Selection intensity and its opportunity among Santal women of Keonjhar , Odisha , India

The present study dealt with the opportunity of natural selection using Crow’s index and Johnston and Kensinger's Index among Santal women of Keonjhar, Odisha, India. Mortality index (Im), Fertility index (If) and Total Selection Intensity index (I) were analyzed among the studied population. The Crow’s total index (It) value was found to be 0.7246. The mortality (Im) component was found to be 0.5385 while the fertility (If) component was found to be 0.1846. The contribution of fertility component is greater than that of mortality component among the present studied population using Crow’s index. According to Johnston and Kesinger the total index (It) was found to be 0.8367. Fertility component was found to be 0.0885, Prenatal mortality component (Ime) and Postnatal mortality component (Ime/Pb) where observed to be 0.1356 and 0.1540, respectively. Therefore, it is clear from the results that prenatal mortality contributes higher than postnatal mortality for selection. i.e., Johnston and Kesinger’s Index (0.8367) contributes higher for the opportunity of natural selection than Crow’s Index (0.7246).


Introduction
Natural selection is one of the principal driving forces of modern biology and adaptive evolution.The term was introduced by Darwin in his book "On the Origin of Species", in 1859 [1].Scientists define "natural selection" specifically as "those mechanisms that contribute to the selection of individuals that reproduce", without regard to whether the basis of the selection is heritable [2,3].With the enhancement of overall facilities related to health, contemporary world is passing through demographic transitions and it has been characterized by reduction in mortality and fertility [4].Anthropologists and sociologists viewed demographic transitions as an evolutionary puzzle, as it seems to breach the instinctive wisdom that developed ecological conditions should enhance fertility rate [5].Intra-species competition among individuals for sexual partners cause diversified fitness; it is an essential condition of natural selection to operate evolution [6].Mating system in any population can strengthen the sexual selection.Sexual selection is generated by the high rate of polygamy (polygyny) [7,8].Fertility and mortality define selection intensity of a group and therefore degree of differences in fertility and mortality is used to determine the fitness of a population [9].Differential DNA replication is used as direct estimate of natural selection in the context of the ecology where an individual survive, breed and flourish, but due to the extended life span of human it is complicated [10].In any population natural selection takes place only when variability of this fitness is present.Reproductive success in humans depend upon the total number of progeny that parents contribute to the next generation [11].
Thus, Crow [10] devised an indirect method, a composite index involving fertility and mortality parameters for postnatal life and which was later on improvised by Johnston and Kensinger [12] to measure the maximum potential rate for prenatal life IJASR|VOL 01|ISSUE 04|2015 www.ssjournals.com of change through differential mortality and fertility.There was several factors viz., social, cultural, religious, ethnic, biogenetics and environmental that leads to differential fertility and mortality among the populations [13].Different studies conducted by scholars in this area of research worldwide including India have investigated the influence of social and cultural factors on overall selection intensity [14][15][16][17][18][19][20][21][22][23][24][25].Hitherto, very limited studies have been conducted among the Schedule tribes of Eastern India.Therefore, the present study aims to reveal the opportunity for natural selection, affective population size and variation in reproductive success among the Santals of Harichandrapur reserved forest area of Keonjhar District, Odisha, India.

Materials and Methods
The data for the present research was collected by (BK) during 2013, in the village Golabandha, Harichandrapur block, Keonjhar district, Odisha.Demographic data were collected from 90 ever married Santal women on fertility (pregnancies, live birth, no. of children etc.) and mortality (still birth, child death before 15 years of age etc.).Keonjhar district lies between 23 1' North to 23 10' North latitude and 86 11' East to 86 23' East longitude [26].Keonjhar is situated 175 km from Cuttack, a major town of Odisha, India.Out of the total 41,947,358 population of Odisha, 22.13 % of the population belongs to scheduled tribes [27].Santals belong to the Proto-Australoid group with dark skin colour, sunken nose and lower forehead.It comprises 1.5% of the total tribal population of Odisha [27].All the data were collected after obtaining the needed approval from the block and village authorities.Ethical clearance was obtained from the appropriate authorities prior to the commencement of the study.Women were informed about the objectives of our study before the collection of data.The collected data included age, ethnicity, sex; the fertility and mortality rates at both prenatal (total conception, abortions, and stillbirths) and postnatal stages, using a pre-tested structured schedule by house-to-house visit following interview.Opportunity for natural selection was computed using internationally accepted indirect method of postnatal [10] and modified formula of Johnston and Kensinger

