Human Reproduction, Vol 13, 1083-1084, Copyright © 1998 by Oxford University Press
WH James
There has been a decline in sex ratio at birth in recent decades in many
countries. The question arises whether polluting environmental endocrine
disrupters may have been responsible. It is suggested here that we are not
(and will not soon become) in a position to know this because: (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 alternative explanations
which themselves offer little prospect for testing. In short, the
population sex ratio at birth seems not to be a useful monitor of
reproductive hazard unless it were to change at a dramatically greater rate
than has ever been reported. This is not to deny that offspring sex ratios
of selected samples of workers have proved useful non-invasive indicators
of reproductive hazard. However, the recent tiny recorded secular declines
in population sex ratios are distracting attention from the huge and
unexplained changes in other monitors of reproductive hazard, e.g. the
widespread decline in dizygotic twinning rates 1960-1980 and the recent
probable decline in sperm counts.
REVIEWS
Was the widespread decline in sex ratios at birth caused by reproductive hazards?
The Galton Laboratory, University College London, UK.
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