Opportunity for Natural Selection Among the Indian Population: Secular Trend, Covariates and Implications

Abstract

Crow's index is widely used for indirect quantitative estimation of natural selection using birth and death rates. The present investigation is based on 179 studies among 144 different endogamous communities belonging to nineteen states and six geographical regions of India, categorized into six social groups. These studies appeared in 33 different years over six decades (1956 to 2007). The secular trend in Crow's index (I(t)) and its mortality and fertility components (I(m) and I(f)) shows a gradual decline in I(t) and radical shift in the relative contributions of I(m) and I(f). Before 1990 the opportunity for natural selection was mainly determined by differential pre-reproductive mortality (I(m)), whereas after 1990 it has been determined by differential fertility (I(f)). To find out the covariates of I(t), I(m) and I(f) sixteen socio-demographic variables were considered, and nine were found to be significantly correlated with I(t): total dependency ratio, decadal growth rate 1991-2001, young age dependency ratio, crude death rate, total fertility rate, child mortality rate, under-5 mortality rate, old age dependency ratio and decadal growth rate 1981-1991. On the basis of multivariate stepwise regression analysis, female literacy emerged as one of the most important predictors of I(t). The declining trend of I(t), Im and I(f) shows that the Indian population is passing through the demographic transition.

Natural selection among coastal populations of India: Trend and extent

“…As apparent from Tables IV and V, the highest selection intensity among non-coastal population was reported for the Mala of Andhra Pradesh (I t ¼ 1.687), whereas the lowest was reported from a coastal population, the Vadabalija of Orissa (I t ¼ 0.221). The average of selection index for neighbouring non-coastal populations was 0.649, while for coastal populations it was 0.683, both of which are slightly higher than the average for the Indian population (Gautam 2009).…”

“…Among Indian populations, the highest was reported for the Kota of Tamil Nadu (I t ¼ 2.25) and lowest for the Ahoms of Assam (I t ¼ 0.218). The average of total selection index for Indian population was reported to be 0.585 (Gautam 2009). …”

“…The Crow's index of opportunity for natural selection merely sets an upper limit on the measure of selective opportunity that can exist in any particular population; it would measure actual selection only, if the heritability of fitness were complete and if birth and death rates were totally determined by genetic factors (Jorde and Durbize 1986); whereas, zero value of index indicates no change in fitness (Livingston and Spuhler 1965). Despite this limitation, Crow's index has been widely used in human populations, because it allows an indirect quantitative estimation of the selection, inherent in the evolutionary process, simply, on the basis of demographic statistics for birth and death rates (Terrenato et al 1979;Hed 1987;Reddy and Chopra 1990;Kapoor et al 2003;Alfonso-Sanchez et al 2004;Gautam 2009). Studies all over the world have supported the contention that the socio-economic and socio-cultural milieus of a population have tremendous impact on the fertility and mortality components of that population and subsequently on selection (Crow 1958;Spuhler 1962Spuhler , 1976Johnston and Kensinger 1971;Tripp-Reimer 1980;Jorde and Durbize 1986;Sarkar et al 1994;Kapoor et al 2003;Gautam 2009).…”

“…Despite this limitation, Crow's index has been widely used in human populations, because it allows an indirect quantitative estimation of the selection, inherent in the evolutionary process, simply, on the basis of demographic statistics for birth and death rates (Terrenato et al 1979;Hed 1987;Reddy and Chopra 1990;Kapoor et al 2003;Alfonso-Sanchez et al 2004;Gautam 2009). Studies all over the world have supported the contention that the socio-economic and socio-cultural milieus of a population have tremendous impact on the fertility and mortality components of that population and subsequently on selection (Crow 1958;Spuhler 1962Spuhler , 1976Johnston and Kensinger 1971;Tripp-Reimer 1980;Jorde and Durbize 1986;Sarkar et al 1994;Kapoor et al 2003;Gautam 2009). At the same time, there are studies that emphasize the role of ecology with respect to selection (Kapoor et al 2003;Gautam et al 2009).…”

“…In India, few studies have demonstrated the role of natural selection in imposing characteristics of fertility and mortality differentials among different populations in different geo-climate areas like plains, deserts, high altitude and forest areas (Ghosh 1970;Barua 1976;Murthy and Ramesh 1978;Chengal Reddy and Lakshanudu 1979;Rao and Murty 1984;Basu et al 1988;Reddy and Chopra 1990;Kapoor and Patra 1998;Kapoor and Kshatriya 2000;Gautam 2006Gautam , 2009. All these studies reveal a relationship between socio-economic status and the index of total selection, but coastal areas and their geo-climate dimensions have been ignored so far.…”