Results and Discussion
The parameters used in calculating the total selection intensity in the study tribal population are presented in Table 1.It is clear from table that the average live birth per mother (X) of 40 Years and above is 2.87 whereas the frequency of premature death (P d ) (those individuals died before 15 years of age) is 0.35.
Table 2 shows the values of the selection intensity indices.The Crow's total index value of the Santal tribe of Golabandha village, Odisha was found to be 0.7246.The mortality component was 0.5385 while the fertility component was found to be 0.1846.The percentage of the fertility component was observed to be 90.70 % while the percentage of mortality component was 9.30 %.Therefore, in total index (I t ) the contribution of fertility component is greater than that of mortality component among Santal tribal population.Johnston and Kesinger [12] have provided the modified formula.According to this modified formula the total index (I t ) was found to be 0.8367.Fertility component was found to be 0.0885, Prenatal mortality component (I me ) and Postnatal mortality component (I me/ P b ) where observed to be 0.1356 and 0.1540, respectively.For total index (I t ) of 0.8367, the percentage of fertility component (79.55 %) exceeds the percentage prenatal mortality component (12.34 %).Therefore, it IJASR|VOL 01|ISSUE 04|2015 www.ssjournals.com is clear from the results that prenatal mortality contributes higher than that of postnatal mortality for selection.i.e., Johnston and Kesinger's Index (0.8367) contributes higher for the opportunity of natural selection than Crow's Index (0.7246).Findings of the present studied population shows that for total index (I t ) the contribution of fertility component is more in selection process (90.70 %) than that of mortality component (9.30 %).The high pre natal mortality in this studied community may be due to the poor health and nutritional status and inadequate prenatal medical facilities available to them due to their low socioeconomic condition.There were various factors responsible for child mortality but it greatly depends upon social status of the family and community, lower the status, higher will be the incidence of mortality [28].Results were also compared (Table 3) using Crow's index values with other available results of fertility and mortality rate among different tribal women of India in their reproductive age's shows disparity with respect to their reproductive success and biological status for natural selection.
Table 3 also shows the State wise comparison of mean live birth, mortality Component (I m ), fertility Component (I f ) and total index (I t ) of the studied tribal women of India.It is evident that the highest number of live birth per mother of 40 Years and above has been observed among the Jaintias of Assam (8.10) [29] and lowest among the Sankar Koch of Meghalaya (2.25) [30].Highest mortality Component (I m ) was found among Pardhans of Andhra Pradesh (0.802) (Murthy and Ramesh, 1978) and lowest among Baiga tribe (0.077) of Madhya Pradesh [31].The fertility component (I f ) was observed to be highest among Kota I (0.815) of Tamilnadu [32] and lowest among Bhoska (0.058) of Uttar Pradesh [33].It is also clear that total index (I t ) was highest among Kota I of Tamilnadu (2.250) [32] and lowest among Mina's of Rajasthan (0.265) [34].While taking percentage of Fertility component, Santals of West Bengal (80.1) [34] had the highest and Bhoska of Uttar Pradesh (20.8) [33] had the lowest .On the other hand percentage of mortality component showed that Bhoska of Uttar Pradesh (79.2) Garg et.al.[33] had the highest value and Santal's of West Bengal (19.9) [34] had the least.

Conclusion
It has been concluded that on an average mortality index (I m ) is relatively higher as compared to the overall fertility index (I f ) among the present study population.Marked decline in the mortality index has been observed in general population in our country due to the better socio-economic development in last few decades, but on the other hand underprivileged section (tribal's) are still facing the problems of booming in their number due to health factor and other living conditions.Thus, health related awareness programme should be organized among such populations under consideration to overcome with reproduction related problems.
[12]: Crow's Index I= I m + I f / P s I m = P d / P s P s = 1-P d I f = V f / X2  Where, I = Index of total selection intensity.I m = Index of selection due to mortality P d = Probability of deaths up to Pre-reproductive age P s = Probability of survival up to reproductive age I f = Index of selection due to fertility V = Variance due to fertility X= Mean number of live births Johnston and Kensinger's Index I = I me + I mc / P b + I f / P b X P s I me = P ed /P b P b = 1 P ed I mc = P d / P s P s = 1 P d I f = V / X 2 Where; I = index of total selection intensity I me = index of total selection due to prenatal mortality P ed = probability to die before birth P b = probability to survive till birth I mc = index of total selection due to postnatal mortality P d = probability to die before reaching reproductive age P s = probability to survive till reproductive age I f = index of total selection due to fertility V = variance due to fertility X 2 = mean number of children per women

Figure 1 (
Figure 1 (a & b): Comparison of fertility component (%) of tribes of 14 States of India.

Figure 2 (
Figure 2 (a & b): Comparison of mortality component (%) of tribes of 14 States of India.