Selection intensities in menopausal and permanent contraceptor women of a rural population in India

Changing fertility and mortality patterns due to socioeconomic forces have a profound effect on natural selection in human populations. The opportunity for selection was estimated in the rural population of Visakhapatnam District, Andra Pradesh, India, in 1979. A total of 1570 women were interviewed, 1544 among them had ever been pregnant. Data were analyzed to compute fertility and mortality components of the population. The index of total selection was found to be low. Selection in relation to birth control reveals that opportunity for selection is lower among women who completed their fertility by family planning methods than in women who completed their fertility by attaining menopause. Further, the results showed that differential fertility and mortality make equal contributions to the total measure of selection in both groups, whereas in developed countries like the US the mortality component contributes only a small fraction to the total index, due to improved health conditions.     

Selection intensities in menopausal and permanent contraceptor women of a rural population in India

Abstract

The opportunity for selection was estimated in the rural population of Visakhapat‐nam District, Andhra Pradesh, India. The index of total selection was found to be low. Selection in relation to birth control reveals that opportunity for selection is lower among the women who completed their fertility by family planning methods than in women who completed their fertility by attaining menopause. Further, the results showed that differential fertility and mortality make equal contributions to the total measure of selection in both groups.     

Variability of genetic load with changing socio-cultural environment

Variability in genetic load has been studied against their contrasting socioeconomic and cultural backgrounds in two endogamous populations, namely, the well-off Brahmins and the low income Jalaris of Visakhapatnam, India. The A (genetic and environmental damage) and B (hidden genetic damage) estimates are higher in Jalaris. Decreased A estimates indicate the better medical care in Brahmins; the value of B could be low since many of the deaths in consanguineous families due to infectious diseases are now rarer. The genetic load (B/A ratio) indicates that the average gamete carries 0.057 and 2.123 deleterious genes, respectively, in Brahmins and Jalaris, which, if made homozygous, would kill an individual before reproductive age. The load is 35 times higher in Jalaris; this may be due to their higher inbreeding level. Contrasting socioeconomic differences and meagre medical aid might add another bias towards relatively higher B/A in Jalaris. In general the observed genetic load in both populations are lower than in other studies which may be due to gradual elimination of deleterious genes by continued practice of inbreeding.     

Population genetics study of the differential fertility in urban populations

In an urban population with widespread birth control practice the distribution of the number of pregnancies, births and abortions was studied in a cohort of women of completed fertility. The mean number of pregnancies per woman was 4.03 +/- 0.08 (sigma = = 2.98); the mean number of births - 1.12 +/- 0.02 (sigma = 0.77). 7.4% of women which had completed their reproductive performance had no pregnancies and 19.5% - no births. The Crow's Index of the Opportunity for Selection and its components connected with differential fertility and differential mortality were estimated. In the population under study two components of selection - selection at the prenatal stages and selection associated with infertility - are shown to be still significant. Such type of selection is exemplified by investigation of couples suffering from repeated spontaneous abortions.     

Genetic-epidemiologic study of reproductive outcomes in the Ozersk population,located in "Maiak" control area

In the population of Ozyorsk town situated in the control area of the nuclear enterprise (Production Association "Mayak") the number of pregnancies and its outcomes was studied in cohort of 2.258 women of completed fertility. The mean number of pregnancies per woman is 5.6 +/- 0.07. The mean size of family is 1.9 +/- 0.02. It was estimated that 2.7% of women had no pregnancies, 4.0% of women had no delivery till the end of their reproductive performance. 4.65% of women contributed nothing to the genofond of the next generation, i.e., they had not any children lived till their reproductive performance (20 years). The Crow Index of Opportunity for Selection and its components connected with differential fertility and differential mortality were estimated. In the population under study tow components of selection--selection at the prenatal stages (72.6%) and selection associated with infertility--are shown to be significant.     

Natural selection among Kinnaura of the Himalayan highland: A comparative analysis with other Indian and Himalayan populations

