WAS THE WIDESPREAD DECLINE IN SEX-RATIOS AT BIRTH CAUSED BY REPRODUCTIVE HAZARDS

There has been a decline in sex ratio at birth in recent decades in ma ny countries. The question arises whether polluting environmental endo crine disrupters may have been responsible. It is suggested here that we are not (and will not soon become) in a position to know this becau se: (i) we do not know what those sex ratios would have been doing in the absence of such proposed polluters and (ii) there are plausible al ternative explanations which themselves offer little prospect for test ing. In short, the population sex ratio at birth seems not to be a use ful monitor of reproductive hazard unless it were to change at a drama tically greater rate than has ever been reported. This is not to deny that offspring sex ratios of selected samples of workers have proved u seful non-invasive indicators of reproductive hazard. However, the rec ent tiny recorded secular declines in population sex ratios are distra cting attention from the huge and unexplained changes in other monitor s of reproductive hazard, e.g. the widespread decline in dizygotic twi nning rates 1960-1980 and the recent probable decline in sperm counts.