Significance of indices of potential selection for residents of the USSR

Crow's indices of the opportunity for selection and their components connected with differential mortality (Im) and differential fertility (If) were estimated for populations of Soviet Union republics and for a number of USSR ethnic groups on the basis of demographic statistics. More than 10-fold decrease in the Im value was revealed in the total population of the USSR during 1926-1987. At present, the Im values in republics vary from 0.020 to 0.094 for urban population and from 0.030 to 0.121 in rural population, the ratio of perinatal mortality in the whole structure of prereproductive mortality being higher in the republics with lower values of the Im. The range of the If values for different peoples (0.148-0.643) is wider than for the populations of the republics (0.326-0.578). Interethnic differences contribute 47% of the variance in fertility. The structure of Crow's indices is given for urban and rural populations of the republics. Genetic implications of the data presented are discussed with respect to possible manifestation of the effects of inter-group selection.     

Study on a Brazilian isolate. II. Opportunity for selection

The opportunity for selection, measured by prereproductive mortality and fertility, was calculated for a small and relatively isolated Brazilian population. The total index of selection opportunity (0.53) was low in comparison to those obtained for other isolated populations. The contribution of prereproductive mortality (Im = 0.28) was 40% higher than that of fertility (If = 0.20).     

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.     

Opportunity for natural selection and gene flow in an isolated Zapotec-speaking community in southern Mexico in the throes of a secular increase in size

Our object in this paper is to analyze the opportunity for natural selection and gene flow in an isolated Zapotec-speaking community in the valley of Oaxaca, southern Mexico, that is undergoing a secular increase in body size. Surveys were conducted in the community in 1968, 1978, and 2000, including anthropometric and census data. No secular change was found in the growth status of schoolchildren and adult height between 1968 and 1978; subsequently, major secular gains in height occurred among children and adolescents between 1978 and 2000. The 1978 household data were used to compute gene flow (3.3%) and opportunity for selection intensity (I = 1.312). Migration and other demographic information was obtained from household census data for 1978 and 2000, and mortality information was extracted from community records and archives. These data were used to compute gene flow and opportunity for natural selection. Gene flow increased from 3.3% to 4.7% and intensity of natural selection decreased from 1.312 to 0.272 from 1978 to 2000. Variance in fertility increased slightly over time (12.25 to 13.69). Opportunity for selection was dominant during the prereproductive period in 1978, but approached 0 for the mortality component in 2000, resulting in a marked decrease in the mortality component (Im) of selection (0.626 and 0.019, respectively) and total opportunity for selection (I = 1.312 and 0.272, respectively). Secular increase in height and markedly decreased opportunity for natural selection (1) were associated with better health and nutritional conditions. Genotype-environment interaction and environmental influences are apparently the predominant causes of the secular trend. If natural selection plays a role in causing the secular trend, it is a small one.     

Genetic demographic description of the Ust-Aldan rural population of Sakha Republic (Yakutia): ethnic, sex, and age compositions, vital statistics, and surname structure

Information on the sex, age, and ethnic compositions; reproductive parameters; intensity of natural selection (Crow's indices); and surname diversity of three rural populations (the Byadi, Dyupsya, and Cheriktey villages) of the Ust-Aldan ulus (district) of Sakha Republic (Yakutia) has been analyzed. The rural Yakut population of the Ust-Aldan ulus is demographically young (the mean age 25-31 years) and characterized by low outbreeding, unfavorable sex ratio in both prereproductive and reproductive ages, and high fertility (3.58-5.45 children surviving until the reproductive age per woman that has completed the reproductive period), although the actual reproductively active period is shorter than half its physiological duration. In the structure of total selection, the differential-fertility component is considerably greater than the differential-mortality component (Itot = 0.625, Im = 0.093, and If = 0.487). In the villages studied, some surnames are accumulated (45-65% of the population have five most frequent surnames), which determines the low surname diversity (alpha = 11.62-25.19) and high random isonymy (Ir = 0.0391-0.0823).     

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.     

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.     

Genetic drift and natural selection in an isolated Zapotec-speaking community in the Valley of Oaxaca, southern Mexico

Genetic drift and natural selection were analyzed in a genetically isolated Zapotec-speaking community in the Valley of Oaxaca, southern Mexico. Moderately intense genetic drift and selection potentials were found. Potential for drift was related to (1) the small effective size of the population, and (2) the exceptionally low number of migrants into the population. Potential for selection was due to (1) an unusually high variance in fertility, and (2) a high contribution of prereproductive mortality. Significant potential for genetic evolution was found due to genetic drift and natural selection.     

DOES INCREASED MORTALITY FAVOR THE EVOLUTION OF MORE RAPID SENESCENCE?

