How Monogamous Are Americans?

While the United States universally prohibits being married to more than one person at the same time, about 28% of people who have more than one child have children from more than one partner. A majority of African American men and a majority of African American women, who have more than one child, have children from more than one partner.

A significantly larger percentage of Americans who ever have one than one child (almost twice as large), will have children from more than one partner at some point in their lives. Of course, a significant percentage of men and women will never have children, or will only have one child in their lifetimes.

This is due predominantly to a series of monogamous relationships that produce children over a lifetime.

Mothers with children from mother than one father

The first national study of the prevalence of multiple partner fertility shows that 28 percent of all U.S. women with two or more children have children by more than one man.

While previous studies have examined how common multiple partner fertility is among younger women, or among women who live in urban areas, the research by Dorius is the first to assess prevalence among a national sample of U.S. women who have completed their child-bearing years. 

Dorius analyzed data on nearly 4,000 U.S. women who were interviewed more than 20 times over a period of 27 years, as part of the National Longitudinal Survey of Youth. The data included detail on individual men in each household, capturing what demographers call "relationship churning." For nonresidential relationships, Dorius triangulated information from mother and child reports to establish common paternity. 

She found that having children by different fathers was more common among minority women, with 59 percent of African American mothers, 35 percent of Hispanic mothers and 22 percent of white mothers reporting multiple partner fertility.

Women who were not living with a man when they gave birth and those with low income and less education were also more likely to have children by different men. But she also found that multiple partner fertility is surprisingly common at all levels of income and education and is frequently tied to marriage and divorce rather than just single parenthood.

From this April 2011 press release.

This is due mostly to serial monogamy. As this 2011 article explains:

Even many of the low-income women who are not married when they have a child intend to get married to their child’s father. According to figures from the Fragile Families and Child Wellbeing Study, half of the children born to poor single moms are the offspring of a couple who are already living together. Only 10% of the kids are conceived with a man the mother doesn’t really know.

The Fragile Families study, summarizes in this June 2011 report, which was less representative because it was limited to urban children found that:

The most disadvantaged U.S. parents are also most likely to have children with more than one partner, creating complex family relationships and potentially exacerbating poverty, according to Marcia Carlson, a sociology professor at the University of Wisconsin, Madison. 

As part of PRB’s 2010-2011 Policy Seminar series, Carlson examined the magnitude and implications of adults having children with more than one partner, a trend called “multi-partner fertility” by demographers and family researchers. She reported findings from the Fragile Families and Child Wellbeing Study, which is following a nationally representative group of nearly 5,000 urban children born in the late 1990s and their parents. 

Among the married parents surveyed, 21 percent had a child by another partner. That is, the mother, father, or both already had a child with someone else. Among the unmarried parents, 63 percent already had a child with another partner. This means that more than half of children with unmarried parents are “born into families with at least one half-sibling,” said Carlson. By the time those children celebrated their fifth birthdays, 71 percent had a half-sibling, reflecting the instability of unwed relationships. (The Fragile Families study found that two out of three couples had split up within five years after an unmarried birth.) 

In 2010, 41 percent of U.S. births were to unmarried parents. As a result, the share of U.S. children whose family lives are shaped by multi-partner fertility is substantial. Carlson also reported the findings of a variety of other studies indicating that as many as one in five children have a half-sibling, and as many as one in three mothers on welfare have a child with more than one partner. 

Overall, her findings suggest that having children with more than one partner is most common among parents who are young, African American, lived with one parent at age 15, and have lower education levels. The fathers were more likely to have spent time in jail and the birth was more likely to be the result of an unintended pregnancy. “The least advantaged couples are most likely to have children with multiple partners,” she said. “We are just beginning to get a handle on what this means for kids and families.”

Fathers with children from more than one mother

A report based upon 2002 survey data looks at multi-partner fertility data for fathers:

Nearly one-half (47 percent) had fathered at least one child.

■ Thirty-nine percent had had children with a single partner, including 17 percent with one child and 22 percent with two or more children.

■ Eight percent had experienced multiple-partner fertility; that is, they had fathered children with more than one mother.

■ Among a subsample of men in the study sample who fathered children, 18 percent reported having children with more than one woman (in separate analyses, not shown here).

The proportion of men who have fathered children with more than one woman increases with age. Analyses of data on our study sample of men aged 15-44 suggest that an estimated 5 percent will experience multiple-partner fertility by age 25 (see Figure 2). This proportion increases to 8 percent by age 30 and 12 percent by age 35. By age 40, an estimated 15 percent (or more than 1 in 7) will have children with more than one woman. 

The 18% figure in the father's survey is not comparable and inherently lower than the 28% figure in the mother's survey, because the mothers survey gave the percentage of mothers with more than one child who have children from different fathers, while the father's study dilutes that number with the 36% of fathers who have only single child.

Thus, 28% of father's who have more than one child have children with different mothers, the same percentage that applies to mothers in the 2011 study.

The father's study also illuminates the fact that the overall percentage of fathers and mothers who have children with more than one partner at any given time is lower than the percentage who will ultimately have children with more than one partner over the course of their lifetimes, which is at least 88% larger in the case of fathers.

Hispanic men are 21% more likely to have children with multiple mothers than non-Hispanic white men (compared to 59% more for Hispanic women relative to non-Hispanic white women). African American men are 229% more likely to have children with multiple mothers than non-Hispanic white men (compared to 269% more for African American women relative to non-Hispanic white women).

Men with children from more than one mother have far more children, on average, than the average man or the average father, with 73% having three or more children.

Men with children from more than one mother are twice as likely to have been incarcerated in their lives than men with children from one mother.

Men with children from more than one mother are likely to have first had sex and to have first had children earlier than average. And, 71% of men with children with more than one mother were married to at least one of the mothers (24% were married to all of the mothers).