In his mindbending 1998 novel, Making History, Stephen Fry imagines using time travel to prevent the birth of Hitler. The novel's premise presents a tempting thought: no Hitler, no Holocaust, no World War II. Why not sacrifice one baby to save so many?

Now think again: If you could do so, would you use time travel to prevent the birth of Columbine killers Dylan Klebold and Eric Harris? Or perhaps amuck Atlanta day trader Mark Barton?

Two economists claim such action has already been taken. They say America's choice to abort 8.1 million babies in the 1970s is the reason for about half of the much-touted 1990s decline in the crime rate. Infants who would have been born then to mothers who were poor or minorities would now be at the prime age and have just the right social profile to be committing crimes.

The researchers also found that the states that introduced legal abortions before Roe v. Wade experienced the decline in crime rates sooner. And those states that had the highest rates of abortion in the early seventies had the biggest dips in their crime rates in the nineties.

Does this mean that widespread abortion (about one-quarter of all pregnancies now end this way) benefits society? The researchers, who claim to be apolitical, estimate the economic benefit to society of abortion-reduced crime at about $30 billion annually. And after claiming they have no policy agenda, the researchers say their study shows the wisdom of allowing women to choose when they will bear children.

"This is not an argument for abortion per se," one of the researchers told the Chicago Tribune. "This is an argument for women not being forced to have children they don't want to have." If that is not code language for abortion on demand, we don't know ...