It is widely believed (following the 1957 hypothesis of G. C. Williams) that greater rates of “extrinsic” (age- and condition-independent) mortality favor more rapid senescence. However, a recent analysis of mammalian life tables failed to find a significant correlation between minimum adult mortality rate and the rate of senescence. This article presents a simple theoretical analysis of how extrinsic mortality should affect the rate of senescence (i.e., the rate at which probability of mortality increases with age) under different evolutionary and population dynamical assumptions. If population dynamics are density independent, extrinsic mortality should not alter the senescence rate favored by natural selection. If population growth is density dependent and populations are stable, the effect of extrinsic mortality depends on the age specificity of the density dependence and on whether survival or reproduction (or both) are functions of density. It is possible that higher extrinsic mortality will increase the rate of senescence at all ages, decrease the rate at all ages, or increase it at some ages while decreasing it at others. Williams's hypothesis is most likely to be supported when density dependence acts primarily on fertility and does not differentially decrease the fertilities of older individuals. Patterns contrary to Williams's prediction are possible when density dependence acts primarily on the survival or fertility of later ages or when most variation in mortality rates is due to variation in nonextrinsic mortality.     

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 and ecologic study of aboriginal inhabitants of the Siberian northeast. III. Demographic structure of three modern population links of Yakutia

Demographic data of genetic interest were studied in three separate populations of Tungus-speaking Evens. They are characterized as expanding populations, rather as a result of migration and admixture, than due to natural increase. The mean and variance of livebirths per female, whose reproduction was completed, were 7.23 and 13.07, respectively. The Crow's index of the opportunity for selection (It) and its components (Im and If) were found to be 0.62, 0.30 and 0.25, respectively. The values of Im and If appeared to be essentially lower than those previously found in other northern populations.     

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.     

Index of opportunity for natural selection among the Gowdas of Kodagahalli village,Karnataka, India

BACKGROUND:

In order to understand how selection is operating in the Gowda population, the index of opportunity for selection was calculated and the present findings were compared with some related findings from other South Indian (SI) populations.

MATERIALS AND METHODS:

Crow (1958) and the modified method by Johnston and Kensinger (1971) were used for the present purpose.

RESULTS AND DISCUSSION:

The index of total selection intensity (I) was found to be moderate taking into consideration the range for many Indian populations. Considering certain differences in fertility and mortality heritable, it appears that natural selection play an important role in shaping the genetic constitution of the Gowda population. Analysis of data indicates that the index due to fertility seems to contribute more towards selection than mortality. This trend might be because of better living condition and health-care system among the Gowdas which have a positive impact on the lower contribution of mortality for the evolution mechanism of the Gowda population through natural selection.     

Genetic structure of an isolated group of the indigenous population of northern Siberia, the Nganasans (Tavginians) of Ta?mir

Demographic data of genetic interest were studied in presently living population in comparison with preseding generations of Nganasans. Decrease of sex ratio in the whole population has been revealed along with the reduction of reproductive and, possibly, effective size. The number and variance of livebirths per female were 7.29 and 9.86 respectively. Crow' index of the opportunity for selection (I) and its components (Im and If) were estimated. I was found to be 1.17, whereas Im and If--1.56 and 0.18 respectively. Linear pattern of settling in the past as well as the type of migration between adjoining subpopulations depended on culture and economy of arctic reindeer hunters as well as landscape character.     

Genetic-demographic characteristics of the rural population of the Republic of Tuva: reproductive indicators and the structure of Crow's indices]

The age limits of the female reproductive function, vital statistics, and Crow's indices were estimated in populations of three districts of the Tuva Republic that were remote from one another. These were the Kyzyl (the Shinaan population), Todzhinskii, and Bai-Taiginskii raions. The monoethnic Shinaan population was characterized by the longest reproductive period (15.88 years) but the lowest average number of pregnancies throughout the reproductive period (5.77); childbirth was an outcome of 86.72% of pregnancies. In the Bai-Taiginskii population, which was also monoethnic but lived in an industrial area of Tuva, these parameters were 12.99 years, 7.06 pregnancies, and 81.97%, respectively. The Todzhinskii population, which was ethnically mixed, exhibited the shortest actual reproductive period (10.72 years) and the greatest average number of pregnancies throughout the reproductive period (7.29), with the proportion of pregnancies ending in childbirth as low as 48.30%. The indices of potential selection and their components related to differential mortality and differential fertility were the following: in the Shinaan population, Itot = 0.59, Im = 0.19, and I(f) = 0.34; in the Bai-Taiginskii population, Itot = 0.48, Im = 0.18, and I(f) = 0.26; and in the Todzhinskii population, Itot = 0.90, Im = 0.23, and I(f) = 0.55. Thus, reproductive parameters in the studied populations of the Tuva Republic were largely determined by the ethnic composition of the population and social factors.     

