"If the misery of the poor be caused not by the laws of nature, but by our institutions, great is our sin."
- Charles Darwin

Jul 24, 2007

Lord of the Placenta - Part II

As highlighted in my previous entry,
Dr. David Menton, writing for the anti-evolution group Answers in Genesis, claims that the placenta proves God’s handiwork. This is an empirical claim and can therefore succeed or fail based on his evidence. But he doesn’t provide any evidence. What he does provide are statements praising how amazing the placenta is (a claim with which I completely agree) and presumes that such amazement could only be produced from a divine origin.

The next time you experience the joy of a baby’s birth, thank the Lord for providing this selfless placenta. And above all, reflect on the fact that our Creator, who at the time of childbirth so mercifully spares the mother from a fatal loss of blood, did not hesitate to shed His own blood in death to save us from sin, death, and the power of the devil.
By Menton’s logic "The Omnipotent Obstetrician" personally intervenes in every pregnancy and, though he provided this selfless placenta out of his love, he presumably then finds the very organ (“the issue of her blood”) loathsome after she gives birth and thinks the new mother should be shunned for several weeks (Leviticus 12:1-5). But then, God’s not too big on anything relating to the birth canal, particularly menstrual blood.

Writing in the aptly named journal Placenta, J.C. Cross and associates published an evolutionary review article entitled "Genes, Development and Evolution of the Placenta." As you probably guessed, the placenta shows no evidence of being divinely inspired but is in fact closely related to structures traced back to egg-laying animals. The chorioallantoic membrane forms the placenta in mammals but also exists, in simpler form, in birds and reptiles. In birds it lies just beneath the eggshell and is integral for gas exchange and the transport of calcium.

If the placenta were so unique, as Menton suggests, we would expect that there would be unique genetic instructions specifying it’s divine role. What we find, however, is just the opposite. Placental genes are a recycled set of instructions for other systems. As Cross et al. explain:

“[E]volution of the placenta among vertebrates did not involve invention of an entirely new set of genes. Rather, nature has re-used existing pathways for functions common to other systems.”
However, this distraction ignores a far more interesting issue than whether or not God places his finger inside every womb. The evolution of the placenta exposes the importance of chemical imprinting and helps to explain why we find ourselves attracted to some people and not others.

As mentioned before, the mother’s body reacts to the implanting blastocyst as a foreign invader (hardly representing an omnipotent intelligence) in what is called an antigenic response. It has been demonstrated experimentally that the larger this antigenic difference is between parents the larger both the placenta and fetus end up being. The genes coding for this antigenic process are known as the major histocompatibility complex, or MHC. Individuals with different MHCs have characteristically unique smells that, while not obviously different on a conscious level, seem to serve a remarkable role in who we view as attractive, or rather, smell as attractive.

As described in New Scientist Swiss researcher Claus Wedekind determined that women were most attracted to the smell of used T-shirts from men who had significantly different MHCs from themselves. This finding was paralleled in rat studies that showed the same phenomenon. The evolutionary logic of this result is simply that variation of immune system genes would benefit parents by confusing those pathogens that have adapted to their own MHCs. Pathogens adapt rapidly and host organisms must constantly be on their toes if they want their progeny to have the same chance they did. Like the Red Queen of Alice in Wonderland, to win the race of evolution you have to run as fast as you can just to stay in the same place.

But is it demonstrated that similar MHCs actually result in greater risk during embryogenesis? In an ironic twist it turns out that it was a deeply religious group that helped reveal this evolutionary process in action. Geneticist Carole Ober from the University of Chicago conducted a study investigating this question of similar MHC effects by getting detailed gynecology information from 111 Hutterite women (a religious sect akin to the Amish). Out of 251 pregnancies, 27 women had experienced miscarriages. The highest miscarriage rates were in those women whose husbands shared the same MHC genes at 16 specific sites, and those that shared just some of these genes were at a higher rate than couples who shared none. Furthermore, since the Hutterites don't use birth control or deodorant, Dr. Ober could be sure that she was witnessing MHC-scent selection in action.

As remarkable as it may seem, B.O. serves a useful purpose. Females demonstrate that they have the ability to clue in on the chemical traces of immune system genes that will confer greater protection during embryogenesis and improved reproductive success. By selecting men who have unique MHCs from themselves women are sniffing out an evolutionary successful strategy.

How small and creatively lethargic Dr. Menton’s theistic hypothesis turns out to be when compared to this remarkable evolutionary insight. It’s unfortunate that Answers in Genesis encourages their members to remain intellectually inbred, but it’s the lack of Dr. Menton’s academic integrity that is truly depressing. By ignoring the scientific literature of his own field and claiming to find answers about embryology from a 6,000 year old collection of mythology he disregards the noble pursuit of genuine science and encourages his readers to remain intellectually stagnant. God, if such a being existed, would be greatly disappointed by such a waste of intellectual capital painstakingly invested through millions of years of natural selection.

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