Mother and son in New Mexico face jail time for incestuous relationship

[Pat Mustard]

Children of sexual relations between close relatives suffer from genetic defects and illnesses to a greater extent than normal children. There was this obscure family of Spanish nobles called the Hapsburgs who are a perfect illustration of what happens when each generation marries its first cousin. Google them some time.

There are plenty of non-related couples who have high risks of certain birth defects as well, just by the nature of their genes and how they match up.  We don't make laws against them having kids.

The risk of genetic defects multiplies massively when both partners have similar genetic profiles. Guess when that happens? Yes, when both sexual partners are closely related, even more so when the relation is in the first degree (parent and child or brother and sister). The fact of the matter is that incest does make it far more likely that children of such a union will have genetic defects that will either make their lives harder or kill them than would normally be the case for children of unrelated persons (unrelated to a reasonable degree, you're not going to get two people who don't share a common ancestor somewhere).