I’ve wondered about that. How would you know whether you are biologically related to anyone you are dating? Two people could have the same bio father and no one would know it.
Scary isn’t it?
In order to avoid the possibility of incest, the burden should be placed where it belongs: with the mothers of the children conceived by IVF and the States could institute blood tests before issuing marriage licenses.
Of course with non-marital cohabitation so common, that would not solve the problem. A worst case scenario would be if a blood test during pregnancy disclosed a problem - then we have more abortions.
Another requirement should be that every birth certificate name the father of the child.
Of course, young women who have unprotected, impulsive sexual activity are not going to compare birth certificates with their sexual partners.
The human race has never needed God’s guidance as much as it does today.
I suppose that concern looms ever larger with today's single-parent families. In the past, you pretty much knew (to some degree of certainty) who your date's parents were... you met them in person. However, the blood tests required as part of marriage license process in the past were never a protection against extended-family nookie. Mostly, the tests were to check for syphilis and other STDs.
Now that DNA tests are available, that *could* be used to check for dangerous similarities. IIRC, most states dropped the blood test requirements before DNA tests were accepted as legal evidence by the courts.