Early-morning births are genetically programmed
Apr 26th 2018
THE notion that nothing good happens after midnight does not seem to apply to times of birth. Around the world the peak hours for vaginal births that have not been induced by drugs fall between 1am and 7am; the numbers then dwindle throughout the rest of the day. This has led many scientists to believe that giving birth during the early morning offers some sort of evolutionary advantage, perhaps gained long ago when hunter-gatherer mothers and their infants would benefit from having their group reunited during the small hours to help with care and to defend them against any predators.
午夜过后没有什么好事会发生的概念，似乎并不适用于孩子出生。在世界各地，没有药物诱导的阴道分娩高峰时间在凌晨1点至7点之间；这些数字在一天余下的时间逐渐减少。这使得许多科学家相信,在凌晨分娩显示某种形式的进化优势，或许这是源于很久以前，采集狩猎族群在这几个小时内聚集在一起，母亲和她们的婴孩们可以在这个时间段获得族群的照顾，并保护他们免受任何食者的侵袭。
The problem with this theory is that almost all the information on the timing of human births comes from modern, urban settings, such as clinics and hospitals, which could produce artificial conditions that skew the variation in timings. Not so, it turns out. As Carlye Chaney of Yale University shows in the American Journal of Physical Anthropology, early-morning births are common to communities with both modern and traditional lifestyles.
这个理论的问题在于，几乎所有关于人类出生时间的信息都来自于现代的城市环境，比如诊所和医院，它们可能会产生人为因素，从而扭曲随着时间推移的改变。事实证明并非如此。正如耶鲁大学的Carlye Chaney在《美国体质人类学杂志》上所展示的那样，凌晨出生在现代和传统的生活方式中都很常见。
The mothers that Ms Chaney and her colleagues chose to study live in Formosa, a rural province in Argentina. They were divided into two groups that were considered to be both culturally and genetically distinct. One group consisted of 1,278 women from the Criollo population, a people of mixed Spanish and indigenous heritage who live relatively modern lives and typically engage in small-scale farming and cattle-ranching. The second group was made up of 1,110 women who belonged to the Wichí and Toba/Qom populations, two of the traditionally nomadic hunter-gatherer peoples who also reside in the Formosa region. Because of Argentine health reforms in the 1980s, which encouraged—and sometimes forced—childbirth to take place in a formal medical setting, all the women in the study gave birth in the delivery room of a rural hospital that recorded the events. Ms Chaney included only full-term births and ignored all Caesarean sections, miscarriages, drug-induced and pre-term births.
Chaney女士和她的同事们选择了在阿根廷农村的Formosa进行研究。他们被分为两组，在文化上和基因上都是不同的。其中一组由来自克里奥罗的1278名妇女组成，他们是西班牙和土著居民，过着相对现代的生活，通常从事小规模农业和畜牧业。第二组由1110名妇女组成，她们属于Wichi和Toba/Qom人口，这是传统上的两个游牧民族，他们也居住在福尔摩沙地区。由于20世纪80年代阿根廷的医疗改革，鼓励甚至有时强迫在正式的医疗环境中进行分娩，所有参与研究的妇女都在乡村医院的产房里分娩并记录。Chaney女士的研究只包括足月分娩，不考虑所有的剖腹产、流产、药物诱导和早产。
If a modern way of life plays a part in favouring early-morning births, Ms Chaney speculated that she would see such timings dominate in the results for the Criollo women, but feature less prominently among the results for the Wichí and Toba/Qom. Not so. The data and additional analysis make it clear that there is no statistical difference in the average birth time found between the two groups. Both showed a surge in births between 2am and 3am, and a big trough around 5pm. More specifically, the average time of birth for the Criollo was 6.34am and that for the Wichí and Toba/Qom was 4.18am.
如果一种现代的生活方式在凌晨分娩中起着一定的作用，Chaney推测她会观察到这种时间支配在Criollo女性的中占大多数，在Wichi和Toba/Qom的女性中却不会那么突出。但事实不这样，数据和其他分析表明，两组之间的平均出生时间没有统计学差异，两者都显示出在凌晨2点到凌晨3点之间的生育高峰，以及下午5点左右是大低谷。更具体地说，Criollo的平均出生时间是早上6：34, Wichi和Toba/Qom的平均出生时间是早上4：18。
Ms Chaney believes that the mechanism driving the tendency for expectant mothers to give birth during the early morning is likely to be melatonin, a hormone which is known to increase at the onset of labour and is predominantly produced by the body between midnight and 5am. That mechanism may well have come about, Ms Chaney suspects, because it was advantageous to go into labour when most help was to hand. Today that means more work for the night shift.
Chaney女士认为，促使准妈妈们在清晨分娩的机制很可能是褪黑激素，这种激素在分娩时就会增加，在主要在午夜和凌晨5点之间由身体产生。Chaney女士怀疑，这一机制的出现，可能是因为这个时间段分娩是有利的，因为该时段大多数人可以提供帮助。今天，这意味着更多的夜间工作。
This article appeared in the Science and technology section of the print edition under the headline "Time to deliver"