariate decomposition for the nonlinear response model was performed to identify and quantify the contribution of demographic, socioeconomic and reproductive correlates, to the change in lifetime fertility between 2003 and 2014. RESULTS: The study included 3,917, 4,002, and 7,332 weighted samples of women of reproductive age in 2003, 2008, and 2014, respectively. The mean number of children born declined from 3.8 (95% CI: 3.6-3.9) in 2003 to 3.5 (95% CI: 3.4--3.7) in 2008 and 3.4 (95% CI: 3.3-3.4) in 2014 (p = 0.001). The expected number of children reduced with the age at first sexual intercourse, the age at first marriage across the survey years, and household wealth index. Women who had lost one or more children in the past were likely to have increased number of children. The changes in the effects of women's characteristics between the surveys explained 96.4% of the decline. The main contributors to the change in lifetime fertility was the different in women level of education. CONCLUSION: The lifetime fertility declined by one-tenth between 2003 and 2014; majorly as a result of the effects of characteristics of women in terms of level of education. These highlights a need to implement education policies that promotes women education focuses on gender equality and women empowerment. Continuous strengthening of the healthcare systems (access to quality antenatal care, skilled delivery, and postpartum care) to reduce child mortality is essential.