Ever kiss your sister? Or your brother, as the case may be? Are you a child born of a sperm donor?

If so, how many brothers and sisters (or more properly, half-brothers and half-sisters) do you have? Would you know one if you saw one?

This isn’t something I have ever given much thought to. I know of families who have 20 or more children; full brothers and sisters, conceived naturally. It isn’t common these days, but they do exist. I have heard of sibling counts much higher; 30, 40, 50, even 60 siblings in polygamous families around the world. In these cases, we are talking about a mix of full and half siblings. There was one in India I was reading about just a few months ago.

A prominent example would be the now infamous bin Laden family, infamous because of the exploits of one of approximately 600 members, Osama bin Laden (now deceased). Married 22 times, with 54 children, Osama was born the 17th child of his father, Mohammed bin Awad bin Laden by his 10th wife.

But how many children could a sperm donor father? Particularly if one donated at multiple fertility clinics?

The question is of more than academic interest if you happened to have been fathered by a sperm donor. How many half-siblings do you have? And how would you identify one in the general population?

Let’s say you grow up, go to college, and fall in love with this fantastic girl who likes all the same things you like. You fit together like a hand in a glove. You find out that you share many things in common, including the fact that both of you were conceived by a sperm donor. In your case, it was because your father was infertile. In her case, her parents are both female, and decided they wanted a child. In fact, your friends say that you look enough alike to be siblings. Are you?

What are the odds, you might think.

Seven years ago, a woman named Cynthia Daily and her partner used a sperm donor to conceive a child. Thinking that it might be nice for her son to someday get to know some of his half sibs, she searched a web-based registry for other children born of the same donor and created an on-line group to track them.

Was she ever surprised! Instead of a handful of kids, today the list tops 150, all fathered by the same sperm donor! And it is likely that there are more, as it is unlikely, for a variety of reasons, that every child who had this particular sperm donor as a parent is a member of her site. It is even possible that children continue to be born with sperm donated by this individual. What a way to make a lasting mark on the world!

It has been said that reproduction is nature’s way of ensuring a lasting legacy down through the ages; that success in life, at least in nature, is represented by how many copies of your genes are passed on to the next generation. If this is so, then sperm donors may have hit upon the ultimate, socially acceptable means of ensuring immortality; of their genetic legacy at any rate.

No one really knows who in the history of mankind has fathered the most children. It is hard to keep track of that because after all, a man may father many children with many different women. And while it is easy to establish who the mother of a child is, before DNA testing, definitively establishing who the father is remained a potentially difficult task.

Historically, the man who may have fathered the most children is said to have been Genghis Kahn, who by some estimates may have fathered between 6000 and 8000 children. DNA studies indicate that one in four Hungarians is descended from Genghis Kahn; a prodigious feat, if true. According to one geneticist, there may be as many as 16 million people alive today that can trace their ancestry to Genghis Kahn; in some areas in Central Asia as many as 8% of the male population.

Of course, Genghis Kahn was not the soul of tact when it came to his amorous conquests, as he raped, pillaged, and murdered his way across the countryside, eliminating the men and taking their women as he pleased. Sperm donors, by contrast, are anonymous and don’t hurt anyone; they perform a humane service, making it possible for couples who otherwise would not be able to reproduce, to do so.

And in the course of things, if one or two, or even 10 or 20 children are produced from the various inseminations, where is the harm? Even “normal” families can have up to 20 kids. The all time documented record live births from a single mother is 69 over 27 pregnancies; 16 pairs of twins, seven sets of triplets and four sets of quadruplets. All the children were born between 1725 and 1765 of the same father; I don’t know how many survived to adulthood.

Once you start getting over 10-20 however, it becomes less of a curiosity and more of an issue. When it gets into the hundreds, particularly in a small area, you start running into potential consanguinity issues. For most of us, the possibility of having sex with an unknown half-sibling is vanishingly small. For those whose sperm donor resulted in hundreds of offspring, the potential, while still small, is much greater. Ms. Daily’s group is among the largest known, however others of 50 or more half sibs are showing up on Web sites and chat rooms.

Donors are normally tagged with unique identifying numbers. But what happens if a donor donates at multiple clinics in the same city, or the same state, or multiple states? Do they have the same identifier at each? Is there a uniform set of laws regulating sperm donations across the country or do they vary from state to state, like other laws? What if a donor is intentionally trying to spread his “heritage” as far as he can; maybe he is trying to outdo Genghis Kahn. Is the system set up to detect such a person?

Do you care? Well you might, if you married that perfect woman, had a bunch of kids, then learned that the two of you were half-siblings. There are reasons why laws against incest exist.

One of these includes preserving the domestic peace. No one would or should accept their child being raped by their spouse.

