Hypotheses on mammalian sex ratio variation at birth

Some comments are made on two hypotheses on the variation of mammalian sex ratios (proportions male) at birth viz. Krackow's developmental asynchrony hypothesis and my parental hormone hypothesis. It seems not unfair to characterise his hypothesis as functioning to support the conventional Mendelian paradigm. In contrast, if my hypothesis were true, some adjustment would have to be made to that paradigm. Here I suggest further ways of testing Krackow's hypothesis experimentally. In contrast, my own hypothesis seems to lend itself also to testing by epidemiological methods; here it is suggested that the offspring sex ratios of several specified categories of ill men should be low. (C) 1998 Academic Press Limited.