Biological fitness and action opportunity of natural selection in an urban population of Cuba: Plaza de la Revolución, Havana

This paper describes the biological fitness of an urban population of Havana city, Plaza de la Revolución, which has the lowest fertility and the highest demographic ageing in Cuba. The aim is to assess the biological fitness of this community through the indexes of action opportunity of natural selection, to determine its evolutionary pattern and the influence of its socio-cultural peculiarity. Demographic data were obtained from the reproductive histories of 1200 women between the ages of 55 and 64. Data concerning mortality and surviving offspring from the first embryonic stages until age of reproduction were also collected. In order to measure the level of biological fitness two indexes were used: the Crow index of action opportunity of natural selection and the corrected index proposed by Johnston and Kensinger, which takes into account prenatal mortality. This corrected index was calculated including and excluding induced abortions in order to evaluate the contribution of these to biological fitness. When only postnatal mortality was considered, the results showed an evolutionary pattern similar to that of developed countries, based on low mortality and fertility. However, when prenatal mortality was taken into account, biological fitness decreased and the corrected index of natural selection was 4.5 times higher than when miscarriages and fetal deaths were not considered. Moreover, this corrected index was 2.65 times higher when induced miscarriages were considered, indicating the large decrease in biological fitness as a result of the current reproductive behaviour of frequent induced abortion.     

A DEMOGRAPHIC TRANSITION ALTERED THE STRENGTH OF SELECTION FOR FITNESS AND AGE‐SPECIFIC SURVIVAL AND FERTILITY IN A 19TH CENTURY AMERICAN POPULATION

Modernization has increased longevity and decreased fertility in many human populations, but it is not well understood how or to what extent these demographic transitions have altered patterns of natural selection. I integrate individual‐based multivariate phenotypic selection approaches with evolutionary demographic methods to demonstrate how a demographic transition in 19th century female populations of Utah altered relationships between fitness and age‐specific survival and fertility. Coincident with this demographic transition, natural selection for fitness, as measured by the opportunity for selection, increased by 13% to 20% over 65 years. Proportional contributions of age‐specific survival to total selection (the complement to age‐specific fertility) diminished from approximately one third to one seventh following a marked increase in infant survival. Despite dramatic reductions in age‐specific fertility variance at all ages, the absolute magnitude of selection for fitness explained by age‐specific fertility increased by approximately 45%. I show that increases in the adaptive potential of fertility traits followed directly from decreased population growth rates. These results suggest that this demographic transition has increased the adaptive potential of the Utah population, intensified selection for reproductive traits, and de‐emphasized selection for survival‐related traits.     

The force of selection on the human life cycle

In this article, I present evidence for a robust and quite general force of selection on the human life cycle. The force of selection acts in remarkably invariant ways on human life histories, despite a great abundance of demographic diversity. Human life histories are highly structured, with mortality and fertility changing substantially through the life cycle. This structure necessitates the use of structured population models to understand human life history evolution. Using such structured models, I find that the vital rates to which fitness is most sensitive are prereproductive survival probabilities, particularly the survival of children ages 0 to 4 years. The fact that the preponderance of selection falls on transitions related to recruitment combined with the late age at first reproduction characteristic of the human life cycle creates a fitness bottleneck out of recruitment. Because of this, antagonistic pleiotropy with any trait that detracts from the constituent transitions to recruitment is expected. I explore the predictors of variation in the force of selection on early survival. High fertility increases the selective premium placed on early survivorship, whereas high life expectancy at birth decreases it.     

Variability of selection opportunities with changing socio-cultural environments

Opportunity for selection has been studied against their contrasting socioeconomic and cultural backgrounds in two endogamous populations, namely, Brahmins and Jalaris of Visakhapatnam, India. Total selection was slightly higher among the better off Brahmins than in Jalaris. But a marked qualitative and quantitative variation was found in the contributing components; the fertility differential was circa 60% in Brahmins while the mortality differential was circa 60% in Jalaris according to the Crow Index. The decreased mortality differential in Brahmins suggests that this component was directly affected by the better socio-economic level and reflects on the population's transitional phase. Further, the If value fell to a half in women who completed their fertility by family planning when compared to women who completed their fertility by menopause, thus reducing the variance in fertility component in the family planning group.     

Mortality changes in a polish rural community (1350–1972) and estimation of their evolutionary significance

Changes in the mortality profiles of the population of 13 villages in central Poland have been studied for the medieval and nineteenth-century periods. Three measures, derived from the demographic data, were analyzed within an evolutionary context: (1) I_m, the opportunity for selection through differential mortality, (2) R_pot, the potential gross reproductive rate, and (3) I_bs, the index of biological state. Changes in these indicators over time denote sharp differences in the opportunity for natural selection through differential mortality. The greatest changes are associated with technological and organizational transformations of the social system, especially during the first half of the nineteenth century.