It's Not Enough to Be 'Wanted': Illegitimacy has risen despite--indeed, because of--legal abortion.

The abortion debate usually centers on the morality of the act itself. But liberalizing abortion rules from 1969 to 1973 ignited vast social changes in America. With the perennial political debate over abortion again consuming the presidential campaign and the Supreme Court, it might be time to evaluate what Roe v. Wade has meant in practical terms.

One often misunderstood fact: Legal abortions just didn't start with Roe, or even with the five states that liberalized abortion laws in 1969 and 1970. Prior to Roe, women could have abortions when their lives or health were endangered. Doctors in some states, such as Kansas, had very liberal interpretations of what constituted danger to health. Nevertheless, Roe did substantially increase abortions, more than doubling the rate per live birth in the five years from 1972 to 1977. But many other changes occurred at the same time:

• A sharp increase in pre-marital sex.

• A sharp rise in out-of-wedlock births.

• A drop in the number of children placed for adoption.

• A decline in marriages that occur after the woman is pregnant.

Some of this might seem contradictory. Why would both the number of abortions and of out-of-wedlock births go up? If there were more illegitimate births, why were fewer children available for adoption?

As to the first puzzle, part of the answer lies in attitudes to premarital sex. With abortion seen as a backup, women as well as men became less careful in using contraceptives as well as more likely to have premarital sex. There were more unplanned pregnancies. But legal abortion did not mean every unplanned pregnancy led to abortion. After all, just because abortion is legal, does not mean that the decision is an easy one.

Many academic studies have shown that legalized abortion, by encouraging premarital sex, increased the number of unplanned births, even outweighing the reduction in unplanned births due to abortion. In the United States from the early 1970s, when abortion was liberalized, through the late 1980s, there was a tremendous increase in the rate of out-of-wedlock births, rising from an average of 5% of all births in 1965-69 to more than 16% two decades later (1985-1989). For blacks, the numbers soared from 35% to 62%. While not all of this rise can be attributed to liberalized abortion rules, it was nevertheless a key contributing factor.

With legalization and women not forced to go through with an unplanned pregnancy, a man might well expect his partner to have an abortion if a sexual encounter results in an unplanned pregnancy. But what happens if the woman refuses? Maybe she is morally opposed to abortion; or perhaps she thought she could have an abortion, but upon becoming pregnant, she decides that she can't go through with it. What happens then?

Many men, feeling tricked into unwanted fatherhood, will likely wash their hands of the affair altogether, thinking, "I never wanted a baby. It's her choice, so let her raise the baby herself." What is expected of men in this position has changed dramatically in the last four decades. The evidence shows that the greater availability of abortion largely ended "shotgun" marriages, where men felt obligated to marrying the woman.

What has happened to these babies of reluctant fathers? The mothers often end up raising the child on their own. Even as abortion has led to more out-of-wedlock births, it has also dramatically reduced adoptions of children born in America by two-parent families. Before Roe, when abortion was much more difficult, women who would have chosen an abortion but were unable to get one turned to adoption as their backup. After Roe, women who turned down an abortion were also the type who wanted to keep the child.

But all these changes--rising out-of-wedlock births, plummeting adoption rates, and the end of shotgun marriages--meant one thing: more single parent families. With work and other demands on their time, single parents, no matter how "wanted" their child may be, tend to devote less attention to their children than do married couples; after all, it's difficult for one person to spend as much time with a child as two people can.

From the beginning of the abortion debate, those favoring abortion have pointed to the social costs of "unwanted" children who simply won't get the attention of "wanted" ones. But there is a trade-off that has long been neglected. Abortion may eliminate "unwanted" children, but it increases out-of-wedlock births and single parenthood. Unfortunately, the social consequences of illegitimacy dominated.

Children born after liberalized abortion rules have suffered a series of problems from problems at school to more crime. The saddest fact is that it is the most vulnerable in society, poor blacks, who have suffered the most from these changes.

Liberalized abortion might have made life easier for many, but like sex itself sometimes, it has had many unintended consequences.

— Mr. Lott is the author of "Freedomnomics," which you can buy from the OpinionJournal bookstore.