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Does science support our laws against incest and cousin marriage? If so, does it also support other laws that would restrict sexual or procreative freedom in the name of genetic health?
To longtime readers of Human Nature, this question should be, if you'll pardon the term, familiar. A few years ago, we looked at the science and ethics of "The Love That Dare Not Speak Its Surname." Then we examined the prevalence of inbreeding in nature. Then we considered the awkward question of why, if incest is too genetically risky to permit, maternity in your 40s isn't.
Now biologist Hamish Spencer and political scientist Diane Paul, writing in PLOS Biology, have reviewed the history of U.S. laws against cousin marriage, along with their scientific basis. And again, the evidence raises unsettling implications.
They start with the statistical case against restricting cousin marriages:
[T]he National Society of Genetic Counselors (NSGC) convened a group of experts to review existing studies on risks to offspring and issue recommendations for clinical practice. Their report concluded that the risks of a first-cousin union were generally much smaller than assumed—about 1.7%-2% above the background risk for congenital defects and 4.4% for pre-reproductive mortality—and did not warrant any special preconception testing. In the authors' view, neither the stigma that attaches to such unions in North America nor the laws that bar them were scientifically well-grounded.
But Paul and Spencer point out that the data aren't clear-cut. First, "statistics on the risks associated with cousin marriage are necessarily averages across many traits, and they are likely to be different for different populations." And second, it's
inappropriate to extrapolate findings from largely outbred populations with occasional first-cousin marriages to populations with high coefficients of inbreeding and vice-versa. Standard calculations, such as the commonly cited 3% additional risk, examine a pedigree in which the ancestors (usually grandparents) are assumed to be unrelated. In North America, marriages between consanguineal kin are strongly discouraged. But such an assumption is unwarranted in the case of UK Pakistanis, who have emigrated from a country where such marriage is traditional and for whom it is estimated that roughly 55%-59% of marriages continue to be between first cousins. Thus, the usual risk estimates are misleading: data from the English West Midlands suggest that British Pakistanis account for only ~4.1% of births, but about 33% of the autosomal recessive metabolic errors recorded at birth.
In other words, the American calculations understate the risk for an already inbred population such as British Pakistanis. And calculations based on British Pakistanis overstate the risk for most American cousin couples. You can't draw a uniform line against cousin marriages based on science. Arguably, for the same reasons, you can't draw a uniform line against sibling incest.
The same case can be made against a uniform age of sexual consent. The authors point out,
Beginning in the 1860s, many states passed anti-miscegenation laws, increased the statutory age of marriage, and adopted or expanded medical and mental-capacity restrictions in marriage law. Thus, laws prohibiting cousin marriage were but one aspect of a more general trend to broaden state authority in areas previously considered private.
As Human Nature has noted before, the age of actual maturity varies considerably depending on the person and the type of maturity (sexual, cognitive, emotional) involved. Granted, lawmakers have to draw lines somewhere. But let's not pretend such consistent lines are consistently apt.
Moreover, Paul and Spencer raise a far more troubling problem: The increase in genetic risk caused by cousin marriages among British Pakistanis may actually be overstated, for a curious reason.
[F]or a variety of reasons (including fear that a cousin marriage would result in their being blamed for any birth defects), UK Pakistanis are less likely to use prenatal testing and to terminate pregnancies. Thus the population attributable risk of genetic diseases at birth due to inbreeding may be skewed by prenatal elimination of affected fetuses in non-inbred populations.
In other words, many of the birth defects cited by British politicians as grounds for restricting cousin marriages may actually be the result not of cousin marriage, but of failure to screen and abort defective fetuses. So, in addition to maternity in your 40s, we now have a second logical target for genetic regulation: If inbreeding is too dangerous, what about "inflicting" maladies on your children by failing to screen the embryos? If you know you carry bad genes—and particularly if you're at higher risk of passing down a serious disease than most sibling couples would be—shouldn't we police your procreation just as carefully?
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Six years ago, President Bush's bioethics council opened its inaugural meeting with a discussion of The Birth-Mark, a Nathaniel Hawthorne short story. Council member Bill May summarized the plot, in which a scientist "loves his wife but kills her in the attempt to remove her single imperfection, a birthmark on her left cheek." For nearly an hour, the council sat around debating what the mark symbolized.