The present investigation on fertility and mortality differential among Kinnaura of the Himalayan highland is based on data collected from 160 post-menopausal women belonging to the middle and high altitude region of Kinnaur district of Himachal Pradesh (Indian Himalayas). Selection potential based on differential fertility and mortality was computed for middle-and high-altitude women. Irrespective of the methodology, the total index of selection was found to be highest among middle-altitude women (0.386) as compared with high-altitude (0.370) women, whereas for the total population it is estimated to be 0.384. It was found that the Kinnaura of the Himalayan highland showing moderate index of total selection and relative contribution of the mortality component (Im) to the index of total selection is higher than the corresponding fertility component (If). The analysis of embryonic and post-natal mortality components shows that the post-natal mortality components are higher in comparison with the embryonic mortality components among highlanders and needs special intervention and health care. The present findings are compared with other Indian tribes as well as non-tribes of the Himalayan region and other parts of the country. It reveals that this index among Kinnaura is moderate than the other population groups; among the Himalayan population, the highest was reported for Galong (It = 1.07) of Arunachal, whereas the lowest was reported from Ahom (It = 0.218) of Manipur. The correlation and regression analysis between total index of selection (It) and fertility (If) and mortality (Im) components for pooled data of populations of the Indian Himalayan states show that If and Im account for 21.6 and 29.1% variability, respectively. In Crow's total index of selection (It) along with strong association, which is significant at the 1% level, this indicates that mortality plays a greater role in natural selection in comparison with fertility among populations of the Indian Himalayas.     

The delineation of fertility strategies in a tribal population of India: the Koyas of Koraput District,Orissa

Demographic data collected for a tribal population of India, the Koyas of Koraput District, Orissa, were examined in light of 2 models of reproductive behavior associated with the economic value of children: the replacement effect and son survivorship motivation. Both models are united in the concept that infant/child mortality affects subsequent fertility. The database consists of retrospective fertility histories of Koya women who had completed their reproductive period. The total number was 260, with the total offspring numbering 1407. 2 distinct cohorts of women were formed for the purpose of analysis, separated only by the criterion of offspring survival: women who had experienced infant child mortality (129 women with 739 children); and women who completed their reproductive period without suffering offspring loss of this nature (132 women with 668 children). The cohort without child loss had a mean parity of 5.10, lower than the average parity of 5.73 recorded for the cohort whose reproductive histories included at least 1 infant/child death. Age specific marital fertility and birth interval analyses indicated that this differential was because of biological, not behavioral, factors. The age pattern of fertility of females suffering offspring mortality failed to demonstrate a high rate of childbearing in the later age intervals of the reproductive period, a characteristic pattern of couples attempting to "replace" lost offspring. Birth interval analysis pointed to biological "interval effect," whereby infant/child mortality caused a cessation of lactation and hence a shortening of postpartum amenorrhea. Computer simulation further indicated that the higher fertility differential of the cohort experiencing offspring loss still did not result in high son survivorship values. The findings agree with earlier studies indicating that for predemographic transitional populations, economically motivated fertility strategies are ineffectual.     

Strategies of adaptation: interpopulation selection differentials

Spatial and temporal variation of selection intensities has been analyzed using published data on Crow's indices in 278 human populations, representing various anthropological types, religions, cultures and a wide spectrum of environmental conditions. Statistical analysis has shown that populations with different types of economy have different adaptive strategies. In tribal populations both components of selection-differential fertility and differential mortality-have equal contributions, vary according to ecological factors and show no decline with time. Urban populations of the industrially developed countries show dramatic selection relaxation; the second component becomes negligible due to a sharp decrease in childhood mortality; fertility and its variance are reducing due to cultural factors (family planning).     

Fitness and fertility among Kalahari !Kung

In this paper we develop a model that examines fertility and childhood mortality patterns and their relationship to environmental variables. Interactions among environmental variables can account for different fertility patterns and different mixes of these variables can produce similar patterns of fertility. Our model attempts to quantify the idea that there is a trade-off between producing a few children likely to survive to reproductive age and producing a greater number of children with lower chances for survival. The optimum mix of these strategies depends on environmental characteristics. We use the model to make predictions about fertility and mortality patterns among two Bushmen populations of southern Africa--the Ghanzi and Ngamiland !Kung--using data collected by Harpending in 1967-1968. The results do not support explanations of the low fertilities observed among !Kung Bushmen women, in whom it is thought that fitness is maximized by limiting fertility, and show no relationship between mortality and family size in either !Kung population. Instead, the number of offspring reaching reproductive age in both populations increases as their completed family size increases. We examine the effects of sex, birth order, and paternal investment on mortality. No sex ratio differences and no differences in mortality by sex or birth order are present. Infant mortality among women who married more than once is significantly higher than among women who married once, suggesting that paternal care has a significant effect.     

