"Reading the internet, or even perusing the scientific literature, you'd get the idea that people are constantly cheating on their spouses. Indeed, scientists have estimated that anywhere from 10-30 percent of men are unknowingly raising children who are not their own. This situation is referred to as cuckoldry, or scientifically as "extra-pair paternity." Now, however, it appears that our estimates of cuckoldry rates were way off.
A new survey published in Trends in Ecology and Evolution sums up a number of recent studies that show the actual rate of cuckolds in the general population, based on genetic testing and ancestor research, is 1-2 percent. This challenges evolutionary psychologists who have suggested that human women "routinely ‘shop around’ for good genes by engaging in extra-pair copulation to obtain genetic benefits." This idea came in part from studying socially monogamous songbirds, which mate for life but have roughly 1 in 10 babies as a result of "extra pair" matings."
[0]: https://arstechnica.com/science/2016/04/cuckoldry-is-incredi...