Today, the council has run its course—the Obama administration will probably replace it with a more sympathetic panel—but the news has come back to birthmarks. The Vascular Birthmarks Foundation and the Vascular Birthmark Institute of New York just held their eighth annual Vascular Birthmarks Conference, at which dozens of families met with doctors to discuss surgery and other medical options. The New York Times reports from the conference:
"We can no longer accept that a child can go through life being severely disfigured, and accept that as their lot," said Dr. [Milton] Waner, the co-director of the Vascular Birthmark Institute. "Something needs to be done, and I believe that every child has the right to look normal." ... Much of the concern, for many families at the conference, was financial. Doctors said insurance providers frequently refused to pay for the treatments, classifying them as cosmetic surgery. "Their definition of cosmetic is very broad," Dr. Waner said. "This is not cosmetic."
Strictly speaking, Dr. Waner is incorrect. Disfigurement per se is cosmetic. Merriam-Webster's medical dictionary, on which the National Institutes of Health rely, defines cosmetic as "of, relating to, or making for beauty." It defines cosmetic surgery as "correcting defects especially of the face." One question is whether insurers should cover such procedures. Beneath that question lies another: Do children need them?
When you read about these kids and the abuse they sometimes endure for looking unusual, your heart goes out to them. One mother tells the Times about a boy who walked past her son and said, "Look at your face. You look ugly." But which is the problem, the birthmark or the bad attitude? Something needs to be done, but is it surgery? Is every child entitled to "look normal"? Or is he entitled to respect regardless of how he looks?
As it happens, surgery for the kid who was called ugly is a no-brainer. That's because his disfigurement had functional effects, enlarging his tongue so he couldn't speak intelligibly. Dr. Waner and others who take on such cases pro bono are doing noble work. But the quest for normality can extend to iffier cases. The Times describes a baby at the conference who "has a circular, purple mark on her forehead about the size of a nickel." Such defects, known as hemangiomas, "often disappear or shrink in 10 to 12 years, but they can have a social and psychological impact—on children in particular, who must live with the stigma of looking different." Is that a good reason for surgery?
I'm not saying kids with purely cosmetic defects don't suffer. They do. But their suffering isn't medical. It's social. Cosmetic surgery changes an otherwise healthy body to fit culturally imposed aesthetic standards. If a purple mark on your forehead is too much to bear, what about male breasts? What about a flat female chest? How far should we extend the "right"—and, implicitly, the obligation—to look normal?
We had a vascular birth mark in my family. It was considerably bigger than a nickel. In time, it subsided and vanished. The child who was born with it had something more important than the right to look normal. She had the right not to.
P.S. It looks like our "discuss" link is still broken, so here's a handmade link to the HN fray in case you'd like to join the discussion: http://fray.slate.com/discuss/forums/2100253/ShowForum.aspx.
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On Friday I wrote about homosexuality, polygamy, and incest. The gist of the piece was that our categorical bans on these practices are losing their justification. As societies embrace privacy, the acceptable basis for restricting sexual behavior has been reduced to harm. And the evidence that these practices are harmful is weak.
In the case of incest, I looked at the scientific objection -- inbreeding -- at a level one step removed. That is, not in brother-sister coupling, but in cousin marriage. This is an emerging controversy in Britain, thanks largely to immigration from Pakistan, where the practice is common.
Over the weekend, two more articles on this topic appeared in the British press. Let's take a look at them.
First, an estimate of the scale of the practice. "Over a billion people worldwide live in regions where 20%-50% of marriages are consanguineous -- that is where the partners are descended from the same ancestor," reports Emma Wilkinson of BBC News. In Britain, Wilkinson cites an unfolding study in Bradford, where half the kids are from Pakistani parents. A pediatrician at the local teaching hospital reports that 70 percent of the first 1,100 Pakistani women recruited for the study are offspring of consanguineous marriages.
Second, some political background, courtesy of Ian Sample in the Guardian. Three years ago, a member of parliament from the left-leaning Labour Party was denounced for suggesting that cousin marriage should be discouraged as a genetically harmful practice. "We have campaigns about the health effects of drinking, smoking and overeating," the MP pointed out. Why not mount a similar information campaign about cousin marriage? A few months ago, a second MP echoed this argument and was rebuked by the prime minister's office.
