Human Nature: Science, Technology, and Life.

Big Sperm Families

Eight hundred years ago, if you wanted to father a swarm of children, you had to seize power, kill men, and collect a harem of women. That's what Genghis Khan did. "An astonishing 8% of males throughout the former lands of the Mongol empire carry the Y chromosome of Genghis Khan," Nicholas Wade reports in his excellent book Before the Dawn. "This amounts to a total of 16 million men, or about 0.5% of the world's total."

Today, if you want to spread your seed around, it's a lot easier. Just make a deposit at a sperm bank.

Thanks to the Donor Sibling Registry, a nine-year-old organization that helps genetic siblings find one another, it's increasingly possible to find out who's been fathering whom in the world of egg and sperm donation. And even when you can't find out who, you can often find out how many. Human Reproduction has just published a survey of parents connected to the registry. The parents had sought out their kids' donor siblings, i.e., kids conceived from the same donor. And guess what? "In several cases, a considerable number of donor siblings had been traced, with 11% (55) of parents who had found their child's donor siblings finding 10 or more, reaching 55 siblings in one instance."

Fifty-five kids from a single donor. Think about that: You have 54 siblings and don't even know who they are. In a town of 5,000 people, what are the chances that somebody close to you—neighbor, mail carrier, waitress, wife—is secretly a relative? And while that's the extreme case, donor reuse seems to be quite common. If 11 percent of donors are being reused 10 or more times, that's a lot of Genghis Khan action. Think of what that's doing to communities, kids' identities, and even biodiversity.

Tabitha Freeman, one of the study's authors, blames lax regulation:

More than 90 percent of parents included in the study came from the United States, where guidelines regulating the use of sperm or eggs are looser than in Britain, she added. "The study is exposing that some clinics are using the same donor for a lot of families," Freeman said. ... "Guidelines suggest this should not be the case but they are not strictly enforced" in the United States, she added.

Maybe while we're beating up on Nadya Suleman, the octuplets' mom, for bearing 14 children, we should stop to think about all the men who have been fathering carloads of kids without even knowing about it. Apparently, the clinic that impregnated Suleman used her to inflate its IVF success rate because she was a reliable producer. That's the same reason a lot of sperm donors get reused. Even if all these kids can be cared for, is there something unhealthy about pumping out child after child from the DNA of one person? Have we had enough of Genghis Khan?

Incest and Eugenics

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?

Marrow With Children

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.

Incest and Delayed Motherhood

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.

Incest in Nature

Six years ago, I wrote about the science and ethics of incest ("The Love That Dare Not Speak Its Surname"). At the time, a study showed that having a child with your first cousin raised the risk of a significant birth defect from about 3-to-4 percent to about 4-to-7 percent. The authors concluded that this difference wasn't enough to justify genetic testing of cousin couples, much less bans on cousin marriage.

Now the incest taboo has taken another hit. Ecologists Kelly Zamudio and Chris Chandler have published a study in Molecular Ecology on sexual selection among spotted salamanders. From this and other research, Science News reporter Ewen Callaway has teased out a fascinating theme: Incest, apparently for sound Darwinian reasons, is surprisingly common in nature.

Through interviews with biologists and ecologists, Callaway looks at several cases. Among spotted salamanders, DNA analysis shows inbreeding "at the level of first cousins, on average. Despite having hundreds of possible mates to choose from, females tended to fertilize their eggs with sperm from related males." Another study found that "Japanese quail prefer first cousins over brothers and sisters and over less-related birds." Among ambrosia beetles: "Brothers and sisters tend to mate." A comparison over two generations of mating found that "inbred beetles fared no worse than outbred insects, and the eggs produced by brother-sister pairs were likelier to hatch than the eggs of unrelated pairs."

At least one fish species similarly prefers brother-sister mating. Scientists "found that fathers from brother-sister couples spent more time, on average, defending their caves and that both parents tended to pay more attention to their kids than unrelated couples." This makes obvious sense. The ecologist who supervised the study reports, "Couples which are full siblings are more cooperative in brood care. ... [T]he males and females stay with the offspring for several weeks and guard them—they defend them—and there's less aggression between full siblings."

These aren't the only rationales for inbreeding. Paraphrasing a Cambridge biologist, Callaway notes, "Many organisms might have slight genetic tweaks or adaptations tuned to their local habitats, and too much genetic mixing with outsiders can dilute these adaptations." Among ambrosia beetles, the practice "may cement the slight genetic differences between the insects," thereby helping to "create new species."

Nor is inbreeding universally taboo among humans. A study in Pakistan found that "three out of five marriages were between first cousins." Another in India that found "one-fifth of marriages occurred between uncles and nieces and a third between first cousins." And before you dismiss this as Eastern barbarism, read up on Charles Darwin and Rudy Giuliani.

The incest taboo does have a firm biological basis. As Callaway explains, "Inbreeding ups the chances that a child will inherit two versions of a disease-causing gene." Data show higher mortality among infants born from first-cousin pairs. But beyond that range, there's evidence that breeding within the family has advantages. Two months ago, a study in Science reported "a significant positive association between kinship and fertility," with a likely "biological basis." The study found "the greatest reproductive success" among "couples related at the level of third and fourth cousins." On average, these cousins produced more kids than less related—and more related—pairs did.

The upshot seems to be that there are advantages and disadvantages to breeding with a relative, and as far as nature is concerned, the ideal course is to strike a balance. You're free to argue that incest is wrong, of course. But be careful what you call unnatural.