School of Public Health, University of California, Berkeley, CA 94720, USA.
Am J Hum Biol. 2013 Jul-Aug;25(4):555-9. doi: 10.1002/ajhb.22414. Epub 2013 Jun 10.
Controversy remains over whether declines in male births reported after population stressors result from either or both reduced conception of males or increased selection in utero against male fetuses. We use monthly birth cohorts to determine if Japanese male births following the Great East Japan Earthquake of 2011 fell below levels expected from female births and from history (i.e., autocorrelation) among cohorts exposed to the Earthquake at or after conception.
We apply interrupted time-series methods to 69 months (i.e., April, 2006 through December, 2011) of birth data from the most and least affected prefectures as well as from the remainder of Japan. We estimate expected male births from female births and from autocorrelation.
Findings varied by distance from the greatest damage but suggest sensitive periods both early and late in gestation when population stressors may induce selection against males in utero. Support for reduced conception of males appeared only in the prefectures most damaged by the Earthquake.
Results align with the claim that natural selection has conserved mechanisms that reduce the odds of a male live birth during stressful times by reducing the conception of males and by increasing the rate of spontaneous abortion among male fetuses.
关于人口压力后报告的男性出生人数下降是由于男性受孕减少还是由于宫内对男性胎儿的选择增加，仍存在争议。我们使用每月出生队列来确定 2011 年日本东部大地震后出生的日本男性是否低于女性出生人数，以及与暴露于地震的队列（受孕时或之后）的历史（即自相关）相吻合。
我们对受灾最严重和受灾最轻的两个县以及日本其他地区的 69 个月（即 2006 年 4 月至 2011 年 12 月）的出生数据应用了中断时间序列方法。我们根据女性出生人数和自相关来估计男性出生人数的预期值。
研究结果因距离最大震度的远近而有所不同，但提示在妊娠早期和晚期存在敏感时期，此时人口压力可能导致宫内对男性胎儿的选择减少。仅在受地震影响最严重的县观察到男性受孕减少的证据。
结果与以下观点一致，即自然选择具有保守机制，通过减少男性受孕和增加男性胎儿自然流产率，降低了在压力时期男性活产的几率。
