March 16, 2006

Pregnancy As A Genetic Tug-Of-War?

I'm still struggling silently to wrap my head around that article from the Times the other day, the one about pregnancy being a subtle struggle between the competing self-interests of the mother and the fetus. It's fascinating stuff, but the genetic/evolutionary interpretations are kind of hard to follow, in that meta-analytical, "i know he knows we know he knows" kind of way.

Still, interesting stuff, and the theories--developed by Dr David Haig of Harvard--are apparently emerging as the first coherent explanation for a variety of pregnancy-related illnesses, and some gene-linked birth disorders.

"Silent Struggle: A New Theory of Pregnancy"
by Carl Zimmer [nyt]
Zimmer expands on the article here, "Mothers, Children, and Genes in Conflict" [the loom via kottke]


Its funny we say its a mother-child conflict, when what is lurking underneath is rather a father's interest that conflict with the mother's interest.... The child is "just" the vehicle of the father's genes (i.e. interest). David Haig (and his former student Jon Wilkins) are extremely good at presenting this fascinating theory in a simple manner. Indeed, it could be even more complicated to understand if they did not put so much efforts in making it transparent. I don't know if they talk about it in the nyt, but this conflict evolves because the mother can have children from many different fathers. So the father of the current child wants most energy put by the mother on HIS gene-transporting offspring, and the mother wants to have many offspring and spread her energy among them. So the hypothesis is that if you find a totally monogamous species (which humans are not), you should not see gene imprinting, gene silencing and genetic conflicts between the father and mother... Interesting, isn't it?

[indeed, but it was the mom vs baby angle that I couldn't quite map out: the mom wants to have as many babies as possible with the least effort, while the baby wants to hoard all the resources--ie, the mom, and her food and attn--for himself to insure his own survival. But of course, the mother wants to insure the kid's survival, too, just not so much. etc. -ed.]

When I read the description of pregnancy as a "two person operation," I am sorry to say that my first thought was that this piece of science will be bent to a political agenda, and that's really not the point. The idea of a genetic conflict with the fetus seems so intuitive, I can't believe we haven't known it all along; Just take a look at your actual kid, and try to tell me they aren't competing for resources. This makes such good sense, it's frightening.

i think the article is actually a veiled pro-choice argument that goes something like this: the fetus is a parasite (fighting for only it's best interests) living off the mother, therefore it can be in the mother's best interest to destroy it.

you think, crazy, huh? google it and see for yourself, there is a lot of writing about the opposite, that it is not a parasite, therefore a human, therefore immoral to kill.

[hmm. I think it's true that the mother's self-interest theory is similar to the "health or safety of the mother" cases of abortion, but I don't necessarily see/make a connection. OTOH, I'm sure for religious pro-life activists, there's no one more certain to be the target of automatic opposition than a Harvard evolutionary biologist. -ed.]

I dont buy it.

The premise of the arguement is that pregnancy is dangerous because of competeing interests of fetus and mother. While there are competing interests which playout under periods of extreme stress (malnutrition and pregancy doent go together well), I think the dangerous part of pregnancy is an accident of evolution related to less subtle issues.

IMHO, the two compteing interests is not mother and fetus, but rather standing upright and intelligence.

The problems women face in giving birth is a collision of two independent pressures on human evolution. Its been argued that human intelligence is now limited by these the physical limitations of the birth canal.

The large heads is necessary to accomodate a rapidly growing brain (delaying brain developement until after birth is apparently not an option) the human brain has expanded in size dramatically in the last million years. It is exapanded because large brain size (and its correlate, intelligence) has been strongly selected; intelligence has increased.

The problem we have today is that the pelvis size of women is too narrow to support the increase in head size for Homo sapiens.

Gorillas dont have the same problem. They have much wider hips which are suited to walking bent over on four limbs. They also have offspring with far smaller heads.


I dont dismiss the biochemical observations that have been made and discussed in the article. I just dont think we know their significance.

The biochemical tug-of-war may be related to the immunological problem of pregnancy: the fetus is basically a semi-foreign graft that in other circumstances would be immunologically rejected in a matter of weeks. I dont think we understand the biochemical interplay of this. Its bound to be complicated.

And no.. I dont think the fetus is a parasite. Wrong analogy leads to wrong thinking.


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