Page Abigail E, Myers Sarah, Dyble Mark, Migliano Andrea Bamberg
Department of Anthropology, University College London, London, UK.
Department of Population Health, London School of Hygiene and Tropical Medicine, London, UK.
Evol Hum Sci. 2019 May 30;1:e5. doi: 10.1017/ehs.2019.4. eCollection 2019.
Male-biased sex ratios have been observed in multiple small-scale societies. Although intentional and systematic female-biased mortality has been posited as an explanation, there is often a lack of ethnographic evidence of systematic female neglect and/or infanticide. The Agta, a foraging population from the Philippines, have a skewed sex ratio of 1.29 (129 males per 100 females) aged 15 years or under. We hypothesised that this skew was caused by greater female deaths, but due to an adaptive response, where more males were produced at birth in reaction to high male-biased extrinsic mortality. To test this hypothesis we utilise census, childcare and mortality data from 915 Agta. The Agta's sex ratio is significantly male-biased in the <1 ( = 48, 2:1) and 1-5 year ( = 170, 1.39:1) age cohorts; however, we find no evidence of systematic female neglect in patterns of childcare. Furthermore, the sex ratio decreases over cohorts, becoming balanced by the end of the juvenile period, owing to significantly higher male mortality. Taken together, these results are not supportive of female infanticide or neglect, and instead suggest an adaptive mechanism, acting as a response to male-biased juvenile mortality, following Fisherian principles of equalising parental investment.
在多个小规模社会中都观察到了男性偏向的性别比例。尽管有人提出故意和系统性的女性偏向死亡率作为一种解释，但往往缺乏关于系统性忽视女性和/或杀婴的人种志证据。阿格塔人是来自菲律宾的一个觅食群体，15岁及以下人群的性别比例为1.29（每100名女性对应129名男性），呈偏态分布。我们假设这种偏态是由更高的女性死亡率造成的，但这是一种适应性反应，即由于男性偏向的外部高死亡率，出生时会有更多男性出生。为了验证这一假设，我们使用了来自915名阿格塔人的人口普查、儿童保育和死亡率数据。在1岁以下（n = 48，2:1）和1 - 5岁（n = 170，1.39:1）年龄组中，阿格塔人的性别比例明显偏向男性；然而，我们在儿童保育模式中没有发现系统性忽视女性的证据。此外，性别比例在各年龄组中呈下降趋势，到青少年期末期趋于平衡，这是由于男性死亡率显著更高。综合来看，这些结果不支持杀婴或忽视女性的行为，而是表明了一种适应性机制，遵循费雪均衡亲代投资的原则，作为对男性偏向的青少年死亡率的一种反应。
