American doctors started using sperm donors regularly in the 1950s, and from the beginning, anonymity was the rule. For decades, doctors didn't even keep records about who gave what to whom. Parents didn't want to know, because almost every family pretended the "social" father was the biological father. The rise of sperm banks in the '80s created a market for donors, as banks sought the smartest, healthiest, sportiest, tallest men they could find, and eagerly advertised their talents. (Click here to read a story about how finding sperm donors has become like shopping for a car.) The sperm banks continued to insist on absolute donor anonymity.

But no law mandates anonymity, and about 20 years ago, the progressive Sperm Bank of California pioneered an "identity-release" program. When they gave sperm, donors could agree to be identified when their children turned 18, if the children were curious. The first "ID-release" kids turned 18 last fall, but so far none has contacted a donor. Other small sperm banks are experimenting with similar programs, but none has advanced as far as the Sperm Bank of California's. Sweden, New Zealand, and parts of Australia have passed laws allowing donors to be identified, though no children have reached adulthood since those laws passed.