PATERNITY FRAUD is more common than most people suppose. Glenn Reynolds quotes one of his readers:

I am familiar with a massive ongoing multi-generational genetic study. . . . (Please don’t mention either it or my name.) The participants were predominantly “greatest generation” and their kids’ generation. Middle-class and white a bit more than the general population. It was looking for hereditary cancers (not too common, maybe 10% or so, last time I checked).

But, of course, in the process of all this, they discovered so-called “false paternities”. (Their rules prohibited them from divulging this info to participants.) Anyway, the overall false paternity rate for this bunch from the “Leave it to Beaver demographic” was about 16%.

16%. One in six. In middle America.

Related: Painless Paternity Tests, but the Truth May Hurt. “Caroline Caskey, chief executive officer of Identigene, a DNA testing company in Houston that has advertised its services nationally in magazines and billboards, said that in about 30 percent of the paternity tests the presumed father turns out to be not the biological father, and that is consistent throughout the industry.” This number is not without selection bias, since people are presumably more likely to opt for a paternity test in cases where paternity is in question.

Also: Mommy’s Little Secret. “In the early 1970s, a schoolteacher in southern England assigned a class science project in which his students were to find out the blood types of their parents. The students were then to use this information to deduce their own blood types (because a gene from each parent determines your blood type, in most instances only a certain number of combinations are possible). Instead, 30 per cent of the students discovered their dads were not their biologically fathers.” And since blood type can’t confirm paternity but only deny it, the actual rate of bastardy could only be higher in this sample.

See also this roundup of other informal sources that pertain to this matter.