The actual risk-multiplication effect of cousin marriage isn't clear. A study I cited six years ago concluded that having a child with your first cousin increased the risk of a significant birth defect from about 3-to-4 percent to about 4-to-7 percent. Wilkinson cites data showing that "since 1997 there have been 902 British children born with neurodegenerative conditions and 8% of those were in Bradford which only has 1% of the population." This appears to be the basis for Sample's report that "rare inherited brain disorders are eight times higher among Pakistani children born to married cousins than those born to unrelated parents." But Wilkinson adds that Australian geneticist Alan Bittles, supposedly the top expert on this subject,
has collated data on infant mortality in children born within first-cousin marriages from around the world and found that the extra increased risk of death is 1.2%. In terms of birth defects, he says, the risks rise from about 2% in the general population to 4% when the parents are closely related.
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.
Which brings us to the Elizabeth Edwards question. As Suz Redfearn reported in Slate four years ago, Edwards gave birth to her two youngest children, Emma Claire and Jack, when she was 48 and 50. Redfearn thinks Edwards used donor eggs. Edwards won't say. If Edwards used her own eggs, the Down syndrome chart puts her probability of the disease at 1 in 11 for Emma Claire and 1 in 6 for Jack. That's two to four times the risk of any birth defect from cousin marriage.
Should women be allowed to have babies well into their 40s? If so, how can you justify restrictions on cousin marriage? For that matter, what about sibling incest? Theoretically, given a pool of recessive disease genes, reproducing with a sibling instead of a first cousin quadruples the risk of defective offspring. This probably overstates the actual effect, since population studies don't show quadrupling as degrees of consanguinity increase. But even if the birth-defect rate is a worst-case 17 percent, that's no higher than the risk of Down syndrome at the age when Elizabeth Edwards had her fourth child.
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.
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Housekeeping note: If you haven't bookmarked the Human Nature home page, I recommend it. It always has the best and freshest news from around the Web in easy-to-click format. Everything I discuss here, plus the stuff I can't get to, is posted there first. So are links to all the latest Human Nature essays and blog items. If you don't have it bookmarked, and the Slate URL is too hard to remember, just type humannature.us.com.
Here's one story you'll find there and in this morning's news batch: U.S. surgeons have begun the long process of repairing a 15-year-old Filipino girl, Jingle Luis, whose feet are so clubbed that they've twisted upside down and backward. The AP story explains:
Jingle's case is more severe than those usually seen by doctors in industrialized countries. "Generally speaking, with modern technology, it doesn't get to this point," said Dr. Terry Amaral, a pediatric orthopedic surgeon who performed the surgery. ... Clubfoot is a relatively common deformity, occurring in about one in 1,000 births. Children are usually treated in infancy with casts or braces that gradually bring the feet into correct alignment. The condition becomes harder to treat if it is not corrected early on.
It sounds like Jingle wasn't treated as a baby because the Philippines lacked the necessary technology. But that's not what happened. Read further:
Amaral said Jingle's case was complicated by the fact that her clubfoot was associated with spina bifida. ... He said doctors who saw Jingle as a baby thought that her spina bifida would shorten her life span and prevent her from walking, so they did not treat the clubfoot. "They felt it wasn't worth managing because of the life expectancy, so they decided to leave it alone," Amaral said.
This is a major factor in treatment decisions around the world. Often, the problem isn't that doctors in less-developed countries can't fix you. It's that resources are limited and that in this context, life-expectancy projections come into play.
In Jingle's case, doctors misjudged the severity of her spina bifida. If she'd been born in the U.S., it's likely that her doctors would have recognized that the defect wasn't so bad. But it's also likely that they would have calculated her prospects differently altogether. That's because life expectancies differ significantly between rich and poor countries, and life expectancies for infants with significant health problems differ even more. Life expectancy isn't a purely biological calculation. It's a socioeconomic calculation.
The interplay of economic progress, life expectancy, and treatment decisions doesn't end in childhood, or with the case of one disabled girl. In fact, it's going to be one of the most powerful forces driving the world in this century and beyond. Thanks to economic and technological progress, life expectancies are rising around the world. Some of this is due to reductions in child mortality. But a lot of it, if not most, is due to increases in the length of old age. As we conquer diseases and improve public health, people in India, China, and elsewhere can expect to live many years longer. That, in turn, is transforming calculations about which conditions are worth treating. If the average woman in Shanghai is probably going to make it to 75 instead of 65, a disease that strikes her at 60 and would take five years to kill her becomes, in utilitarian terms, a disease worth treating.
What's happening, in short, is an increase not just in our technological ability, but in our moral expectations. It's a wonderful thing. But it's going to be incredibly expensive.