Wrong Baby Daddy? It's Not Likely, Science Says

father and son playing soccer
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Contrary to what daytime talk shows might have you believe, men are rarely hoodwinked into raising children who aren't their own, according to several recent studies.

In fact, the studies suggest that the rate of misattributed fatherhood has remained low — at around 1 to 2 percent — for hundreds of years.

The findings challenge the evolutionary idea that "women 'shop around' for good genes" for their children by having sex outside a monogamous relationship, said Maarten Larmuseau, a researcher at the Belgian university KU Leuven who wrote a review article on the topic, published today (April 5) in the journal Trends in Ecology & Evolution.

Previously, researchers estimated that 10 to 20 percent of children are raised by men who are alleged to be, but are not actually, their biological fathers.

Researchers have theorized that, from an evolutionary perspective, cheating has advantages for both men and women. For men, it provides an opportunity to have more children (and thus, further the spread of their genes in the gene pool). And for women, cheating may allow them to have children with a man who is more "genetically fit" than their long-term partner, or who can help ensure that they will have children if their partner is infertile.

But in 2013, Larmuseau and his colleagues found that the rate of misattributed fatherhood in the region of Flanders, Belgium, was only about 1 percent in each generation for the past 500 years.

At the time the study was published, the researchers didn't know whether their finding would hold true in other parts of the world. But more recently, studies in South Africa, Italy, Spain and Mali have had similar results, with rates of misattributed fatherhood ranging from about 1 to 1.7 percent per generation in those areas. [The Sex Quiz: Myths, Taboos and Bizarre Facts]

One way that these studies estimated the rate of misattributed fatherhood was to compare the Y chromosomes of men who supposedly shared a common paternal ancestor, to see how often their genes said they were related and how often there was a mismatch. (Men inherit their Y chromosome from their father.)

"The surprising result of these new studies is that human [rates of misattributed fatherhood] have stayed near constant, at around 1 percent, across several human societies over the past several hundred years," Larmuseau and his colleagues wrote in their new study.

The findings also suggest that the supposed advantages of cheating for women are offset by the costs — for example, if a man finds out that he is not the father, he (and his relatives) may reduce their involvement in the child's life, the researchers said.

"The (potential) genetic benefits of extra-pair children [or offspring outside a monogamous relationship] are unlikely to be offset by the (potential) costs of being caught, particularly in such a long-lived species as humans, with heavy offspring dependence and massive parental investment," the researchers said.

Future studies will allow researchers to look in more detail at the rates of misattributed fatherhood among people with various ethnic and socioeconomic backgrounds, the researchers said.

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Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.