Reproductive characteristics of families from Wielkie Drogi village and opportunity for natural selection among them

Abstract

In a village Wielkie Drogi situated near Cracow in Southern Poland 65 married couples were interviewed in June 1983 with respect to dates of marriages, births, abortions, birth control practices, separations etc. Average age at first marriage among those couples was 22.3 years for females and 25.1 years for males, These results are in agreement with the data for the whole country collected in 1970-s (table 1). Females of Wielkie Drogi completed their reproductive period of life at 29.1 years on the average (age at last childbirth), so that only 6 years out of their whole potential reproductive life span was effectively used for childbearing. Generation length calculated as average age of mother at childbirth is in the investigated group 25.9 years. This figure is close to the world average being slightly higher than in Socialist countries. Birth spacing (proto- and intergenetic intervals) turned out to be in concordance with natural fertility demographic models. Birth intervals length increases with age of women (table 3). Opportunity for selection indices (Crow's I, I, and Ip) calculated for the group studied have relatively low values comparable with those for other populations of non-Malthusian type of fertility (table 5). On grounds of lengths of birth intervals fecundity of couples was determined and its heritablity estimated. Average value of standarized fecundity measure (F) turned out to be insignificantly different from zero, as expected, while repeatablity value (r) measuring heritability turned out to be insignificantly different from zero too (table 6). Therefore it might be concluded that practicaaly all fertility differentials observed in Wielkie Drogi are due to environmental influences leaving thus no room for natural selection operation Summing up it might be said that the opportunity for selection among people of Wielkie Drogi is slight, so small that on grounds of the present material it cannot be detected.