One of the quasi-facts which I often stumble upon is the idea that in 10 percent of cases paternity is misattributed. That is, the presumed father is cuckolded. I often encounter this "fact" in a biological context, where someone with an advanced degree in biology will relate how it turns out that there is a great deal of delicacy in situations of transplant matching because of this fact. When pressed on the provenance of this fact most demur. The reason people demur is that the factual basis of this assertion is very thin. In particular, very high estimates of cuckoldry come from databases of disputed paternity, which are obviously going to be a biased sample. A more thorough survey suggests that there is a wide variation in misattributed paternity across populations. In the interests of disabusing the public of this myth, I point to a paper from Germany, Estimating the Prevalence of Nonpaternity in Germany. The sample consists of the families of children who require bone marrow transplants. The authors note two important conditions: 1) the details of the results as they might relate to paternity are not divulged, 2) none of the parents refused to be typed. Since susceptibility to childhood cancers are evenly distributed across the population the biases introduced in other surveys presumably do not apply to this situation. Why does any of this matter? Because models of paternity uncertainty are important priors in shaping our view of the course of human evolutionary history. Sexual jealousy and mate guarding loom large in evolutionary psychology. I don't particularly know how high paternity certainty impacts these arguments, but it needs to be brought to the fore, rather than relying on an old chestnut of wisdom based on nothing. And yet as suggested by the title, I grant that this result may not be generalized. But it's a place to start. Perhaps in some societies paternity certainty really is low. That's something to consider. Though at least in the developed West that does not seem to be the case (OK, at least in Germany!).