Opportunity for natural selection in a Basque population and its secular trend: evolutionary implications of epidemic mortality

Analysis of the interaction between mortality patterns and opportunity for natural selection could help to elucidate potential evolutionary implications of epidemic mortality. In this paper secular trends are studied in relation to Crow's index (It) and its components of mortality (Im) and fertility (If), using parish records for family reconstitution in a Basque population. A principal components analysis (91% of the variance accounted for) showed marked quantitative and qualitative variations of Im and If depending on the stage of demographic transition of the population analyzed: In pretransitional societies the opportunity for natural selection is determined mainly by differential prereproductive mortality, whereas in posttransitional societies selection resulting from differential fertility plays a key role. The highest values for the mortality component (range 0.81-1.26) and for the relative contribution of Im, to It (range 47.1-57.2%) were observed in periods with a high incidence of infectious diseases and when the most severe mortality crises were detected (1830-1859, 1860-1889, and 1890-1919). A differential incidence of epidemic mortality was also found at prereproductive ages (before 16 years) and at reproductive ages (16-45 years), which provides strong support for the idea of the long-term genetic consequences of mortality crises.     

Are husbands a barrier to women's family planning use? The case of Morocco

Little is known about men's role in the adoption of family planning. Recent studies suggest that men may be a barrier to women's use of family planning. However, it is not clear whether husbands represent a true or a perceived barrier. Using the 1992 Morocco Demographic and Health Survey data, this study examines (1) whether women and men report concordant fertility desires, discussions, and contraceptive use; (2) the accuracy of women's perceptions of their husbands' fertility desires; and (3) whether husbands are a barrier to women's family planning use. The results demonstrate that, controlling for women's own fertility desires, husbands' true fertility desires are associated with family planning use. Likewise, women who perceive their husbands to want fewer children than they want are more likely to use family planning. Future fertility and family planning programs need to include men to reduce their role as both perceived and true barriers to family planning use.     

Fertility and legal abortion in England and Wales: performance indicators for family planning services.

The relation between fertility rates and legal abortion rates was investigated in a sample of health authorities in England and Wales to see how these varied. Total period fertility rates and total period legal abortion rates were derived from the average number of live births or legal abortions that would be experienced per woman if women experienced the age specific rates of the year in question throughout their childbearing years. The sample of 30 health authorities was selected by taking the districts with the highest and lowest fertility rates in each English region and in Wales in 1986. Total period fertility rates varied from 1.37 in Riverside to 2.42 in Tower Hamlets, while abortion rates varied from 0.25 in East Yorkshire to 0.99 in Riverside. When the two rates were added to provide a potential fertility rate it became clear that some districts with similar potential fertility rates had very different underlying component rates. Such comparisons can be used for service monitoring, indicating the need for better abortion and family planning services in districts with high fertility rates and for better family planning services in those with high abortion rates.     

The fifth freedom

Women in developing countries suffer considerable morbidity and mortality due to inability to control their own fertility and lack of access to family planning services. Over 500,000 deaths each year are related to pregnancy. Two thirds of these maternal deaths could be prevented by providing contraception to those women who wish to use it in developing countries. There is no tenable ethical defence of cultural and religious behaviour which denies a women a choice as to whether she will undertake a pregnancy or not. Implementaion of the principles of the programme of action from the 1994 Cairo Population Conference would, through empowering women to control their own fertility, have a huge impact on maternal health in the developing world. [Kincaid-Smith is president of the World Medical Association].     

THE FIFTH FREEDOM

Women in developing countries suffer considerable moribidity and mortality due to inability to control their own fertility and lack of access to family planning services. Over 500,000 deaths each year are related to pregnancy. Two thirds of these maternal deaths could be prevented by providing contraception to those women who wish to use it in developing countries. There is no tenable ethical defence of cultural and religious behaviour which denies a woman a choice as to whether she will undertake a pregnancy or not. Implementation of the principles of the programme ofactionfrom the 1994 Cairo Population Conference would, through empowering women to control their own fertility, have a huge impact on maternal health in the developing world.     

Child mortality, social status, and fertility in India

The incidence of child mortality in relation to the social status and fertility of Indian women was investigated on the assumptions that: 1) the higher the social status, the lower the child mortality rate; and 2) the lower the child mortality rate, the lower the family size. 311 married women in Chandigarh were grouped into 4 status categories: (1) higher educated working women (95); (2) higher educated nonworking women (75); (3) less educated nonworking women (75); and (4) less educated working women (66). The 311 women gave birth to a total of 1075 children (960 living and 115 who had died, mostly between the ages 0-5 years). Percentage of children living (89%) was different for each status category: 93% for category 1; 92% for category 2; 91% for category 3; and 81% for category 4. When analyzed by proportion of women who had lost children in each status category, the relationship between child mortality and social status confirmed the assumption that the higher the social status, the lower the mortality. In category 1, 87% had not experienced any child mortality in their family; in category 2, the figure was 77%; category 3, 72%; and category 4, 48%. The findings also confirmed the other assumption that the lower the mortality rate, the lower the fertility (Table 2).     

