It's a belief touted¹ in chick flicks² and in university dorm rooms. But the idea that women's menstrual cycles become synchronised when they spend time together is a myth, one expert has claimed.

“女生在一起待久了，经期会同步”这个看法经常出现在年轻女性电影中和大学宿舍里。但有专家说这个看法是错误的。

Dr Alexandra Alvergne, associate professor in biocultural anthropology⁴ at the University of Oxford⁵, says this theory is flawed, and women's periods overlapping⁶ is more likely down to chance than an evolutionary⁸ adaptation.

牛津大学生物文化人类学副教授亚历山德拉•埃尔沃格尼博士说这个理论是错误的，并且女性经期重叠现象更可能只是巧合而非进化过程中的适应性变化。

It is a popular belief that women who live together synchronise³ their menstrual cycles, and that it's mediated⁹ by their pheromones.

大多数人认为住在一起的女性经期会同步，并且这是由她们的信息素调节的。

These are the airborne molecules¹⁰ that enable members of the same species to communicate non-verbally.

信息素是由空气传播的分子，使得相同物种能够进行非言语交流。

The idea originated in a study published in the journal Nature in 1971, which looked at 135 American college students living in a dormitory and recorded data on when their periods began.

这种想法来自《自然》杂志在1971年发布的一项研究。研究观察了住在宿舍的135名美国大学生，并且记录了她们经期开始的时间。

The dorm had four corridors each with around 25 girls living in single and double rooms.

宿舍有四条走廊，各有约25名女生分别住在单人或双人宿舍。

Based on the analysis of around eight menstrual cycles per woman, the study reported an increase in synchronisation - that is, a decrease in the difference between the date their period began for room mates and among closest friends.

研究分析了每个女生的大约八个月经周期，随之发现同步率的升高。也就是说他们发现室友之间或者好朋友之间月经开始时间的差异越来越小。

But among random¹¹ pairings in the dormitory, there was no decrease.

但是在那些随意配对的宿舍里，没有发现差异的减少。

The author hypothesised so-called synchronisation was driven by the amount of time that women spent together, as this would allow for pheromone communication.

于是作者就假设这所谓的同步与女性相处时间的长短有关。时间越长，越有利于信息素的传递。

Since then, so-called 'socially mediated synchrony' has been intensely studied in various groups of women, such as room mates, co-workers, lesbian couples and women from high fertility populations – and in a number of animal species, including rats, baboons¹² and chimpanzees.

自此，所谓的“社交性调节同步性”又在许多女性群体中得以深入研究，如室友，同事，同性情侣以及高生育率地区的女性。人们还在一些动物中对此进行研究，比如老鼠，狒狒和黑猩猩。

The theory goes that synchronisation leads to females becoming sexually receptive - which is known as being 'on heat' in the animal kingdom - at the same time.

理论认为同步性使得女性在同一时间易于交配，在动物世界里，这也叫做“处于发情期”。

The most popular one is that it enables females to minimise the risk of being monopolised by a single dominant¹³ male, and thus make it easier for them to have more than one mate.

其中最普遍的理论是经期同步使得女性把她们被一个占主导地位的男性完全控制的危险降到了最低，因此她们更容易拥有一个以上的伴侣。

In fact, one analysis of 19 primate¹⁴ species found a dominant male had less control over reproduction if all females were receptive at the same time.

实际上，一项对十九种灵长类生物的分析显示：如果所有的雌性都在同一时间处于发情期，唯一的占主导的雄性对于繁殖的控制力会减弱。

However, there is now accumulating evidence that casts serious doubt on the existence of the phenomenon¹⁵.

然而，越来越多的证据对此现象的存在提出了深深的怀疑。

First, the original 1971 study was criticised on methodological grounds.

首先，有人批评了1971年原始研究的方法依据。

Second, a number of studies with both human groups and non-human species failed to replicate¹⁶ the initial findings, with at least as many studies reporting positive results as studies reporting negative ones.

其次，一系列的研究，无论是在人类群体还是非人类物种，都没能复证当初的结果。得到肯定结果的研究数量和得到否定结果的数量一样多。

Mathematical analyses have also revealed that some degree of synchrony is to be expected given shifts in female reproductive system over time.

数学分析也显示，考虑到女性月经周期一直在不停变化，某些程度的同步性是完全有可能的。

No adaptive process needs to be invoked¹⁷ to explain what is observed.

不需要任何的适应性过程来解释观察到的现象。

In other words, synchrony - or the overlap⁷ of cycles between females - is best explained by chance.

也就是说，解释同步性，或者女性之间经期的重叠最好的理由就是偶然性。

There is now overwhelming evidence to suggest that menstrual synchrony in humans is no more than a quirk¹⁸ derived¹⁹ from a study using flawed methods that has since turned into an urban myth.

现在越来越多的证据表明，经期同步只是因为当初研究方法错误，随后成为了一个谣传，实际上它只是一个偶发的事件。