Community psychological stressor-induced secondary sex ratio decline after a seismic sequence in the Greek island of Zakynthos.

The secondary sex ratio (the ratio of boys to girls at birth) may demonstrate a decline following community stress-inducing major destructive events. This study aims to investigate whether or not moderate adverse life events, in conjunction with endogenous psychological characteristics, can induce sufficient community stress to affect the sex ratio. From April 3rd to May 8th 2006 a moderate sized earthquake sequence occurred offshore the Greek island of Zakynthos, which had been hit by a destructive earthquake half a century earlier. The monthly sex ratio after the earthquake sequence was estimated and compared with that of previous and following years. Eleven months after the onset of the earthquakes the sex ratio fell to 1.000, and during the next two months (March and April) it declined further to 0.612. The sex ratio one year before its decline was 1.158 and over a total 6-year period, 3 years before and 3 years after the sequence, it was 1.063; the March-April decline in male births is significant (OR=0.53, 95% CI=0.32-0.86, p=0.013, and OR=0.57, 95% CI=0.36-0.91, p=0.023, respectively). Also, the number of boys relative to girls in March-April 2007 was significantly lower than during the same months 3 years before and after the sequence (OR=0.50, 95% CI=0.31-0.82, p=0.007). The findings suggest that basic biological characteristics, such as the sex ratio, can be affected by psychological stressors interwoven with the pertaining psychology of the population.