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.