Fertility and mortality differentials among selected tribal population groups of north-western and eastern India

Selection potential based on differential fertility and mortality has been computed for six tribal groups inhabiting different geo-climatic conditions, namely: Sahariya, Mina and Bhil of the State of Rajasthan, north-western India, and Munda, Santal and Lodha of the State of West Bengal, eastern India. Irrespective of the methodology, the total index of selection was found to be highest among Lodhas (0.668), followed by Sahariyas (0.524), Santals (0.462), Bhils (0.386), Mundas (0.353) and Minas (0.334). Incidentally, Lodha and Sahariya are two of the seventy-four notified primitive tribal groups of India, and these two study populations show the highest index of total selection, mainly because of a higher embryonic and postnatal mortality. The relative contribution of the fertility component to the index of total selection is higher than the corresponding mortality component in all tribal groups. The analysis of postnatal mortality components indicates that childhood mortality constitutes the bulk of postnatal mortality, suggesting that children under 5 years need better health care in these tribal groups.     

Reproductive mortality and its relation to different methods of birth control

This report evaluates the decrease in maternal mortality and its relation to family planning methods in Sweden during the years 1911-80. In the 1930s fertility was low but illegal abortions were at a high level and the associated maternal death rate was 18.5 per 1000 women. With the legalization of abortion and the introduction of modern contraceptive methods, the crude reproductive mortality rate in 1965-70 was 1.7 per 100,000 women and this was reduced still further, especially for younger women, by the late 1970s. Standardized reproductive mortality was then 80% higher than the crude rate, indicating the importance of modern family planning methods. Mortality associated with oral contraceptive or IUD use in Sweden during the 1960s and 1970s was lower than in England and the US. Mortality associated with sterilization was 6.2 per 100,000 procedures.     

Selection intensities in mothers of twins and in mothers of singletons

Abstract

Opportunity for selection was assessed in a group of mothers with twins and was compared with estimates obtained in mothers who gave birth to singletons only from the same population. Both groups were matched on a number of confounding variables in the framework of a case/control methodology. Two time periods involving demographic changes were studied separately. After appropriate adjustment for the increased family size of mothers of twins, results show that selection intensities are greater in twin‐bearing mothers than in controls. The fertility component of the selection index is lower than that of mortality if childless women are taken into account. However, the index of opportunity for selection is rather low by current standards but, given the methodology used, should reflect genetic rather than environmental selection. Notwithstanding, it would be difficult to explain the recent change in the twinning rates in the population by the actual level of selection indices.     

Heritability of fertility in human populations and the structure of Crow's index

Heritability of fertility was determined in populations with natural character of reproduction (Middle Asia Republics) and in populations with family planning (Middle Russia). The material was collected by interviewing the married women of postreproductive age. The heritability of fertility was estimated as a doubled coefficient of correlations between sisters for effective fertility. In populations with natural character of reproduction the heritability was about 50% and it did not differ from O in the populations with family planning. The values of heritability were used in the components of the Crow index analysis. The main contribution into broad-sense heritability of fertility comes from additive component, as shown in an Asia population (Turkmen). The values of heritability of fecundability (86%) and of postpartum sterility (66%) have been calculated for the same population.     

Fertility and mortality differentials among the population groups of the Himalayas

Selection potential based on differential fertility and mortality has been computed for 24 Himalayan populations classified into four groups: Himalayan populations with Asian affinities (HPA), Brahmans, Rajputs, and Scheduled Castes (Shilpkars). Irrespective of the methodology followed, the total index of selection was found to be highest (0.794) in Barbatiyas (HPA) and lowest (0.428) in Rajputs. The relative contribution of fertility component (If) to the index of total selection (It) is higher than the corresponding mortality component (Im) in all 24 groups. An analysis of correlation and regression on different components of the indices of selection performed among these 24 Himalayan populations revealed that the contributions of If in determining It are stronger than Im. Further, both If and Im are strongly associated with It and account for 76% and 67% of total variability in It, respectively. Examination of the relationship of the selection potential with the differential altitude and social categories showed a decrease in the index from high altitude to low altitude. Similarly, an inverse relationship was found between various indices and social categories. Himalayan populations with Asian affinities (HPA) in the present study reveal higher values of selection potential. Interestingly, these populations invariably reside in high altitude areas where health and communication infrastructures are poorly developed. Thus, the differential pattern of fertility and mortality among the Himalayan populations indicates that they are passing through a stage of transition, as is evident from the decrease in various selection indices. It is also apparent that groups that are less developed socioeconomically, as well as those inhabiting high altitude regions, are lagging behind in this process.