Why Do Our Shark Weeks Sync?

Ever moved into a college residence or an apartment and noticed that after a while you and your roommates have the same cycle? Maybe at one point it was different, but ever so slowly, month by month each menstrual cycle in the household synchronized? We all hear about this anomaly growing up and have maybe noticed it; but have we ever really explored why this happens? After all, it's kind of a fascinating thing don't you think? Over the years, the only scientific explanation I have heard for this occurrence is that it has to do with menstruators' pheromones apparently interacting with one another, causing their menses to synchronize. However, this is a rather simplistic explanation and I still want to know why? Why do our pheromones interact with one another, and what is the deeper, perhaps evolutionary reasoning behind this?

First things first, due to the fact that there is insufficient scientific research to explain why exactly this happens, it has been called a myth, or coincidence. But I refuse to settle with this, because I have seen it happen everywhere I have lived or worked and have observed as it has changed over time. There are four weeks in a month, and seven days in a week- so how can it be merely coincidence that our cycles may synchronize to the exact day? For this reason, I have chosen to do some research into why this phenomenon occurs, and when the conversation around it began to arise. There are several pretty fascinating explanations as to why this occurs. Conversations around menstrual synchronization began in 1971 when a female researcher named Martha McClintock studied the cycles of 35 women. As a result, her findings were that menstruators who were friends or roommates had a similar onset date of menstruation compared to menstruator pairings that did not spend much time together. Due to Martha's work, menstrual synchrony is also known as the "McClintock effect". On the contrary, according to a 2006 PubMed research study, menstrual cycles do not synchronize. Even more confusing, is another PubMed study published in 1997 that concludes that menstrual periods do synchronize, but only under optimal conditions. Due to the ambiguity of these answers, ultimately, it is up to you to decide why you think this happens (and I will continue to believe it serves a mystical evolutionary purpose).

Martha McClintock - researcher of human pheromones and menstrual synchrony

According to McClintock, the reasoning behind menstrual synchrony was that it "was an evolved strategy among females to co-operate with each other - to stop becoming a kind of harem for a single dominant man". In other words, if menstruators were all fertile at the same time, it would not allow one single dominant male to reproduce with all of them, thus creating more co-operation among menstruators and less manipulation by males wanting to reproduce. Due to the fact this study came out in 1970s during the second wave of feminism, many believe this theory has feminist undertones because "the idea that females would co-operate in the face of male domination is attractive".

Equally as interesting, is the idea that there is such thing as "menstrual alphas and betas". Menstrual alphas are individuals whom cause other menstruators around them to synchronize to their periods. Whereas, menstrual betas are apparently individuals whom will synchronize to menstrual alphas because of the power of their pheromones.

"I've got a classic beta womb. My friend Suzanne has an alpha womb. She will bring anyone on within a 10-mile radius. She walks in menstruating, everyone is reaching for the tampons."

"If I spend any period of time with a woman who is menstruating, I will start my period," says Inez, 26. "My womb is a huge team player. It just wants to be one of the girls."

Personally, I also have some theories behind the McClintock effect, although they are not backed by scientific studies in any way. From a survival standpoint, individuals are considered vulnerable when they are on their cycle merely due to the fact that blood can attract wild animals (although there are studies that claim this not to be true). With this in mind, would it not be safer for menstruators to synchronize their periods so that there are more of them to defend themselves? Hypothetically, the higher the numbers of menstruators, the safer they are to fight off wild animals due to the power of having more individuals. Secondly, we see that certain animals only reproduce during a certain time of year, or during certain times...So, is it maybe possible that at one time in history, humans also only reproduced during certain times - and if menstruators all cycled together, this also meant power in numbers. Also, in relation to McClintock's theory, if everyone was fertile at the same time this meant more accessibility to reproduction and more genetic variation, which is good for evolution as it allows "speciation through the accumulation of adaptive genetic differences among reproductively isolated populations". To simplify, more genetic variation allows for adaptations or mutations to occur, which may result in easier survival methods for a species.

Whether menstrual synchrony is a myth or not, you can't deny that the theories behind it are interesting. Regardless of the large body of evidence that may explain it as a mere coincidence over reality, I like to believe it is true as I have experienced it any time I have worked with female colleagues or lived with female roommates. After all, as inconvenient as they may seem at times, periods are magic and I do believe in a more spiritual meaning behind menstruation and the idea that a menstrual cycle is the same length as the lunar cycle. Do you believe in this phenomenon, and if you do, are you a menstrual beta or a menstrual alpha?