[The Bacon Guy]

Quote by: Soil So there are some good reasons for banning incest. But many of the laws against it were laid down long before genetics was understood. So some other forces must be at play.

Instinctive revulsion to an act which threatens your species’ gene pool. This trait would preserve the genetic fitness of an individual's offspring and therefore be perpetuated throughout the generations until we have a near-universal "yuck" response to the idea of incest.

Also, there's a theory in psychoanalysis that having more than one sexual relationship within a family causes strain and is therefore undesirable. This also could explain the development of the "yuck" response.

Quote by: Soil And now that our knowledge of genetics is increasing should we not review those laws?

Although we've established that there are sound reasons not to be banging your sister, I don't agree that it should be illegal to practice incest. First of all, not all couples want to have children and an incestuous union is therefore not necessarily going to be endangering a child.

Also, more importantly, it is not at all consistent with the way we treat other relationships. It is not, under any other circumstances, a crime for two people with a risky combination of genes to have sex or marry. The risk of a child having Down’s syndrome increases greatly with the age of the mother, yet we don't set an upper age limit for sex or childbirth.

The only genuine reason incest is treated differently is because of the instinctive revulsion people have towards it. The issue of genetics is a red herring thrown in to try to rationally justify this revulsion and therefore make banning the practice of incest seem more palatable.

It's the same with so many other things. People begin with their response to something and then attempt to find a way to rationalise it, instead of doing things correctly, i.e. the other way round.