Invisible family

Children of sperm donors find themselves wondering about their invisible family, and the remote but still real possibility that whoever they meet just might be a half brother or half sister.

From the Washington Times:

Many adults born from a sperm donor constantly look for their "dads" and worry about dating someone who is a biological sibling. Ten percent say they felt like a "freak of nature."
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These findings, released May 31 by the Commission on Parenthood's Future at the Institute for American Values, are intended to start a national conversation about the ethics, meaning and practice of donor conception.
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One way to handle this would be to treat sperm donation "like an open adoption," where prospective parents and donors meet and stay in contact, Mrs. Clark said. Instead, men can sign up with multiple sperm banks and make donations under different names. "There's no accountability," she said.

Anonymity in sperm donations is not an easy sell, however. After the United Kingdom passed a law in 1996 to allow donor-conceived offspring to trace their genetic parents, sperm donations fell, the British Fertility Society said.

This may be an area where the ever-falling price of genetic testing may have an impact.  If you're seriously interested in someone as a romantic partner, get tested.  If you turn out to have a quarter of your genes in common, you're half-siblings.  The cheaper this testing gets, the earlier in the relationship it makes sense to have it done.