It's a subject that many people are uncomfortable with. "Everyone either is or knows and has a deep personal connection to someone who is divorced, cohabiting, or gay," Schulz writes. "Great numbers of people simply want to avoid awkward talk of what are seen as primarily personal issues or issues of individual morality."
Nonetheless, it is an uncomfortable truth that children of divorce and children with unmarried parents tend to do much worse in life than children of two-parent families. (I'll leave aside the sensitive issue of children of same-sex marriages, since these haven't existed in a non-stigmatized atmosphere long enough to produce measurable results.)
As Schulz points out, that uncomfortable truth is not controversial among social scientists. It is affirmed by undoubted liberals such as Harvard's David Ellwood and Christopher Jencks.
Growing up outside a two-parent family means not just lower incomes and less social mobility, Schulz argues. It also reduces human capital -- "the knowledge, education, habits, willpower -- all the internal stuff that is largely intangible a person has that helps produce an income."
While children are born with certain innate capacities, those capacities can be broadened or narrowed by their upbringing. The numbers indicate that single or divorced parents -- however caring and dedicated -- are unable, on average, to broaden those capacities as much as married parents can.
These differences have sharp implications for upward mobility. Schulz points to an Economic Mobility Project analysis showing that, among children who start off in the bottom third of the income distribution, only 26 percent with divorced parents move up, compared to 42 percent born to unmarried mothers (who may marry later, of course) and 50 percent who grow up with two married parents.
All this matters more than it used to because two-parent families are much more uncommon than they used to be. In 1960 about three-fourths of Americans 18 and over were married. In 2011, less than half were.
One reason is that people are getting married later in life. Back in 1959, one of the last years of the Baby Boom, most American women got married before they turned 21.