What is the biological function for PMS?

[ecoteat]

In other words, WHY do we (or some of us anyway) have such a miserable few days each cycle? I generally understand what is going on in the body that causes women to feel bloated, achy, tired, cranky, depressed, etc, but what is the purpose of it?

I think I could be at peace with being completely mentally miserable for a couple days once in a while if I had a sense of what the evolutionary advantage is. Like I don't mind bleeding at all; I understand the function of it and the role it plays and I find a method that works for me to tolerate it until it passes. But PMS... not so much.

[Bugglette]

The body produces large amounts of progesterone and other hormones directly after ovulation, in order to aid in conception and implantation.  Which is why early PG symptoms and PMS symptoms are very similar (maybe not woman to woman, cycle/PG to cycle/PG, but generally across the population).  I have no idea why some perfectly healthy women, who produce proper hormones at proper times, do not experience "PMS" ....I think the instance is only like 30% of the female population experiences PMS, but I am also not sure what the true definition of PMS is (based on the study).  Hopefully that all made sense, lol.

ETA:  So, in other words, PMS (in itself) may not be evolutionarily important, it is (in some women) a by-product of evolutionary necessary reproductive hormones.  I also want to clarify that NOT having PMS symptoms does not necessarily mean that your body is not producing the proper hormones, every body reacts differently to hormonal changes...for those (a purported 66% of women (not clear if it is all women, or just those of child bearing age?)) who do not experience PMS

Edited by Bugglette - 5/6/11 at 10:54am

[ecoteat]

Thanks! I think I do understand the *how*, but what I don't get is the *why*. For example, we have eyelashes to protect our eyes, we have a heightened sense of smell while pregnant to help protect us from toxins, we experience pain so that we are alerted when there is something wrong in our body, etc. To carry that further, we experience mood swings just before our period so that (fill in the blank). I'd like to find out what fills in that blank. I doubt that the human body has created such an unpleasant effect of a normally operating biological function for no reason.

Or maybe I (and tons of other women) are more hormonally imbalanced that I ever thought and there is actually something wrong. But that is as unsettling a thought as an unpleasant biological function with no purpose!

[Bugglette]

Sometimes there is no WHY, especially if it does not negatively effect our reproduction or survival, which is what selective evolution protects (the survival of the species).  Maybe it protects the non-fertile female from being bothered by males looking to mate?  By making her moody and more apt to stay away from pestering suitors.  Especially seeing as that human (and other closely related primate) males do not innately sense when the females are fertile, and need other signs to determine prime reproductive periods.  It's an interesting question....sorry I answered more to the HOW in the first post , I was reading a lot of similar questions on other boards (most from many years ago) and that was a better response for one I REALLY wanted to reply to, but knew the original posters would probably not see it, lol.

*Edited for wording