Catalano Ralph, Casey Joan A, Bruckner Tim A
School of Public Health, University of California, Berkeley, Berkeley, CA, USA.
Environmental Health Sciences, Columbia University, New York, NY, USA.
Evol Med Public Health. 2020 Apr 21;2020(1):225-233. doi: 10.1093/emph/eoaa012. eCollection 2020.
The sex ratio of human birth cohorts predicts the health and longevity of their members. Most literature invokes natural selection in support of the argument that heritable tendencies to produce male or female offspring induce oscillation in the sex ratio and its sequelae. Tests of the argument remain exceedingly rare because they require vital statistics describing many generations of a population both unaffected by migration and exposed to an exogenous stressor virulent enough to change the sex ratio at birth. We contribute to the literature by using time-series modeling to detect oscillation in the best data currently available for such a test.
We apply rigorous time-series methods to data describing Sweden from 1751 through 1830, a period when the population not only aged in place without migration, but also exhibited the effects of an Icelandic volcanic eruption including a historically low secondary sex ratio. That very low sex ratio should have induced oscillation if heritable mechanisms appear in humans.
We detected oscillation in the ratio but not that predicted by heritable tendencies to produce males or females. We found peak-to-trough oscillation at 14 rather than the approximately 32 years expected from the heritable tendencies argument.
Our findings suggest that mechanisms other than perturbation of heritable tendencies to produce males or females induce oscillation in the human secondary sex ratio. These other mechanisms may include reproductive suppression and selection .
The male to female ratio in human birth cohorts predicts longevity but its variation over time remains unexplained. We test the long-held theory that the ratio oscillates due to heritable tendencies to produce males or females. We find oscillation, but it appears due to social processes rather than heritable mechanisms.
人类出生队列的性别比可预测其成员的健康与寿命。大多数文献援引自然选择来支持这样的观点，即产生男性或女性后代的遗传倾向会导致性别比及其后果出现波动。对这一观点的检验极为罕见，因为它们需要描述一个不受移民影响且暴露于足以改变出生时性别比的外源性压力源的多代人口的生命统计数据。我们通过使用时间序列建模来检测目前可用于此类检验的最佳数据中的波动，从而为该文献做出贡献。
我们将严格的时间序列方法应用于描述1751年至1830年瑞典的数据，这一时期人口不仅原地老龄化且无移民，还受到冰岛火山爆发的影响，包括出现历史上较低的第二性别比。如果人类中存在遗传机制，那么极低的性别比应该会引发波动。
我们检测到了该比例的波动，但并非由产生男性或女性后代的遗传倾向所预测的那样。我们发现峰值到谷值的波动周期为14年，而非遗传倾向观点所预期的约32年。
我们的研究结果表明，除了产生男性或女性后代的遗传倾向受到干扰之外，其他机制也会导致人类第二性别比出现波动。这些其他机制可能包括生殖抑制和选择。
人类出生队列中的男女比例可预测寿命，但随时间的变化仍无法解释。我们检验了长期以来的理论，即该比例因产生男性或女性后代的遗传倾向而波动。我们发现了波动，但似乎是由社会过程而非遗传机制导致的。
