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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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If you're tired of reading about how dead Hillary Clinton is or how long it'll take her to admit it, fly with me across the Atlantic for a couple of minutes. A monumental debate is going on in the British House of Commons over the Human Fertilisation and Embryology Bill, which will influence how governments around the world regulate family and reproductive issues in the next century.
Everything's on the table in this free-for-all: late-term abortions, human-animal hybrids, and IVF for lesbians and unmarried women.
The liberals are steamrolling the conservatives. None of the proposed restrictions has passed. But what's really intriguing is the difference in vote counts among the various issues. It tells us something about which values people care about most. Is it life? Sex? Human dignity?
Here's how many members of Parliament voted for each proposed restriction:
A. Ban abortions after 22 weeks instead of the current 24 weeks: 233.
B. Require clinics to consider the "need for a father" in approving women for IVF: 217.
C. Ban abortions after 20 weeks: 190.
D. Ban the use of gutted animal eggs to make human embryos for research: 176.
E. Ban genetic testing of embryos to choose (for implantation and birth) those that could grow tissue for transplant to an already-born sibling: 163.
F. Ban abortions after 16 weeks: 84.
So the most popular restriction was on late-term abortions. Chalk one up for life.
But wait: The number of votes to prevent lesbian parenthood beat out the number of votes to prevent abortions after 20 weeks. From this, you could make a pretty good argument that feminists are right: Some supporters of abortion restrictions care more about regulating sex and family structure than about protecting life.
Personally, I'm sure of this. The proof is that most people who support abortion bans also support exceptions for rape and incest, where the life considerations are the same, but the sex and family-structure considerations are different.
Now look at the vote count on banning human-animal hybrids. The hybrids in question aren't equal mixtures of human and animal. They're fully human cell nuclei cloned inside eviscerated animal eggs, for lack of available human eggs. In other words, the animal contribution is minimal, almost inconsequential. Furthermore, the embryos are just for research and cell derivation, not for procreation. I'm not saying this is unobjectionable. I'm just pointing out that the degree of mixture is trivial.
Nevertheless, the number of votes to ban it is more than double the number of votes to ban abortions after 16 weeks. To that extent, "human dignity" beats out life. It seems that keeping our DNA separate from that of animals is more important than saving those second-trimester babies.
But that's still not the headline, in my book. The headline is that restrictions on lesbian IVF and trivial species mixture outpolled restriction of genetic testing to choose embryos for tissue harvesting. The common term for this practice is "savior siblings." Here's the prototypical situation: Your daughter has a serious disease. She needs compatible bone marrow. The best way to get it is for you and your spouse to make another baby and transplant its bone marrow to her. But not all your offspring will have tissue that matches hers. To guarantee a match, you need to make a batch of embryos, implant one that matches, and forget about the rest.
The happy ending is that your daughter is saved, and you've made another child to love. But you've also crossed a line. You've made a bunch of human embryos and then flushed them not because of anything wrong with them, but because they weren't useful. And if there's no tissue match, you've crossed that line for nothing.
In my view, the rise of this mentality -- the reconceptualization of human beings as medical tools and resources -- is way more dangerous than gender upheaval, species-mixing, or even abortion. Abortions, no matter what you think of them, are defensive. Tissue harvesting, on the other hand, carries an affirmative mandate. It entitles you, and arguably obliges you, to deliberately create new human life, which will then live or die based on its utility to others.
Contrary to pro-life rhetoric, there's no broad incentive to increase the number of abortions. But there's plenty of incentive to increase the number of sibling saviors. That's why sibling saviors scored so well in the House of Commons. This is one thing I've learned from covering biotechnology: Bad things don't happen because they're bad. They happen because they're good.
Keep an eye on this utilitarian mindset as we continue to take ourselves apart. As the British debate illustrates, it'll be hard to stop.