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  • Some combination of what kids see their parents do and the stress from relationship transitions and resulting household configurations explains most of the likelihood that kids will grow up to have children with more than one partner. Tweet This
  • Multipartner fertility doesn’t seem to contribute much to the growing gap between rich and poor. Tweet This

My best friend from college used to attend church with her never-married boyfriend, who sometimes brought his son; the son didn’t attend every other Sunday when he was with his mother and stepfather (and older half-sister from his mother’s previous union and younger half-sister born to his mother and stepfather). I wrote that sentence carefully in the hope that you would only have to read it once, but it wasn’t easy—having children with more than one partner creates complex families.

It is commonly known that children of divorce have more fragile marriages than children from intact families. Trude Lappegård and Elizabeth Thomson add a layer to what we know about how much family behaviors are passed from parents to children by investigating whether children with half-siblings are themselves more likely to have children with more than one partner. If you prefer jargon, they investigated the "Intergenerational Transmission of Multipartner Fertility."

Don’t let either the jargon or the complexity fool you into rolling your eyes and dismissing an investigation of multipartner fertility as some esoteric academic endeavor. 

First, it matters in the lives of kids with half-siblings. They have disadvantages that cannot be explained by the circumstances leading to multipartner fertility. That means a child whose parents have divorced and whose mom has remarried is at higher risk of negative outcomes, plus the kid whose mom has another child after remarrying is still at higher risk of things like aggressive behaviordelinquency, school detachment, and depression in adolescence

Second, a lot of kids have half-siblings. Divorce and remarriage is only one of the many pathways. Consider also lone motherhood followed by a union with a different man, and childbearing in cohabitations that subsequently dissolve. In short, half-siblings don’t come only from messy circumstances like a parent’s affair that did (or didn’t) lead to divorce; they also come about from fairly common paths through early adulthood. About 20% of all births in the United States are to cohabiting couples, and a majority of children who experience maternal cohabitation will also see it end—possibly to be followed by another partnership that may or may not produce more children. One-third of women in the U.S. with more than one child have a child with more than one man.

The fact that children are increasingly likely to have a half-sibling or two led Lappegård and Thomson to ask whether multipartner fertility (also known as multiple partner fertility) is “passed down” from parents to children the way divorce and early childbearing (and education and church-going and even toothbrushing) are passed down. None of us are clones of our parents, but our behavior is often more like theirs than we would sometimes like to believe. Do kids who experience half-siblings recreate that situation in their own family lives?

The short answer is yes, but the most important nuance to that answer is that only a small part of the intergenerational association is explained by social class. There is a huge class gap in American marriage with college graduates being much more likely to marry than those with less education. This means that those with less education (and less earning power) are more likely to experience some of the life events that enhance the probability of multipartner fertility, like childbirth while cohabiting. So, it could be that the story is all about social class, and if so, it would read something like this: men without secure employment are less likely to marry, and therefore their children are both less likely to get a college degree and more likely to have half-siblings. In the next generation, the lack of a college degree could lead to the same employment insecurity, lack of marriage, and multipartner fertility. In short, poor economic prospects in the first generation could lead to half-siblings in both the second and third generations.

But that isn’t what Lappegård and Thomson found. Education mattered, but it explained only a small fraction of the intergenerational transmission of multipartner fertility. Socialization and stress seemed to explain more. For instance, those with only younger half-siblings were more likely to have children with more than one partner than those with only older half-siblings. Those with younger half-siblings are like my two sons, now adults—young men who have been through a parental divorce and maternal repartnering, and who now have three half-sisters in elementary school. Lappegård and Thomson’s research indicates that even though my three daughters are disadvantaged relative to kids whose parents have had children only with each other, they are at a lower risk than my sons of having multipartner fertility—provided that neither their father nor I have children with anyone else. Kids with both younger and older half-siblings are at the greatest risk of producing complex families themselves, according to the study.

In short, some combination of what kids see their parents do, and the stress from relationship transitions and resulting household configurations explains most of the likelihood that kids will grow up to have children with more than one partner. For the reproduction of unequal family lives, this is relatively good news: it indicates that multipartner fertility doesn’t seem to contribute much to the growing gap between rich and poor. For the quite large pool of children with half-siblings, however, it means that they are likely to hand down disadvantages they have experienced.

Lappegård and Thomson argue that their initial evidence on the intergenerational transmission of multipartner fertility might reveal a general process because the results were very similar for Norway and Sweden. In fact, another recent study using U.S. data validates that claim. It also found strong evidence for kids’ family building patterns resembling their parents, and with little of the association explained by socioeconomic status. The authors of the U.S. study concluded that mothers may pass on personality traits and relationship skills that contribute to unstable partnerships. 

What all this means for me is that I must remain a work in progress. My kids have been dealt hands that seem to predict unstable family lives in their futures, but, just like in 5-card draw, I can do my best to replace some of their weaker cards with stronger ones by compensating for some of my weaker traits and continuing to build my relationship skills. Lappegård and Thomson’s study documents that my kids are at a higher risk for multipartner fertility, but in the end, their ability to create a stable family life for their children is up to them.

Laurie DeRose is a Research Assistant Professor at the Maryland Population Research Center at the University of Maryland at College Park and a senior fellow with the Institute for Family Studies. She is also Director of Research for the World Family Map project.