Tuesday, March 24, 2009

More on the topic of concealed ovulation in humans

There was an entry in this blog a few weeks about what seemed to me to be a puzzle, namely, how can we understand “concealed ovulation” in humans from the perspective of evolutionary biology. I recently happened upon the book “The Third Chimpanzee” by evolutionary biologist Jared Diamond. He writes, on page 78 of my paperback copy, that “…the most hotly debated problem in the evolution of human reproduction is to explain why we ended up with concealed ovulation….”.

I suppose I must admit I found it gratifying that at least I wasn’t being a dunderhead in writing about this puzzle. That is, if distinguished professional biologists cannot agree on the reason for this trait, then a layman in the area (such as myself) certainly has the right to be puzzled by it.

At any rate, Diamond goes on to say that there are at least six current theories about why the trait evolved. As I understand his more lengthy explanations, it evolved for one of the following reasons:
1. To enhance cooperation among males (he considers this one to be rather male chauvinist for some reason)
2. To cement the bonds between mates
3. To enhance the probability of the female to receive her fair portion of meat from male hunters
4. To force the male into a permanent marriage bond (he considers this one to be “gender neutral” in a gender politics context)
5. To encourage seevral males to help her, and to at least not kill the infant (this one, by Sarah Hrdy, he applauds as a welcome “feminist” perspective)
6. Because a woman that had a tendency to conceal ovulation could not avoid the risk and pain of childbirth, and hence left more descendants that did those that did not conceal it (this is the theory that Nancy Burly suggested in about 1979, and the one that I mentioned as being a common sense explanation in my earlier post).

I find it rather regrettable that Diamond seems to place so much emphasis on being politically correct. For example, he approves of number 5 because it “overturns masculine sexism and transfers sexual power to women”. This seems an odd reason to like a hypothesis, for shouldn’t scientific truth be the only guide for favoring an explanation of any natural phenomena? Nevertheless, the several pages he devotes to this issue involve some intriguing speculation, and I find it quite interesting.


belleshpgrl said...

It never occurred to me that as a woman I ovulate unknown even to myself. If I wasn't on birth control I wouldn't know I recently ovulated until the day I begin menstruating. That's fascinating.

Perhaps it is simply a matter of overall species preservation. Why be so specific in theories? Why can't the whole theory be if the woman conceals ovulation, there is no immediate competition between any genders. Why don't these theories also apply to other species? Is it because we are the only one capable of speech and complex thought? Is this why love exists? To mate for a period of time because no one knows how to propagate the species otherwise?

It's an interesting debate and since I am not a biologist or anthropologist my ideas are the most base.

Tom said...

Yes, I agree that it is fascinating. And it does appear that other species conceal ovulation. At least, this is what I have read. For example, a wikipedia article at http://en.wikipedia.org/wiki/Concealed_ovulation claims it is present in several other species of mammals. You raise a good question, though, about whether in humans it is due to complex thought. Diamond's reason number 6 (Nancy Burly, 1979) would seem consistent with that. BTW, it is my layman's understanding of modern-day evolutionary biology that "propagation of the species" arguments are largely rejected, and that evolution operates on either at the gene level, or at the individual organism level.

Fred said...

Tom, enjoyed reading your blog. I read several. Nothing offensive at all. I don't know music in the detail you discuss, but it sounds good.

Concerning hidden ovulation, I think we could have a discussion on that. For instance is it really hidden in some women. I would think they would have some awareness of period timing, physical changes, moods. They may wish or even psychologically need to suppress or exhibit this ovulation period for all sorts of reasons such as avoiding pregnancy, encouraging pregnancy, attracting and keeping males, conforming or rebelling to societies views and morals, trapping males, and innocent pregnancy syndrome. They also as well as males may want to extend their genes into the pool, a form of self survival even after death. There may be a reason they don't time ovulation if they have multiple partners to increase the random gene pool selection. And as you mention, women may want protection by a male even if the child is not that male's, something many males want to avoid. The consequences of all these actions on selection and evolution in the species is interesting and in some cases may conflict with behavior intentions.

I've read women are attracted to sex (often the case) with physically strong men of angular faces. This may be an instinct for submission, protection, or strong-body-gene desire. On the other hand in today's society, these men may wander and not provide shelter and protection as much so as say an engineer type. So there may be very deep conflicting drives in women that even vary with their hormones changing during a single month each month. I think it must be hell to be a women knowing she has only a limited supply of eggs, limited years for attracting at least some men, and knowing she needs to select a good gene donor, but also a co-nester. It almost seems beyond belief that it works at all.

The burden of raising a child alone in today's world and in the past is great. Many people just punt --further increasing the likelihood that mates will be damaged and not fulfill roles so desired by women (and men). I think we are seeing increasing numbers of males and females being childless and even avoiding commitments. Who are these people? Is it bringing us down or making us stronger to have them step out of the gene propagation game? If they are thinkers, sensitive artists and the like, we may be losing something. Where have the singers gone? Where have the warriors gone? Where have the selfless gone? Where have the real leaders gone? What I see today is lackluster talent, political hacks, greedy business men and women, who don't care about future generations or hardly even next week. I'm afraid the masses may be getting more stupid. This is just the opposite of what we need in a complex society. Fred

Tom said...

Fred, I agree that people on the average seem to be getting less intelligent. The odd thing is that there is a significant subset of people that seem to be getting smarter. I recall Stephen Weinberg writing in one of his books that each year the new crop of physics grad students appears to be sharper than before.

I tend to blame televison and the media for the general dumbing down...maybe video games and cell phones play a role in this too, but I am not sure.

Re whether ovulation is not hidden in some women...you may be right, that some small percentage do sense when it happens. But the puzzle still remains, of why it is hidden in most cases.