Prince William and his bride, Catherine Middleton, exchanged vows.

You needn't be a royal watcher to join wholeheartedly in the rejoicing at a wedding. And we should celebrate -- not because the principals are royalty, but because marriage itself badly needs reinforcing.

For the past several decades, we've been conducting an experiment to determine whether marriage really matters all that much to society. The results are in. But the news hasn't yet been taken on board.

College-educated, upper-middle-class strivers are not the ones who need reminding about the importance of marriage. Among the upper middle class, marriage continues to be the norm.

Among the lower middle class, though, marriage rates have collapsed. This has created a cultural gulf between classes in America that affects every aspect of life and arguably threatens the cohesion of America itself.

This territory has been explored by Kay Hymowitz in her 2006 book, "Marriage and Caste in America," as well as by scholars like Sara McLanahan, Barbara Dafoe Whitehead and David Popenoe, among others.

Charles Murray's forthcoming book, "Coming Apart at the Seams," which he previewed in a recent lecture at the American Enterprise Institute, examines marriage as one of four key virtues that conduce to a healthy polity (the others are industriousness, piety and honesty).

Echoing George Gilder, Murray notes that marriage is crucial because it "civilizes men." Married men don't just earn more and have significantly lower rates of criminality, substance abuse, depression and poor health than single men. They also contribute more social capital to society.

Married men are far more likely to coach Little League, volunteer at church and shovel their elderly neighbor's walk. Married people, far more than singles (there are exceptions, of course), take responsibility not just for themselves and their children, but for the community.

In 1960, Murray observes, 88 percent of upper-middle-class adults were married. In 2010, the figure was 83 percent. A small drop. But among the working class, 83 percent of whom were married in 1960, the figure today is 43 percent. What does that mean?

It means that life for adults is more chaotic and less rewarding. Married mothers have far lower rates of depression than single or cohabiting mothers. Married women also experience much less domestic violence.

Married couples build more wealth than singles or cohabiting couples. Married adults are also healthier, live longer (particularly men) and are more likely to report that they are happy with their lives.

Children pay an even higher price. As Hymowitz writes: "... if you want to analyze the inequality problem -- start with the marriage gap. Virtually all -- 92 percent -- of children whose families make over $75,000 per year are living with [married] parents. On the other end of the income scale, the situation is reversed: Only 20 percent of kids in families earning under $15,000 live with both parents."

The evidence is overwhelming. Parental behavior -- that is, choosing to wait until marriage to have children, or not -- is the key determinant of success for children. "Children of single mothers," Hymowitz writes, "have lower grades and educational attainment than kids who grow up with married parents, even after controlling for race, family background, and IQ."

And it isn't just the presence of a man in the house that makes married families more successful. "Poverty rates of cohabiting-couple parents are double those of married couples, even controlling for education, immigration status and race."

For those who love social science statistics, there are reams of them about the poor outcomes for kids whose parents didn't marry. They are far more likely to suffer from ill health (physical and mental), joblessness and substance abuse than are kids from intact families. They are 40 times more likely to become victims of sexual abuse. And they are far more likely to become unwed parents themselves.

So by all means raise a glass -- not so much to William and Kate, who've been well feted, but to the institution that holds the secret of success for the rest of us.

Examiner Columnist Mona Charen is nationally syndicated by Creators Syndicate.