Imagine this, a man’s worst nightmare (besides the abolition of football): All the women in his life are on their cycles. At the same time. Sound like science fiction? Try science fact. Women who spend at least three days a week in close contact with other women eventually start to see their menstrual cycles come into sync with each other (provided they are all healthy and not pregnant). Why is this? The answer deals with humans as a species and our need to reproduce effectively, and also with how our bodies are designed to work to accomplish this.
Humans are a social species, like many others. We gather in groups for protection, for companionship, and for survival. More members in the group means more food can be gathered, more tasks can be accomplished. Living in groups also gave early humans a bigger gene pool for reproduction. The problem with human reproduction is, how do you ensure as many babies are being born as possible to ensure survival as a species?
Hormones. We all secrete hormones through our skin. They convey many different, important messages, though many people have lost the ability to consciously receive and interpret them. Hormones can tell us if someone else is healthy or sick, male or female, happy or unhappy. Someone else’s hormones can also affect your body and your own hormone production. A recent study found that women secrete hormones during their ovulatory cycle (fertile window) that make men view them as being more attractive and more open to sex. Another study has found that women can tell if a man is aroused simply by his sweat. Hormones in the man’s sweat increase if he is aroused, and women subconsciously pick up on these “clues”.
But how do hormones make women’s cycles sync together? As said before, hormones from someone else can affect your own hormone production. Biologically, the way to ensure maximum reproduction is to have maximum opportunities for reproduction. Early human groups resembled harems, with several women to a few men. This meant there were many women to get pregnant, but not many men to impregnate them. Nature’s answer to this problem was simple: Women would produce hormones during their fertile period that could jumpstart other women’s bodies into being fertile as well. Of course this takes time, which is why today it takes a few months for women to “get in sync”. But back then women spent more time together than today, so their bodies were in sync before they even reached puberty. Women being fertile together gives the males a better chance at producing more offspring, since women are only fertile for a few days each month, and can only have one baby a year, whereas males are fertile all the time, and can produce as many offspring as there are available, healthy females.
Conclusion: Women get their periods together not to terrorize men, but as a biological response to hormones and the human instinct to reproduce (though some would say we have accomplished a little TOO well).