Another reason has to do with genetic considerations; inbreeding causes undesirable recessive genes to more easily combine and result in genetic defects. European royalty was a good example of this problem; a very small gene pool due to excessive inbreeding. Royalty had to marry royalty, with the result that everyone was related. Numerous genetic defects cropped up, hemophilia being the most famous. So much so that it has been referred to as “the Royal Disease.”

In animals, inbreeding is frequently used to strengthen a particular line with genetic traits that the breeder is interested in. Of course with animals, the defectives resulting from unfavorable combinations of undesirable and potentially lethal recessives are culled; something that is not socially acceptable in human cultures.

And of course, there is the fact that the incest taboo is universal in human culture.

So how does the socially mobile offspring of a sperm donor handle this situation? Will the new question asked when boy meets girl be “what’s your donor number?” That might not be a bad idea.

How many children are born here in the United States each year using donated sperm? There are estimates, which range from 30,000 to 60,000. Some say it is more than that. No one really knows, because mothers are asked to report their child’s birth to the sperm bank voluntarily; it isn’t a requirement. Wendy Kramer, founder of the Donor Sibling Registry, estimates that only 20 to 40 percent of mothers actually do so.

Ms. Kramer set up the Donor Sibling Registry in 2000, to help connect donor families. The registry allows you to register the birth of your child and find half siblings using the number assigned to the sperm donor. It’s been 11 years now, and the groups just keep on growing larger. One sperm donor on the site has discovered that he now has 70 children. Who knows? It may be 71 by now.

Other countries limit the number of children a given sperm donor can father. In many, such as Britain, France, and Sweden, the limit is 10. Not here in the U.S. There are guidelines, published by the American Society for Reproductive Medicine, which recommends no more than 25 births by the same donor per 800,000 persons. But nothing is enforced.

The issue isn’t just the potential problems that could result from the children, there are issues concerning the sperm donors themselves, many of whom are aghast at the number of children they have “fathered.”

“When I asked specifically how many children might result, I was told nobody knows for sure but that five would be a safe estimate,” said a sperm donor in Texas who asked that his name be withheld because of privacy concerns. “I was told that it would be very rare for a donor to have more than 10 children.” He later discovered in the Donor Sibling Registry that some donors had dozens of children listed. “It was all about whatever they could get away with,” he said of the sperm bank to which he donated. “It is unfair and reprehensible to the donor families, donors and donor children.” [1]

The most telling paragraph to me, in the story cited above was the last:

Experts are not certain what it means to a child to discover that he or she is but one of 50 children — or even more. “Experts don’t talk about this when they counsel people dealing with infertility,” Ms. Kramer said. “How do you make connections with so many siblings? What does family mean to these children?”

Indeed, what does family mean to these children? I mentioned above that the incest taboo is universal among human cultures. But what if you were not raised with the person? Even if you find out later, will it make any difference?

A case which occurred in England in 2008 may hold a clue. Danielle Heaney and Nick Cameron have something in common; they share a mother. Both were raised not knowing about the other. In point of fact, they look nothing alike. They only met for the first time when in their 20’s. And it was love at first sight, and being half-sibs bothers them not a whit.

For them, the “domestic peace” issues do not exist; they were raised apart. The same would be true with half-sibs from sperm donor parents; at least ones raised in different families. The “universal incest taboo” is obviously not an issue either. It probably would have been had they been raised together, just like it is for the vast majority of the human population. It still might be for most people in their circumstance; obviously though, not for everyone.

The only issue that remains is the genetic issue. And the law of course, which recognizes them as half-sibs and their relationship as incestuous; at least in England. Apparently incest is not illegal in France (which may explain a few oddities about the French.) On the genetic front, they realize that they can’t have kids, and accept that. And in today’s society, there are many ways to keep from having children so that need not be an issue.

One has to wonder; if left unchecked, how will the proliferation of babies from the same donor affect society? It’s been hundreds of years, and the number of males carrying Genghis Kahn’s genetic markers have increased to 16 million. Seems like a lot, but with over 7 billion humans on the globe it is just a drop in the bucket. Even with hundreds of kids from the same donor, the population of the U.S. is over 300 million; again, a drop in the bucket. What if a few sibs do hook up? Where’s the harm?

Will half-sibs share the same view as Nick and Danielle? No big deal? Get your tubes tied, or the big V, and get on with life? Will it become just another “alternate lifestyle” as two star-crossed lovers struggle to get along, stigmatized because, “through no fault of their own”, they happen to share a common sperm donor?

And if that becomes ok, what about the incest taboo itself? Does it go away, yet another casualty of a permissive society, changing social mores, and modern methods of birth control? And yet, who can fault the well meaning people, on both sides, who are simply trying to help people have children who otherwise, for whatever reason, could not?

As the line in Wicked goes, “Sure, I meant well, but look what well meant did.”