Environmental chemicals and changes in sex ratio: Analysis over 250 years in Finland

It has been proposed that environmental chemicalization is responsible for the recent decline in male ratio, but these speculations are based on stati stics going back only a few decades. The objective of this study was to eva luate whether Finnish long-term data are compatible with the hypothesis tha t the decrease in the ratio of male to female births in industrial countrie s is caused by environmental factors. We analyzed the sex ratio of births f rom the files of Statistics Finland and all live births in Finland from 175 1 to 1997. Running averages of 9 years (1751-1904) or 5 years (1905-1997) w ere analyzed for sex ratios. Additionally, to identify potential explanatio ns for the findings, births from 1990 to 1997 were correlated with various family parameters. We found an increase in the proportion of males from 175 1 to 1920; this was followed by a decrease and interrupted by peaks in birt hs of males during and after World War I and World War II. None of the fami ly parameters (paternal age, maternal age, age difference of parents, birth order) could explain the time trends. The turning point of male proportion precedes the period of industrialization or the introduction of pesticides or hormonal drugs, rendering a causal association unlikely. Moreover the t rends are similar to those observed in other countries with worse pollution and much greater pesticide use.