Interesting free article up at Science:
How often are children genetically unrelated to their presumed fathers?
Tackling a touchy subject, genetic detective finds only 1% of European children have unexpected paternity
It notes that earlier, much higher, estimates for Western societies were just guesswork:
In the absence of reliable numbers, scientists speculated. In his 1991 book The Third Chimpanzee: The Evolution and Future of the Human Animal, biologist Jared Diamond claimed the adultery rate among humans was between 5% and 30%. In a widely cited 1997 paper, University of Reading evolutionary biologist Mark Pagel argued EPP was so common in humans that babies evolved to be indistinguishable at birth, concealing their true paternity as a protective mechanism.
Eventually, a consensus emerged, based mostly on back-of-the-envelope calculations from early genetic paternity testing. In an article in The Lancet published the same year as Diamond’s book, researchers reported the idea that 10% of children were the product of a clandestine affair, but complained there were no solid data to either confirm or disprove the figure. Nonetheless, it continued to be repeated by journalists and researchers. Eventually it took on a life of its own.
But the new type of research seems to confirm that this was an overestimate:
Subsequent studies elsewhere in Europe by Larmuseau and others came up with essentially the same results: In European societies since at least the Middle Ages, the likelihood a child’s recorded father wasn’t the genetic father was vanishingly small—typically 1%, or less.But, there are those societies still where things are very different:
The obsession with genetic paternity isn’t universal. South American tribes such as the Yanomami believe multiple men can contribute to a child’s paternity by having sex with the same woman. Among the Nyimba of Nepal, women traditionally have multiple husbands—all of whom are expected to act as fathers to all of their spouse’s children. “There are lots of examples that counter this stereotype of wily women versus bamboozled men,” says Brooke Scelza, an evolutionary biologist at the University of California, Los Angeles.
One of the best documented is found among the Himba people of Namibia. When Scelza first visited Himba villages 15 years ago, she was surprised by how openly women discussed children fathered with partners outside of marriage. “It ran against so much of what we as evolutionary biologists think,” she says. “This looked really different from what Maarten Larmuseau and other people were finding in Europe.”
Intrigued, Scelza worked with the community to conduct anonymized paternity testing. The results showed the EPP rate among the Himba was 48%. Fathers were usually aware of which children were theirs biologically, while simultaneously considering themselves the social and legal fathers of all their wives’ children. “It’s not that they’re being duped—these men still really consider themselves the social fathers, even if they’re not the biological fathers,” Scelza says. “It really shows the importance of getting this kind of data from other regions.”