Saturday, January 24, 2009

The Evolutionary Puzzle of Concealed Ovulation

Comments on The Accidental Mind, by David J. Linden

I am fascinated by this excellent book. It deals with how the brain, especially the mind, has evolved, and emphasizes that the brain is not an efficiently designed gizmo. Rather, he arguer that it is a serendipitous kludge put together willy-nilly through many diverse evolutionary steps, with many subsystems inefficiently built on top of each other. It is a tightly argued book, and makes good cases for explaining how brain evolution gives rise to a wide range of human behaviors and emotions (love, memory, dreams, and God, as stated on the cover).
However, one argument he makes leaves me puzzled. He discusses, on page 149, the question “why do humans have concealed ovulation and recreational sex?”. This is, seemingly, two different questions, is it not? The first part, about concealed ovulation, is very interesting to speculate on from the perspective of evolution. The second part of the question though seems to me to be not a weighty one. For isn’t the obvious answer that it is fun and feels good? Don’t all animals, in a sense, engage in recreational sex? No animal, as far as I can tell, does it because it is intentionally going about the business of procreating. Now, that of course is the effect of it, and in fact why nature has made it feel good. If it didn’t, an animal would be disinclined to perform the act, and its genes would not be in the gene pool. So it seems to me. I am a simple layman in this area, so I could be way off base here, and maybe not fully understanding some subtlety in the question.
Let me turn to the first part of the question, that about concealed ovulation. He presents a hypothesis to answer this, attributed to Noonan and Alexander of the University of Michigan. This hypothesis is that concealed ovulation evolved as a means of keeping the male around. Reasonable sounding, as one can see that from a game theory perspective that if ovulation were evident to a male, he might leave upon having sex with an ovulating female to have impregnate another female. Since he is not sure, and he doesn’t want to take a chance that any offspring that the first women has are in fact from another male, he sticks around. He does not want to waste resources raising another males offspring (which would not propagate his genes). Presumably, a male sticking around does, according to this explanation, tend to increase the chances of the woman’s offspring surviving and passing on her genes. Amusing if this is true: maybe this is an indication that we males are good for something after all.
We must quickly add though that male usefulness may not follow as being true today. A protective male could have been much more useful in prehistoric times to provide protection against invaders, predators, and other violent enemies.
But it is not so clear to me that this hypothesis makes sense from a “selfish gene” point of view (the Richard Dawkins book of that name makes perfect sense to me, so I look at everything about evolution from that perspective). It seems to involve assuming that a given male consciously wants to maximize his genes representation in the gene pool, doesn’t it? And as I said above, it seems to me that all animals, including humans, engage in sexual activity because of the pleasure it brings. Putting ones genes into the gene pool, i.e., procreating, is a byproduct from the animal’s point of view.
The other thing that bothers me is that this Noonan-Alexander hypothesis only seems to explain why ovulation is hidden from the male. It is not clear that it explains why it is hidden from the female as well, who will have, presumably, a more nuanced sense of what her body is doing that an external male would have.
Why, I wonder, do people not consider what seems to me to be a more simple explanation of concealed ovulation? Namely this: humans have gradually evolved conceptual knowledge of consequences, or “cause and effect”, and must have long ago (in prehistoric times) figured out that the sex act could result in babies. Perhaps, once a woman knew that to be the case, she would be more inclined to abstain from sex when she was aware that she was ovulating. If she did abstain, she would be able to enjoy all the “recreational sex” she wanted, but she would less likely to be impregnated. To be sure, there have no doubt been times when a woman wanted to have children, but it is easy to imagine that babies could have been a severe burden at many times in human history. Hence, on this view, the woman that somehow mutated a tendency to conceal the fertile times could give rise to more offspring than would a woman that avoided sex when she knew she was ovulating. The latter type of woman would be gradually supplanted in the gene pool, and women with concealed ovulation would thrive.
I seem to recall that in one of the many books I have read on “evolutionary biology” that this theory of mine has been considered by others and soundly rejected. If anyone can enlighten me as to exactly why it is faulty, I would be most grateful.
Note: There is a wikipedia entry on "concealed ovulation", but it does not discuss why it evolved. It does point out that some other mammals, such as rhesus monkeys, have it.


Mike said...

This post makes me want to look at The Accidental Mind.

I am equally skeptical when it comes to evolutionary hypotheses that rely on any conscious desire for an organism to replicate. However, I am not sure that the "protective male hypothesis" necessarily implies that a given male consciously wants to maximize his genes representation. Couldn't it be that, in the same way that humans have a instinct that sex "feels good," human males have an instinct that it "feels right" to protect their offspring? This does not seem to me to imply that a male must be conscious of the genetic consequences.

Tom said...

Yes, I agree that an instinctual desire to stick around and protect offspring would confer an advantage to a given male's offspring surviving and hence make it more likely that he passes on his genes. Indeed, I would think that that surely is the reason for male participating in helping raise offspring in any species where the male does so. It is just not clear to me how concealed ovulation on the part of the female might make him more likely to do that (unless it would be from a conceptual point of view on the part of the male). The other thing is that concealed ovulation in humans involves the interval of fertility being concealed from the female as well as from the male. Perhaps in some circuitous way this could contribute to the male having an instinct to stick around to help raise the offspring, though I have to admit I cannot see right now how it might. My point was that it just seems more direct to go with the Nancy Burley hypothesis that it has to do with how females that learn to avoid sex during a sensed ovulation, either because they want to avoid the ordeal of childbirth or because they do not want babies to care for, get displaced in the gene pool by those who cannot tell when it occurs. I realize that this hypothesis does not seem to be considered nowadays, but I do not understand what has shot it down.