We have just stumbled across a paper that is very intriguing if you are not up with this tricky little evolutionary twist. Tim Bruckner and colleagues at University of California Irvine and Berkeley, have reported that the odds of a male fetus dying – called the ‘fetal death sex ratio’ – were increased above the expected odds during September 2001. They are actually not the first to investigate this issue – in California, the fetal death sex ratio increased one month after the attacks, and the odds of a newborn being a boy – the secondary sex ratio – decreased three and four months, but not 8, 9 or 10 months after the September 11 attacks.
What makes the Bruckner et al study new is in part its sheer size – they looked at USA-wide data – 156 thousand fetal deaths from 1996 – 2002. This is not short on power. They also had an hypothesis up front – which was supported. Their results show that pregnant women at more than 20 weeks gestation were stressed all over the country – no surprises there. What is the tricky little evolutionary twist? Well, apparently, those in the know will not be at all surprised by this – natural disasters are known to have this effect – male fetuses are more sensitive than female fetuses to maternal corticosteroids produced after the twentieth week of gestation and, as a result, they are more likely to die than female fetuses are. The most accepted interpretation is that this is a quirk of evolution whereby the mother’s total yield of grandchildren is increased. Either that or it is a fluke. Either way, that a truly horrible event in New York can increase the likelihood of a male (but not a female) fetus in Dakota dying, is, to me, fearfully and wonderfully complex.
Bruckner, T., Catalano, R., & Ahern, J. (2010). Male fetal loss in the U.S. following the terrorist attacks of September 11, 2001 BMC Public Health, 10 (1) DOI: 10.1186/1471-2458-10-273
Catalano R, Bruckner T, Gould J, Eskenazi B, & Anderson E (2005). Sex ratios in California following the terrorist attacks of September 11, 2001. Human reproduction (Oxford, England), 20 (5), 1221-7 PMID: 15734763
Catalano R, Bruckner T, Marks AR, & Eskenazi B (2006). Exogenous shocks to the human sex ratio: the case of September 11, 2001 in New York City. Human reproduction (Oxford, England), 21 (12), 3127-31 PMID: 16936298