Over four decades the age for tying the knot has risen steadily to a new high of nearly 27 for women and 29 for men, according to Census figures.

"Family" is undergoing some major shifts, including a decline in marriage and an increase in unwed 20-something motherhood. The authors of the new report on marriage think the big question is not why young women are having babies, but why they are not getting married.

In the Wall Street Journal, researchers Kay Hymowitz, W. Bradford Wilcox and Kelleen Kaye wrote that "young single mother" summons an image of a teen high-school dropout, while the reality is, increasingly, a high school graduate in her 20s who may even live with the baby's father.

"If 30 is the new 20, today's unmarried 20-somethings are the new teen moms. And the tragic consequences are much the same: children raised in homes that often put them at an enormous disadvantage from the very start of life."

The trio are among co-authors of a new report called "Knot Yet: The Benefits and Costs of Delayed Marriage in America," which was sponsored by the National Campaign to Prevent Teen and Unplanned Pregnancy, the National Marriage Project at the University of Virginia, and the RELATE Institute.

The shift to an older group, they said, is part of "an unexpected consequence of delaying marriage. Over four decades the age for tying the knot has risen steadily to a new high of nearly 27 for women and 29 for men, according to Census figures."

An article in The Atlantic tries to answer that question.

"This is a complex economic mystery that we've explored often at The Atlantic," wrote that magazine's Derek Thompson, "but we take a big bite out of it by focusing on three factors: 1. The changing (of the) meaning of marriage in America; 2. declining wages for low-skill men; and 3. the declining costs of being a single person."

It matters because there's a real downside to the decline of marriage for the kids, the report's authors told the Deseret News. Cohabiting couples are twice as likely to break up, compared to married couples, said Wilcox. “Marriage is an institution that is surrounded by legal, religious and cultural meanings that people tend to take more seriously.” Children don't flourish when their lives and those of their parents are unstable, they said.

Thompson said several factors "mussed up" the traditional union, not least of which is that women are not apt to marry if they don't see men available to marry them as being a good catch from stability and economic points of view. He points to William Julius Wilson's argument that high unemployment and incarceration makes the dating pool a shallow pond in which to fish. That, a women's increasing financial security, and lower cost of being single may all contribute to making women less apt to marry.

Thompson also points to a connection between modern household innovations that reduce the workload of caring for children as enabling more women to be moms, as well.

Those likely aren't the only factors. Some experts have said that no-fault divorce laws have made it easier to break up families, to the detriment of children. Lawmakers have taken notice. For instance, in Iowa several Republicans recently suggested banning no-fault divorce in families that have minor children.

Instead, wrote O. Kay Henderson of RadioIowa, "they’d have to show a spouse was guilty of adultery, had been sent to prison on a felony conviction, had physically or sexually abused someone in the family, or had abandoned the family for at least a year."

Feelings have run hot on both sides of that proposal.

Other research has shown a decline in cultural commitment to marriage. An article on the 2012 "State of Our Unions" reported that "largely unnoticed and unaddressed, 'middle America' is abandoning marriage, with harsh ramifications for children, stability and the future."

The solution, according to the National Marriage Project report, includes dumping marriage penalties and disincentives that discourage unwed mothers, the poor and those who are older from marrying; increasing the child tax credit; helping young men achieve and thus become more marriageable; offering marriage education for new stepfamilies; and generally investing in relationships.

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