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Incest & delayed mother, an analogy

Gene Expression
By Razib Khan
May 20, 2008 8:49 AMNov 5, 2019 9:29 AM


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Will Saletan makes an analogy between cousin marriage and delayed (i.e., 40something) motherhood:

If Bittles' numbers are correct, they substantiate a somewhat embarrassing point made by defenders of cousin marriage. Embarrassing, that is, to all of us good Western folk who turn up our noses at the practice. The British Down's Syndrome Association has posted a chart showing the risk of producing a baby with the syndrome at various maternal ages. From age 20 to age 31, the risk doubles. From 31 to 35, it doubles again. From 35 to 38, it doubles again. From 38 to 41, it more than doubles again. Each delay multiplies the risk as much as cousin marriage multiplies the risks of all birth defects combined. By age 45, the probability of Down syndrome alone roughly matches the 4 percent cumulative risk of birth defects from cousin marriage.

This is too extreme a comparison, I doubt that the recessive diseases are as globally problematic as Down syndrome. That being said, I think it is correct that the increased risks as woman get older can be analogized to increased risk due to inbreeding, even if I'd move the age comparison back a little from 45. But I really don't see the embarrassment here in the comparison; I think many people would be extremely concerned if most women only started having families in their late 30s. Some Pakistanis in the UK are basically telling British public health officials to not interfere with a practice which they wish to maintain. If there was a similar subculture which encouraged women to delay childbearing no matter what until around 40 I think we'd think it was strange, and we would all have to take up the implied costs because of higher risk pregnancies. Late childbearing is a function of an intersection of social conditions and personal choices; e.g., waiting until finding a husband, waiting until graduate school is finished, and so forth. By analogy, sometimes cousins do fall in love and marry even without a cultural preference. So be it. A proactive preference for cousin marriages is not exactly the same, just as a proactive demand that women not start bearing children until they reach their late 30s is not the same as outcomes emergent from other life choices. Saletan also ends the piece the without hitting all the angles:

For what it's worth, it looks as though Britain may take a middle course: no legal restrictions on cousin marriage, but no indifference, either. Bittles and others are proposing to reduce birth defects through counseling, genetic screening, and public education in communities that practice cousin marriage. My guess is that this is how governments will manage unconventional sex practices in the next century. We can't stop people from doing what they want to do. We'll tell them what's generally dangerous.

And if they can adequately reduce the medical risks, by wearing a condom or taking a genetic test, we'll look the other way. We'll speak the language of science, or none at all.

And what if they don't? What if they have a moral objection to abortion? But still want a biological family? In the UK they have a National Health Service, so will everyone pay for one couples' choices?

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